Exilispira thermophila gen. nov., sp. nov., an anaerobic, thermophilic spirochaete isolated from a deep-sea hydrothermal vent chimney.

A novel thermophilic, anaerobic bacterium, strain RASEN(T), was isolated from a deep-sea hydrothermal vent chimney sample collected in the Iheya North field, Okinawa Trough, Japan, at a water depth of 982 m. The cells were motile, Gram-negative and helical with hooked ends, 0.23-0.28x15-27 microm in size with an approximate wavelength of 1.1-1.5 microm. Growth of the strain was observed at 37-60 degrees C (optimum 50 degrees C), in 2.5-3.5 % (w/v) NaCl (optimum 2.5-3 % NaCl) and at pH 6.0-7.5 (optimum pH 7.0). The strain grew on yeast extract only of the substrates examined in this study. The G+C content of the genomic DNA was 27.1 mol%. Major fatty acids for the strain were C(16 : 0), C(18 : 1)(Delta9) trans, C(18 : 0) and C(18 : 1)(Delta9) cis. Based on comparative 16S rRNA gene sequence analysis, strain RASEN(T) formed a deeply branching lineage within the phylum Spirochaetes and had only low levels of sequence similarity with other species of the phylum (range of similarity 72.1-80.6 %). Hence, we propose the name Exilispira thermophila gen. nov., sp. nov. The type strain of Exilispira thermophila is strain RASEN(T) (=JCM 14728(T) =NBRC 103205(T) =KCTC 5595(T)).