Anticyanobacterial effect of l-lysine on Microcystis aeruginosa

Abstract

Cyanobacterial blooms can cause serious environmental problems and threaten aquatic organisms and human health. It is therefore essential to effectively control cyanobacterial blooms in aquatic ecosystems. In the present study, the anticyanobacterial effect of L-lysine on Microcystis aeruginosa was examined. The results showed that the growth of M. aeruginosa (>90%) was effectively inhibited by L-lysine at dosages of 5.0, 6.5, and 8.0 mg L⁻¹ after 3 d treatment. The content of superoxide anion radicals, MDA content and SOD activity in M. aeruginosa cells increased after 1 d of treatment with L-lysine (3.0, 5.0, 6.5, and 8.0 mg L⁻¹), revealing that L-lysine induced oxidative stress in the cyanobacterial cells. The chlorophyll-a and protein contents in M. aeruginosa treated with L-lysine (3.0, 5.0, 6.5, and 8.0 mg L⁻¹) decreased after 2 d, indicating damage of the photosynthetic system by L-lysine treatment. Additionally, the production of exopolysaccharide by M. aeruginosa also increased and the expression of polysaccharide synthesis genes was upregulated by 3.0 mg L⁻¹ L-lysine after 3 d of treatment. In response to the algicidal effects of L-Lysine, M. aeruginosa upregulated exopolysaccharide synthesis. Electron microscopic observations demonstrated that the cell membrane of M. aeruginosa was broken down during treatment with L-lysine (≥3.0 mg L⁻¹). Our results revealed that the effects of L-lysine on M. aeruginosa cells were comprehensive, and L-lysine is therefore an efficient anticyanobacterial reagent.