Rhodovulum tesquicola sp. nov., a haloalkaliphilic purple non-sulfur bacterium from brackish steppe soda lakes.

Two strains of purple non-sulfur bacteria (A-36s(T) and A-51s) were isolated from brackish steppe soda lakes of southern Siberia. Genetically, the isolates were related most closely to the type strains of Rhodovulum steppense and Rhodovulum strictum, from which they differed at the species level (98.5% 16S rRNA gene sequence similarity, 40-53% DNA-DNA relatedness). Cells of the two strains were ovoid to rod-shaped, 0.4-0.8 µm wide and 1.0-2.5 µm long, and motile by means of a polar flagellum. They contained internal photosynthetic membranes of vesicular type and photosynthetic pigments (bacteriochlorophyll a and carotenoids of the spheroidene series). The strains were obligate haloalkaliphiles, growing over wide ranges of salinity (0.3-10.0% NaCl) and pH (7.5-10.0), with growth optima at 1.0-3.0% NaCl and pH 8.5-9.0. Photoheterotrophic and chemoheterotrophic growth occurred with a number of organic compounds and biotin, p-aminobenzoate, thiamine and niacin as growth factors. No anaerobic respiration on nitrite, nitrate or fumarate and no fermentation were demonstrated. The strains grew photolithoautotrophically and chemolithoautotrophically with sulfide, sulfur and thiosulfate, oxidizing them to sulfate. Sulfide was oxidized via deposition of extracellular elemental sulfur. No growth with H(2) as the electron donor was observed. The major fatty acid was C(18:1) (78%). The major quinone was ubiquinone Q-10. The DNA G+C content of strain A-36s(T) was 65.4 mol% (T(m)). According to genotypic and phenotypic characteristics, the investigated strains were assigned to a novel species of the genus Rhodovulum, for which the name Rhodovulum tesquicola sp. nov. is proposed. The type strain is A-36s(T) ( = VKM B-2491(T) = ATCC BAA-1573(T)), which was isolated from steppe soda lake Sul'fatnoe (Zabaikal'skii Krai, southern Siberia, Russia).