Departamento de Microbiología, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE), Montevideo, Uruguay.
Ecología Funcional de Sistemas Acuáticos, CURE-Rocha, Universidad de la República, Uruguay; Sección Limnología, IECA, Facultad de Ciencias, Universidad de la República, Uruguay.
Harmful Algae. 2020 Jul;97:101854. doi: 10.1016/j.hal.2020.101854. Epub 2020 Jun 24.
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.
铜绿微囊藻复合群（MAC）的水华由产毒和非产毒种群的混合物组成，但决定它们相对丰度和变化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，因此它们可以用来提高产毒和非产毒种群丰度的可预测性。在这项工作中，研究了 MAC 产毒种群对不同水体（水库、河流和河口）中广泛盐度（0-33）和温度（10-36°C）梯度的环境条件的响应及其与形态（生物大小）的关系。采集了表层以下水样，并分为 4 个大小类（网孔尺寸〈20 µm、20-60 µm、60-150 µm 和〉150 µm），并评估了每个大小类别的 3 个毒性指标（mcyE 基因和转录本拷贝数和微囊藻毒素浓度）。对于所有大小类，样品中 mcyE 基因拷贝数的对数与相应生物体积分数的对数成正比，表明 MAC 生物体积是毒性潜力的良好指标。当通过 mcyE 转录本丰度和微囊藻毒素浓度分析毒性时，最大大小类（>150 µm）显示出两种指标的最高毒性值。然而，在保留在 60 到 150 µm 大小类别的群体中，每细胞的 mcyE 转录和毒素产量更高，其次是单细胞（<20 µm）。在水库中，环境变异性较低，mcyE 基因拷贝的总丰度与 MAC 生物体积显著相关，而与环境条件无关。然而，当对从水库到河口的数据进行建模时，生物体积和温度（盐度和风速强度的贡献较小）被选入最佳模型。根据这些结果，MAC 生物体积的大小分布似乎是活性毒素产生的良好预测指标，60-150 µm 大小类别的群体是更高毒性的良好指标。这些结果可用于根据群落的大小结构预测 MAC 毒性。
