Spirochaeta psychrophila sp nov., a psychrophilic spirochaete isolated from subseafloor sediment, and emended description of the genus Spirochaeta

An obligately anaerobic, psychrophilic spirochaete, strain MO-SPC1(T), was isolated from a methanogenic microbial community grown in a continuous-flow bioreactor. Originally, this community was obtained from subseafloor sediments off the Shimokita Peninsula of Japan in the north-western Pacific Ocean. The cells were motile, Gram-stain-negative, helical, 0.25 0.55x3.6-15 mu m, with a wavelength of approximately 0.5-0.6 jim. Strain MO-SPC1(T) grew at 0 18 degrees C (optimally at 15 degrees C), at pH 6.0-7.5 (optimally at pH 6.8-7.0) and in 20-70 g NaCl (optimally at 30-40 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-SPC1T were diphosphatidylglycerol, phosphatidylglycerol, unknown phospholipids and an unknown lipid. The major cellular fatty acids (>5% of the total)-were C-14:0, C-16:0, iSO-C-13:0 iSO-C-14:0 iSO-C-15:0 anteiso-Ciao and anteiso-C15:0. To the best of our knowledge, this is the first report of the fatty acids iso-C-13:0 and anteiso-C-13:0 from a species of the genus Spirocha eta. lsoprenoid quinones were not found. The G+C content of the genomic DNA was 39.8 molok. 16S rRNA gene sequence-based phylogenetic analysis showed that strain MO-SPC1(T) was affiliated with the genus Spirochaeta, and its closest relatives were Spirochaeta isovalerica MA-2(T) (95.6% sequence identity) and Spirochaeta litoralis R1(T) (89.4 %). Based on its phenotypic characteristics and phylogenetic traits, strain MO-SPC1(T) is placed in a separate taxon at the level of a novel species within the genus Spirochaeta, for which the name Spirochaeta psychrophila sp. nov. is proposed, reflecting its true psychrophilic physiology. The type strain is MO-SPC1(T) (=JCM 17280(T)=DSM 23951(T)). To our knowledge, this is the first report of an isolate of the phylum Spirochaetes from a deep-sea sedimentary environment.and of an obligately psychrophilic nature.