A bright pink to red-coloured, phototropic, purple non-sulfur bacterium, designated strain TUT3530(T), was isolated from pond water. Cells of the novel isolate were found to be Gram-negative, motile, budding rods. Cell extracts from phototrophically grown cultures had absorption maxima at 378, 482, 512, 550, 590, 800 and 850 nm, indicating the presence of bacteriochlorophyll a and carotenoids of the spirilloxanthin series. The intracytoplasmic membrane system was of the lamellar type. Anaerobic photo-organotrophy with simple organic acids such as pyruvate was the preferred mode of growth. Aerobic growth at full atmospheric oxygen tension and anaerobic denitrifying growth in darkness were also possible. Photolithotrophic growth occurred with thiosulfate, but not with sulfide or hydrogen, as the electron donor. No growth factors were required. The major whole-cell fatty acid was C(18 : 1)omega7c. The major quinones were ubiquinone-10 and rhodoquinone-10. A phylogenetic analysis based on 16S rRNA gene sequences and studies involving DNA-DNA hybridization demonstrated that strain TUT3530(T) occupies a distinct taxonomic position within the genus Rhodoplanes. On the basis of these data, strain TUT3530(T) represents a novel species of the genus Rhodoplanes, for which the name Rhodoplanes serenus sp. nov. is proposed. The type strain is TUT3530(T) (=DSM 18633(T)=NBRC 102049(T)).