Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
Department of Biological Environment, Faculty of Bioresource Sciences, Akita Prefectural University, Nakano Shimoshinjo, Akita City, Akita, Japan.
Biosci Biotechnol Biochem. 2021 Dec 22;86(1):78-91. doi: 10.1093/bbb/zbab179.
Toxic cyanobacterial blooms frequently develop in eutrophic freshwater bodies worldwide. Microcystis species produce microcystins (MCs) as a cyanotoxin. Certain bacteria that harbor the mlr gene cluster, especially mlrA, are capable of degrading MCs. However, MC-degrading bacteria may possess or lack mlr genes (mlr+ and mlr- genotypes, respectively). In this study, we investigated the genotype that predominantly contributes to biodegradation and cyanobacterial predator community structure with change in total MC concentration in an aquatic environment. The 2 genotypes coexisted but mlr+ predominated, as indicated by the negative correlation between mlrA gene copy abundance and total MC concentration. At the highest MC concentrations, predation pressure by Phyllopoda, Copepoda, and Monogononta (rotifers) was reduced; thus, MCs may be toxic to cyanobacterial predators. The results suggest that cooperation between MC-degrading bacteria and predators may reduce Microcystis abundance and MC concentration.
有毒蓝藻水华经常在全球富营养化的淡水体中发生。微囊藻属产生微囊藻毒素（MCs）作为一种蓝藻毒素。某些含有 mlr 基因簇的细菌，特别是 mlrA，能够降解 MCs。然而，MC 降解菌可能具有或缺乏 mlr 基因（分别为 mlr+和 mlr-基因型）。在这项研究中，我们调查了在水生环境中总 MC 浓度变化时，对生物降解和蓝藻捕食者群落结构起主要作用的基因型。这两种基因型共存，但 mlr+占优势，这表明 mlrA 基因拷贝丰度与总 MC 浓度呈负相关。在 MC 浓度最高时，被 Phyllopoda、Copepoda 和 Monogononta（轮虫）捕食的压力降低；因此，MC 可能对蓝藻捕食者有毒。结果表明，MC 降解菌和捕食者之间的合作可能会降低微囊藻的丰度和 MC 浓度。
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