Psychromonas kaikoae sp nov., a novel piezophilic bacterium from the deepest cold-seep sediments in the Japan Trench

Two strains of obligately piezophilic bacteria were isolated from sediment collected from the deepest cold-seep environment with chemosynthesis-based animal communities within the Japan Trench, at a depth of 7434 m. The isolated strains, JT7301 and JT7304(T), were closely affiliated with members of the genus Psychromonas on the basis of 16S rDNA sequence analysis. Hybridization values for DNA-DNA relatedness between these strains and the Psychromonas antarctica reference strain were significantly lower than that accepted as the phylogenetic definition of a species. The optimal temperature and pressure for growth of the isolates were 10 degreesC and 50 MPa and they produced both eicosapentaenoic acid (C20:5omega3) and docosahexaenoic acid (C22:6) in the membrane layer. Based on the taxonomic differences observed, the isolated strains appear to represent a novel obligately piezophilic Psychromonas species. The name Psychromonas kaikoae sp. nov. (type strain JT7304(T) = JCM 11054(T) = ATCC BAA-363(T)) is proposed. This is the first proposed obligately piezophilic species of the genus Psychromonas.