Characterization of a new strain of a purple nonsulfur bacterium from a thermal spring

Abstract

A new budding nonsulfur purple bacterium of the genus Rhodobacter (strain Ku-2) was isolated from a mat of a moderately thermal spring (Baikal rift zone, Buryat Republic, Russia). The bacterium had lamellar photosynthetic membranes, which are typica of only one Rhodobacter species, Rba. blasticus. The cells contined spheroidene carotenoids and bacteriochlorophyll a (Bchl a). In vivo absorption spectrum of the cells had the major maximum at 863 nm and an additional peak at 887 nm, which is characteristic of the pigment-protein complexes of Bchl a-containing membranes. The previously described Rba. blasticus strains did not exhibit a 887-nm maximum. The new isolate was photoheterotrophic, with optimal growth occurring at 35 degrees C, 3 g/L NaCl, and pH 7-8. The DNA G+C content was 64.4 mol %. The similarity between the 16S rRNA gene sequences of strain Ku-2 and the Rba. blasticus type strain was 98.7%. The similarity between the PufM amino acid sequences of strain Ku-2 and the previously studied Rba. blasticus strain was 89.0%. Thus, the bacterial strain Ku-2 belonged to the genus Rhodobacter and was phylogenetically related to Rba. blasticus.