Colwellia piezophila sp nov., a novel piezophilic species from deep-sea sediments of the Japan Trench

Two strains of obligately piezophilic bacteria were isolated from sediment collected from the bottom surface of a small canyon on the seaward slope of the Japan Trench at a depth of 6278 m. The isolated strains, Y223G(T) and Y251E, are closely affiliated with members of the genus Colwellia on the basis of 16S rRNA gene sequence analysis. The G+C contents of both strains were about 39 mol%. DNA-DNA hybridization values between these strains and Colwellia reference strains were significantly lower than those accepted as the phylogenetic definition of a species. The novel strains are Gram-negative, polarly flagellated and facultatively anaerobic. The optimal pressure for growth was 60 MPa at both 4 and 10 degreesC; the most rapid growth rate was observed at 10 degreesC and 60 MPa. No growth occurred at 15 degreesC under any pressure studied. The major isoprenoid quinone is Q-8. The predominant cellular fatty acids are C16:0 and C16:1. Based on the taxonomic differences observed, the isolated strains appear to represent a novel obligately piezophilic Colwellia species. The name Colwellia piezophila sp. nov. (type strain Y223G(T) = JCM 11831(T) = ATCC BAA-637(T)) is proposed.