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

Researchers isolated two obligately piezophilic bacterial strains (JT7301 and JT7304T) from sediment collected at 7,434 meters depth in the Japan Trench's deepest cold-seep environment. Through 16S rRNA gene sequence analysis, DNA-DNA hybridization, and phenotypic characterization, these strains were identified as members of a novel species within the genus Psychromonas. The isolates are Gram-negative rods that require high pressure (optimal 50 MPa) and cold temperatures (optimal 10°C) for growth, and cannot survive at atmospheric pressure. They are facultatively anaerobic chemo-organotrophs with a DNA G+C content of 43.8 mol%. Notably, these strains produce both eicosapentaenoic acid and docosahexaenoic acid, unusual among piezophilic bacteria which typically produce only one of these long-chain polyunsaturated fatty acids. The strains showed less than 27% DNA-DNA relatedness to the reference species Psychromonas antarctica, well below the species definition threshold. The authors propose the name Psychromonas kaikoae sp. nov., with JT7304T as the type strain, representing the first obligately piezophilic species within the genus Psychromonas.

Key findings

• Two obligately piezophilic bacterial strains isolated from 7,434 m depth in Japan Trench cold-seep sediments represent a novel Psychromonas species with optimal growth at 50 MPa and 10°C
• The new species Psychromonas kaikoae cannot grow at atmospheric pressure and shows less than 27% DNA-DNA relatedness to the reference species P. antarctica
• P. kaikoae uniquely produces both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), whereas most piezophilic bacteria produce only one of these long-chain polyunsaturated fatty acids
• This is the first identified obligately piezophilic species within the genus Psychromonas, expanding the diversity of cultured deep-sea piezophilic bacteria