Sphaerochaeta multiformis sp. nov., an anaerobic, psychrophilic bacterium isolated from subseafloor sediment, and emended description of the genus Sphaerochaeta

An anaerobic, psychrophilic bacterium, strain MO-SPC2T, was isolated from a methanogenic microbial community in a continuous-flow bioreactor that was established from subseafloor sediments collected from off the Shimokita Peninsula of Japan in the north-western Pacific Ocean. Cells were pleomorphic: spherical, annular, curved rod, helical and coccoid cell morphologies were observed. Motility only occurred in helical cells. Strain MO-SPC2T grew at 0–17 °C (optimally at 9 °C), at pH 6.0–8.0 (optimally at pH 6.8–7.2) and in 20–40 g NaCl l−1 (optimally at 20–30 NaCl l−1). The strain grew chemo-organotrophically with mono-, di- and polysaccharides. The major end products of glucose fermentation were acetate, ethanol, hydrogen and carbon dioxide. The abundant polar lipids of strain MO-SPC2T were phosphatidylglycolipids, phospholipids and glycolipids. The major cellular fatty acids were C14 : 0, C16 : 0 and C16 : 1ω9. Isoprenoid quinones were not detected. The G+C content of the DNA was 32.3 mol%. 16S rRNA gene-based phylogenetic analysis showed that strain MO-SPC2T was affiliated with the genus Sphaerochaeta within the phylum Spirochaetes , and its closest relatives were Sphaerochaeta pleomorpha GrapesT (88.4 % sequence identity), Sphaerochaeta globosa BuddyT (86.7 %) and Sphaerochaeta coccoides SPN1T (85.4 %). Based on phenotypic characteristics and phylogenetic traits, strain MO-SPC2T is considered to represent a novel species of the genus Sphaerochaeta , for which the name Sphaerochaeta multiformis sp. nov. is proposed. The type strain is MO-SPC2T ( = JCM 17281T = DSM 23952T). An emended description of the genus Sphaerochaeta is also proposed.