Allelopathic interactions between Lemna minor and Microcystis aeruginosa are influenced by the antimalarial drug lumefantrine

The aquatic macrophyte Lemna minor and cyanobacterium Microcystis aeruginosa coexist and alternate in freshwater ecosystems, and nutrient changes, physical conditions, and micropollutants such as pharmaceuticals drive their succession. However, the effects of the antimalarial drug Lumefantrine on allelopathic interactions have not been previously investigated. This study investigated the effect of Lumefantrine on the allelopathic interactions between L. minor and M. aeruginosa. The drug adversely affected pigment levels at 1000 µg L^-1 on day one, while the highest levels were observed at the same concentration on days three and five in M. aeruginosa cultures. The intracellular hydrogen peroxide (H₂O₂) and lipid peroxidation (MDA) levels and peroxidase (POD) and glutathione S-transferase (GST) activity of L. minor and M. aeruginosa increased at varying degrees depending on the concentration of Lumefantrine. Increased concentrations of Lumefantrine induced higher microcystin content in M. aeruginosa. L. minor significantly decreased the growth and increased GST and POD activities of M. aeruginosa on day five of the assay. The introduction of Lumefantrine further altered these parameters when the species were co-cultured. Similarly, M. aeruginosa inhibited the growth of L. minor. The combination of M. aeruginosa and Lumefantrine increased GST activity compared with M. aeruginosa alone. Microcystin content was higher in co-cultures without Lumefantrine than in those exposed to the drug. These results show that allelopathic interactions between L. minor and M. aeruginosa are influenced by Lumefantrine and may have implications for managing freshwater ecosystems.