PORPHYROBACTER TEPIDARIUS SP-NOV, A MODERATELY THERMOPHILIC AEROBIC PHOTOSYNTHETIC BACTERIUM ISOLATED FROM A HOT-SPRING

A new thermophilic bacterium, strain OT3(T) (T = type strain), was iso lated from a brackish hot spring, Strain OT3(T) is an obligate aerobe that synthesizes bacteriochlorophyll a and has a photosynthetic appara tus, This isolate is a thermophilic bacterium with an optimal growth t emperature of 40 to 48 degrees C, The cells are nonmotile, ovoid to sh ort rods. An analysis of 16S rRNA sequences revealed that the nem stra in farms a coherent cluster with members of the alpha-4 group of the a lpha subclass of the Proteobacteria, which contains the genera Erythro bacter, Erythromicrobium, and Porphyrobacter. The closest relative is Porphyrobacter neustonensis, with a 168 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 derivat ives, nostoxanthin, and bacteriorubixanthinal. Growth occurs with gluc ose, acetate, glutamate, butyrate, Casamino Acids, and yeast extract a s sole energy sources, The pigment composition and nutritional profile of the new isolate are similar to the pigment composition and nutriti onal 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 sug gest that the new isolate is closely related to P. neustonensis. Conse quently, we assign the new isolate to the genus Porphyrobacter and pro pose the name Porphyrobacter tepidaris sp, nov, for it; the type strai n of P, tepidarius is strain OT3 (= DSM 10595).