Blooms of the Microcystis aeruginosa complex (MAC) consist of mixtures of toxin-producing and non-toxin-producing populations, but the environmental conditions that determine their relative abundance and shift are not clear. Morphological traits reflect the responses of MAC organisms to environmental changes, thus they could be useful to improve the predictability of the abundance of both toxic and nontoxic populations. In this work, the response of MAC toxic populations to environmental conditions and their relationship with morphology (size of organisms) were investigated in different water bodies (reservoir, river, and estuary) covering wide salinity (0–33) and temperature (10–36 °C) gradients. Sub-surface water samples were collected and divided into 4 size classes (mesh size 〈20 µm, 20–60 µm, 60–150 µm and〉 150 µm) and three toxicity proxies were assessed (mcyE gene and transcripts copy numbers and microcystin concentration) for each size-class. For all the size-classes, the logarithm of the number of mcyE gene copies per sample was proportional to the logarithm of the corresponding biovolume fraction, showing that MAC biovolume is a good indicator of toxicity potential. When toxicity was analyzed through mcyE transcript abundance and microcystin concentration, the largest size fraction (>150 µm) showed the highest toxicity values of both proxies. Nevertheless, mcyE transcription and toxin production per cell were higher in the colonies retained in the 60 to 150 µm size fractions, followed by single cells (<20 µm). At the reservoir, where environmental variability is low, the total abundance of mcyE gene copies was significantly explained by MAC biovolume, regardless of the environmental conditions. However, when data from the reservoir to the estuary were modeled, biovolume and temperature (with a minor contribution of salinity and wind intensity) were selected in the best models. According to these results, the size distribution of MAC biovolume appears as a good predictor of active toxin production, being the colonies in the 60–150 µm size fraction good indicators of higher toxicity. These results can be used to predict MAC toxicity based on the size structure of the community.

在花开的铜绿微囊藻复合物（MAC）由产生毒素的人群和不产生毒素的人群组成，但是决定其相对丰度和迁移的环境条件尚不清楚。形态特征反映了MAC生物对环境变化的响应，因此它们对于提高有毒和无毒种群数量的可预测性很有用。在这项工作中，研究了MAC毒性种群对环境条件的反应及其与形态（生物体大小）的关系，研究范围涉及盐度（0-33）和温度（10-33）的不同水体（水库，河流和河口）。 36°C）梯度。收集地下水样并将其分为4个尺寸类别（网孔尺寸<20 µm，20–60 µm，60–150 µm和> 150 µm），并评估了三种毒性代理（每个大小类别的mcyE基因和转录本拷贝数和微囊藻毒素浓度）。对于所有大小分类，每个样品中mcyE基因拷贝数的对数与相应生物量组分的对数成正比，表明MAC生物量是毒性潜力的良好指标。通过mcyE转录本丰度和微囊藻毒素浓度分析毒性时，最大尺寸分数（> 150 µm）显示出两个代理的最高毒性值。尽管如此，在60至150 µm大小的级分中保留的菌落中，每个细胞的mcyE转录和毒素产量更高，其次是单个细胞（<20 µm）。在环境变异性较低的水库中，不管环境条件如何，MAC生物体积均能明显解释mcyE基因的拷贝。但是，当对从储层到河口的数据进行建模时，最好的模型中选择了生物量和温度（盐度和风强度的贡献很小）。根据这些结果，MAC生物体积的大小分布似乎可以很好地预测活性毒素的产生，它是60-150 µm大小级分中的菌落，具有较高的毒性。这些结果可用于根据社区的规模结构预测MAC毒性。