Desulfovibrio subterraneus sp. nov., a mesophilic sulfate-reducing deltaproteobacterium isolated from a deep siliceous mudstone formation

Abstract

A novel mesophilic sulfate-reducing bacterium, strain HN2T, was isolated from groundwater sampled from the subsurface siliceous mudstone of the Wakkanai Formation located in Horonobe, Hokkaido, Japan. The bacterium was Gram-negative and vibrio-shaped, and its motility was conferred by a single polar flagellum. Cells had desulfoviridin. Catalase and oxidase activities were not detected. It grew in the temperature range of 25–40 °C (optimum, 35 °C) and pH range of 6.3–8.1 (optimum, pH 7.2–7.6). It used sulfate, thiosulfate, dimethyl sulfoxide, anthraquinone-2,6-disulfonate, Fe3+, and manganese oxide, but not elemental sulfur, nitrite, nitrate, or fumarate as electron acceptors. The strain showed weak growth with sulfite as the electron acceptor. Fermentative growth with pyruvate, lactate and cysteine was observed in the absence of sulfate, but not with malate or fumarate. NaCl was not required, but the strain tolerated up to 40 g l–1. Strain HN2T did not require vitamins. The major cellular fatty acids were iso-C15 : 0 (23.8 %), C18 : 1  ω9t (18.4 %), C18 : 0 (15.0 %), C16 : 0 (14.5 %), and anteiso-C17 :0 (10.1 %). The major respiratory quinone was menaquinone MK-6(H2). The G+C content of the genomic DNA was 56.7 mol%. Based on 16S rRNA gene sequence analysis, the closest phylogenetic relative of strain HN2T is Desulfovibrio psychrotolerans JS1T (97.0 %). Digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) values of the strains HN2T and D. psychrotolerans JS1T were 22.2 and 79.8 %, respectively. Based on the phenotypic and molecular genetic evidence, we propose a novel species, D. subterraneus sp. nov. with the type strain HN2T (=DSM 101010T=NBRC 112213T).