Rhodovulum iodosum sp. nov. and Rhodovulum robiginosum sp. nov., two new marine phototrophic ferrous-iron-oxidizing purple bacteria.

Two new strains of marine purple bacteria, N1T and N2T, were isolated from coastal sediment of the North Sea (Germany) with ferrous iron as the only electron donor for anoxygenic photosynthesis. The isolates are the first salt-dependent, ferrous-iron-oxidizing purple bacteria characterized so far. Analysis of 16S rRNA gene sequences revealed an affiliation with the genus Rhodovulum, which until now comprises only marine species. The sequence similarity of both strains was 95.2%, and their closest relative was Rhodovulum adriaticum. Like all known Rhodovulum species, the new strains had ovoid to rod-shaped cells, contained bacteriochlorophyll a and carotenoids of the spheroidene series, and were able to oxidize sulfide and thiosulfate. Like Rhodovulum adriaticum, both strains were unable to assimilate sulfate; for growth they needed a reduced sulfur source, e.g. thiosulfate. In contrast to the new strains, none of the known Rhodovulum species tested was able to oxidize ferrous iron or iron sulfide. In growth experiments, strains N1T and N2T oxidized 65 and 95%, respectively, of the ferrous iron supplied. Electron diffraction analysis revealed ferrihydrite as the main product of ferrous iron oxidation. In addition, traces of magnetite were formed. Strains N1T (= DSM 12328T) and N2T (= DSM 12329T) are described as Rhodovulum iodosum sp. nov. and Rhodovulum robiginosum sp. nov., respectively.