Shewanella psychrophila sp. nov. and Shewanella piezotolerans sp. nov., isolated from west Pacific deep-sea sediment

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Abstract
TwoShewanella-like bacterial strains, WP2Tand WP3T, which were isolated from west Pacific deep-sea sediment, were studied to determine their taxonomic position. Cells of the two bacteria were facultatively anaerobic, Gram-negative rods and motile by means of a single polar flagellum. Strain WP2Twas psychrophilic, growing optimally at about 10–15 °C, whereas strain WP3Twas psychrotolerant, growing optimally at 15–20 °C. The two strains grew in the pressure range 0.1–50 MPa, with optimal growth at 20 MPa. Strain WP3Twas able to use nitrate, fumarate, trimethylamineN-oxide (TMAO), DMSO and insoluble Fe(III) as terminal electron acceptors during anaerobic growth, whereas strain WP2Twas able to use only nitrate, TMAO and DMSO. The 16S rRNA gene sequences of strains WP2Tand WP3Twere 97 % identical, and showed highest similarity (97 %) to those ofShewanella fidelisKMM 3589 andShewanella benthicaATCC 43992T, respectively. ThegyrBgene sequences of strains WP2Tand WP3Twere also determined, and showed highest similarity to those ofShewanella violaceaJCM 10179T(90 %) andShewanella sairaeSM2-1T(87 %), respectively. Contrary to the 16S rRNA gene sequence results, the phylogeny based ongyrBgene sequence analysis placed strain WP2T,S. violaceaandS. benthicain one group, while strain WP3Tgrouped withS. fidelisandS. sairae. DNA–DNA hybridization experiments supported the placement of strain WP2TwithS. violaceaandS. benthica. Phylogenetic evidence, together with DNA–DNA relatedness and phenotypic characteristics, indicated that the two new strains represented two novel deep-seaShewanellaspecies. The namesShewanella psychrophilasp. nov. (type strain WP2T=JCM 13876T=CGMCC 1.6159T) andShewanella piezotolerans(type strain WP3T=JCM 13877T=CGMCC 1.6160T) are proposed.

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