Current IssueEditorial BoardOnline First ArticlesArchive
Current IssueEditorial BoardOnline First ArticlesArchive

ABSTRACT

The soil microorganism promotes soil fertility, plant productivity and ecosystem services. Recent molecular research suggests that the soil microorganism has been significantly underestimated. In addition to metagenomic analyses. Metatranscriptomic and Metaproteomics studies targeting the functional part of the microbiome are becoming more common and microorganism functional role and plant-microbe interactions require better understanding. These are crucial for understanding the microbiome’s functional role and for figuring out how microbes and plants interact. Plant growth-promoting rhizobacteria (PGPRs) are helpful bacteria that colonize the roots of plants to stimulate plant growth. They benefit plants in several ways, including enhancing nutrient synthesis and uptake, as well as preventing disease. Understanding plant-microbe interactions in natural and agroecosystems can improve soil fertility and high-yield food production.

INTRODUCTION

Global population expansion has led to a rise in demand for agricultural products. Increased production depletes topsoil, reduces organic matter content and negatively impacts soil ecology. Soil bacteria play a crucial role in maintaining soil ecology and ensuring stability under disturbance. Inadequate land usage can contaminate groundwater, plant disease outbreaks and air pollution. The population’s awareness of environmental issues highlights the need for sustainable and healthy food choices. Therefore, environment-friendly alternatives for sustainable agriculture are gaining popularity. Sustainable agroecosystems as extremely resilient, adaptive and varied (Suresh et al., 2025: de Corato and Towards, 2020). These challenges are interconnected, with variety providing greater adaptability and adaptation is an important component of resilience in agroecosystems. The variety of soil bacteria, which plays an important role in nutrient recycling and soil formation, are a critical issue in sustainable agriculture. The essential issue to be examined is the functional diversity of soil bacteria, not their taxonomic organization. A better knowledge of the role of microorganisms in agroecosystem functioning, particularly in plant development and soil fertility, is critical for sustainable agricultural output.
 
Soil microorganisms
 
Distribution
 
Microorganisms comprise roughly 17% of the world’s biomass (Bar-On et al., 2018). Soil is the most complicated environment for microbial life, with around 4-5 x 1030 cells (Dubey et al., 2019). The soil microorganism primarily consists of bacteria, archaea, fungi, protozoa and viruses etc. According to Mendes et al., (2013), 1gm of soil contains approximately 108-109 bacteria, 107-108 viruses and 105-106 fungal cells. Soil microbial communities provide ecological services such as nutrient recycling, carbon sequestration, water retention, plant growth promotion and defense (O’Brienet_al2016; Jansson et al., 2019; Thakur et al., 2019). The rhizosphere is a biological hotspot that influences microbial community composition through interactions between plants-microbes and microbes-microbes. Plant roots produce organic chemicals that promote microbial activity (Fan et al., 2017). Bacterial community composition varies significantly across bulk and rhizospheric soils, resulting in reduced diversity from bulk soil to roots (Fan et al., 2017; Unnikrishnan et al., 2023). Tobacco and Arabidopsis plants have a significantly higher number of microorganisms in their rhizosphere compared to bulk soil (Bakker et al., 2013). The soil microbiome’s geographical heterogeneity is affected by both environmental factors and population processes (Ettema et al., 2002). Plant root exudates in the rhizosphere and environmental conditions influence soil microbial colonization, which can be biotic or abiotic. Li et al., (2014) conducted studies in corn fields. The study found that Proteobacteria, Actinobacteria and Bacteroidetes, dominated the rhizosphere soil microbiota, accounting for 73-80% of total reads compared to 46-56% in bulk soil. The rhizosphere had lower abundances of Acidobacteria, Firmicutes, Gemmatimonadetes, Nitrospira and Chloroflexi, compared to the bulk soil (Li et al., 2014). Fan et al., (2017) examined the microbial population in wheat fields, focusing on three soil compartments: firmly and loosely attached soil and bulk soil. The study found that Proteobacteria, Actinobacteria and Acidobacteria dominated all soils. Actinobacteria, Alphaproteobacteria, Bacteroidetes and Verrucomicrobia were more abundant, while Chloroflexi, Gammaproteobacteria and Deltaproteobacteria were less abundant in tightly bound soils compared to others. Actinobacteria were found to be more abundant in closely bound soil due to their ability to produce antibiotics, while Alphaproteobacteria were present due to their rapid proliferation. Rchiad et al., (2022) found that in a semiarid agroecosystem, soil microbiota diversity does not decrease with depth, although microbial profiles differed. The study identified 43 microbial phyla, with 12 impacted by soil depth. Microbial communities transitioned from top (0-15 cm) to deep (30-60 cm) at the phylum/family level. The abundance of Verrucomicrobia and Bacteroidetes decreased with soil depth. Depth affects the quantity of soil functional genes, with the majority of functional categories found in the top or deepest layers (Rchiad et al., 2022).
 
Beneficial interactions between plant-microbes
 
Bio-stimulant microbes
 
In nature, microbes and plants coexist, but they can be free-living, attached or form a symbiotic relationship with the host plants. Various relationships exist, including parasitism, mutualism and commensalism. Plants have interacted with a wide variety of plant growth-promoting rhizobacteria (PGPR) throughout their evolutionary history. Bacterial rhizobiome mapping is advancing fast due to novel identification methods, huge genome-sequencing strategies and current developments in metagenomics. These findings identified new bacterial species and how they promote plant growth and serve as biocontrol (Tabish Akhtar  et al., 2020; Khan, 2019). By fixing atmospheric nitrogen, producing siderophores, plant growth hormones (cytokinin’s, auxins and gibberellins), volatile compounds and solubilizing nutrients and minerals (phosphorus, potassium, zinc, etc.), microorganisms that live in soil can indirectly stimulate plant growth. Certain PGPR species also contribute to a plant’s ability to withstand stress. They can boost the plant’s ability to absorb heavy metals or other harmful substances and assist the host plant in overcoming salinity and drought stress (Li et al., 2014; Aira et al., 2010; Husna et al., 2023). PGPRs are crucial bacteria for agriculture because they promote plant growth. Biological nitrogen fixation through raising nitrogen content, biomass, germination rate and chlorophyll. These can increase crop productivity, hydraulic activity, shoot and root length and leaf area. In addition to giving plants resistance to biotic (pathogen fungi, bacteria, yeast, insects, pests, etc.) and abiotic (flood, drought, salinity, heavy metals, temperature, etc.) stress, they can also make nitrogen from the soil available to plants in inorganic forms (ammonium, nitrate) (Yadav et al., 2018). Aspergillus, Rhizoctonia, Penicillium, Talaromyces and Trichoderma are the genera that contain fungi that stimulate plant growth. Of these, Trichoderma sp. (T. harzianum and T. viride) and Penicillium chrysogenum are the most promising for increasing plant growth (Adedayo et al., 2023).
 
Biological nitrogen fixation
 
Plants can use nitrogen from soil in both inorganic (nitrate, ammonium) and organic forms (amino acids, urea and short peptides). Organic forms can only be exploited under specific conditions (Eva et al., 2019). Plants cannot utilize the abundant elemental dinitrogen (N2) found in the Earth’s atmosphere. Fowler et al., (2015) computed 473 Tg N of physiologically accessible nitrogen from 4 x 109 Tg N of dinitrogen gas (Fowler et al., 2015; Ladha et al., 2022).
       
Bacteria having biological nitrogen fixation (BNF) capacity are classified into three types: associated, free-living and symbiotic bacteria. Free-living N2-fixing bacteria from several genera, including Gluconacetobacter, Azospirillum and Azotobacter spp., contribute minimally to the total BNF. Rhizobia, a type of symbiotic bacteria that fixes nitrogen, accounts for the majority of BNF (Ladha et al., 2022). Rhizobium are the symbiotic bacteria found in leguminous plants. Non-symbiotic N2-fixing bacteria include cyanobacteria (Anabaena, Nostoc and other blue-green algae), as well as other genera including Azotobacter, Beijerinckia and Clostridium. Nitrogen-fixing bacteria, including Azospirillum sp. (rice, maize and wheat), Azotobacter sp., Klebsiella sp. and Alcaligenes sp., reside in the rhizospheric zone and transport fixed nitrogen to plants. Endophytic nitrogen-fixing microbes are found in cereals, grasses, sugarcane, Azoarcus sp. (sorghum, rice, kallar grass), Gluconacetobacter diazotrophicus (sugarcane, sorghum), Herbaspirillum sp. (rice, sugarcane, sorghum) and Burkholderia sp. (rice) (Eva et al., 2019; Ladha et al., 2022; Turan et al., 2016).
 
Phytohormone production
 
Phytohormones are chemical molecules that affect plant physiological processes, even in low quantities. Soil bacteria can create phytohormones, making them a possible source of these compounds. Microorganisms produce plant growth hormones, including auxins (indole-3-acetic acid), cytokinins, gibberellins, ethylene and abscisic acids. Synthesis requires significant amounts of metabolic energy and nutrients (Ladha et al., 2022; de Bruijn et al., 2022: Anjum et al., 2007). Stress-related regulators of plant immunity, such as jasmonic acid, ethylene and salicylic acid, provide a core signaling backbone to coordinate defense responses against phytopathogens (Matilla et al., 2018). Bacteria from the Rhizobium, Sinorhizobium, Bradyrhizobium, Azospirillum, Bacillus, Paenibacillus and Pseudomonas genera can produce phytohormones such as auxins, ABA, gibberellins and cytokinins, which enhance plant growth and productivity in natural conditions (Galler and Levy 2023; Ladha et al., 2022).

While all plant-associated bacteria produce auxins all PGP microorganisms cannot produce gibberellin. This capability is linked to root-associated microorganisms. Approximately 80% of rhizospheric bacteria produce auxins, primarily indole-3-acetic acid (IAA). Tryptophan is the primary precursor for IAA production in bacteria. Bacteria that increase IAA production can consume tryptophan found in root exudates. Azospirillum brasilense has five distinct tryptophan-dependent and independent routes, with unknown biosynthesis intermediates (Matilla and Krell, 2018). IAA, a bacterial phytohormone that promotes lateral root formation and root elongation is the most widely studied. Plant hormones are particularly effective during stressful situations. Bacterial auxins can help plants cope with stress when they cannot make enough (Ahmad et al., 2019). Bacterial species capable of producing IAA include Pseudomonas fluorescens, Pseudomonas syringae, Agrobacterium tumefaciens, Pantoea agglomerans, Azospirillum brasilense, Bacillus cereus, Bacillus amyloliquefaciens, Bradyrhizobium sp. and Rhizobium sp., (Matilla and Krell, 2018). Shahzad et al. (2017) found that inoculating rice plants with Pantoea dispersa RWL-3, Micrococcus yunnanensis RWL-2, Staphylococcus epidermidis RWL-7 and Micrococcus luteus RWL-3 led to significant increases in dry biomass, root and shoot length, protein and chlorophyll content (Chaudhary et al., 2022; Shahzad et al., 2017). Fungi that produce IAA include Aspergillus, Mortierella, Talaromyces, Trichoderma spp., Fusarium, Penicillium. Penicillium janczewskii suppresses the phytopathogen Rhizoctonia solani, which causes stem rot (Adedayo et al., 2023).
       
Abscisic acid (ABA) is a stress hormone that triggers photoperiodic blooming and promotes plant growth and development. It affects plant responses to different environmental stresses such cold, salt and desiccation (Ahmad et al., 2019). Plant-associated bacteria can create ABA, which boosts phytohormone levels in plants. Plant with altered ABA production or insensitivity are more resistant to infections than wild-type plants, as ABA plays an important role in modifying plant defense mechanism (Matilla and Krell, 2018). Endophytic bacteria that produce ABA include Achromobacter xylosoxidans, Brevibacterium halotolerans, Bacillus pumilus, Bacillus licheniformis and Lysinibacillus fusiformis (Salazar-Cerezo  et al., 2018).                              

Gibberellin (GA) is a phytohormone that promotes stem elongation and leaf expansion. Exogenous GA can enhance parthenocarpy in fruits, cause bolting, break tuber dormancy and increase fruit size and bud count. Gibberellin production by soil microorganisms can affect nodulation and plant growth, either positively or negatively. These microorganisms can cause nodule organogenesis and prevent nodulation during infection (Ahmad et al., 2019). Rhizobium phaseoli, the first known bacterium capable of producing GA, generates both GA1 and GA4. Acetobacter diazotrophicus, Azospirillum lipoferum and Herbaspirillum seropedicae produce biologically active GA1 and GA3, as reported in (Salazar-Cerezo et al., 2018). Adedayo and Babalola (2023) discovered that GA-producing fungi, such as Cladosporium sp., enhance tomato plant growth and contribute to pea plant colonization.
       
Cytokinin (CK) stimulates root development, plant cell division and hair creation, activate dormant buds and promotes seed germination. These plant hormones regulate nodulation, apical dominance and nitrogen fixation. PGPRs in Pseudomonas and Bacillus produce cytokinin, particularly zeatin (Yadav et al., 2018; Ladha et al., 2022). Rhizobium spp. and Pseudomonas fluorescens are bacteria that produce cytokinin (de Garcia Salamone  et al., 2006).
 
Major nutrients solubilization
 
Soil microorganisms play an important part in nutrient cycling. Crops that remain in the soil provide carbon, energy and nutrients to microorganisms. Rhizobium bacteria can solubilize nutrients like phosphorus, potassium, iron and zinc, boosting their availability for plants (Ramadan et al., 2016). Phosphorus (P) is crucial for the overall growth and development of plants. Soil has copious P in both organic and inorganic forms (apatite and secondary minerals like Fe, Al and Ca phosphates). Despite its abundance in soil as an insoluble nutrient, P is a significant growth-limiting factor. Soluble phosphorus in soil regulates its availability to plants (Matilla and Krell, 2018; Sakure and Bhosale, 2019). PGP bacteria act as a biological rescue mechanism by solubilizing insoluble inorganic P in soil and making it available to plants in the form of orthophosphate. The primary mechanism of P solubilization is the formation of organic acids. As a result, insoluble P is converted to its soluble form. Organic acids generated in soil can lower pH and bind mineral ions, leading to phosphate solubilization (Matilla and Krell, 2018). Gram-negative PGPRs mostly generate gluconic and 2-ketogluconic acids. Phosphate-solubilizing PGPRs create several organic acids, including isobutyric, lactic, isovaleric, glycolic, acetic, oxalic, malonic and succinic acids (Matilla and Krell, 2018). PGP microbes capable of phosphate solubilization include Arthrobacter, Azotobacter, Bacillus, Beijerinckia, Burkholderia, Citrobacter, Enterobacter, Erwinia, Flavobacterium, Halolamina, Microbacterium, Pantoea, Paenibacillus, Pseudomonas, Rhizobium, Rhodococcus, Serratia and Thiobacillus (Yadav et al., 2018; Matilla and Krell, 2018; Chaudhary et al., 2022). Potassium (K) is the third important macronutrient for plant growth and agricultural output. Soil contains about 90% potassium in the form of insoluble rocks and silicate minerals. The soluble form of potassium is found in soil in low concentrations. Inadequate fertilizer application can lead to potassium shortage, a severe limitation in crop productivity. Potassium deficiency leads to underdeveloped roots, tiny seeds, decreased agricultural yields and slower growth.   Soil bacteria can solubilize potassium, providing an alternate supply for plants. Potassium-solubilizing microorganisms (KSMs) produce and secrete organic acids to convert insoluble potassium into a form that plants can absorb. Many bacteria, including Acidithiobacillus ferrooxidans, Bacillus edaphicus, Bacillus mucilaginosus, Bacillus circulans, Paenibacillus sp., Burkholderia sp. and Pseudomonas sp., can solubilize K+ in into an accessible form. These bacteria improve K+ availability in agricultural soils (Mathur et al., 2019). Adedayo and Babalola found that Ceriporia lacerata, Aspergillus awamori and Penicillium digitatum can solubilize phosphate using organic acids and phytase (Adedayo and Babalola, 2023). Trichoderma sp. boosted mineral and nutrient absorption (N, K and P), while T. viride fungus increased soil nitrogen content (Adedayo and Babalola, 2023).
 
Iron solubilization and siderophore production
 
The soil limits the availability of essential micronutrients. Soil bacteria create siderophores, which are essential for iron-feeding in plants. These substances have a strong affinity for iron (III), the most prevalent type of iron in nature and are low molecular weight chelators. The iron solubilization method is based on the production of a stable siderophore. The Fe+3 complex can be absorbed by plants (Matilla and Krell, 2018; Mathur et al., 2019). Currently, there are roughly 500 siderophores known to exist. Pseudomonas fluorescens promotes plant development by producing pyoverdine and other siderophores. Microorganisms can create siderophoric chemicals such as catechol, carboxylate, hydroxamate and phenolate, which help protect plants from infections. Bacteria having iron chelation characteristics include Azotobacter, Bacillus, Enterobacter, Arthrobacter, Nocardia and Streptomyces (Ramadan et al., 2016). Siderophores increase the plant’s iron nutritional status and promote growth. Bacterial siderophores may chelate Fe+3 from soil, making it available to phytosidero-phores. However, the specific method remains uncertain. Plants can incorporate Fe+3-pyoverdine complexes, increasing the iron content of their tissues. Bacterial siderophores indirectly promote plant growth by reducing the availability of iron for phytopathogens (Matilla and Krell, 2018). Environmental factors affecting siderophore synthesis include pH, iron levels, trace elements and sufficient phosphorus, carbon and nitrogen supplies (Mathur et al., 2019). Siderophores transfer iron into bacteria through a system of ferric-specific ligands and membrane receptors, which operate as chelating agents. Siderophores inhibit pathogen growth by sequestering a restricted supply of iron (III) in the rhizosphere (Ramadan et al., 2016).
 
Soil microbes biocontrol activity
 
Excessive use of chemicals in agriculture, including pesticides, insecticides, herbicides and fertilizers, harms consumer health, biomagnification and economic loss (Tandon and Vats, 2016; Vats et al., 2017). Biological control organisms are non-disease-resistant organisms that inhibit the activities of plant diseases in soil (Saxena et al., 2019). Agents of microbiological control can protect plants through both direct and indirect interactions with diseases. Indirect mechanisms include ISR (microbial-induced systemic resistance), nutrition and space competition, which do not require pathogen interaction. Lytic enzymes and antibiotics are directly inhibiting pathogens (Kohl et al., 2019). Numerous bioactive compounds are produced by bacterial isolates with biocontrol agents, including antibiotics, volatiles, siderophores and growth-promoting compounds. With other microbes, these bacteria can compete and adapt quickly to environmental stress (Saxena et al., 2019). Trichoderma spp. generates antifungal volatile organic compounds (VOCs), including 6-pentyl-2H-pyran-2-one (PP) (Adedayo and Babalola, 2023). Various bacteria, such as Agrobacterium, Pseudomonas, Bacillus, Pantoea, Serratia, Stenotrophomonas, Streptomyces and Trichoderma, have been studied for antibiotic manufacturing capacity (Ramadan et al., 2016; Kohl et al., 2019). Some bacterial species and strains for producing agroinoculants, including Agrobacterium tumefaciens, Streptomyces lydicus, Bacillus subtilis, Burkholderia cepacia, Alcaligenes sp., Serratia marcescens GPS5, Erwinia amylovora and Streptomyces griseoviridis. Biocontrol strains produce a variety of antibiotics, including polyketides, phenazine, heterocyclic nitrogenous compounds, phenylpyrroles, aminopolyols, cyclic lipopeptides and volatile antibiotics (Saxena et al., 2019; Arseneault and Filion 2017; Glick, 2020). Several studies have found that biocontrol bacterial strains produce antibiotics to target diseases (Ram et al., 2018; Glick, 2020; Kenawy et al., 2019). Ongena and Jacques (2008) studied the formation of fengycin, iturin and surfactin by Bacillus sp. Raaijmakers and Mazzola (2012) studied the formation of antibiotic metabolites (phenazine, 2, 4-diacetylphloro-glucinol and pyrrolnitrin) in Pseudomonas sp. Adedayo and Babalola (2023) found that T. harzianum inhibited the growth of phytopathogen fungus including F. oxysporum, Phythium sp. and R. solani. Gliocladium virens generates gliovirin, an antibiotic that prevents the growth of F. oxysporum, Pythium ultimum.
 
Quorum sensing interference with virulence
 
Bacteria use quorum sensing (QS), which includes autoinducers that are extracellular signaling molecules to communicate cell density. As the bacterial population grows, gene expression changes due to the advantages of certain processes that are exclusive to this group. QS controls processes like as antibiotic synthesis, biofilm development and virulence factor secretion. The expression of bacterial pathogenicity in plants depends on quorum sensing (QS). Plant pathogenic strains such Pseudomonas syringae, Pantoea stewartii, Erwinia chrysanthemi and Burkholderia glumae require QS to colonize and express virulence proteins (Quiñones  et al. 2005; Koutsoudis et al., 2006; Hussain et al., 2008; Kang et al., 2018). Plant and microbe extracts with QS inhibitory action have been employed to treat multi-drug-resistant bacteria and in the food packaging industry (Mookherjee et al., 2018). Quorum quenching (QQ), or interference with pathogen QS, is a viable biocontrol method (Mookherjee et al., 2018; Noorashikin et al., 2016; Torabi Delshad  et al., 2018). QQ interference can occur in three ways: stopping signal molecule manufacturing, degrading signal molecules and blocking signal corpuscle receptors (Torabi Delshad  et al., 2018). BCAs can disrupt QS against pathogens by blocking the formation of enzymatic breakdown molecules such as lactonases, pectinases and chitinases that cause infections (Brígidoet_al2019; Panpatte et al., 2020). AHLs (Acyl-homoserine lactones), autoinducers, degrading bacteria include Bacillus sp., Acinetobacter sp., Burkholderia sp., Serratia sp., Lysinibacillus sp., Pseudomonas sp., Strepsporangium sp., Rhodococcus sp., Myroides sp. and Enterobacter sp. (Noorashikin et al., 2016; Chan et al., 2011; Ma et al., 2013). It has been demonstrated that AHL-degrading Lysinibacillus reduces the amount of potato soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum (Garge et al., 2016; Jose et al., 2019).
 
Lytic enzymes
 
The generation of lytic enzymes is one potential pathogen-killing strategy. PGPRs inhibit fungal pathogens (Fusarium oxysporum, Sclerotinia sclerotiorum and Botrytis cinerea) and other soil-borne pathogens by secreting enzymes like chitinases, proteases, hydrolases and glucanases (Ramadan et al., 2016; Mathur et al., 2019). BCAs primarily inhibit the growth of soil-borne pathogens by producing and secreting cell wall lytic enzymes (CWLEs) (Singh et al., 2017). CWLEs damage the structural integrity of the target pathogen’s cell wall. The cell wall of fungi is pathogenic and consists primarily of chitin and β-1,4-N-acetyl glucosamine. CWLEs, including β-1,3-glucanase and chitinase, are involved in the majority of BCAs. CWLEs neutralize the pathogen inhibitory effect by lysing cell walls (Goswami et al., 2016). PGPRS inhibits well-known phyto-pathogens such as Rhizoctonia solani and Phytophthora capsici (Kannojia et al., 2019; Islam et al., 2016).
 
Induced systemic resistance
 
Beneficial bacterial strains manage diseases by inducing systemic resistance (ISR). Biocontrol agents and Microbial metabolites can trigger a plant’s immune response, leading to disease resistance (Ramadan et al., 2016). Plants identify microbial molecules (exopolysaccharide, lipopolysaccharide and chitin oligosaccharide) generated by helpful microbes. Bacterial species such as Bacillus amyloliquefaciens, B. atrophaeus, B. cereus, B. megaterium, B. subtilis, Paenibacillus alvei, Pseudomonas fluorescens, Pseudomonas aeruginosa and Streptomyces pactum are effective against viral, fungal, bacterial, infections via ISR (Yu et al., 2022). ISR involves plant hormones such as ethylene, jasmonic acid and salicylic acid. Plant defense against phytopathogens involves the ethylene and jasmonic acid signaling pathways. ISR manifests as changes in cell wall integrity, biochemistry and physiology. Bacterial strains having ISR-eliciting characteristics have been shown to effectively combat a variety of fungal infections. Bacteria such as Pseudomonas fluorescens, Pseudomonas aeruginosa, Bacillus amyloliquefaciens, B. subtilis, B. pumilus, B. pasteurii, B. cereus, B. sphaericus and B. mycoides, have been identified (Panpatte et al., 2020; Kannojia et al., 2019). Cotton plants treated with P. chrysogenum exhibited ISR against T. viride, Verticillium dahlia, P. simplicissimum, T. harzianum and Acremonium sclerotigenum effectively induced ISR in agricultural plants including cucumber and tomato (Adedayo and Babalola, 2023).
 
Synergistic microbial mechanisms
 
Plants were more effectively inoculated with bacterial consortia compared to single strains. IAA and ACC deaminase synthesis have been shown to have synergistic effects on N2 fixation (Ma et al., 2004; Serova et al., 2017; Defez et al., 2016; Defez et al., 2019; Nascimento et al., 2012; Nascimento et al., 2019; Alemneh et al., 2020), stress tolerance (Defez et al., 2019; Nascimento et al., 2012; Nascimento et al., 2019; Alemneh et al., 2020; Orozco-Mosqueda et al., 2020) and phosphate solubilization (Alemneh et al., 2021). IAA and ACC deaminase play multiple roles in BNF fixation, including enhancing nodule formation, increasing rhizobia competitiveness, suppressing nodule senescence and upregulating genes linked with legume-rhizobia symbiosis (Alemneh et al., 2020). Knockout and overproducing strains of the ACC deaminase gene were used to study its role in nodule formation (Alemneh et al., 2021). In terms of plant colonization and nodulation, the mutant strain of Mesorhizobium loti ACC deaminase that overproduces the enzyme performed better than the wild type (Ma et al., 2004). In Mesorhizobium loti, the acdS gene is located in the symbiotic island and its expression is controlled by the N2 fixation regulator NifA2 (Nukui et al., 2006). Senescent nodules have enhanced expression and transcription of PsACS2, which encodes ACC synthase, an enzyme implicated in ethylene production (Serova et al., 2017). PGP bacteria produce ACC deaminase can improve nitrogen fixation by increasing the lifespan of functioning nodules. Comparing 31-day-old nodules of a transformed Mesorhizobium sp. expressing ACC deaminase to its parental strain devoid of this activity, Nascimento et al., (2012) discovered nitrogenase activity. Compared to the ACC deaminase mutant strain, Nascimento et al., (2019) discovered that the Pseudomonas fluorescens YsS6 strain that produces ACC deaminase enhanced the nodulation capacity of alpha- and beta-rhizobia. Free-living ACC deaminase-producing bacteria promote rhizobia nodulation. IAA, a biomolecule, plays a role in legume-rhizobia interactions by regulating nodule primordium formation and cell division. IAA affects the expression of genes involved in rhizobia and nodule formation in plant cells (Alemneh 2020). Camerini et al., (2008) found a link between IAA and nodulation, with IAA-negative Rhizobium leguminosarum bv. viciae producing fewer nodules than the parent strain. Additionally, using IAA-producing nodule-enhancing rhizobacteria as a co-inoculum promoted rhizobia colonization due to their production of caproic acid (Alemneh et al., 2020). Ensifer meliloti RD64-induced 45-day-old nodules with IAA overproduction showed a longer nitrogen-fixing zone and a lower senescent zone compared to the wild-type strain (Defez et al., 2016). Scientists investigated the impact of ACC deaminase and IAA on the stress response (Defez et al., 2019; Orozco-Mosqueda  et al., 2019). Interaction between the two properties was shown when Pseudomonas sp. UW4 trehalose (treS) and ACC deaminase (acdS) mutant strains (mutated at one or both features) were used as bioinoculant on tomato plants under salt stress. The impact of single gene mutations is greater than that of multiple ones (Orozco-Mosqueda  et al., 2019). Alemneh et al., (2021) found ACC deaminase-producing bacteria capable of phosphate solubilization, indicating ACC deaminase-mediated P solubilization. Inoculating chickpeas with ACC expressing Burkholderia sp. 12F led to increased P nutrition and enhanced nodulation rates. Metabolomic investigations of the soil microbiome are crucial for understanding plant-soil-microbe interactions, as synergy can occur between bacteria, arbuscular mycorrhizal fungi and bacterial ACC deaminase (Orozco-Mosqueda  et al., 2020).

CONCLUSION

The soil system’s complexity, including stratification and microhabitats, promotes the growth of a diversified microbial community. The most difficult task at the moment is analyzing data from microbial communities. Understanding bacterial functional groups and community dynamics is crucial for knowing how soil ecosystems work, in addition to taxonomy. The rhizosphere is a hotspot for the microorganism and microbial gene transfer and contains a wealth of genetic capabilities, making PGPR genetic engineering a valuable tool for sustainable agriculture. What impact do environmental changes have on soil ecology and how may sustainable agriculture methods maintain this function? It is unclear how they are shaped by plant-microorganism interactions. Plant genome engineering is a tool for sustainable agriculture that utilizes unique plant-microbe communication. Sustainable agriculture requires a better understanding of soil-microbe-plant systems and their impact on short- and long-term sustainability. Future research should focus on utilizing genetically engineered plants and microorganisms for sustainable agriculture.
 

ACKNOWLEDGEMENT

The authors are thankful to the convenor, Department of Botany, Prof. Sarita Srivastava and Principal, Prof. Ajay Prakash Khare, CMP Degree College, University of Allahabad, for providing the necessary facilities to carry out the research.
 
Author’s contribution
 
All authors made substantial contributions to the conception and design, acquisition of data, or analysis and interpretation of data.
 
Funding
 
The authors declare that no funding was received for the present work.

CONFLICT OF INTEREST

The authors express no conflict of interest.

REFERENCES


  1. Adedayo, A.A. and Babalola, O.O. (2023). Fungi that promote plant growth in the Rhizosphere boost crop growth. J. Fungi. 9: 239. 

  2. Ahmad, M., Nadeem, S.M. and Zahir, Z.A. (2019). Plant-microbiome Interactions in Agroecosystem: An Application. In Microbiome in Plant Health and Disease; Springer: Singapore. pp. 251-291.

  3. Aira, M., Gómez-Brandón, M., Lazcano, C., Bååth, E. (2010). Plant genotype strongly modifies the structure and growth of maize rhizosphere microbial communities. Soil Biol. Biochem.  42: 2276-2281.

  4. Alemneh, A.A., Zhou, Y., Ryder, M.H. and Denton, M.D. (2020). Mechanisms in plant growth-promoting rhizobacteria that enhance legume-rhizobial symbioses. J. Appl. Microbiol. 129: 1133-1156.  

  5. Alemneh, A.A., Zhou, Y., Ryder, M.H. and Denton, M.D. (2021). Is phosphate solubilizing ability in plant growth-promoting rhizobacteria isolated from chickpea linked to their ability to produce ACC deaminase? J. Appl. Microbiol. 131: 2416-2432. 

  6. Anjum, M.A., Sajjad, M.R., Akhtar, N., Qureshi, M.A., Iqbal, A., Jami, A.R., Mahmud-ul-Hasan. (2007). Response of cotton to plant growth promoting Rhizobacteria (PGPR) inoculation under different levels of nitrogen. Journal of Agricultural Research.  45 (Suppl 2): 135-143.

  7. Arseneault, T., Filion, M. (2017). Biocontrol through antibiosis: Exploring the role played by subinhibitory concentrations of antibiotics in soil and their impact on plant pathogens. Can. J. Plant Pathol. 39: 267-274.

  8. Bakker, P., Berendsen, R., Doornbos, R., Wintermans, P. and Pieterse, C. (2013). The rhizosphere revisited: Root microbiomics. Front. Plant Sci. 4: 165.  

  9. Bar-On, Y.M., Phillips, R., Milo, R. (2018). The biomass distribution on Earth. Proc. Natl. Acad. Sci. USA. 115: 6506-6511.

  10. Brígido, C., Singh, S., Menéndez, E., Tavares, M.J., Glick, B.R., Félix, M.d.R., Oliveira, S. and Carvalho, M. (2019). Diversity and functionality of culturable endophytic bacterial communities in Chickpea plants. Plants. 8: 42.

  11. Camerini, S., Senatore, B., Lonardo, E., Imperlini, E., Bianco, C., Moschetti, G., Rotino, G.L., Campion, B. and Defez, R. (2008). Introduction of a novel pathway for IAA biosynthesis to rhizobia alters vetch root nodule development. Arch. Microbiol. 190: 67-77.

  12. Chaudhary, P., Agri, U., Chaudhary, A., Kumar, A. and Kumar, G. (2022). Endophytes and their potential in biotic stress management and crop production. Front. Microbiol. 13: 933017. 

  13. Chan, K.G., Atkinson, S., Mathee, K., Sam, C.K., Chhabra, S.R., Cámara, M., Koh, C.L. and Williams, P. (2011). Characterization of N-acylhomoserine lactone-degrading bacteria associated with the Zingiber officinale (ginger) rhizosphere: Co-existence of quorum quenching and quorum sensing in Acinetobacter and Burkholderia. BMC Microbiol. 11: 51.

  14. de Bruijn, F.J. and Hungria, M. (2022). Biological Nitrogen Fixation. In Good Microbes in Medicine, Food Production, Biotechnology, Bioremediation and Agriculture; John Wiley and Sons, Ltd.: Hoboken, NJ, USA, pp. 466-475.   

  15. de Corato, U. (2020). Towards new soil management strategies for improving soil Quality and ecosystem services in sustainable agriculture: Editorial overview. Sustainability. 12: 9398.  

  16. de Garcia Salamone, I.E., Hynes, R.K. and Nelson, L.M. (2006). Role of Cytokinins in Plant Growth Promotion by Rhizosphere Bacteria. In PGPR: Biocontrol and Biofertilization; Siddiqui, Z.A., Ed.; Springer: Dordrecht, The Netherlands, pp. 173- 195, ISBN 978-1-4020-4152-5. 

  17. Defez, R. andreozzi, A., Romano, S., Pocsfalvi, G., Fiume, I., Esposito, R., Angelini, C. and Bianco, C. (2019). Bacterial IAA-Delivery into Medicago Root Nodules Triggers a Balanced Stimulation of C and N Metabolism Leading to a Biomass Increase. Microorganisms. 7: 403.  

  18. Defez, R., Esposito, R., Angelini, C. and Bianco, C. (2016). Over- production of Indole-3-Acetic acid in Free-Living Rhizobia Induces Transcriptional Changes Resembling Those Occurring in Nodule Bacteroids. Mol. Plant Microbe Interact. 29: 484-495. 

  19. Dubey, D.-A., Malla, M., Khan, F., Chowdhary, K., Yadav, S., Kumar, A., Sharma, S., Khare, P.K., Khan, M. and Khan, M. (2019). Soil microbiome: A key player for conservation of soil health under changing climate. Biodivers. Conserv. 28: 2405-2429. 

  20. Ettema, C.H. and Wardle, D.A. (2002). Spatial soil ecology. Trends Ecol. Evol. 17: 177-183. 

  21. Eva, L. and Gyongyver, M. (2019). Is PGPR an Alternative for NPK Fertilizers in Sustainable Agriculture? In Microbial Interventions in Agriculture and Environment; Springer: Cham, Switzerland, pp. 51-62. ISBN 9789811383908. 

  22. Fan, K., Cardona, C., Li, Y., Shi, Y., Xiang, X., Shen, C., Wang, H., Jack, G. and Chu, H. (2017). Rhizosphere-associated bacterial network structure and spatial distribution differ significantly from bulk soil in wheat crop fields. Soil Biol. Biochem. 113: 275-284. 

  23. Fowler, D., Steadman, C.E., Stevenson, D., Coyle, M., Rees, R.M., Skiba, U.M., Sutton, M.A., Cape, J.N., Dore, A.J. and Vieno, M. (2015). Effects of global change during the 21st century on the nitrogen cycle. Atmos. Chem. Phys. 15: 13849-13893. 

  24. Garge, S.S. and Nerurkar, A.S. (2016). Attenuation of quorum sensing regulated virulence of Pectobacterium carotovorum subsp. carotovorum through an AHL Lactonase Produced by Lysinibacillus sp. Gs50. PLoS ONE. 11: e0167344.  

  25. Geller, A.M. and Levy, A. (2023). “What I cannot create, I do not understand”: Elucidating microbe-microbe interactions to facilitate plant microbiome engineering. Curr. Opin. Microbiol. 72: 102283. 

  26. Goswami, D., Thakker, J.N. and Dhandhukia, P.C. (2016). Portraying mechanics of plant growth promoting rhizobacteria (PGPR): A review. Cogent Food Agric. 2: 1127500. 

  27. Glick, B.R. (2020). Biocontrol of Bacteria and Fungi. In Beneficial Plant-Bacterial Interactions; Glick, B.R., Ed.; Springer International Publishing: Cham, Switzerland. pp. 181-230, ISBN 978-3-030-44368-9.

  28. Goswami, D., Thakker, J.N. and Dhandhukia, P.C. (2016). Portraying mechanics of plant growth promoting rhizobacteria (PGPR): A review. Cogent Food Agric. 2: 1127500.  

  29. Husna, Hussain, A., Shah, M., Hamayun, M., Iqbal, A., Qadir, M., Alataway, A., Dewidar, A.Z., Elansary, H.O. and Lee, I.J. (2023). Phyto- hormones producing rhizobacteria alleviate heavy metals stress in soybean through multilayered response. Microbiol. Res. 266: 127237. 

  30. Hussain, M.B.B.M., Zhang, H.B., Xu, J.L., Liu, Q., Jiang, Z. and Zhang, L.H. (2008). The acyl-homoserine lactone-type quorum- sensing system modulates cell motility and virulence of Erwinia chrysanthemi pv. zeae. J. Bacteriol. 190: 1045-1053. 

  31. Islam, S., Akanda, A.M., Prova, A., Islam, M.T. and Hossain, M.M. (2016). Isolation and identification of plant growth promoting rhizobacteria from Cucumber rhizosphere and Their effect on plant growth promotion and disease suppression. Front. Microbiol. 6: 1360. 

  32. Jansson, J.K. and Hofmockel, K.S. (2020). Soil microbiomes and climate change. Nat. Rev. Microbiol. 18: 35-46. 

  33. Jose, P., Ramasamy, K., Kwon, S.-W., Veeranan, J., Murugaiyan, S., Gopal, N.O., Kumutha, K. and Anandham, R. (2019). Interference in quorum sensing and virulence of the phytopathogen Pseudomonas syringae pv. passiflorae by Bacillus and Variovorax species. BioControl. 64: 423-433. 

  34. Kang, B.R. anderson, A.J. and Kim, Y.C. (2018). Hydrogen Cyanide Produced by Pseudomonas chlororaphis O6 Exhibits Nematicidal Activity against Meloidogyne hapla. Plant Pathol. J. 34: 35-43. 

  35. Kannojia, P., Choudhary, K.K., Srivastava, A.K. and Singh, A.K. (2019). PGPR Bioelicitors: Induced Systemic Resistance (ISR) and Proteomic Perspective on Biocontrol. In PGPR Amelioration in Sustainable Agriculture; Elsevier: Amsterdam, The Netherlands, ISBN 978-0-12-816019-0. 

  36. Kenawy, A., Joe Dailin, D., Abo-Zaid, G., Malek, R.A., Ambehabati, K., Zakaria, K., Sayyed, R. and El Enshasy, H. (2019). Biosynthesis of Antibiotics by PGPR and Their Roles in Biocontrol of Plant Diseases. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland, pp. 1-35, ISBN 9789811369858. 

  37. Khan, A.A.H. (2019). Plant-Bacterial Association and Their Role as Growth Promoters and Biocontrol Agents. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland, pp. 389-419, ISBN 978981 1369858.  

  38. Köhl, J., Kolnaar, R. and Ravensberg, W.J. (2019). Mode of action of microbial biological control agents against plant diseases: Relevance beyond efficacy. Front. Plant Sci. 10: 845.  

  39. Koutsoudis, M.D., Tsaltas, D., Minogue, T.D. and von Bodman, S.B. (2006). Quorum-sensing regulation governs bacterial adhesion, biofilm development and host colonization in Pantoea stewartii subspecies stewartii. Proc. Natl. Acad. Sci. USA 103, 5983-5988. 

  40. Ladha, J.K., Peoples, M.B., Reddy, P.M., Biswas, J.C., Bennett, A., Jat, M.L. and Krupnik, T.J. (2022). Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems. Field Crops Res. 283: 108541. 

  41. Li, X., Rui, J., Mao, Y., Yannarell, A. and Mackie, R. (2014). Dynamics of the bacterial community structure in the rhizosphere of a maize cultivar. Soil Biol. Biochem. 68: 392-401.  

  42. Ma, A., Lv, D., Zhuang, X. and Zhuang, G. (2013). Quorum Quenching in Culturable Phyllosphere Bacteria from Tobacco. Int. J. Mol. Sci. 14: 14607-14619.

  43. Ma, W., Charles, T.C. and Glick, B.R. (2004). Expression of anexo- genous 1-aminocyclopropane-1-carboxylate deaminase gene in Sinorhizobium meliloti increases its ability to nodulate alfalfa. Appl. Environ. Microbiol. 70: 5891-5897.

  44. Mathur, A.; Koul, A.; Hattewar, J. (2019). Plant Growth-promoting Rhizobacteria (PGPRs): Significant Revolutionary Tools for Achieving Long-Term Sustainability and Combating the Biotic Stress Caused by the Attack of Pathogens Affecting Crops in Agriculture. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland. pp. 379-388, ISBN 9789811369858.

  45. Matilla, M. and Krell, T. (2018). Plant growth promotion and biocontrol mediated by plant-associated bacteria. In plant mcrobiome: Stress response; Springer: Cham, Switzerland. pp. 45- 80. ISBN 978-981-10-5513-3. 

  46. Mendes, R., Garbeva, P. and Raaijmakers, J.M. (2013). The rhizosphere microbiome: Significance of plant beneficial, plant pathogenic and human pathogenic microorganisms. FEMS Microbiol. Rev. 37: 634-663. 

  47. Mookherjee, A., Singh, S. and Maiti, M.K. (2018). Quorum sensing inhibitors: Can endophytes be prospective sources? Arch. Microbiol. 200: 355-369. 

  48. Nascimento, F.X., Brígido, C., Glick, B.R., Oliveira, S. and Alho, L. (2012). Mesorhizobium ciceri LMS-1 expressing an exogenous 1 aminocyclopropane-1-carboxylate (ACC) deaminase increases its nodulation abilities and chickpea plant resistance to soil constraints. Lett. Appl. Microbiol. 55: 15-21.

  49. Nascimento, F.X., Tavares, M.J., Franck, J., Ali, S., Glick, B.R. and Rossi, M.J. (2019). ACC deaminase plays a major role in Pseudomonas fluorescens YsS6 ability to promote the nodulation of Alpha- and Betaproteobacteria rhizobial strains. Arch. Microbiol. 201: 817-822.

  50. Noorashikin, M.N., Li, L.Y., Karim, M., Daud, H.M. and Natrah, F.M.I. (2016). Screening and identification of quorum sensing degraders from live feed Artemia. J. Environ. Biol. 37: 811-816. 

  51. Nukui, N., Minamisawa, K., Ayabe, S.-I. and Aoki, T. (2006). Expression of the 1-aminocyclopropane-1-carboxylic acid deaminase gene requires symbiotic nitrogen-fixing regulator gene nifA2 in Mesorhizobium loti MAFF303099. Appl. Environ. Microbiol. 72: 4964-4969.

  52. O’Brien, S.L., Gibbons, S.M., Owens, S.M., Hampton-Marcell, J., Johnston, E.R., Jastrow, J.D., Gilbert, J.A., Meyer, F. and Antonopoulos, D.A. (2016). Spatial scale drives patterns in soil bacterial diversity. Environ. Microbiol. 18: 2039-2051. 

  53. Ongena, M, Jacques, P. (2008). Bacillus lipopeptides: Versatile weapons for plant disease biocontrol. Trends Microbiol. 16: 115-125.

  54. Orozco-Mosqueda, M.d.C., Duan, J., DiBernardo, M., Zetter, E., Campos- García, J., Glick, B.R. and Santoyo, G. (2019). The production of acc deaminase and trehalose by the plant growth promoting bacterium pseudomonas sp. uw4 synergistically protect tomato plants against salt stress. Front. Microbiol. 10: 1392. 

  55. Orozco-Mosqueda, M.d.C., Glick, B.R. and Santoyo, G. (2020). ACC deaminase in plant growth-promoting bacteria (PGPB): An efficient mechanism to counter salt stress in crops. Microbiol. Res. 235: 126439. 

  56. Panpatte, D., Jhala, Y. and Vyas, R. (2020). Signaling pathway of induced systemic resistance. In molecular aspects of plant beneficial microbes in Agriculture; Elsevier: Amsterdam, The Netherlands, pp. 133-141, ISBN 978-0-12-818469-1.

  57. Quiñones, B., Dulla, G. and Lindow, S.E. (2005). Quorum sensing regulates exopolysaccharide production, motility and virulence in Pseudomonas syringae. Mol. Plant Microbe Interact. 18: 682-693. 

  58. Raaijmakers, J.M. and Mazzola, M. (2012). Diversity and natural functions of antibiotics produced by beneficial and plant pathogenic bacteria. Annu. Rev. Phytopathol. 50: 403-424. 

  59. Ram, R.M., Keswani, C., Bisen, K., Tripathi, R., Singh, S.P. and Singh, H.B. (2018). Biocontrol Technology; Elsevier: Amsterdam, The Netherlands. pp. 177-190.

  60. Ramadan, E., Abdelhafez, A., Enas, A. and Saber, F. (2016). Plant growth promoting rhizobacteria and their potential for biocontrol of phytopathogens. Afr. J. Microbiol. Res. 10: 486-504.

  61. Rchiad, Z., Dai, M., Hamel, C., Bainard, L.D., Cade-Menun, B.J., Terrat, Y., St-Arnaud, M. and Hijri, M. (2022). Soil depth significantly shifted microbial community structures and functions in a semiarid prairie agroecosystem. Front. Microbiol. 13: 815890. 

  62. Sakure, S. and Bhosale, S. (2019). Actinobacteria for Biotic Stress Management. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland, pp. 363-378, ISBN 9789811369858.

  63. Salazar-Cerezo, S., Martínez-Montiel, N., García-Sánchez, J., Pérez- Y-Terrón, R. and Martínez-Contreras, R.D. (2018). Gibberellin biosynthesis and metabolism: A convergent route for plants, fungi and bacteria. Microbiol. Res. 208: 85-98. 

  64. Saxena, P., Srivastava, J., Pandey, S., Srivastava, S., Maurya, N., Chand, K., Mishra, S., Asthana, G., Bhargava, P. and Kumar, R. (2019). Plants for biocontrol and biological control of plant pathogens. In plant biotic interactions; Springer: Cham, Switzerland. pp. 147-179. ISBN 978-3-030-26656-1. 

  65. Serova, T.A., Tikhonovich, I.A. and Tsyganov, V.E. (2017). Analysis of nodule senescence in pea (Pisum sativum L.) using laser microdissection, real-time PCR and ACC immunolocali- zation. J. Plant Physiol. 212: 29-44.

  66. Shahzad, R., Waqas, M., Khan, A.L., Al-Hosni, K., Kang, S.M., Seo, C.W. and Lee, I.J. (2017). Indoleacetic acid production and plant growth promoting potential of bacterial endophytes isolated from rice (Oryza sativa L.) seeds. Acta Biol. Hung.  68: 175-186.

  67. Singh, V.K., Singh, A.K. and Kumar, A. (2017). Disease management of tomato through PGPB: Current trends and future perspective. 3 Biotech. 7: 255.

  68. Suresh A., Ashraf, A.M., Sree, V.S., Dhas, A.K.S. and Chacko, J.P. (2025). Plant-microbe interactions and rhizosphere dynamics for sustainable agriculture: A review. Agricultural Reviews. 1-9. doi: 10.18805/ag.R-2829.

  69. Tabish, A., Kumar, S., Kumar, S. and  Meena, M.R. (2020). Importance of plant growth promoting rhizobacteria (PGPR) in agriculture: A review. Bhartiya Krishi Anushandhan Patrika. 35(1 and 2): 75-78. doi: 10.18805/BKAP200.

  70. Tandon, S. and Vats, S. (2016). Microbial biosynthesis of Cadmium sulfide (CDS) nanoparticles and their characterization. Eur. J. Pharm. Med. Res. 3: 545-550. 

  71. Thakur, M.P. and Geisen, S. (2019). Trophic regulations of the soil microbiome. Trends Microbiol. 27: 771-780. 

  72. Torabi Delshad, S., Soltanian, S., Sharifiyazdi, H. and Bossier, P. (2018). Effect of quorum quenching bacteria on growth, virulence factors and biofilm formation of Yersinia ruckeri in vitro and an in vivo evaluation of their probiotic effect in rainbow trout. J. Fish. Dis. 41: 1429-1438.

  73. Turan, M., Topcuoglu, B., Kitir, N., Alkaya, Ü., Erçelik, F., Nikerel, E., Günes, A., Turan, M., Topcuoglu, B. and Kitir, N. (2016). Plant Growth Promoting Rhizobacteria’s (PGPR’s) Enzyme Dynamics in Soil Remediation. In Soil Contamination- Current Consequences and Further Solutions; IntechOpen: London, UK, ISBN 978-953-51-2816-8. 

  74. Unnikrishnan, M.A., Rajalekshmi, K. and Bindhu, P.S. (2023). Soil degradation vs soil retrogression: A review. Agricultural Reviews. 44(4): 509-515. doi: 10.18805/ag.R-2241.

  75. Vats, S. and Bhargava, P. (2017). Alternate Energy: Fuel for “Modi’s India” and “Smart cities”. Int. J. Curr. Res. 9: 49090-49097.

  76. Yadav, A.N., Kumar, V., Dhaliwal, H., Prasad, R. and Saxena, A. (2018). Microbiome in Crops: Diversity, Distribution and Potential Role in Crop Improvement. In New and Future Developments in Microbial Biotechnology and Bioengineering: Crop Improvement through Microbial Biotechnology; Elsevier: Amsterdam, The Netherlands, pp. 305-332, ISBN 978-0- 444-63987-5. 

  77. Yu, Y., Gui, Y., Li, Z., Jiang, C., Guo, J. and Niu, D. (2022). Induced systemic resistance for improving plant immunity by beneficial microbes. Plants. 11: 386.
Published In
Indian Journal of Agricultural Research
Article Metrics
Metrics Icon
0
Views
0
Citations
Reviewed By
Share Article
Download Article
In this Article
    Contact us
    Follow us

    ABSTRACT

    The soil microorganism promotes soil fertility, plant productivity and ecosystem services. Recent molecular research suggests that the soil microorganism has been significantly underestimated. In addition to metagenomic analyses. Metatranscriptomic and Metaproteomics studies targeting the functional part of the microbiome are becoming more common and microorganism functional role and plant-microbe interactions require better understanding. These are crucial for understanding the microbiome’s functional role and for figuring out how microbes and plants interact. Plant growth-promoting rhizobacteria (PGPRs) are helpful bacteria that colonize the roots of plants to stimulate plant growth. They benefit plants in several ways, including enhancing nutrient synthesis and uptake, as well as preventing disease. Understanding plant-microbe interactions in natural and agroecosystems can improve soil fertility and high-yield food production.

    INTRODUCTION

    Global population expansion has led to a rise in demand for agricultural products. Increased production depletes topsoil, reduces organic matter content and negatively impacts soil ecology. Soil bacteria play a crucial role in maintaining soil ecology and ensuring stability under disturbance. Inadequate land usage can contaminate groundwater, plant disease outbreaks and air pollution. The population’s awareness of environmental issues highlights the need for sustainable and healthy food choices. Therefore, environment-friendly alternatives for sustainable agriculture are gaining popularity. Sustainable agroecosystems as extremely resilient, adaptive and varied (Suresh et al., 2025: de Corato and Towards, 2020). These challenges are interconnected, with variety providing greater adaptability and adaptation is an important component of resilience in agroecosystems. The variety of soil bacteria, which plays an important role in nutrient recycling and soil formation, are a critical issue in sustainable agriculture. The essential issue to be examined is the functional diversity of soil bacteria, not their taxonomic organization. A better knowledge of the role of microorganisms in agroecosystem functioning, particularly in plant development and soil fertility, is critical for sustainable agricultural output.
     
    Soil microorganisms
     
    Distribution
     
    Microorganisms comprise roughly 17% of the world’s biomass (Bar-On et al., 2018). Soil is the most complicated environment for microbial life, with around 4-5 x 1030 cells (Dubey et al., 2019). The soil microorganism primarily consists of bacteria, archaea, fungi, protozoa and viruses etc. According to Mendes et al., (2013), 1gm of soil contains approximately 108-109 bacteria, 107-108 viruses and 105-106 fungal cells. Soil microbial communities provide ecological services such as nutrient recycling, carbon sequestration, water retention, plant growth promotion and defense (O’Brienet_al2016; Jansson et al., 2019; Thakur et al., 2019). The rhizosphere is a biological hotspot that influences microbial community composition through interactions between plants-microbes and microbes-microbes. Plant roots produce organic chemicals that promote microbial activity (Fan et al., 2017). Bacterial community composition varies significantly across bulk and rhizospheric soils, resulting in reduced diversity from bulk soil to roots (Fan et al., 2017; Unnikrishnan et al., 2023). Tobacco and Arabidopsis plants have a significantly higher number of microorganisms in their rhizosphere compared to bulk soil (Bakker et al., 2013). The soil microbiome’s geographical heterogeneity is affected by both environmental factors and population processes (Ettema et al., 2002). Plant root exudates in the rhizosphere and environmental conditions influence soil microbial colonization, which can be biotic or abiotic. Li et al., (2014) conducted studies in corn fields. The study found that Proteobacteria, Actinobacteria and Bacteroidetes, dominated the rhizosphere soil microbiota, accounting for 73-80% of total reads compared to 46-56% in bulk soil. The rhizosphere had lower abundances of Acidobacteria, Firmicutes, Gemmatimonadetes, Nitrospira and Chloroflexi, compared to the bulk soil (Li et al., 2014). Fan et al., (2017) examined the microbial population in wheat fields, focusing on three soil compartments: firmly and loosely attached soil and bulk soil. The study found that Proteobacteria, Actinobacteria and Acidobacteria dominated all soils. Actinobacteria, Alphaproteobacteria, Bacteroidetes and Verrucomicrobia were more abundant, while Chloroflexi, Gammaproteobacteria and Deltaproteobacteria were less abundant in tightly bound soils compared to others. Actinobacteria were found to be more abundant in closely bound soil due to their ability to produce antibiotics, while Alphaproteobacteria were present due to their rapid proliferation. Rchiad et al., (2022) found that in a semiarid agroecosystem, soil microbiota diversity does not decrease with depth, although microbial profiles differed. The study identified 43 microbial phyla, with 12 impacted by soil depth. Microbial communities transitioned from top (0-15 cm) to deep (30-60 cm) at the phylum/family level. The abundance of Verrucomicrobia and Bacteroidetes decreased with soil depth. Depth affects the quantity of soil functional genes, with the majority of functional categories found in the top or deepest layers (Rchiad et al., 2022).
     
    Beneficial interactions between plant-microbes
     
    Bio-stimulant microbes
     
    In nature, microbes and plants coexist, but they can be free-living, attached or form a symbiotic relationship with the host plants. Various relationships exist, including parasitism, mutualism and commensalism. Plants have interacted with a wide variety of plant growth-promoting rhizobacteria (PGPR) throughout their evolutionary history. Bacterial rhizobiome mapping is advancing fast due to novel identification methods, huge genome-sequencing strategies and current developments in metagenomics. These findings identified new bacterial species and how they promote plant growth and serve as biocontrol (Tabish Akhtar  et al., 2020; Khan, 2019). By fixing atmospheric nitrogen, producing siderophores, plant growth hormones (cytokinin’s, auxins and gibberellins), volatile compounds and solubilizing nutrients and minerals (phosphorus, potassium, zinc, etc.), microorganisms that live in soil can indirectly stimulate plant growth. Certain PGPR species also contribute to a plant’s ability to withstand stress. They can boost the plant’s ability to absorb heavy metals or other harmful substances and assist the host plant in overcoming salinity and drought stress (Li et al., 2014; Aira et al., 2010; Husna et al., 2023). PGPRs are crucial bacteria for agriculture because they promote plant growth. Biological nitrogen fixation through raising nitrogen content, biomass, germination rate and chlorophyll. These can increase crop productivity, hydraulic activity, shoot and root length and leaf area. In addition to giving plants resistance to biotic (pathogen fungi, bacteria, yeast, insects, pests, etc.) and abiotic (flood, drought, salinity, heavy metals, temperature, etc.) stress, they can also make nitrogen from the soil available to plants in inorganic forms (ammonium, nitrate) (Yadav et al., 2018). Aspergillus, Rhizoctonia, Penicillium, Talaromyces and Trichoderma are the genera that contain fungi that stimulate plant growth. Of these, Trichoderma sp. (T. harzianum and T. viride) and Penicillium chrysogenum are the most promising for increasing plant growth (Adedayo et al., 2023).
     
    Biological nitrogen fixation
     
    Plants can use nitrogen from soil in both inorganic (nitrate, ammonium) and organic forms (amino acids, urea and short peptides). Organic forms can only be exploited under specific conditions (Eva et al., 2019). Plants cannot utilize the abundant elemental dinitrogen (N2) found in the Earth’s atmosphere. Fowler et al., (2015) computed 473 Tg N of physiologically accessible nitrogen from 4 x 109 Tg N of dinitrogen gas (Fowler et al., 2015; Ladha et al., 2022).
           
    Bacteria having biological nitrogen fixation (BNF) capacity are classified into three types: associated, free-living and symbiotic bacteria. Free-living N2-fixing bacteria from several genera, including Gluconacetobacter, Azospirillum and Azotobacter spp., contribute minimally to the total BNF. Rhizobia, a type of symbiotic bacteria that fixes nitrogen, accounts for the majority of BNF (Ladha et al., 2022). Rhizobium are the symbiotic bacteria found in leguminous plants. Non-symbiotic N2-fixing bacteria include cyanobacteria (Anabaena, Nostoc and other blue-green algae), as well as other genera including Azotobacter, Beijerinckia and Clostridium. Nitrogen-fixing bacteria, including Azospirillum sp. (rice, maize and wheat), Azotobacter sp., Klebsiella sp. and Alcaligenes sp., reside in the rhizospheric zone and transport fixed nitrogen to plants. Endophytic nitrogen-fixing microbes are found in cereals, grasses, sugarcane, Azoarcus sp. (sorghum, rice, kallar grass), Gluconacetobacter diazotrophicus (sugarcane, sorghum), Herbaspirillum sp. (rice, sugarcane, sorghum) and Burkholderia sp. (rice) (Eva et al., 2019; Ladha et al., 2022; Turan et al., 2016).
     
    Phytohormone production
     
    Phytohormones are chemical molecules that affect plant physiological processes, even in low quantities. Soil bacteria can create phytohormones, making them a possible source of these compounds. Microorganisms produce plant growth hormones, including auxins (indole-3-acetic acid), cytokinins, gibberellins, ethylene and abscisic acids. Synthesis requires significant amounts of metabolic energy and nutrients (Ladha et al., 2022; de Bruijn et al., 2022: Anjum et al., 2007). Stress-related regulators of plant immunity, such as jasmonic acid, ethylene and salicylic acid, provide a core signaling backbone to coordinate defense responses against phytopathogens (Matilla et al., 2018). Bacteria from the Rhizobium, Sinorhizobium, Bradyrhizobium, Azospirillum, Bacillus, Paenibacillus and Pseudomonas genera can produce phytohormones such as auxins, ABA, gibberellins and cytokinins, which enhance plant growth and productivity in natural conditions (Galler and Levy 2023; Ladha et al., 2022).

    While all plant-associated bacteria produce auxins all PGP microorganisms cannot produce gibberellin. This capability is linked to root-associated microorganisms. Approximately 80% of rhizospheric bacteria produce auxins, primarily indole-3-acetic acid (IAA). Tryptophan is the primary precursor for IAA production in bacteria. Bacteria that increase IAA production can consume tryptophan found in root exudates. Azospirillum brasilense has five distinct tryptophan-dependent and independent routes, with unknown biosynthesis intermediates (Matilla and Krell, 2018). IAA, a bacterial phytohormone that promotes lateral root formation and root elongation is the most widely studied. Plant hormones are particularly effective during stressful situations. Bacterial auxins can help plants cope with stress when they cannot make enough (Ahmad et al., 2019). Bacterial species capable of producing IAA include Pseudomonas fluorescens, Pseudomonas syringae, Agrobacterium tumefaciens, Pantoea agglomerans, Azospirillum brasilense, Bacillus cereus, Bacillus amyloliquefaciens, Bradyrhizobium sp. and Rhizobium sp., (Matilla and Krell, 2018). Shahzad et al. (2017) found that inoculating rice plants with Pantoea dispersa RWL-3, Micrococcus yunnanensis RWL-2, Staphylococcus epidermidis RWL-7 and Micrococcus luteus RWL-3 led to significant increases in dry biomass, root and shoot length, protein and chlorophyll content (Chaudhary et al., 2022; Shahzad et al., 2017). Fungi that produce IAA include Aspergillus, Mortierella, Talaromyces, Trichoderma spp., Fusarium, Penicillium. Penicillium janczewskii suppresses the phytopathogen Rhizoctonia solani, which causes stem rot (Adedayo et al., 2023).
           
    Abscisic acid (ABA) is a stress hormone that triggers photoperiodic blooming and promotes plant growth and development. It affects plant responses to different environmental stresses such cold, salt and desiccation (Ahmad et al., 2019). Plant-associated bacteria can create ABA, which boosts phytohormone levels in plants. Plant with altered ABA production or insensitivity are more resistant to infections than wild-type plants, as ABA plays an important role in modifying plant defense mechanism (Matilla and Krell, 2018). Endophytic bacteria that produce ABA include Achromobacter xylosoxidans, Brevibacterium halotolerans, Bacillus pumilus, Bacillus licheniformis and Lysinibacillus fusiformis (Salazar-Cerezo  et al., 2018).                              

    Gibberellin (GA) is a phytohormone that promotes stem elongation and leaf expansion. Exogenous GA can enhance parthenocarpy in fruits, cause bolting, break tuber dormancy and increase fruit size and bud count. Gibberellin production by soil microorganisms can affect nodulation and plant growth, either positively or negatively. These microorganisms can cause nodule organogenesis and prevent nodulation during infection (Ahmad et al., 2019). Rhizobium phaseoli, the first known bacterium capable of producing GA, generates both GA1 and GA4. Acetobacter diazotrophicus, Azospirillum lipoferum and Herbaspirillum seropedicae produce biologically active GA1 and GA3, as reported in (Salazar-Cerezo et al., 2018). Adedayo and Babalola (2023) discovered that GA-producing fungi, such as Cladosporium sp., enhance tomato plant growth and contribute to pea plant colonization.
           
    Cytokinin (CK) stimulates root development, plant cell division and hair creation, activate dormant buds and promotes seed germination. These plant hormones regulate nodulation, apical dominance and nitrogen fixation. PGPRs in Pseudomonas and Bacillus produce cytokinin, particularly zeatin (Yadav et al., 2018; Ladha et al., 2022). Rhizobium spp. and Pseudomonas fluorescens are bacteria that produce cytokinin (de Garcia Salamone  et al., 2006).
     
    Major nutrients solubilization
     
    Soil microorganisms play an important part in nutrient cycling. Crops that remain in the soil provide carbon, energy and nutrients to microorganisms. Rhizobium bacteria can solubilize nutrients like phosphorus, potassium, iron and zinc, boosting their availability for plants (Ramadan et al., 2016). Phosphorus (P) is crucial for the overall growth and development of plants. Soil has copious P in both organic and inorganic forms (apatite and secondary minerals like Fe, Al and Ca phosphates). Despite its abundance in soil as an insoluble nutrient, P is a significant growth-limiting factor. Soluble phosphorus in soil regulates its availability to plants (Matilla and Krell, 2018; Sakure and Bhosale, 2019). PGP bacteria act as a biological rescue mechanism by solubilizing insoluble inorganic P in soil and making it available to plants in the form of orthophosphate. The primary mechanism of P solubilization is the formation of organic acids. As a result, insoluble P is converted to its soluble form. Organic acids generated in soil can lower pH and bind mineral ions, leading to phosphate solubilization (Matilla and Krell, 2018). Gram-negative PGPRs mostly generate gluconic and 2-ketogluconic acids. Phosphate-solubilizing PGPRs create several organic acids, including isobutyric, lactic, isovaleric, glycolic, acetic, oxalic, malonic and succinic acids (Matilla and Krell, 2018). PGP microbes capable of phosphate solubilization include Arthrobacter, Azotobacter, Bacillus, Beijerinckia, Burkholderia, Citrobacter, Enterobacter, Erwinia, Flavobacterium, Halolamina, Microbacterium, Pantoea, Paenibacillus, Pseudomonas, Rhizobium, Rhodococcus, Serratia and Thiobacillus (Yadav et al., 2018; Matilla and Krell, 2018; Chaudhary et al., 2022). Potassium (K) is the third important macronutrient for plant growth and agricultural output. Soil contains about 90% potassium in the form of insoluble rocks and silicate minerals. The soluble form of potassium is found in soil in low concentrations. Inadequate fertilizer application can lead to potassium shortage, a severe limitation in crop productivity. Potassium deficiency leads to underdeveloped roots, tiny seeds, decreased agricultural yields and slower growth.   Soil bacteria can solubilize potassium, providing an alternate supply for plants. Potassium-solubilizing microorganisms (KSMs) produce and secrete organic acids to convert insoluble potassium into a form that plants can absorb. Many bacteria, including Acidithiobacillus ferrooxidans, Bacillus edaphicus, Bacillus mucilaginosus, Bacillus circulans, Paenibacillus sp., Burkholderia sp. and Pseudomonas sp., can solubilize K+ in into an accessible form. These bacteria improve K+ availability in agricultural soils (Mathur et al., 2019). Adedayo and Babalola found that Ceriporia lacerata, Aspergillus awamori and Penicillium digitatum can solubilize phosphate using organic acids and phytase (Adedayo and Babalola, 2023). Trichoderma sp. boosted mineral and nutrient absorption (N, K and P), while T. viride fungus increased soil nitrogen content (Adedayo and Babalola, 2023).
     
    Iron solubilization and siderophore production
     
    The soil limits the availability of essential micronutrients. Soil bacteria create siderophores, which are essential for iron-feeding in plants. These substances have a strong affinity for iron (III), the most prevalent type of iron in nature and are low molecular weight chelators. The iron solubilization method is based on the production of a stable siderophore. The Fe+3 complex can be absorbed by plants (Matilla and Krell, 2018; Mathur et al., 2019). Currently, there are roughly 500 siderophores known to exist. Pseudomonas fluorescens promotes plant development by producing pyoverdine and other siderophores. Microorganisms can create siderophoric chemicals such as catechol, carboxylate, hydroxamate and phenolate, which help protect plants from infections. Bacteria having iron chelation characteristics include Azotobacter, Bacillus, Enterobacter, Arthrobacter, Nocardia and Streptomyces (Ramadan et al., 2016). Siderophores increase the plant’s iron nutritional status and promote growth. Bacterial siderophores may chelate Fe+3 from soil, making it available to phytosidero-phores. However, the specific method remains uncertain. Plants can incorporate Fe+3-pyoverdine complexes, increasing the iron content of their tissues. Bacterial siderophores indirectly promote plant growth by reducing the availability of iron for phytopathogens (Matilla and Krell, 2018). Environmental factors affecting siderophore synthesis include pH, iron levels, trace elements and sufficient phosphorus, carbon and nitrogen supplies (Mathur et al., 2019). Siderophores transfer iron into bacteria through a system of ferric-specific ligands and membrane receptors, which operate as chelating agents. Siderophores inhibit pathogen growth by sequestering a restricted supply of iron (III) in the rhizosphere (Ramadan et al., 2016).
     
    Soil microbes biocontrol activity
     
    Excessive use of chemicals in agriculture, including pesticides, insecticides, herbicides and fertilizers, harms consumer health, biomagnification and economic loss (Tandon and Vats, 2016; Vats et al., 2017). Biological control organisms are non-disease-resistant organisms that inhibit the activities of plant diseases in soil (Saxena et al., 2019). Agents of microbiological control can protect plants through both direct and indirect interactions with diseases. Indirect mechanisms include ISR (microbial-induced systemic resistance), nutrition and space competition, which do not require pathogen interaction. Lytic enzymes and antibiotics are directly inhibiting pathogens (Kohl et al., 2019). Numerous bioactive compounds are produced by bacterial isolates with biocontrol agents, including antibiotics, volatiles, siderophores and growth-promoting compounds. With other microbes, these bacteria can compete and adapt quickly to environmental stress (Saxena et al., 2019). Trichoderma spp. generates antifungal volatile organic compounds (VOCs), including 6-pentyl-2H-pyran-2-one (PP) (Adedayo and Babalola, 2023). Various bacteria, such as Agrobacterium, Pseudomonas, Bacillus, Pantoea, Serratia, Stenotrophomonas, Streptomyces and Trichoderma, have been studied for antibiotic manufacturing capacity (Ramadan et al., 2016; Kohl et al., 2019). Some bacterial species and strains for producing agroinoculants, including Agrobacterium tumefaciens, Streptomyces lydicus, Bacillus subtilis, Burkholderia cepacia, Alcaligenes sp., Serratia marcescens GPS5, Erwinia amylovora and Streptomyces griseoviridis. Biocontrol strains produce a variety of antibiotics, including polyketides, phenazine, heterocyclic nitrogenous compounds, phenylpyrroles, aminopolyols, cyclic lipopeptides and volatile antibiotics (Saxena et al., 2019; Arseneault and Filion 2017; Glick, 2020). Several studies have found that biocontrol bacterial strains produce antibiotics to target diseases (Ram et al., 2018; Glick, 2020; Kenawy et al., 2019). Ongena and Jacques (2008) studied the formation of fengycin, iturin and surfactin by Bacillus sp. Raaijmakers and Mazzola (2012) studied the formation of antibiotic metabolites (phenazine, 2, 4-diacetylphloro-glucinol and pyrrolnitrin) in Pseudomonas sp. Adedayo and Babalola (2023) found that T. harzianum inhibited the growth of phytopathogen fungus including F. oxysporum, Phythium sp. and R. solani. Gliocladium virens generates gliovirin, an antibiotic that prevents the growth of F. oxysporum, Pythium ultimum.
     
    Quorum sensing interference with virulence
     
    Bacteria use quorum sensing (QS), which includes autoinducers that are extracellular signaling molecules to communicate cell density. As the bacterial population grows, gene expression changes due to the advantages of certain processes that are exclusive to this group. QS controls processes like as antibiotic synthesis, biofilm development and virulence factor secretion. The expression of bacterial pathogenicity in plants depends on quorum sensing (QS). Plant pathogenic strains such Pseudomonas syringae, Pantoea stewartii, Erwinia chrysanthemi and Burkholderia glumae require QS to colonize and express virulence proteins (Quiñones  et al. 2005; Koutsoudis et al., 2006; Hussain et al., 2008; Kang et al., 2018). Plant and microbe extracts with QS inhibitory action have been employed to treat multi-drug-resistant bacteria and in the food packaging industry (Mookherjee et al., 2018). Quorum quenching (QQ), or interference with pathogen QS, is a viable biocontrol method (Mookherjee et al., 2018; Noorashikin et al., 2016; Torabi Delshad  et al., 2018). QQ interference can occur in three ways: stopping signal molecule manufacturing, degrading signal molecules and blocking signal corpuscle receptors (Torabi Delshad  et al., 2018). BCAs can disrupt QS against pathogens by blocking the formation of enzymatic breakdown molecules such as lactonases, pectinases and chitinases that cause infections (Brígidoet_al2019; Panpatte et al., 2020). AHLs (Acyl-homoserine lactones), autoinducers, degrading bacteria include Bacillus sp., Acinetobacter sp., Burkholderia sp., Serratia sp., Lysinibacillus sp., Pseudomonas sp., Strepsporangium sp., Rhodococcus sp., Myroides sp. and Enterobacter sp. (Noorashikin et al., 2016; Chan et al., 2011; Ma et al., 2013). It has been demonstrated that AHL-degrading Lysinibacillus reduces the amount of potato soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum (Garge et al., 2016; Jose et al., 2019).
     
    Lytic enzymes
     
    The generation of lytic enzymes is one potential pathogen-killing strategy. PGPRs inhibit fungal pathogens (Fusarium oxysporum, Sclerotinia sclerotiorum and Botrytis cinerea) and other soil-borne pathogens by secreting enzymes like chitinases, proteases, hydrolases and glucanases (Ramadan et al., 2016; Mathur et al., 2019). BCAs primarily inhibit the growth of soil-borne pathogens by producing and secreting cell wall lytic enzymes (CWLEs) (Singh et al., 2017). CWLEs damage the structural integrity of the target pathogen’s cell wall. The cell wall of fungi is pathogenic and consists primarily of chitin and β-1,4-N-acetyl glucosamine. CWLEs, including β-1,3-glucanase and chitinase, are involved in the majority of BCAs. CWLEs neutralize the pathogen inhibitory effect by lysing cell walls (Goswami et al., 2016). PGPRS inhibits well-known phyto-pathogens such as Rhizoctonia solani and Phytophthora capsici (Kannojia et al., 2019; Islam et al., 2016).
     
    Induced systemic resistance
     
    Beneficial bacterial strains manage diseases by inducing systemic resistance (ISR). Biocontrol agents and Microbial metabolites can trigger a plant’s immune response, leading to disease resistance (Ramadan et al., 2016). Plants identify microbial molecules (exopolysaccharide, lipopolysaccharide and chitin oligosaccharide) generated by helpful microbes. Bacterial species such as Bacillus amyloliquefaciens, B. atrophaeus, B. cereus, B. megaterium, B. subtilis, Paenibacillus alvei, Pseudomonas fluorescens, Pseudomonas aeruginosa and Streptomyces pactum are effective against viral, fungal, bacterial, infections via ISR (Yu et al., 2022). ISR involves plant hormones such as ethylene, jasmonic acid and salicylic acid. Plant defense against phytopathogens involves the ethylene and jasmonic acid signaling pathways. ISR manifests as changes in cell wall integrity, biochemistry and physiology. Bacterial strains having ISR-eliciting characteristics have been shown to effectively combat a variety of fungal infections. Bacteria such as Pseudomonas fluorescens, Pseudomonas aeruginosa, Bacillus amyloliquefaciens, B. subtilis, B. pumilus, B. pasteurii, B. cereus, B. sphaericus and B. mycoides, have been identified (Panpatte et al., 2020; Kannojia et al., 2019). Cotton plants treated with P. chrysogenum exhibited ISR against T. viride, Verticillium dahlia, P. simplicissimum, T. harzianum and Acremonium sclerotigenum effectively induced ISR in agricultural plants including cucumber and tomato (Adedayo and Babalola, 2023).
     
    Synergistic microbial mechanisms
     
    Plants were more effectively inoculated with bacterial consortia compared to single strains. IAA and ACC deaminase synthesis have been shown to have synergistic effects on N2 fixation (Ma et al., 2004; Serova et al., 2017; Defez et al., 2016; Defez et al., 2019; Nascimento et al., 2012; Nascimento et al., 2019; Alemneh et al., 2020), stress tolerance (Defez et al., 2019; Nascimento et al., 2012; Nascimento et al., 2019; Alemneh et al., 2020; Orozco-Mosqueda et al., 2020) and phosphate solubilization (Alemneh et al., 2021). IAA and ACC deaminase play multiple roles in BNF fixation, including enhancing nodule formation, increasing rhizobia competitiveness, suppressing nodule senescence and upregulating genes linked with legume-rhizobia symbiosis (Alemneh et al., 2020). Knockout and overproducing strains of the ACC deaminase gene were used to study its role in nodule formation (Alemneh et al., 2021). In terms of plant colonization and nodulation, the mutant strain of Mesorhizobium loti ACC deaminase that overproduces the enzyme performed better than the wild type (Ma et al., 2004). In Mesorhizobium loti, the acdS gene is located in the symbiotic island and its expression is controlled by the N2 fixation regulator NifA2 (Nukui et al., 2006). Senescent nodules have enhanced expression and transcription of PsACS2, which encodes ACC synthase, an enzyme implicated in ethylene production (Serova et al., 2017). PGP bacteria produce ACC deaminase can improve nitrogen fixation by increasing the lifespan of functioning nodules. Comparing 31-day-old nodules of a transformed Mesorhizobium sp. expressing ACC deaminase to its parental strain devoid of this activity, Nascimento et al., (2012) discovered nitrogenase activity. Compared to the ACC deaminase mutant strain, Nascimento et al., (2019) discovered that the Pseudomonas fluorescens YsS6 strain that produces ACC deaminase enhanced the nodulation capacity of alpha- and beta-rhizobia. Free-living ACC deaminase-producing bacteria promote rhizobia nodulation. IAA, a biomolecule, plays a role in legume-rhizobia interactions by regulating nodule primordium formation and cell division. IAA affects the expression of genes involved in rhizobia and nodule formation in plant cells (Alemneh 2020). Camerini et al., (2008) found a link between IAA and nodulation, with IAA-negative Rhizobium leguminosarum bv. viciae producing fewer nodules than the parent strain. Additionally, using IAA-producing nodule-enhancing rhizobacteria as a co-inoculum promoted rhizobia colonization due to their production of caproic acid (Alemneh et al., 2020). Ensifer meliloti RD64-induced 45-day-old nodules with IAA overproduction showed a longer nitrogen-fixing zone and a lower senescent zone compared to the wild-type strain (Defez et al., 2016). Scientists investigated the impact of ACC deaminase and IAA on the stress response (Defez et al., 2019; Orozco-Mosqueda  et al., 2019). Interaction between the two properties was shown when Pseudomonas sp. UW4 trehalose (treS) and ACC deaminase (acdS) mutant strains (mutated at one or both features) were used as bioinoculant on tomato plants under salt stress. The impact of single gene mutations is greater than that of multiple ones (Orozco-Mosqueda  et al., 2019). Alemneh et al., (2021) found ACC deaminase-producing bacteria capable of phosphate solubilization, indicating ACC deaminase-mediated P solubilization. Inoculating chickpeas with ACC expressing Burkholderia sp. 12F led to increased P nutrition and enhanced nodulation rates. Metabolomic investigations of the soil microbiome are crucial for understanding plant-soil-microbe interactions, as synergy can occur between bacteria, arbuscular mycorrhizal fungi and bacterial ACC deaminase (Orozco-Mosqueda  et al., 2020).

    CONCLUSION

    The soil system’s complexity, including stratification and microhabitats, promotes the growth of a diversified microbial community. The most difficult task at the moment is analyzing data from microbial communities. Understanding bacterial functional groups and community dynamics is crucial for knowing how soil ecosystems work, in addition to taxonomy. The rhizosphere is a hotspot for the microorganism and microbial gene transfer and contains a wealth of genetic capabilities, making PGPR genetic engineering a valuable tool for sustainable agriculture. What impact do environmental changes have on soil ecology and how may sustainable agriculture methods maintain this function? It is unclear how they are shaped by plant-microorganism interactions. Plant genome engineering is a tool for sustainable agriculture that utilizes unique plant-microbe communication. Sustainable agriculture requires a better understanding of soil-microbe-plant systems and their impact on short- and long-term sustainability. Future research should focus on utilizing genetically engineered plants and microorganisms for sustainable agriculture.
     

    ACKNOWLEDGEMENT

    The authors are thankful to the convenor, Department of Botany, Prof. Sarita Srivastava and Principal, Prof. Ajay Prakash Khare, CMP Degree College, University of Allahabad, for providing the necessary facilities to carry out the research.
     
    Author’s contribution
     
    All authors made substantial contributions to the conception and design, acquisition of data, or analysis and interpretation of data.
     
    Funding
     
    The authors declare that no funding was received for the present work.

    CONFLICT OF INTEREST

    The authors express no conflict of interest.

    REFERENCES


    1. Adedayo, A.A. and Babalola, O.O. (2023). Fungi that promote plant growth in the Rhizosphere boost crop growth. J. Fungi. 9: 239. 

    2. Ahmad, M., Nadeem, S.M. and Zahir, Z.A. (2019). Plant-microbiome Interactions in Agroecosystem: An Application. In Microbiome in Plant Health and Disease; Springer: Singapore. pp. 251-291.

    3. Aira, M., Gómez-Brandón, M., Lazcano, C., Bååth, E. (2010). Plant genotype strongly modifies the structure and growth of maize rhizosphere microbial communities. Soil Biol. Biochem.  42: 2276-2281.

    4. Alemneh, A.A., Zhou, Y., Ryder, M.H. and Denton, M.D. (2020). Mechanisms in plant growth-promoting rhizobacteria that enhance legume-rhizobial symbioses. J. Appl. Microbiol. 129: 1133-1156.  

    5. Alemneh, A.A., Zhou, Y., Ryder, M.H. and Denton, M.D. (2021). Is phosphate solubilizing ability in plant growth-promoting rhizobacteria isolated from chickpea linked to their ability to produce ACC deaminase? J. Appl. Microbiol. 131: 2416-2432. 

    6. Anjum, M.A., Sajjad, M.R., Akhtar, N., Qureshi, M.A., Iqbal, A., Jami, A.R., Mahmud-ul-Hasan. (2007). Response of cotton to plant growth promoting Rhizobacteria (PGPR) inoculation under different levels of nitrogen. Journal of Agricultural Research.  45 (Suppl 2): 135-143.

    7. Arseneault, T., Filion, M. (2017). Biocontrol through antibiosis: Exploring the role played by subinhibitory concentrations of antibiotics in soil and their impact on plant pathogens. Can. J. Plant Pathol. 39: 267-274.

    8. Bakker, P., Berendsen, R., Doornbos, R., Wintermans, P. and Pieterse, C. (2013). The rhizosphere revisited: Root microbiomics. Front. Plant Sci. 4: 165.  

    9. Bar-On, Y.M., Phillips, R., Milo, R. (2018). The biomass distribution on Earth. Proc. Natl. Acad. Sci. USA. 115: 6506-6511.

    10. Brígido, C., Singh, S., Menéndez, E., Tavares, M.J., Glick, B.R., Félix, M.d.R., Oliveira, S. and Carvalho, M. (2019). Diversity and functionality of culturable endophytic bacterial communities in Chickpea plants. Plants. 8: 42.

    11. Camerini, S., Senatore, B., Lonardo, E., Imperlini, E., Bianco, C., Moschetti, G., Rotino, G.L., Campion, B. and Defez, R. (2008). Introduction of a novel pathway for IAA biosynthesis to rhizobia alters vetch root nodule development. Arch. Microbiol. 190: 67-77.

    12. Chaudhary, P., Agri, U., Chaudhary, A., Kumar, A. and Kumar, G. (2022). Endophytes and their potential in biotic stress management and crop production. Front. Microbiol. 13: 933017. 

    13. Chan, K.G., Atkinson, S., Mathee, K., Sam, C.K., Chhabra, S.R., Cámara, M., Koh, C.L. and Williams, P. (2011). Characterization of N-acylhomoserine lactone-degrading bacteria associated with the Zingiber officinale (ginger) rhizosphere: Co-existence of quorum quenching and quorum sensing in Acinetobacter and Burkholderia. BMC Microbiol. 11: 51.

    14. de Bruijn, F.J. and Hungria, M. (2022). Biological Nitrogen Fixation. In Good Microbes in Medicine, Food Production, Biotechnology, Bioremediation and Agriculture; John Wiley and Sons, Ltd.: Hoboken, NJ, USA, pp. 466-475.   

    15. de Corato, U. (2020). Towards new soil management strategies for improving soil Quality and ecosystem services in sustainable agriculture: Editorial overview. Sustainability. 12: 9398.  

    16. de Garcia Salamone, I.E., Hynes, R.K. and Nelson, L.M. (2006). Role of Cytokinins in Plant Growth Promotion by Rhizosphere Bacteria. In PGPR: Biocontrol and Biofertilization; Siddiqui, Z.A., Ed.; Springer: Dordrecht, The Netherlands, pp. 173- 195, ISBN 978-1-4020-4152-5. 

    17. Defez, R. andreozzi, A., Romano, S., Pocsfalvi, G., Fiume, I., Esposito, R., Angelini, C. and Bianco, C. (2019). Bacterial IAA-Delivery into Medicago Root Nodules Triggers a Balanced Stimulation of C and N Metabolism Leading to a Biomass Increase. Microorganisms. 7: 403.  

    18. Defez, R., Esposito, R., Angelini, C. and Bianco, C. (2016). Over- production of Indole-3-Acetic acid in Free-Living Rhizobia Induces Transcriptional Changes Resembling Those Occurring in Nodule Bacteroids. Mol. Plant Microbe Interact. 29: 484-495. 

    19. Dubey, D.-A., Malla, M., Khan, F., Chowdhary, K., Yadav, S., Kumar, A., Sharma, S., Khare, P.K., Khan, M. and Khan, M. (2019). Soil microbiome: A key player for conservation of soil health under changing climate. Biodivers. Conserv. 28: 2405-2429. 

    20. Ettema, C.H. and Wardle, D.A. (2002). Spatial soil ecology. Trends Ecol. Evol. 17: 177-183. 

    21. Eva, L. and Gyongyver, M. (2019). Is PGPR an Alternative for NPK Fertilizers in Sustainable Agriculture? In Microbial Interventions in Agriculture and Environment; Springer: Cham, Switzerland, pp. 51-62. ISBN 9789811383908. 

    22. Fan, K., Cardona, C., Li, Y., Shi, Y., Xiang, X., Shen, C., Wang, H., Jack, G. and Chu, H. (2017). Rhizosphere-associated bacterial network structure and spatial distribution differ significantly from bulk soil in wheat crop fields. Soil Biol. Biochem. 113: 275-284. 

    23. Fowler, D., Steadman, C.E., Stevenson, D., Coyle, M., Rees, R.M., Skiba, U.M., Sutton, M.A., Cape, J.N., Dore, A.J. and Vieno, M. (2015). Effects of global change during the 21st century on the nitrogen cycle. Atmos. Chem. Phys. 15: 13849-13893. 

    24. Garge, S.S. and Nerurkar, A.S. (2016). Attenuation of quorum sensing regulated virulence of Pectobacterium carotovorum subsp. carotovorum through an AHL Lactonase Produced by Lysinibacillus sp. Gs50. PLoS ONE. 11: e0167344.  

    25. Geller, A.M. and Levy, A. (2023). “What I cannot create, I do not understand”: Elucidating microbe-microbe interactions to facilitate plant microbiome engineering. Curr. Opin. Microbiol. 72: 102283. 

    26. Goswami, D., Thakker, J.N. and Dhandhukia, P.C. (2016). Portraying mechanics of plant growth promoting rhizobacteria (PGPR): A review. Cogent Food Agric. 2: 1127500. 

    27. Glick, B.R. (2020). Biocontrol of Bacteria and Fungi. In Beneficial Plant-Bacterial Interactions; Glick, B.R., Ed.; Springer International Publishing: Cham, Switzerland. pp. 181-230, ISBN 978-3-030-44368-9.

    28. Goswami, D., Thakker, J.N. and Dhandhukia, P.C. (2016). Portraying mechanics of plant growth promoting rhizobacteria (PGPR): A review. Cogent Food Agric. 2: 1127500.  

    29. Husna, Hussain, A., Shah, M., Hamayun, M., Iqbal, A., Qadir, M., Alataway, A., Dewidar, A.Z., Elansary, H.O. and Lee, I.J. (2023). Phyto- hormones producing rhizobacteria alleviate heavy metals stress in soybean through multilayered response. Microbiol. Res. 266: 127237. 

    30. Hussain, M.B.B.M., Zhang, H.B., Xu, J.L., Liu, Q., Jiang, Z. and Zhang, L.H. (2008). The acyl-homoserine lactone-type quorum- sensing system modulates cell motility and virulence of Erwinia chrysanthemi pv. zeae. J. Bacteriol. 190: 1045-1053. 

    31. Islam, S., Akanda, A.M., Prova, A., Islam, M.T. and Hossain, M.M. (2016). Isolation and identification of plant growth promoting rhizobacteria from Cucumber rhizosphere and Their effect on plant growth promotion and disease suppression. Front. Microbiol. 6: 1360. 

    32. Jansson, J.K. and Hofmockel, K.S. (2020). Soil microbiomes and climate change. Nat. Rev. Microbiol. 18: 35-46. 

    33. Jose, P., Ramasamy, K., Kwon, S.-W., Veeranan, J., Murugaiyan, S., Gopal, N.O., Kumutha, K. and Anandham, R. (2019). Interference in quorum sensing and virulence of the phytopathogen Pseudomonas syringae pv. passiflorae by Bacillus and Variovorax species. BioControl. 64: 423-433. 

    34. Kang, B.R. anderson, A.J. and Kim, Y.C. (2018). Hydrogen Cyanide Produced by Pseudomonas chlororaphis O6 Exhibits Nematicidal Activity against Meloidogyne hapla. Plant Pathol. J. 34: 35-43. 

    35. Kannojia, P., Choudhary, K.K., Srivastava, A.K. and Singh, A.K. (2019). PGPR Bioelicitors: Induced Systemic Resistance (ISR) and Proteomic Perspective on Biocontrol. In PGPR Amelioration in Sustainable Agriculture; Elsevier: Amsterdam, The Netherlands, ISBN 978-0-12-816019-0. 

    36. Kenawy, A., Joe Dailin, D., Abo-Zaid, G., Malek, R.A., Ambehabati, K., Zakaria, K., Sayyed, R. and El Enshasy, H. (2019). Biosynthesis of Antibiotics by PGPR and Their Roles in Biocontrol of Plant Diseases. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland, pp. 1-35, ISBN 9789811369858. 

    37. Khan, A.A.H. (2019). Plant-Bacterial Association and Their Role as Growth Promoters and Biocontrol Agents. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland, pp. 389-419, ISBN 978981 1369858.  

    38. Köhl, J., Kolnaar, R. and Ravensberg, W.J. (2019). Mode of action of microbial biological control agents against plant diseases: Relevance beyond efficacy. Front. Plant Sci. 10: 845.  

    39. Koutsoudis, M.D., Tsaltas, D., Minogue, T.D. and von Bodman, S.B. (2006). Quorum-sensing regulation governs bacterial adhesion, biofilm development and host colonization in Pantoea stewartii subspecies stewartii. Proc. Natl. Acad. Sci. USA 103, 5983-5988. 

    40. Ladha, J.K., Peoples, M.B., Reddy, P.M., Biswas, J.C., Bennett, A., Jat, M.L. and Krupnik, T.J. (2022). Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems. Field Crops Res. 283: 108541. 

    41. Li, X., Rui, J., Mao, Y., Yannarell, A. and Mackie, R. (2014). Dynamics of the bacterial community structure in the rhizosphere of a maize cultivar. Soil Biol. Biochem. 68: 392-401.  

    42. Ma, A., Lv, D., Zhuang, X. and Zhuang, G. (2013). Quorum Quenching in Culturable Phyllosphere Bacteria from Tobacco. Int. J. Mol. Sci. 14: 14607-14619.

    43. Ma, W., Charles, T.C. and Glick, B.R. (2004). Expression of anexo- genous 1-aminocyclopropane-1-carboxylate deaminase gene in Sinorhizobium meliloti increases its ability to nodulate alfalfa. Appl. Environ. Microbiol. 70: 5891-5897.

    44. Mathur, A.; Koul, A.; Hattewar, J. (2019). Plant Growth-promoting Rhizobacteria (PGPRs): Significant Revolutionary Tools for Achieving Long-Term Sustainability and Combating the Biotic Stress Caused by the Attack of Pathogens Affecting Crops in Agriculture. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland. pp. 379-388, ISBN 9789811369858.

    45. Matilla, M. and Krell, T. (2018). Plant growth promotion and biocontrol mediated by plant-associated bacteria. In plant mcrobiome: Stress response; Springer: Cham, Switzerland. pp. 45- 80. ISBN 978-981-10-5513-3. 

    46. Mendes, R., Garbeva, P. and Raaijmakers, J.M. (2013). The rhizosphere microbiome: Significance of plant beneficial, plant pathogenic and human pathogenic microorganisms. FEMS Microbiol. Rev. 37: 634-663. 

    47. Mookherjee, A., Singh, S. and Maiti, M.K. (2018). Quorum sensing inhibitors: Can endophytes be prospective sources? Arch. Microbiol. 200: 355-369. 

    48. Nascimento, F.X., Brígido, C., Glick, B.R., Oliveira, S. and Alho, L. (2012). Mesorhizobium ciceri LMS-1 expressing an exogenous 1 aminocyclopropane-1-carboxylate (ACC) deaminase increases its nodulation abilities and chickpea plant resistance to soil constraints. Lett. Appl. Microbiol. 55: 15-21.

    49. Nascimento, F.X., Tavares, M.J., Franck, J., Ali, S., Glick, B.R. and Rossi, M.J. (2019). ACC deaminase plays a major role in Pseudomonas fluorescens YsS6 ability to promote the nodulation of Alpha- and Betaproteobacteria rhizobial strains. Arch. Microbiol. 201: 817-822.

    50. Noorashikin, M.N., Li, L.Y., Karim, M., Daud, H.M. and Natrah, F.M.I. (2016). Screening and identification of quorum sensing degraders from live feed Artemia. J. Environ. Biol. 37: 811-816. 

    51. Nukui, N., Minamisawa, K., Ayabe, S.-I. and Aoki, T. (2006). Expression of the 1-aminocyclopropane-1-carboxylic acid deaminase gene requires symbiotic nitrogen-fixing regulator gene nifA2 in Mesorhizobium loti MAFF303099. Appl. Environ. Microbiol. 72: 4964-4969.

    52. O’Brien, S.L., Gibbons, S.M., Owens, S.M., Hampton-Marcell, J., Johnston, E.R., Jastrow, J.D., Gilbert, J.A., Meyer, F. and Antonopoulos, D.A. (2016). Spatial scale drives patterns in soil bacterial diversity. Environ. Microbiol. 18: 2039-2051. 

    53. Ongena, M, Jacques, P. (2008). Bacillus lipopeptides: Versatile weapons for plant disease biocontrol. Trends Microbiol. 16: 115-125.

    54. Orozco-Mosqueda, M.d.C., Duan, J., DiBernardo, M., Zetter, E., Campos- García, J., Glick, B.R. and Santoyo, G. (2019). The production of acc deaminase and trehalose by the plant growth promoting bacterium pseudomonas sp. uw4 synergistically protect tomato plants against salt stress. Front. Microbiol. 10: 1392. 

    55. Orozco-Mosqueda, M.d.C., Glick, B.R. and Santoyo, G. (2020). ACC deaminase in plant growth-promoting bacteria (PGPB): An efficient mechanism to counter salt stress in crops. Microbiol. Res. 235: 126439. 

    56. Panpatte, D., Jhala, Y. and Vyas, R. (2020). Signaling pathway of induced systemic resistance. In molecular aspects of plant beneficial microbes in Agriculture; Elsevier: Amsterdam, The Netherlands, pp. 133-141, ISBN 978-0-12-818469-1.

    57. Quiñones, B., Dulla, G. and Lindow, S.E. (2005). Quorum sensing regulates exopolysaccharide production, motility and virulence in Pseudomonas syringae. Mol. Plant Microbe Interact. 18: 682-693. 

    58. Raaijmakers, J.M. and Mazzola, M. (2012). Diversity and natural functions of antibiotics produced by beneficial and plant pathogenic bacteria. Annu. Rev. Phytopathol. 50: 403-424. 

    59. Ram, R.M., Keswani, C., Bisen, K., Tripathi, R., Singh, S.P. and Singh, H.B. (2018). Biocontrol Technology; Elsevier: Amsterdam, The Netherlands. pp. 177-190.

    60. Ramadan, E., Abdelhafez, A., Enas, A. and Saber, F. (2016). Plant growth promoting rhizobacteria and their potential for biocontrol of phytopathogens. Afr. J. Microbiol. Res. 10: 486-504.

    61. Rchiad, Z., Dai, M., Hamel, C., Bainard, L.D., Cade-Menun, B.J., Terrat, Y., St-Arnaud, M. and Hijri, M. (2022). Soil depth significantly shifted microbial community structures and functions in a semiarid prairie agroecosystem. Front. Microbiol. 13: 815890. 

    62. Sakure, S. and Bhosale, S. (2019). Actinobacteria for Biotic Stress Management. In Plant Growth Promoting Rhizobacteria for Sustainable Stress Management; Springer: Cham, Switzerland, pp. 363-378, ISBN 9789811369858.

    63. Salazar-Cerezo, S., Martínez-Montiel, N., García-Sánchez, J., Pérez- Y-Terrón, R. and Martínez-Contreras, R.D. (2018). Gibberellin biosynthesis and metabolism: A convergent route for plants, fungi and bacteria. Microbiol. Res. 208: 85-98. 

    64. Saxena, P., Srivastava, J., Pandey, S., Srivastava, S., Maurya, N., Chand, K., Mishra, S., Asthana, G., Bhargava, P. and Kumar, R. (2019). Plants for biocontrol and biological control of plant pathogens. In plant biotic interactions; Springer: Cham, Switzerland. pp. 147-179. ISBN 978-3-030-26656-1. 

    65. Serova, T.A., Tikhonovich, I.A. and Tsyganov, V.E. (2017). Analysis of nodule senescence in pea (Pisum sativum L.) using laser microdissection, real-time PCR and ACC immunolocali- zation. J. Plant Physiol. 212: 29-44.

    66. Shahzad, R., Waqas, M., Khan, A.L., Al-Hosni, K., Kang, S.M., Seo, C.W. and Lee, I.J. (2017). Indoleacetic acid production and plant growth promoting potential of bacterial endophytes isolated from rice (Oryza sativa L.) seeds. Acta Biol. Hung.  68: 175-186.

    67. Singh, V.K., Singh, A.K. and Kumar, A. (2017). Disease management of tomato through PGPB: Current trends and future perspective. 3 Biotech. 7: 255.

    68. Suresh A., Ashraf, A.M., Sree, V.S., Dhas, A.K.S. and Chacko, J.P. (2025). Plant-microbe interactions and rhizosphere dynamics for sustainable agriculture: A review. Agricultural Reviews. 1-9. doi: 10.18805/ag.R-2829.

    69. Tabish, A., Kumar, S., Kumar, S. and  Meena, M.R. (2020). Importance of plant growth promoting rhizobacteria (PGPR) in agriculture: A review. Bhartiya Krishi Anushandhan Patrika. 35(1 and 2): 75-78. doi: 10.18805/BKAP200.

    70. Tandon, S. and Vats, S. (2016). Microbial biosynthesis of Cadmium sulfide (CDS) nanoparticles and their characterization. Eur. J. Pharm. Med. Res. 3: 545-550. 

    71. Thakur, M.P. and Geisen, S. (2019). Trophic regulations of the soil microbiome. Trends Microbiol. 27: 771-780. 

    72. Torabi Delshad, S., Soltanian, S., Sharifiyazdi, H. and Bossier, P. (2018). Effect of quorum quenching bacteria on growth, virulence factors and biofilm formation of Yersinia ruckeri in vitro and an in vivo evaluation of their probiotic effect in rainbow trout. J. Fish. Dis. 41: 1429-1438.

    73. Turan, M., Topcuoglu, B., Kitir, N., Alkaya, Ü., Erçelik, F., Nikerel, E., Günes, A., Turan, M., Topcuoglu, B. and Kitir, N. (2016). Plant Growth Promoting Rhizobacteria’s (PGPR’s) Enzyme Dynamics in Soil Remediation. In Soil Contamination- Current Consequences and Further Solutions; IntechOpen: London, UK, ISBN 978-953-51-2816-8. 

    74. Unnikrishnan, M.A., Rajalekshmi, K. and Bindhu, P.S. (2023). Soil degradation vs soil retrogression: A review. Agricultural Reviews. 44(4): 509-515. doi: 10.18805/ag.R-2241.

    75. Vats, S. and Bhargava, P. (2017). Alternate Energy: Fuel for “Modi’s India” and “Smart cities”. Int. J. Curr. Res. 9: 49090-49097.

    76. Yadav, A.N., Kumar, V., Dhaliwal, H., Prasad, R. and Saxena, A. (2018). Microbiome in Crops: Diversity, Distribution and Potential Role in Crop Improvement. In New and Future Developments in Microbial Biotechnology and Bioengineering: Crop Improvement through Microbial Biotechnology; Elsevier: Amsterdam, The Netherlands, pp. 305-332, ISBN 978-0- 444-63987-5. 

    77. Yu, Y., Gui, Y., Li, Z., Jiang, C., Guo, J. and Niu, D. (2022). Induced systemic resistance for improving plant immunity by beneficial microbes. Plants. 11: 386.
    In this Article
      Contact us
      Follow us
      Published In
      Indian Journal of Agricultural Research

      Editorial Board

      View all (0)