Paramecium jenningsi effectively grazes on toxic Raphidiopsis raciborskii and degrades cylindrospermopsin: Implications for control harmful cyanobacterial blooms

Harmful cyanobacterial blooms (HCB) represent a serious threat to aquatic ecosystems due to their production for potent toxins that have negative effects on plant, animal and human health. Although grazing process can be exploited to reduce harmful cyanobacteria in eutrophic waters, the feeding capacity and detoxification capability of the grazer should be considered as key traits of a safe biocontrol agent. In this study, laboratory experiments were conducted to investigate the grazing rate of the ciliate Paramecium jenningsi on toxic Raphidiopsis raciborskii and potential cylindrospermopsin (CYN) degradation during feeding process. P. jenningsi efficiently ingested R. raciborskii cells with high growth (0.1- 0.26 d⁻¹) and grazing rates (0.1-1.4 × 10⁴ cyanobacterial cells ciliate ⁻¹ d⁻¹), varying with the initial ciliate density. CYN concentrations within Raphidiopsis cells displayed an elevation under grazing conditions (5.3-7.2 pg cell⁻¹) compared to control cultures (4.4 pg cell⁻¹). CYN concentrations within the ciliate cells showed a reduction (degradation rate =121-276 pg ciliate⁻¹ d⁻¹) and became undetectable after all Raphidiopsis cells were grazed out, indicating that this ciliate could not accumulate CYN within its body during feeding process. Therefore, P. jenningsi could be used as a safe bioagent for the biocontrol of HCBs in water sources. However, a further in situ study is needed for a possible application of Paramecium species for mitigation of toxic cyanobacteria and their cyanotoxins in the natural environment.