Methanolinea tarda gen. nov., sp. nov., a methane-producing archaeon isolated from a methanogenic digester sludge.

A novel methane-producing archaeon, strain NOBI-1(T) was isolated from an anaerobic, propionate-degradation enrichment culture, which was originally obtained from a mesophilic methanogenic sludge digesting municipal sewage sludge. Cells were non-motile, rod-shaped, 0.7-1.0 microm by 2.0 microm, and formed multicellular filaments longer than 8 microm. Growth was observed between 35 and 55 degrees C (optimum 50 degrees C) and pH 6.7 and 8.0 (optimum pH 7.0). The G+C content of the genomic DNA was 56.3 mol%. The strain utilized H(2) and formate for growth and methane production. Based on comparative sequence analyses of the 16S rRNA gene and mcrA gene (encoding the alpha subunit of methyl-coenzyme M reductase, a key enzyme in the methane-production pathway), strain NOBI-1(T) was affiliated with the order Methanomicrobiales, but it was significantly distant from any other known species within the order. The most closely related species based on 16S rRNA and mcrA gene sequence similarity were respectively 'Candidatus Methanoregula boonei' (93.7% 16S rRNA gene sequence similarity) and Methanocorpusculum parvum (74.2% deduced McrA amino acid sequence similarity to the type strain). These phenotypic and genetic properties justified the creation of a novel species of a new genus for the strain, for which we propose the name Methanolinea tarda gen. nov., sp. nov. The type strain of Methanolinea tarda is strain NOBI-1(T) (=DSM 16494(T) =JCM 12467(T) =NBRC 102358(T)).