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 (Тricolor) 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.

分层湖（meromictic lakes）广泛分布于地球表面，但绝大多数为水深大于15米的大型水体，这类水体的水柱稳定性较强。特列奇茨夫特诺耶湖（Trekhtsvetnoe，又称三色湖）是已被报道的最小分层湖之一，但其短水柱中存在极为显著且稳定的分层现象，与经典的温格拉茨基柱（Winogradsky column）实验体系高度相似。我们对该水体的碳循环与硫循环过程开展了深度表征，发现其能量流动主要通过硫化氢（H₂S）的产生、扩散与氧化过程介导。该湖的化学跃层（chemocline）中形成了一层细菌聚集体——我们将其命名为“生物滤层（biofilter layer）”，因其可高效拦截水柱底部的还原性气体流。该层的不产氧光合细菌（anoxygenic photosynthetic bacteria）密度极高，据我们目前所知，这是分层湖中已记录到的最高密度水平。尤为引人注目的是，该层几乎被单一物种褐素弧状绿菌（Chlorobium phaeovibrioides）主导。宏基因组（metagenomic）数据显示，该优势种群的遗传多样性极低，近乎克隆均一性。这一特征与其伴随的噬菌体（bacteriophages）密切相关：噬菌体施加了显著的选择压力，促使优势菌株发生CRISPR-Cas系统（CRISPR-Cas）的适应性进化。尽管如此，该生物滤层仍可长期保持稳定，几乎完全拦截了挥发性还原性化合物。这种在短水柱中形成的显著分层现象，加之特列奇茨夫特诺耶湖易于抵达的采样便利性，使其成为研究天然高密度微生物系统形成机制以及此类环境下微生物进化过程的极具吸引力的模型体系。