Abstract：
Cyanobacterial blooms affect biotic interactions in aquatic ecosystems, including those involving heterotrophic bacteria. Ultra-small microbial communities are found in both surface water and groundwater and include diverse heterotrophic bacteria. Although the taxonomic composition of these communities has been described in some environments, the involvement of these small cells in the fate of environmentally relevant molecules has not been investigated. Here, we aimed to test if small-sized microbial fractions from a polluted urban lagoon were able to degrade the cyanotoxin microcystin (MC). We obtained cells after filtration through 0.45 as well as 0.22 μm membranes and characterized the morphology and taxonomic composition of bacteria before and after incubation with and without microcystin-LR (MC-LR). Communities from different size fractions (< 0.22 and < 0.45 μm) were able to remove the dissolved MC-LR. The originally small-sized cells grew during incubation, as shown by transmission electron microscopy, and changed in both cell size and morphology. The analysis of 16S rDNA sequences revealed that communities originated from < 0.22 and < 0.45 μm fractions diverged in taxonomic composition although they shared certain bacterial taxa. The presence of MC-LR shifted the structure of < 0.45 μm communities in comparison to those maintained without toxin. Actinobacteria was initially dominant and after incubation with MC-LR Proteobacteria predominated. There was a clear enhancement of taxa already known to degrade MC-LR such as Methylophilaceae. Small-sized bacteria constitute a diverse and underestimated fraction of microbial communities, which participate in the dynamics of MC-LR in natural environments.
摘要：
蓝藻水华影响水生生态系统中的生物相互作用，包括那些涉及异养细菌的。在地表水和地下水中都发现了超小型微生物群落，其中包括多种异养细菌。尽管在某些环境中已经描述了这些群落的分类组成，尚未研究这些小细胞与环境相关分子的命运有关。这里,我们旨在测试污染的城市泻湖中的小型微生物部分是否能够降解蓝藻毒素微囊藻毒素（MC）。我们通过0.45和0.22μm膜过滤后获得了细胞，并表征了在与微囊藻毒素-LR（MC-LR）孵育前后细菌的形态和分类组成。来自不同尺寸级分(<0.22和<0.45μm)的群落能够除去溶解的MC-LR。最初的小细胞在孵育过程中生长，如透射电子显微镜所示，细胞大小和形态都发生了变化。对16SrDNA序列的分析表明，尽管它们共享某些细菌类群，但起源于<0.22和<0.45μm部分的群落在分类组成上存在差异。与不含毒素的群落相比，MC-LR的存在改变了<0.45μm群落的结构。放线菌最初占主导地位，与MC-LR变形菌孵育后占主导地位。已知降解MC-LR的类群有明显的增强，例如嗜甲基科。小型细菌构成了微生物群落的多样性和被低估的一部分，参与自然环境中MC-LR的动力学。
