ABSTRACT: Biodegradation is the most effective way to transform hepatotoxic microcystins produced by cyanobacteria in natural environments. An increasing number of new bacterial strains capable of microcystin degradation are being discovered, and there is still only one fully described metabolic pathway responsible for degradation, encoded by the mlr gene cluster. We aimed to identify microcystin-degrading bacteria in assemblages from water and bottom sediment of the eutrophic freshwater Lake Mikolajskie, Poland. Bacteria from water and sediment differed in taxonomic composition, and only in the community from sediment was the mlrA gene detected. In the presence of microcystins, bacteria from the sediment showed higher proteolytic activity, while in the water community, there was no change in the activity of proteases. Bacterial assemblages from both environments also showed different time profiles of microcystin utilization. All these results indicate that other metabolic pathways may be involved in the degradation of microcystins by bacteria living in the water and bottom sediment. Identified microcystin-degrading and potentially microcystin-degrading bacteria belong to Betaproteobacteria (genera: Hydrogenophaga, Comamonas, Rhodoferax) and Gammaproteobacteria (genera: Acinetobacter, Citrobacter, Rahnella, Serratia, Pseudomonas, Stenotrophomonas), according to denaturing gradient gel electrophoresis analysis, as well as isolation and testing of the properties of individual strains. No bacteria belonging to family Sphingomonadaceae (Alphaproteobacteria) were identified, which, until recently, were considered to be the main microcystin degraders. Several bacterial taxa detected in this study have never been previously described as potential microcystin degraders: Comamonas sp., Hydrogenophaga sp., Rhodoferax sp., Citrobacter sp., and Serratia sp.

中文翻译：

---

富营养化淡水湖中水和底部沉积物细菌群落对微囊藻毒素的降解

摘要：生物降解是在自然环境中转化由蓝细菌产生的肝毒性微囊藻毒素的最有效方法。已经发现越来越多的能够降解微囊藻毒素的新细菌菌株，并且仍然只有一个由mlr基因簇编码的，描述完整的代谢途径负责降解。我们的目的是从富营养化淡水波兰米科拉伊斯基湖的水和底部沉积物中鉴定出降解微囊藻毒素的细菌。来自水和沉积物的细菌的生物分类组成有所不同，只有在来自沉积物的社区中，mLR检测到一个基因。在存在微囊藻毒素的情况下，来自沉积物的细菌显示出更高的蛋白水解活性，而在水群落中，蛋白酶的活性没有变化。来自两种环境的细菌集合也显示出不同的微囊藻毒素利用时间曲线。所有这些结果表明，其他代谢途径可能与生活在水和底部沉积物中的细菌降解微囊藻毒素有关。鉴定出的降解微囊藻毒素的细菌和可能降解微囊藻毒素的细菌分别属于Betaproteobacteria细菌（属：Hydrogenophaga，Comamonas，Rhodoferax）和Gammaproteobacteria细菌（属：不动杆菌属，根据变性梯度凝胶电泳分析，以及分离和测试各个菌株的特性，对柠檬酸杆菌，拉氏菌，沙雷氏菌，假单胞菌，嗜单胞菌）进行了分析。没有发现属于Sphingomonadaceae（Alphaproteobacteria）属的细菌，直到最近，这些细菌仍被认为是主要的微囊藻毒素降解剂。在这项研究中检测到的几种细菌类群以前从未被描述为潜在的微囊藻毒素降解剂：Comamonas sp。，Hydrogenophaga sp。，Rhodoferax sp。，Citrobacter sp。和沙雷氏菌