Methanobacterium aarhusense sp nov., a novel methanogen isolated from a marine sediment (Aarhus Bay, Denmark)

Strain H2-LRT, a 5-18 mum long and 0.7 mum wide filamentous, mesophilic, moderately halophilic, non-motile hydrogenotrophic methanogen, was isolated from marine sediment of Aarhus Bay, Denmark, 1.7 m below the sediment surface. On the basis of 16S rRNA gene comparison with sequences of known methanogens, strain H2-LRT could be affiliated to the genus Methanobacterium. The strain forms a distinct line of descent within this genus, with Methanobacterium oryzae (95.9% sequence identity) and Methanobacterium bryantii (95.7% sequence identity) as its closest relatives. The 16S rRNA-based affiliation was supported by comparison of the mcrA gene, which encodes the a-subunit of methyl-coenzyme M reductase. Strain H2-LRT grew only on H-2/CO2. The DNA G+C content is 34.9 mol%. Optimum growth temperature was 45degreesC. The strain grew equally well at pH 7.5 and 8. No growth or methane production was observed below pH 5 or above pH 9. Strain H2-LRT grew well within an NaCl concentration range of 100 and 900 mM. No growth or methane production was observed at 1 M NaCl. At 50 mM NaCl, growth and methane production were reduced. Based on 16S rRNA gene sequence analysis, the isolate is proposed to represent a novel taxon within the genus Methanobacterium, namely Methanobacterium aarhusense sp. nov. The type strain is H2-LRT (=DSM 15219(T)=ATCC BAA-828(T)).