Changes in Chemical Structure of n-Acyl Homoserine Lactones and Their Effects on Microcystin Expression from Microcystis aeruginosa PCC7806

Harmful algal blooms (HABs) of Microcystis aeruginosa can pose severe public health hazards due to potent toxins released by this cyanobacterial species. To elucidate the biological mechanism of M. aeruginosa PCC7806 and to identify the best treatment to reduce toxin production, 18 homoserine lactones (HSLs) of different chemical structures were synthesized and used at the concentration of 50 mg/L applied to algal blooms at the early log phase. The effectiveness of treatment was based on physiological responses after cells reached the stationary stage. Results indicated that C3-HSL with phenyl and ether groups, and C6-HSL with oxo groups showed a greater reduction in microcystin content (80–100% reduction). A C4-HSL with a hydroxyl group showed a reduction of at least 25% in all physiological parameters analyzed. Thus, structural changes to the HSLs can influence cell toxin production. The understanding of biological mechanisms can lead to novel approaches and strategies to control cyanobacteria and HABs.