Communities of anoxygenic phototrophic bacteria in the saline soda lakes of the Kulunda steppe (Altai Krai)

Abstract

The saline soda lakes of the Kulunda steppe (Altai krai) are small and shallow; they are characterized by a wide range of salinity and alkalinity, as well as by the extreme instability of their water and chemical regimes. Accumulations of anoxygenic phototrophic bacteria (APB) visible to the unaided eye were noted only in several lakes with high rates of sulfate reduction in their bottom sediments. However, enumeration of APB cells by inoculation revealed their presence in all 17 lakes. APB cell numbers varied from 103 to 109 CFU cm−3. In the APB communities of all lakes, purple sulfur bacteria of the family Ectothiorhodospi- raceae were predominant. In 14 out of the 17 lakes, purple nonsulfur bacteria of the family Rhodobacteraceae were also detected (103–107 CFU cm−3). Purple sulfur bacteria of the family Chromatiaceae were less abundant: Halochromatium sp. (104–107 CFU cm−3) were found in six lakes, while Thiocapsa sp. (104 CFU cm3) were detected in one lake. On the whole, the APB communities of the soda lakes of the Kulunda steppe were characterized by the low diversity and evenness of their species compositions, as well as by the pronounced dominance of the members of the family Ectothiorhodospiraceae. There was no correlation between the structures of the APB communities and alkalinity. However, the dependence of the species composition of APB (mainly ectothiorhodospiras) on water mineralization was revealed. High mineralization (above 200 g l−1) was a limiting factor that affected the APB communities on the whole, restricting the APB species diversity to extremely halophilic bacteria of the genus Halorhodospira.