[Characteristics of sulfur bacteria from lakes of the Mari ASSR].

Five karst lakes were investigated in the Mari Autonomous Republic. The vertical distribution of thionic bacteria in water was correlated to the distribution and content of dissolved sulphides. The concentration of thionic bacteria was higher in more productive lakes. A symbiotic culture of thionic and denitrifying bacteria, but not Thiobacillus denitrificans, was isolated from water of these lakes.