Presence of a Novel Methanogenic Archaeal Lineage in Anaerobic Digesters Inferred from mcrA and 16S rRNA Gene Phylogenetic Analyses

To find taxonomically novel methanogenic archaea, a clone analysis targeting mcrA gene (a functional molecular marker of methanogenic archaea) was conducted for four anaerobic granular sludges. Several mcrA gene phylotypes were clearly different from those of other groups of known methanogens. These were found to belong to an unidentified group called as MCR-2b group. Comparative phylogenetic analysis of deduced amino acid of McrA and 16S rRNA gene sequences revealed that the MCR2-b McrA group is possibly derived from a novel methanogen group; the 16S rRNA gene sequences have been classified into an uncultured archaeal group WCHA1-57. The result suggests that WCHA1-57 archaeal group may represent a putative new order of the methanogenic archaeal group that contributes to methane production in anaerobic digesters.