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

Simple SummaryHarmful algal blooms caused byMicrocystis aeruginosathreaten aquatic ecosystems and human health. This study explores the combined effects of two natural allelochemicals, P-tert-butylcatechol (TBC) and L-lysine, in controllingM. aeruginosa. When combined at low concentrations (0.04 mg/L TBC + 1 mg/L L-lysine), they achieved over 90% growth inhibition within 96 h. The treatment damaged algal cell membranes, reduced photosynthetic efficiency, and triggered oxidative stress. Furthermore, intracellular and extracellular microcystin levels decreased significantly compared to untreated algae, minimizing ecological risks. These findings highlight the potential of the combination of TBC and L-lysine as a safe and cost-effective strategy for mitigating harmful algal blooms.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 ofMicrocystis aeruginosaby 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 inhibitedM. aeruginosagrowth 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,Fv/Fm, YII, α, and rETRmax, 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 ofM. aeruginosawere 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 mitigatingM. aeruginosa-dominated harmful algal blooms.