Despite free-living protozoa being a major factor in modifying aquatic autotrophic biomass ciliate cyanobacteria interactions and their functional ecological roles have been poorly described, especially with toxic cyanobacteria. Trophic relationships have been neglected and grazing experiments give contradictory evidence when toxic taxa such as Microcystis are involved. Here two toxic Microcystis strains (containing microcystins), one non-toxic Microcystis strain and a non-toxic green alga, Chlorella vulgaris, were used to investigate predator-prey interactions with a phagotrophic ciliate, Blepharisma americanum. Flow cytometric analysis for microalgal measurements and a rapid UHPLC-MS/MS protocol to quantify microcystins showed non-toxic photosynthetic microbes were significantly grazed by B. americanum, which sustained ciliate populations. In contrast, despite constant ingestion of toxic Microcystis rapid egestion of cells occurred. The lack of digestion resulted in no significant control of toxic cyanobacteria densities, a complete reduction in ciliate numbers, and no observable encystment or cannibalistic behaviour (gigantism). Individual B. americanum morphological responses (biovolume and cell width) showed a significant decrease over time when sustained on non-toxic Microcystis compared 55 to grazed C. vulgaris populations, supporting previous studies that cyanobacteria may be a relatively poor source of nutrition. Results here provide an insight into the ecological interactions of ciliates and cyanobacteria, and for the first time B. americanum is shown to have the capacity to suppress potentially bloom-forming cyanobacteria. However, grazing can be significantly altered by the presence of microcystins, which could have an impact on bloom dynamics and overall community structure.

中文翻译：

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纤毛虫 Blepharisma americanum 与有毒（Microcystis spp.）和无毒（Chlorella vulgaris, Microcystis sp.）光合微生物之间的捕食者-猎物相互作用

尽管自由生活的原生动物是改变水生自养生物质纤毛虫蓝藻相互作用的主要因素，但它们的功能生态作用却鲜为人知，尤其是对有毒蓝藻。当涉及微囊藻等有毒分类群时，营养关系被忽视，放牧实验给出了相互矛盾的证据。在这里，使用两种有毒微囊藻菌株（含有微囊藻毒素）、一种无毒微囊藻菌株和一种无毒绿藻小球藻来研究捕食者-猎物与吞噬纤毛虫 Blepharisma americanum 的相互作用。用于微藻测量的流式细胞术分析和用于量化微囊藻毒素的快速 UHPLC-MS/MS 协议表明，美洲双歧杆菌显着地放牧无毒光合微生物，从而维持纤毛虫种群。相比之下，尽管不断摄入有毒微囊藻，但仍会发生细胞快速摄入。缺乏消化导致对有毒蓝藻密度没有显着控制，纤毛虫数量完全减少，并且没有可观察到的包囊或同类相食行为（巨人症）。与 55 与放牧的普通 C. vulgaris 种群相比，在无毒微囊藻上维持个体 B. americanum 形态学反应（生物量和细胞宽度）随着时间的推移显示出显着下降，支持先前的研究，即蓝藻可能是相对较差的营养来源。此处的结果提供了对纤毛虫和蓝藻的生态相互作用的深入了解，并且首次证明 B. americanum 具有抑制可能形成水华的蓝藻的能力。然而，