Thiocapsa litoralis, sp. nov., a new purple sulfur bacterium from microbial mats of the White Sea

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)

Phylogenetic relationships among budding purple bacteria of the genus Rhodopseudomonas

Phylogenetic relationships within a group of budding purple nonsulfur bacteria of the genus Rhodopseudomonas were studied by DNA-DNA hybridization. Most of the strains were new isolates from natural environments with a wide ränge of physicochemical conditions.A total of 32 strains were analyzed, includ- ing the type strains of Rhodopseudomonas palustris, Rps. rutila, Rps. marina, and Rps. acidophila. Nine phylo- genetically remote clusters were revealed, showing an average DNA-DNA horaology of 15%. One of the Clusters contained the type strain of Rps. marina, isolated front marine habitats, and two new isolates from hot ffeshwater springs. These new isolates tumed out to be facultative halophiles with a salinity Optimum of 1-3% and were assigned to Rps. marina on the basis of their phenotypic characteristics and DNA-DNA homology of 60% with the type strain of this species. The type strain of Rps. acidophila was not specifically related to any other strain used during this investigation. The remaining 26 isolates and the type strains of Rps. palustris and Rps. rutila were very similar phenotypically, but formed seven phylogenetically remote clusters including 13 genospecies; none of the new isolates were closely related to the type strains of Rps. palustris and Rps. rutila, which also proved to be phylogenetically distinct. Thus, the Rps. palustris-like bacteria, which are widespread in nature and comprise phenotypically a homogeneous group, appear to be phylogenetically diverse. The prospects for developing a Classification system for these budding purple nonsulfur bacteria that would be in agreement with their phylogenetic relationships are discussed. Possible correlation between the phylogenetic relationships of these bacteria and the ecological peculiarities of their natural habitats is also considered