Two new strains of marine purple bacteria, N1and N2, 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 , which until now comprises only marine species. The sequence of both strains was 95·2%, and their closest relative was . Like all known species, the new strains had ovoid to rod-shaped cells, contained bacteriochlorophyll a and carotenoidc of the spheroidene series, and were able to oxidize sulfide and thiosulfate. Like , 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 species tested was able to oxidize ferrous iron or iron sulfide. In growth experiments, strains N1and N2oxidized 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 N1(= DSM 12328) and N2(= DSM 12329) are described as sp. nov. and sp. nov., respectively.


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