Anoxygenic phototrophic bacteria from gypsum karst lakes of Lithuania

The spatial distribution and composition of anoxygenic phototrophic bacteria in the enriched bacterial communities from different depths of karst lakes Kirkilai and Ramunelis was studied using spectrophotometric analysis, as well as microbiological and molecular methods. In Lake Kirkilai, the highest bacterial abundance was measured in the metalimnion and near the bottom (up to 10.7 × 10⁶ cell/mL); in Lake Ramunelis it was in the anoxic hypolimnion (up to 22.4 × 10⁶ cell/mL). Increased water mineralization (0.5–1.2 g/L) with the domination of SO ₄ ^2? and Ca²⁺ ions created favorable conditions for the development of sulfate-reducing bacteria; hydrogen sulfide produced as a result of their life activity facilitated the development of sulfur-oxidizing bacteria. The pigment analysis of phototrophic green and purple sulfur bacteria showed the domination of green sulfur bacteria in the enrichment culture. The results of phylogenetic analysis showed that Chlorobium limicola dominated in the enrichment culture for the green sulfur bacteria, whereas purple nonsulfur bacteria of the genus Rhodopseudomonas dominated in the enrichment culture for the purple sulfur bacteria.