Comparative analysis of methanogen diversity in the rumen of crossbred buffalo and cattle in the Philippines by using the functional gene mcrA

Comparative analyses of methanogen diversity in the rumen of crossbred buffalo and cattle fed the same diet in the Philippines was performed by cloning the methyl coenzyme M reductase A (mcrA) gene. The cattle and buffalo libraries consisted of 50 clones each. Comparative analysis of the amino acid sequence revealed that these 2 libraries differed significantly (P < 0.01). The deduced amino acid sequences of the clones were classified into 9 operational taxonomic units (OTUs) in buffalo and 11 OTUs in cattle. Sequence similarity between the clones and known cultured methanogens ranged from 86 to 97 % for buffalo and 84 to 99 % for cattle. Methanobrevibacter species were predominant in buffalo (64 % of the clones), and an unknown mcrA was predominant in cattle (52 % of the clones). A large number of clones with low similarity to cultivated methanogens was observed in both buffalo and cattle, suggesting the presence of an unknown methanogen species in their rumen.