Studies small meromictic lake Trekhtzetnoe

The meromictic lakes are widely distributed on our planet, however most of them are relatively large water bodies with the depth > 15 m. contributing to the stabilization of the water column. Trekhtsvetnoe (?ricolor) lake is one of the smallest meromictic lakes described. Nevertheless it features very sharp and stable stratification over short water column that makes it reminiscent well known Winogradsky column experiments.We characterised in depth the processes of carbon and sulfur cycles in this water body and found that the bulk of energy flow there is mediated H2S production/diffusion/oxidation.The bacterial plate (that we term “biofilter layer” since it efficiently intercepts the current of the reduced gazes from the bottom part of the water column) is formed within the chemocline in Trekhcvetnoe lake. This layer features extreme density of anoxygenic photosynthetic bacteria that represents, up to our knowledge, the highest value ever found in the meromictic lakes. Strikingly this layer is heavily dominated by a single species Chlorobium phaeovibrioides. Metagenomic data indicate that the dominant population possessed very low genetic diversity been close to clonal homogeneity. It is associated with the viruses (bacteriophages) that appear to exert substantial pressure causing CRISPR-Cas adaptation in the dominant strain.Nevertheless the biofilter layer remains stable in the time ensuring almost complete intercept of the volatile reduced compounds.These well pronounced stratification found over short water column coupled with relative ease of the access to Trekhtsvetnoe Lake makes this water body a very attractive model to study the mechanisms shaping natural high-density microbial systems and microbial evolution in such conditions.