Characterization of genomes assembled from metagenomes of biofilms residing in mesophilic and thermophilic biogas reactors.

Background: Previous studies on the , recently assigned to the novel archaeal phylum , reported on the dominance of these within the anaerobic carbohydrate cycle performed by the deep marine biosphere. For the first time, members of this phylum were identified also in mesophilic and thermophilic biogas-forming biofilms and characterized in detail.

Results: Metagenome shotgun libraries of biofilm microbiomes were sequenced using the Illumina MiSeq system. Taxonomic classification revealed that between 0.1 and 2% of all classified sequences were assigned to Individual metagenome assemblies followed by genome binning resulted in the reconstruction of five metagenome-assembled genomes (MAGs) of . MAGs were estimated to be 65-92% complete, ranging in their genome sizes from 1.1 to 2.0 Mb. Phylogenetic classification based on core gene sets confirmed their placement within the phylum clustering as a separate group diverging from most of the recently known clusters. The genetic repertoire of these MAGs indicated an energy metabolism based on carbohydrate and amino acid fermentation featuring the potential for extracellular hydrolysis of cellulose, cellobiose as well as proteins. In addition, corresponding transporter systems were identified. Furthermore, genes encoding enzymes for the utilization of carbon monoxide and/or carbon dioxide via the Wood-Ljungdahl pathway were detected.

Conclusions: For the members of detected in the biofilm microbiomes, a hydrolytic lifestyle is proposed. This is the first study indicating that members contribute presumably to hydrolysis and subsequent fermentation of organic substrates within biotechnological biogas production processes.