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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 °C and 50 MPa and they produced both eicosapentaenoic acid (C20:5ω3) 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.

9 páginas.-- 3 figuras.-- referencias.-- El autor González Grau, Juan Miguel pertenece actualmente al Instituto de Recursos Naturales y Agrobiología de Sevilla, A new anaerobic, thermophilic, CO-utilizing marine bacterium, strain JMT, was isolated from a submarine hot vent in Okinawa Trough. Cells of strain JMT were non-motile thin straight rods, sometimes branching, with a cell wall of the Gram-positive type, surrounded with an S-layer. Chains of three to five cells were often observed. The isolate grew chemolithotrophically on CO, producing equimolar quantities of H2 and CO2 (according to the equation CO+H2O-->CO2+H2) and organotrophically on peptone, yeast extract, starch, cellobiose, glucose, galactose, fructose and pyruvate, producing H2, acetate and CO2. Growth was observed from 50 to 80 degrees C with an optimum at 70 degrees C. The optimum pH was 6.8-7.1. The optimum concentration of sea salts in the medium was 20.5-25.5 g l(-1). The generation time under optimal conditions was 7.1 h. The DNA G+C content was 33 mol %. Growth of isolate JMT was not inhibited by penicillin, but ampicillin, streptomycin, kanamycin and neomycin completely inhibited growth. The results of 16S rDNA sequence analysis revealed that strain JMT belongs to the Thermoanaerobacter phylogenetic group within the Bacillus-Clostridium subphylum of Gram-positive bacteria but represents a separate branch of this group. On the basis of morphological and physiological features and phylogenetic data, this isolate should be assigned to a new genus, for which the name Carboxydobrachium is proposed. The type species is Carboxydobrachium pacificum; the type strain is JMT (= DSM 12653T)., The authors are grateful to G. A. Zavarzin and A. V. Lebedinsky, Institute of Microbiology, Russian Academy of Sciences, for helpful discussions. This work was supported by the Russian Foundation for Basic Research, grants nos 96-04-49463 and 99-04-48360, the ‘Biodiversity’ program of the Russian Ministry of Science and Technology, a NATO CLG grant to T. S. and F. T. R. and by NSF LEXEN Program support to F. T. R. and J. M. G.

An obligately piezophilic bacterium was isolated from sediment collected from the bottom of the Japan Trench at a depth of 7542 m. The isolated strain, designated K41GT, was closely affiliated with members of the genus Psychromonas on the basis of 16S rRNA gene sequence analysis. Levels of DNA–DNA relatedness between strain K41GT and Psychromonas reference strains were significantly lower than that accepted as the phylogenetic definition of a species. The optimal temperature and pressure for growth of strain K41GT were 6 °C and 60 MPa, respectively. The DNA G+C content was 39.1 mol%. Whole-cell fatty acids consisted of significant amounts of unsaturated fatty acids C16 : 1 (37 %) and C14 : 1 (17 %), saturated fatty acid C16 : 0 (31 %) and polyunsaturated fatty acid C22 : 6 (8 %). Based on the taxonomic differences observed, strain K41GT is considered to represent a novel obligately piezophilic Psychromonas species. The name Psychromonas hadalis (type strain, K41GT=JCM 11830T=ATCC BAA-638T) is proposed. This is the second species of obligately piezophilic bacteria to be proposed in the genus Psychromonas.

A novel piezotolerant, mesophilic, facultatively anaerobic, organotrophic, polarly flagellated bacterium (strain LT13aT) was isolated from a deep sediment layer in the Nankai Trough (Leg 190, Ocean Drilling Program) off the coast of Japan. This organism used a wide range of organic substrates as sole carbon and energy sources: pyruvate, glutamate, succinate, fumarate, lactate, citrate, peptone and tryptone. Oxygen, nitrate, fumarate, ferric iron and cystine were used as electron acceptors. Maximal growth rates were observed at a hydrostatic pressure of 10 MPa. Hydrostatic pressure for growth was in the range 0·1–50 MPa. Predominant cellular fatty acids were 16 : 1ω7c, 15 : 0 iso, 16 : 0 and 13 : 0 iso. The G+C content of the DNA was 44·9 mol%. On the basis of 16S rRNA gene sequences, strain LT13aT was shown to belong to the γ-Proteobacteria, being closely related to Shewanella putrefaciens (98 %), Shewanella oneidensis (97 %) and Shewanella baltica (96 %). Levels of DNA homology between strain LT13aT and S. putrefaciens, S. oneidensis and S. baltica were T represents a novel species. Genetic evidence and phenotypic characteristics showed that isolate LT13aT constitutes a novel species of the genus Shewanella. Because of the deep origin of the strain, the name Shewanella profunda sp. nov. is proposed, with LT13aT (=DSM 15900T=JCM 12080T) as the type strain.

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, Y223GT 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 °C; the most rapid growth rate was observed at 10 °C and 60 MPa. No growth occurred at 15 °C 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 Y223GT=JCM 11831T=ATCC BAA-637T) is proposed.