Roseinatronobacter thiooxidans Gen. Nov., sp. Nov., a new alkaliphilic aerobic bacteriochlorophyll-alpha-containing bacteria from a soda lake

Several samples of microbial mat obtained from soda lakes of the Kunkurskaya steppe (Chita oblast) abundantly populated by purple bacteria were screened for the presence of heterotrophic alkaliphiles capable of oxidizing sulfur compounds to sulfate. This capacity was found in only one pigmented strain, ALG 1, isolated on medium with acetate and thiosulfate at pH 10. The strain was found to be a strictly aerobic and obligately heterotrophic alkaliphile. Growth on medium with acetate was possible within a narrow pH range from 8.5 to 10.4. The strain formed a reddish orange carotenoid and bacteriochlorophyll a. Pigments were synthesized only at high concentrations of nitrogen-containing organic compounds (peptone or yeast extract). The production of bacteriochlorophyll a was maximal under microaerobic conditions in darkness. Strain ALG 1 could oxidize sulfide, thiosulfate, sulfite, and elemental sulfur to sulfate. In heterotrophically growing culture (pH 10), thiosulfate was not oxidized until the late logarithmic phase. The sulfur-oxidizing activity was maximal at the most alkaline pH values. The notable increase in the efficiency of organic carbon utilization observed in the presence of thiosulfate suggested that the bacterium was a sulfur-oxidizing lithoheterotroph. The phylogenetic analysis of the 16S rRNA gene showed strain ALG 1 to be a member of the alpha-3 subgroup of proteobacteria and to constitute a distinct branch located between nonsulfur purple bacteria Rhodobacter and Rhodovulum. Based on the unique phenotypic properties and the results of phylogenetic analysis, the alkaliphilic isolate ALG 1 was assigned to a new genus and species Roseinatronobacter thiooxidans with the type strain DSZM-13087.