New strains of an aerobic anoxygenic phototrophic bacterium Porphyrobacter donghaensis isolated from a Siberian thermal spring and a weakly mineralized lake

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A strain of aerobic anoxygenic phototrophic bacteria (AAPB) isolated from the surface of a cyanobacterial mat of an Eastern Siberian thermal spring (40°C) and designated Se-4 was identified as Porphyrobacter donghaensis according to its 16S rRNA gene sequence. A DNA–DNA hybridization level of 95% was determined between strain Se-4 and the type strain of this species, SW-132^T. The isolate was an obligate aerobe, forming orange round colonies on solid media, which turn red in the course of growth. The cells were motile rods capable of branching. The cells divided by uniform fission by constriction. Optimal growth was observed at pH 7.5 and NaCl concentrations from 0 to 1 g/L. The pigments present were carotenoids and bacteriochlorophyll a. Another Porphyrobacter donghaensis strain, Noj-1, isolated from a purple mat developing on the surface of a coastal set-up in a steppe weakly mineralized (1.5 g/L) soda lake Nozhii (Eastern Siberia) possessed similar characteristics. Thus, the AAPB species Porphyrobacter donghaensis was shown to occur, apart from marine environments (its known habitat), also in weakly mineralized soda lakes and freshwater thermal springs. Description of the species Porphyrobacter donghaensis was amended.