A new phototrophic purple sulfur bacterium, isolated from benthic microbial mats from the White Sea littoral zone, is described. Individual cells were spherical, non-motile and lacked gas vesicles. In pure cultures cells appeared in regular platelet-like arrangements of four, eight or sixteen cells. Cell division occurred inside a common envelope, surrounded by a thick capsule. Internal photosynthetic membranes were of the vesicular type. The colour of cell suspensions was pink to rose-red. Bacteriochlorophyll a and carotenoids of the spirilloxanthin series were found as photosynthetic pigments. Under anoxic conditions in the light, photolithoautotrophic growth occurred with sulfide, thiosulfate, sulfite and elemental sulfur as electron donors. Sulfur globules were stored as an intermediary oxidation product and were visible microscopically inside the cells. In the presence of sulfide and bicarbonate, photomixotrophic growth occurred with a number of organic substrates. Sulfate could serve as sole assimilatory source of sulfur. Chemolithoautotrophic growth in the dark was possible with sulfide and thiosulfate as electron donors. Optimum growth occurred in the presence of 1% NaCl, at pH 6.5 and at 30 degrees C. The DNA base composition of the type strain, BM5T, was 64.0 mol% G+C. According to 16S rDNA sequence information and DNA-DNA hybridization, the new isolate clearly belongs to the genus Thiocapsa, but is sufficiently different from other recognized Thiocapsa species to be described as a new species of this genus for which the name Thiocapsa litoralis sp. nov. is proposed. The type strain is BM5T (= ATCC 700894).


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