%0 Journal Article %A Maruyama, A %A Honda, D %A Yamamoto, H %A Kitamura, K %A Higashihara, T %T Phylogenetic analysis of psychrophilic bacteria isolated from the Japan Trench, including a description of the deep-sea species Psychrobacter pacificensis sp. nov. %D 2000 %J International Journal of Systematic and Evolutionary Microbiology, %V 50 %N 2 %P 835-846 %@ 1466-5034 %R https://doi.org/10.1099/00207713-50-2-835 %I Microbiology Society, %X Phylogenetic positions of psychrophilic bacteria isolated from the Japan Trench were determined by sequencing analysis of PCR-amplified bacterial small subunit (16S) rRNA genes. Between surface and deep-sea psychrophiles, distinct positions clearly differed within the gamma-Proteobacteria. In phylogenetic analysis using neighbour-joining, maximum-parsimony and maximum-likelihood, strains from surface seawater were inferred to be located in the Halomonas aquamarina-meridiana clade within the family Halomonadaceae. Strains from deep seawater (5000-6000 m), however, formed a novel monophyletic clade within the Moraxella-Psychrobacter branch in the family Moraxellaceae, showing separation from terrestrial and Antarctic relatives. These deep-sea strains were also discriminated from other known Psychrobacter species in phenotype, e.g. limited growth in the absence of NaCl (optimum at about 3% NaCl), positive urease activity, acid production from xylose and arabinose, and the presence of multiple fimbriae. DNA relatedness values among six deep-sea strains were > 85% in DNA-DNA hybridization experiments and > 98% in aligned 16S rDNA sequences. From this evidence, a new species, Psychrobacter pacificensis, is proposed for these deep-sea psychrophiles; the type strain of Psychrobacter pacificensis is strain NIBH P2K6T (= IFO 16270T). Occurrence of psychrobacters in cold Japan Trench deep seawater and at the Antarctic sea surface suggests that deep-sea bacterial habitation and evolution have been mediated by global deep-ocean circulation linked to the sinking of cooled seawater in polar regions. %U https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/00207713-50-2-835