Sulfurimonas lacustris sp. nov. and Sulfurimonas limnophila sp. nov. from the chemocline of a meromictic brackish lake

Two novel sulphur-oxidizing bacteria, designated strains SulA T and SulB T , were isolated from the chemocline of a meromictic brackish lake, Lake Harutori, Japan. Strains SulA T and SulB T grew over temperature ranges of 5–37 and 5–32 °C, pH ranges of 6.2–8.1 and 6.2–8.5 and NaCl ranges of 0–4.7 and 0–1.8 g l −1 , respectively. Both strains utilized sulphide and elemental sulphur as electron donors and nitrate, nitrite and 3 and 5% O 2 as electron acceptors. Thiosulphate served as an electron donor for SulA T but not for SulB T , representing the first report of inability to grow on thiosulphate within the genus Sulfurimonas . Their major cellular fatty acids were C 16:1 ω 7 c and C 16:0 . The complete genomes of strains SulA T and SulB T consist of a circular chromosome and a plasmid, with genome sizes of 2.41 and 2.29 Mb and G+C contents of 39.1 and 34.6 mol%, respectively. Phylogenetic trees based on 16S rRNA gene sequences and whole-genome data placed both strains in a distinct clade within the genus Sulfurimonas . Average nucleotide identity and digital DNA–DNA hybridization values between the novel strains and previously described Sulfurimonas species were below the thresholds for species delineation. Based on the physiological, chemotaxonomic and genomic characteristics, strains SulA T (=JCM 39401 T =DSM 113753 T ) and SulB T (=JCM 39402 T =DSM 113750 T ) are proposed as representatives of two novel species, Sulfurimonas lacustris sp. nov. and Sulfurimonas limnophila sp. nov., respectively.