Mass development of purple sulfur bacteria Chromatium okenii (Ehrb. 1838) Perty 1852 in a small town lake Dachnoe (Togliatti, Samara region)

We have previously shown that in stratified lakes with anoxic hypolimnion in the forest-steppe zone of the Middle Volga basin the colonial species with small cells lacking flagella and regulating their buoyancy by gas vacuoles usually dominate among planktonic Chromatiaceae. However, mass development of large-celled mobile purple sulfur bacteria Chromatium okenii (Ehrb. 1838) Perty 1852 in the plankton of lakes of the region was found for the first time in the summer of 2014. In small lake Dachnoe (Vasilyevsky system of lakes, Togliatti, Samara region) Chromatium okenii forms a narrow peak at a depth of 2.4 (July) - 2.3 m (September). The maximal abundance of Chr. okenii was 0.44×10 6 cells/ml (69,7-74,2% of the total cell number of purple sulfur bacteria), biomass - 65.3 mg/l (97-98,9% of their total biomass). Chr. okenii was accompanied by another two motile species of Chromatiaceae, Allochromatium cf. vinosum (Ehrenberg 1838) Imhoff et al. 1998 and Chr. weissei Perty 1852, and colonial species with gas vacuoles, Thiopedia rosea.