Characterization of thermotolerant phototrophic bacteria, Rhodoplanes tepidicaeni sp. nov. and Rhodoplanes azumiensis sp. nov., isolated from a geothermal spring.

Two strains of thermotolerant phototrophic alphaproteobacteria, designated strains TUT3542 and TUT3581, were isolated from sediment mud and cyanobacterial mats in a geothermal spring in Japan, respectively, and taxonomically characterized. Both the strains were budding motile rods and were able to grow at 45 °C. Phototrophically grown cells of strains TUT3542 and TUT3581 produced pink and brownish red cultures, respectively, and showed in vivo absorption maxima at 800, 858-859 and 892-895 nm in the near infrared region, indicating the presence of a core reaction centre and peripheral pigment complexes with bacteriochlorophyll a. The intracytoplasmic membrane system was of the lamellar type parallel to the cytoplasmic membrane. 16S rRNA gene sequence comparisons showed that strains TUT3542 and TUT3581 had the highest similarity level to Rhodoplanes oryazae NBRC 109406 (99.6 %) and Rhodoplaneselegans AS130 (99.3 %), respectively. Genomic DNA-DNA reassociation studies revealed that strains TUT3542 and TUT3581 had hybridization levels of less than 62 and 56 % to the type strains of all established species of the genus Rhodoplanes, respectively. The G+C contents of genomic DNA were 67.7 mol% for strain TUT3542 and 70.4 mol% for strain TUT3581. Results of phenotypic studies showed that the two novel strains could be differentiated from any of the previously described Rhodoplanes species. Thus, the author proposes the names Rhodoplanes tepidicaeni sp. nov. for strain TUT3542 and Rhodoplanes azumiensis sp. nov. for strain TUT3581. The type strain of Rhodoplanes tepidicaeni is TUT3542 (=KCTC 15602=NBRC 112815) and the type strain of Rhodoplanes azumiensis is TUT3581 (=KCTC 15603=NBRC 112816).