Comparative phenotypic and genomic analysis of the methanogen Methanomethylovorans thermophila L2FAW and its phylogenomic placement within the Genome Taxonomy Database

The genome of the methylotrophic methanogen <i>Methanomethylovorans thermophila</i> L2FAW is not included in the Genome Taxonomy Database (GTDB) so far, even though the strain was first described in 2005. To evaluate its genomic characteristics and placement in the GTDB, we sequenced the genome of <i>M. thermophila</i> L2FAW via <i>Illumina</i> shotgun and Oxford <i>Nanopore</i> sequencing and subsequently did hybrid assembly. The assembled genome consists of 2.25 Mbp (contigs ≥500 bp) with a G+C content of 40 mol%. The quality of the genome is good, which is already apparent from the low L50 (=1) and L90 (=2) metrics. Our assembled genome was highly similar to the metagenome-assembled genome <i>Methanomethylovorans sp014361205</i> (GCA_014361205.1_ASM1436120v1_genomic) with an average nucleotide identity of 99.9%. Even though KEGG Mapper Reconstruction results revealed that <i>M. thermophila</i> L2FAW harbours all the enzymes necessary for acetoclastic and hydrogenotrophic methanogenesis and <i>gapseq</i> predicted formate as a potential substrate for <i>M. thermophila</i> L2FAW, no metabolic activity could be observed on acetate, H₂-CO₂ (80:20 vol/vol, 2,000 mbar) and on a mixture of H₂-CO₂ and formate in lab tests; thus, the obligate methylotrophic lifestyle of the phenotype was confirmed.