Characterization of three spiral-shaped purple nonsulfur bacteria isolated from coastal lagoon sediments, saline sulfur springs, and microbial mats: emended description of the genus Roseospira and description of Roseospira marina sp. nov., Roseospira navarrensis sp. nov., and Roseospira thiosulfatophila sp. nov.

Three new spirilloid phototrophic purple nonsulfur bacteria were isolated in pure culture from three different environments: strain CE2105 from a brackish lagoon in the Arcachon Bay (Atlantic coast, France), strain SE3104 from a saline sulfur spring in the Pyrenees (Navarra, Spain) , and strain AT2115 a microbial mat (Tetiaroa Atoll, Society Islands). Single cells of the three strains were spiral-shaped and highly motile. Their intracellular photosynthetic membranes were of the vesicular type. Bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series were present as photosynthetic pigments. Optimal growth occurred under photoheterotrophic conditions and in the presence of 0.5–4% w/v NaCl. These features are similar to those described for Roseospira mediosalina. Comparative sequence analysis of their 16S rRNA genes placed these strains within the α-subclass of Proteobacteria, in a cluster together with Roseospira mediosalina and Rhodospira trueperi. They form a closely related group of slightly to moderately halophilic spiral-shaped purple nonsulfur bacteria. However, the three new isolates exhibited some differences in their physiology and genetic characteristics. Consequently, we propose that they are members of three new species within the genus Roseospira, Roseospira marina sp. nov., Roseospira navarrensis sp. nov., and Roseospira thiosulfatophila sp. nov., with strains CE2105, SE3104, and AT2115 as the type strains, respectively. As a consequence, an emended description of the genus Roseospira is also given.