Biological Science Department, Kent State University, Kent Ohio 44242, U.S.A.
Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, 1 Tiantan Xi Li, Beiing 100050, China.
Harmful Algae. 2020 Sep;98:101895. doi: 10.1016/j.hal.2020.101895. Epub 2020 Aug 29.
Microcystins (MCs) are among the predominant cyanotoxins that are primarily degraded by heterotrophic bacteria in various freshwater environments, including Lake Erie, a Laurentian Great Lake. However, despite the prevalence of MCs in Lake Erie basins, our knowledge about the taxonomic diversity of local MC-degrading bacteria is largely limited. The current study obtained thirty-four MC-degrading bacterial pure isolates from Lake Erie surface water and characterized their taxonomical and phenotypic identities as well as their MC-degradation rates under different pH, temperature, availability of organic substrates and with other MC-degrading isolates. Obtained MC-degrading isolates included both Gram-positive (18 isolates of Actinobacteria and Firmicutes) and Gram-negative bacteria (16 isolates of Gamma-proteobacteria); and 7 of these isolates were motile, and 13 had the capacity to form biofilms. In general, MC-degradation rates of the isolates were impacted by temperature and pH but insensitive to the presence of cyanobacterial exudates. At the optimal temperature (30-35°C) and pH (7-8), individual isolates degraded MC-LR, the most abundant MC isomer, at an average of 0.20 µg/mL/hr. With additions of cyanobacterial exudates, only Pseudomonas sp. LEw-2029, a non-motile biofilm maker, showed increased MC degradation (0.25 µg/mL/hr). Five out of nine tested dual culture mixtures showed rises in MC degradation rates than their corresponding monocultures; the highest rate reached 0.40 µg/mL/hr for the pair LEw-(1132 + 2029). PCR amplification of mlrA genes yielded negative results for all isolates; subsequent enzyme assay-Mass Spectrum analysis identified no product associated with the mlr gene-based MC degradation pathway. Collectively, our results demonstrated that a diversity of indigenous Lake Erie bacteria can degrade MCs via a novel mlr-independent pathway. Obtained MC degraders, especially Pseudomonas sp. LEw-2029, may serve as candidates for the development of biological filters to remove cyanotoxins in water treatment systems.
微囊藻毒素（MCs）是主要由异养细菌降解的优势蓝藻毒素之一，存在于包括伊利湖在内的各种淡水环境中，伊利湖是一个大湖。然而，尽管 MCs 在伊利湖流域很普遍，但我们对当地 MC 降解细菌的分类多样性的了解还很有限。本研究从伊利湖地表水获得了 34 株 MC 降解细菌纯培养物，并对其分类和表型特征以及在不同 pH 值、温度、有机底物可利用性下的 MC 降解率进行了研究，同时还研究了与其他 MC 降解菌的共培养。获得的 MC 降解菌包括革兰氏阳性菌（放线菌和厚壁菌门 18 株）和革兰氏阴性菌（γ-变形菌门 16 株）；其中 7 株为运动菌，13 株具有形成生物膜的能力。一般来说，温度和 pH 值对分离物的 MC 降解率有影响，但对蓝藻分泌物的存在不敏感。在最佳温度（30-35°C）和 pH 值（7-8）下，个别分离物以平均 0.20 µg/mL/hr 的速度降解 MC-LR，这是最丰富的 MC 同型物。加入蓝藻分泌物后，只有非运动性生物膜形成菌 Pseudomonas sp. LEw-2029 表现出 MC 降解增加（0.25 µg/mL/hr）。在 9 种测试的双培养混合物中，有 5 种的 MC 降解率高于其相应的单培养物；最高速率为 0.40 µg/mL/hr，对应于 LEw-（1132 + 2029）对。所有分离物的 mlrA 基因 PCR 扩增均为阴性结果；随后的酶谱分析未鉴定出与 mlr 基因为基础的 MC 降解途径相关的产物。总的来说，我们的研究结果表明，伊利湖土著细菌的多样性可以通过一种新的 mlr 独立途径降解 MCs。获得的 MC 降解菌，尤其是 Pseudomonas sp. LEw-2029，可能成为开发生物过滤器去除水处理系统中蓝藻毒素的候选物。
