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

¹ Department of Environmental Systems Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan
² Subground Animalcule Retrieval (SUGAR) Program, Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Kanagawa 237-0061, Japan
³ Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8566, Japan
⁴ Research Institute of Genome-Based Biofactory, National Institute of Advanced Industrial Science and Technology (AIST), Sapporo, Hokkaido 062-8517, Japan
⁵ Department of Civil Engineering, Tohoku University, Sendai 980-8579, Japan

Correspondence
Hiroyuki Imachi
imachi{at}jamstec.go.jp

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 µm by 2.0 µm, and formed multicellular filaments longer than 8 µm. Growth was observed between 35 and 55 °C (optimum 50 °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 H₂ 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).

The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain NOBI-1^T is AB162774 (other 16S rRNA gene clonal sequences have been deposited as accession numbers AB233309, AB233010 and AB233299–AB233302). The GenBank/EMBL/DDBJ accession numbers for the mcrA gene sequences of strains NOBI-1^T and SANAE are respectively AB300466 and AB300467.

Details of 16S rRNA gene phylotypes obtained from the sludge, information on relative abundance of various groups of organisms and a graph of methane production by strain NOBI-1^T are available as supplementary material with the online version of this paper.