Thiobacillus sedimenti sp. nov., a chemolithoautotrophic sulphur-oxidizing bacterium isolated from freshwater sediment

A sulphur-oxidizing bacterium, designated strain SCUT-2^T, was isolated from freshwater sediment collected from the Pearl River in Guangzhou, PR China. This strain was an obligate chemolithoautotroph, utilizing reduced sulphur compounds (elemental sulphur, thiosulphate, tetrathionate and sulphite) as the electron donor. Growth of strain SCUT-2^T was observed at 20–40 ℃ (optimum at 30 °C), pH 5.0–9.0 (optimum at 6.0), and NaCl concentration range of 0–9 g L⁻¹ (optimum at 1 g L⁻¹). The major cellular fatty acids were C_16:0 ω7c and cyclo-C_17:0. The DNA G + C content of the complete genome sequence was 66.8 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain SCUT-2^T formed a lineage within the genus Thiobacillus, showing gene sequence identity of 98.0% with its closest relative Thiobacillus thioparus THI 115. The genome of strain SCUT-2^T contains multiple genes encoding sulphur-oxidizing enzymes that catalyse the oxidation of reduced sulphur compounds, partial genes that are necessary for denitrification, and the genes encoding cbb₃-type cytochrome c oxidase, aa₃-type cytochrome c oxidase and bd-type quinol oxidase. Facultative anaerobic growth occurs when using nitrate as the electron acceptor and thiosulphate as the electron donor. On the basis of phenotypic, chemotaxonomic, genotypic and phylogenetic analysis, strain SCUT-2^T (= GDMCC 1.4108^T = JCM 39443^T) is deemed to represent a novel Thiobacillus species, for which we propose the name Thiobacillus sedimenti sp. nov.