Comparative biodiversity of microbiome in different treatment groups
The estimated DNA concentration and nanopore read statistics in different treatment groups are presented in Table 2. The comparative microbiome diversity in different treatment groups were studied using Shannon index and rarefaction curve are presented in Fig 1 and 2 respectively, it reveals variation in microbiome community between treatment 1 and the other treatment groups. The results of this study indicate that there is diversity of methanogens in Pulikulam cattle and they vary under different dietary regimen. The rumen microbiota could be affected either by the geographical locations
(Guan et al., 2008), host
(Handerson et al., 2015; Guan et al., 2008; Roehe et al., 2016) or by the diet of the animal.
Zhou et al., (2009) reported that methanogen composition varied between cattle herds of different feed efficiency. Difference in the rumen microbiota composition was observed between breeds fed on a similar diet
(Paz et al., 2016). Handerson et al., (2015) reported that rumen microbiome varies depending upon the feed.
Effect of different dietary diets on methanogens community
A total of 125,442; 214613; 126123 and 126405 raw reads per sample were generated from treatment 1, treatment 2, treatment 3 and treatment 4 samples respectively. After removal of unclassified reads a total of 139, 428, 110 and 144 archaeal reads were retained for further analysis which is 0.1, 0.3, 0.08 and 0.1 per cent of total microbial reads in treatment1, treatment 2, treatment 3 and treatment 4 respectively. All filtered reads in the present study were affiliated to the rumen archaea. Total rumen archaeal phylum reads in different treatment groups is presented in Table 3. The ruminal archaea community in all the treatments were dominated by phylum Euryarchaeota. The archaea belonging to the other phylum Crenarchaeota and Thaumarchaeota were also present in all the treatments but the representation was lower than phylum Euryarchaeota. Phylum Candidatus Korarchaeota were present in treatment 2 and treatment 4 and phylum Candidatus Micrarchaeota was present only in treatment 2.
These results of this study concur to the previous reports
(Abecia et al., 2014; Xue et al., 2020), where Crenarchaeota methanogens have acknowledged in the rumen. Sulfolobales are physiologically and morphologically distinguished archaea, belonging to the phylum Crenarchaeota which occurs mainly in extreme thermo acidophilic ecosystems
(Quehenberger et al., 2017). Dias et al., (2017) had reported that species
Sulfolobus thuringiensis was in abundance they reported that
S. thuringiensis was distributed up to 0.1 per cent of total archaea in dairy calves.
Malik et al., (2021) also reported the presence of
S. thuringiensis in livestock. However, the methanogenic capabilities of genera Sulfolobus and their influence to the ruminal methanogensis needs to be explored. Among the eight
Sulfolobus species established in the literature,
S. islandicus, S. solfataricus and
S. acidocaldarius are best defined members of the genus. While
S. islandicus is used as a model organism for comparative genomics and genetics
(Reno et al., 2009) and for host virus interactions (
Held and Whitaker, 2009). In this study all three
Sulfolobus species were identified in the Pulikulam cattle.
Ruminal archaeal abundance percentage in different treatment groups at class level is presented in Table 4. Methanogens belonging to a total of four classes were identified in this study. Methanogens associated with the class Methanomicrobia were dominant in all the treatments. Methanogens associated with the class Thermoplasmata was absent in treatment 3.
Ruminal archaeal abundance percentage in different treatment groups at order and family level is presented in Table 5. Methanogens belonging to five orders were identified. The methanogens affiliated to the order Methanomicrobiales were predominant in treatment 1 (14 %) and treatment 2 (16.30 %). Order methanococcales (15 %) was predominant in treatment 3 and order Methanos arcinales (18%) was predominant in treatment 4. Methonogens belong to Methanomassiliicoccales was distributed at lower frequency in treatment 1, 2 and 4 and not present in treatment 3. In treatment 1, Methanococcales was the second most abundant methoanogen (10%) followed by Methanobacteriales (8%) and Methanosarcinales (5%). In treatment 2, Methanobacteriales (11%) was the second most abundant methoanogen followed by Methanosarcinales (10.6%) and Methanococcales (7%). Methanomicrobiales (12%). In treatment 3 Methanosarcinales and Methanobacteriales abundance were present in equal amount. In treatment 4, Methanomicrobiales (9.6%) was the fourth abundant methonogen. Methanobacteriales and Methanococcales held second and third ranks in the abundance.
The results of this finding is similar to the finding of
Sadan et al., (2019) in Vechur cattle, another native cattle breed of India. The authors had reported that Methanobactetriales, Methanomassiliicoccales and Methanomicrobiales were the predominant methanogen orders in rumen of Vechur cattle.
Xue et al., (2016) reported that Methanobacteriales was the predominant archaea of rumen microbiota in the natural qrazing Yak in Sichuan. Other studies have reported an unprecedented greater abundance of Methanomicrobiales in cattle
(Tajima et al., 2001; Shin et al., 2004) and buffaloes (
Chaudhary and Sirohi, 2009;
Singh et al., 2011; Singh et al., 2012). Previous studies have also reported that majority of the archaeal sequences retrieved from bovine rumens and cattle dung belonged to order Methanomicrobiales and Methanobacteriales
(Rastogi et al., 2008; Tatsuoka et al., 2004). In contrast to the finding of the present study,
Malik et al., (2021) reported that Methanomicrobiales proportion was less than 4 per cent of the total archaea in both cattle and buffaloes and the abundance frequency was consistent with the global data sets (
Janssen and Kirs 2008;
Handerson et al., 2015; Zhou et al., 2009). This could be due to the different DNA isolation methods, primer sets and animal diets.
Methanomassiliicoccales is a novel group of archaea related to Thermoplasmatales
(Horz et al., 2012). Methanomassiliicoccales are methylotrophic methanogens that utilize methanol and methylamines for producing methane
(Lang et al., 2015; Sollinger et al., 2016).
In this study methanogen belonging to the order Methanomassiliicoccales was not present in treatment 3, diet of this treatment formulated with high energy contains more amount of maize than the other treatment group’s diets. A decrease in rumen pH due to high grain feeding is possibly a general cause for the stimulation or suppression of a particular type of methylotrophs in the rumen
(Lana et al., 1998). The Methanomassiliicoccales may have specific properties that allowed their survival or inhibition during variable pH. The relative abundance of Methanomass iliicoccales affected by the diet rather than the host. Similarly,
Xue et al., (2016) reported that methanogen Methanomass iliicoccales was absent in domesticated Yak maintained at China.
In this present study methanogens belonging to Methanosarcinales were present in all the treatment groups. Methanosarcinales grow on a broad range of substrates such as H
2, CO
2, methanol, methylamines and acetate. This is the only methanogen order capable of performing acetoclastic methanogenesis (
Kendall and Boone, 2006).
Malik et al., (2021) reported that methanogens belonging to Methanosarcinales were distributed at very small frequencies in both the cattle and buffaloes, their abundance was significantly greater in cattle compared to in buffaloes. Presence of Methanosarcinales in rumen was reported by (
Patterson and Hespell, 1979;
Jarvis et al., 2000) in both cattle and buffalo. VFA produced during digestion in the rumen are generally absorbed by the rumen epithelium and subsequently converted to animal proteins and therefore not available for utilization as a carbon source by Methanosarcinales residing in rumen. Therefore, abundance of Methanosarcinales was minimal in rumen of cattle (
Zinder, 1993). H
2/CO
2 is the only carbon source available in plenty for methanogens hence, hydrogenotrophic methanogens (Methanomicrobiales and Methanobacteriales) that are capable of using H
2/CO
2 can multiply easily and their abundance were high in cattle rumen. Similarly,
Denman et al., (2007) reported that the methanogens belonging to order Methanobacteriales was the major hydrogenotrophic methanogens in rumen of Brahman-crossbred (
Bos indicus) steers.
In the present study methanogens belonging to 11 families were identified. Rumen archaeal composition at family level in different treatment groups are given in Fig 3, 4, 5 and 6. Families Methanocorpusculaceae, Methanomicro biaceae Methanoregulaceae Methanospirillaceae were affiliated to the order Methanomicrobiales. Methanoregulaceae distributed at lower frequency was present only in treatment 2 and treatment 3. Family Methanospirillaceae was present only in treatment 2 and treatment 4. Orders Methanosarcinales, Methanobacteriales and Methanococcales were characterized by two families of each. Methanothermaceae belonging to the order Methanobacteriales present only in treatment 4. Methanomassiliicoccaceae was absent in treatment 3.
In this study at the species level methanogen
M. labreanum belonging to order methanomicrobiales was the predominant species in all the treatment groups. The heat map comparison of different archaeal abundance at species level in different treatment groups is given in Fig 7.
Methanococcus maripaludis, Methanococcus aeolicus, Methanobrevibacter millerae and
Methanobrevibacter olleyae hold second, third and fourth predominant species in treatment 1. Abundance of species
M. millerae and
M. olleyae were similar. On the other hand, in treatment 2,
M. labreanum, M. maripaludis, M. millerae and
Methanosarcina mazei were the top four predominant species. Abundance of
M. millerae and
M. mazei were similar in this treatment
. Abundance of
M. olleyae was high compared to other treatments.
M. labreanum, M. olleyae, M. maripaludis and
Methanococcus voltae were the predominant species in treatment 3. Abundance of
M. maripaludis and
M. voltae were similar in this treatment. In treatment 4,
M. labreanum was the predominant species followed by
Methanococcus vannielii, M maripaludis and
Methanobrevibacter smithii hold second and third position. Abundance of species
, M maripaludis and
M smithii were similar in this treatment. In the present study, species
Sulfolobus acidocaldarius,
Sulfolobus islandicus,
Sulfolobus solfataricus, Sulfolobus sp. A20 and Sulfolobus
tokodaii were identified in treatment 1. Species
Ferroplasma acidarmanus,
Picrophilus torridus,
Thermoplasma acidophilum,
Thermoplasma volcanium, Thermoplasmatales archaeon BRNA1 species belonging to order Thermoplasmatales were also identified in the rumen of Pulikulam cattle.
Similar to the finding of this study, in Murrah buffalo of India the majority of methanogens belonged to the genus methanomicrobium (
Chaudhary and Sirohi, 2009).
Shin et al., (2004) reported that 85 per cent of the total clones from the rumen of cattle belong to the order Methanomicrobiales, out of 104 clones 61 clones were resembling
M. mobile.
In contrary,
(Ozutsumi et al., 2012), Lwin et al., (2012) and
Franzolin et al., (2012) have identified Methanobrevibacter as the dominant genus in Holstein cattle, water buffaloes and crossbred buffalo, respectively. In another study
Jeyanathan et al., (2011) reported that in New Zealand Methanobrevibacter spp. were dominant in cattle.
Leahy et al., (2013) also reported that in the cow rumen,
Methanobrevibacter reported to be the dominant genus of the archaeal domain. In the present study
Methanocella arvoryzae was identified only in treatment 2.
Malik et al., (2021) reported that species
M. arvoryzae, was identified in the buffalo rumen at a very low frequency.