Enhanced Lethal Effects of Combined P-tert-Butylcatechol and L-Lysine on Microcystis aeruginosa.

Allelochemicals are recognized as promising algaecides due to their environmental safety. Para-tert-butylcatechol (TBC) and L-lysine exhibit significant potential in suppressing harmful algal blooms (HABs); however, their combined effects and algae inhibition mechanisms remain unelucidated. Therefore, this study systematically investigated the growth inhibition of Microcystis aeruginosa by TBC and L-lysine individually and in combination, while simultaneously examining their combined effects on algal growth, cell membrane integrity, photosynthetic activity, antioxidant responses, and microcystin production. The results revealed a significant interactive effect between TBC (0.04 mg/L) and L-lysine (1 mg/L), achieving over 90% growth inhibition within 96 h. The combined treatment significantly inhibited M. aeruginosa growth through impaired photosynthetic efficiency and elevated oxidative stress. Compared to the control group, the treatment group exhibited a continuous decline in chlorophyll-a content, phycobiliprotein levels, F_v/F_m, YII, α, and rETR_max, while phosphoenolpyruvate carboxylase (PEPC) activity decreased by 96.48% by day 8. And antioxidant enzymes, including superoxide dismutase (SOD) and reduced glutathione (GSH), showed a progressive increase in activity. In addition, the structure and integrity of the cell membrane of M. aeruginosa were damaged after treatment, and the conductivity of the treatment groups increased continuously from 2.32 to 4.63 μs/cm. In addition, under combined treatment, intra- and extracellular microcystin levels initially increased (peaking at day 2) but sharply declined thereafter, becoming significantly lower than controls by day 8. These findings highlight the potential of combining TBC and L-lysine as an eco-friendly and cost-effective strategy for mitigating M. aeruginosa-dominated harmful algal blooms.