Algal blooms threaten human health and aquatic ecosystem through the production of microcystins (MCs) by toxic strains. The accumulation of rare earth elements (REEs) in water affects the growth and physiological activities of algae. However, whether or how REEs affect cellular microcystins (MCs) is largely unknown. In this study, the effects of lanthanum ion [La(III)], a type of REE, on the MCs in Microcystis aeruginosa were investigated, and the mechanism of the effect was analyzed using ecological stoichiometry. The different concentrations of La(III) were selected to correlate environmental pollution status. Low-dose La(III) (0.2, 2.0, and 4.0 μM) exposure increased the total content of MCs and the percentage contents of microcystin-YR (MC-YR) and microcystin-LW (MC-LW) and decreased the percentage content of microcystin-LR (MC-LR). High-dose La(III) (8.0, 20, 40, and 60 μM) exposure decreased the total content of the MCs, increased the percentage content of MC-LR, and decreased the percentage contents of MC-YR and MC-LW. The changes in the total MCs content were positively associated with the ratios of C:P and N:P in algal cells. The composition of MCs was dependent on the ratio of C:N in algal cells; for example, the percentage content of MC-LR decreased and the percentage content of MC-YR and MC-LW increased as the ratio of C:N in algal cells increased. In conclusion, La(III) could affect the content and composition of MCs via changes in the growth and chlorophyll-a content of Microcystis aeruginosa, and these effects depended on the ratios of C:P, N:P, and C:N in Microcystis aeruginosa. Such changes may influence the toxicity of Microcystis blooms. The results provides a new insight into the mechanism of REEs effects on algal toxins and provide references for evaluating environmental risks of REEs pollution in aquatic ecosystems.

藻华通过有毒菌株产生微囊藻毒素（MC）威胁着人类健康和水生生态系统。水中稀土元素（REEs）的积累会影响藻类的生长和生理活性。但是，稀土元素是否或如何影响细胞微囊藻毒素（MCs）尚不清楚。在这项研究中，镧离子[La（III）]，一种稀土元素，对铜绿微囊藻MCs的影响进行了调查，并使用生态化学计量学分析了其作用机理。选择不同浓度的La（III）来关联环境污染状况。低剂量La（III）（0.2、2.0和4.0μM）暴露会增加MC的总含量以及微囊藻毒素-YR（MC-YR）和微囊藻毒素-LW（MC-LW）的百分比含量，并降低百分比含量微囊藻毒素-LR（MC-LR）。高剂量La（III）（8.0、20、40和60μM）暴露会降低MC的总含量，增加MC-LR的百分比含量，并降低MC-YR和MC-LW的百分比含量。总MC含量的变化与藻类细胞中C：P和N：P的比例呈正相关。MC的组成取决于藻类细胞中C：N的比例。例如，随着藻类细胞中C：N比的增加，MC-LR的百分比含量降低，MC-YR和MC-LW的百分比含量增加。总之，La（III）可能通过生长和叶绿素的变化影响MC的含量和组成。一个的内容铜绿微囊藻，并且这些效果取决于C的比率：P，N：P，和C：N在铜绿微囊藻。此类变化可能会影响微囊藻开花的毒性。研究结果为稀土元素对藻毒素的作用机理提供了新的认识，并为评价水生生态系统中稀土元素污染的环境风险提供了参考。