Porphyrobacter tepidarius sp. nov., a moderately thermophilic aerobic photosynthetic bacterium isolated from a hot spring

A new thermophilic bacterium, strain OT3T (T = type strain), was isolated from a brackish hot spring. Strain OT3T is an obligate aerobe that synthesizes bacteriochlorophyll a and has a photosynthetic apparatus. This isolate is a thermophilic bacterium with an optimal growth temperature of 40 to 48 degrees C. The cells are nonmotile, ovoid to short rods. An analysis of 16S rRNA sequences revealed that the new strain forms a coherent cluster with members of the alpha-4 group of the alpha subclass of the Proteobacteria, which contains the genera Erythrobacter, Erythromicrobium, and Porphyrobacter. The closest relative is Porphyrobacter neustonensis, with a 16S rRNA sequence similarity of 96.8%. The in vivo absorption spectrum has maxima at 460, 494, 596, 800, and 870 nm. The main carotenoids are OH-beta-carotene sulfate derivatives, nostoxanthin, and bacteriorubixanthinal. Growth occurs with glucose, acetate, glutamate, butyrate, Casamino Acids, and yeast extract as sole energy sources. The pigment composition and nutritional profile of the new isolate are similar to the pigment composition and nutritional profile of P. neustonensis. Although there are marked differences in cell morphology between the new isolate and the budding bacterium P. neustonensis, the results of phenotypic and genetic comparisons suggest that the new isolate is closely related to P. neustonensis. Consequently, we assign the new isolate to the genus Porphyrobacter and propose the name Porphyrobacter tepidarius sp. nov. for it; the type strain of P. tepidarius is strain OT3 (= DSM 10595).