Halothiobacillus diazotrophicus sp. nov., a chemolithoautotrophic sulphur-oxidizing and nitrogen-fixing bacterium isolated from freshwater

A sulphur-oxidizing and nitrogen-fixing bacterium, designated strain LS2^T, was isolated from freshwater collected from the Pearl River in Guangzhou, PR China. The strain was an obligate chemolithoautotroph, utilizing reduced sulphur compounds (sulphide, sulphite, elemental sulphur, thiosulphate and tetrathionate) as energy sources and electron donors. Diazotrophic growth of strain LS2^T was observed at 15–40 °C, pH 5–9, with a NaCl concentration range of 0–0.68 mol l⁻¹ and with oxygen content higher than 21 %. The major cellular fatty acids were summed feature 8 (comprising C_18 : 1 ω7c and/or C_18 : 1 ω6c) and C_16 : 0. The DNA G+C content of the complete genome sequence was 60.7 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain LS2^T formed a lineage within the family Halothiobacillaceae , showing gene sequence identity of 96.8 % with its closest relative Halothiobacillus neapolitanus c2. The genome of strain LS2^T contains multiple genes encoding sulphur-oxidizing enzymes that catalyse the oxidation of reduced sulphur compounds and an nif complex encoding enzymes for nitrogen fixation. In addition, the genome contains genes encoding cbb₃ -type cytochrome c oxidase, aa₃ -type cytochrome c oxidase, bd-type quinol oxidase and cytochrome o oxidase, which enable the survival strain LS2^T under oxic and microaerophilic conditions. On the basis of phenotypic, genotypic and phylogenetic data, strain LS2^T is considered to represent a novel species of the genus Halothiobacillus , for which the name Halothiobacillus diazotrophicus sp. nov. is proposed. The type strain is LS2^T (=GDMCC 1.4095^T=JCM 39442^T).