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

Abstract

Two Shewanella-like bacterial strains, WP2T and 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 WP2T was psychrophilic, growing optimally at about 10–15 °C, whereas strain WP3T was 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 WP3T was able to use nitrate, fumarate, trimethylamine N-oxide (TMAO), DMSO and insoluble Fe(III) as terminal electron acceptors during anaerobic growth, whereas strain WP2T was able to use only nitrate, TMAO and DMSO. The 16S rRNA gene sequences of strains WP2T and WP3T were 97 % identical, and showed highest similarity (97 %) to those of Shewanella fidelis KMM 3589 and Shewanella benthica ATCC 43992T, respectively. The gyrB gene sequences of strains WP2Tand WP3 T were also determined, and showed highest similarity to those of Shewanella violacea JCM 10179T (90 %) and Shewanella sairae SM2-1T (87 %), respectively. Contrary to the 16S rRNA gene sequence results, the phylogeny based on gyrB gene sequence analysis placed strain WP2T, S. violacea and S. benthica in one group, while strain WP3T grouped with S. fidelis and S. sairae. DNA–DNA hybridization experiments supported the placement of strain WP2T with S. violacea and S. benthica. Phylogenetic evidence, together with DNA–DNA relatedness and phenotypic characteristics, indicated that the two new strains represented two novel deep-sea Shewanella species. The names Shewanella psychrophila sp. nov. (type strain WP2T=JCM 13876T=CGMCC 1.6159T) and Shewanella piezotolerans (type strain WP3T=JCM 13877T=CGMCC 1.6160T) are proposed.