Diversity of methanogenic archaea in a biogas reactor fed with swine feces as the mono-substrate by mcrA analysis.

Methanogenesis from the biomass in the anoxic biogas reactors is catalyzed by syntrophic cooperation between anaerobic bacteria, syntrophic acetogenic bacteria and methanogenic archaea. Understanding of microbial community composition within the biogas reactors may improve the methane production from biomass fermentation. In this study, methanogenic archaea diverity of a biogas reactor supplied with swine feces as mono-substrate under mesophilic conditions was investigated. Community composition was determined by analysis of methyl coenzyme reductase subunit A gene (mcrA) clone library consisting of 123 clones. Statistical analysis of mcrA library indicated that all major groups of methanogens from our biogas reactor were detected. In the library, 57.7% clones were affiliated to Methanobacteriales, 34.2% to Methanomicrobiales, 2.4% to Methanosarcinales and about 5.7% clones belonged to unclassified euryarchaeota. Over 90% of the methanogenic archaea from our biogas reactor were postulated to be hydrogenotrophic methanogens. Comparing with other previous studies reporting that hydrogenotrophic methanogens are dominant species in the biogas plants, this study firstly reported that Methanobacteriales instead of Methanomicrobiales are the most predominant methanogenic archaea in the biogas reactor fed with swine feces as sole substrate.