Physiological and biochemical characteristics and ecological risk assessment of Microcystis aeruginosa under Malathion stress
The extensive agricultural application of organophosphorus pesticides (OPPs) has established them, alongside nitrogen and phosphorus nutrients, as core pollutants in agricultural non-point source contamination, necessitating urgent clarification of their composite ecological effects on aquatic ecosystems. This study systematically investigated the concentration gradient effects and ecological risk mechanisms of malathion, a heavily utilized OPP, on the bloom-forming cyanobacterium Microcystis aeruginosa. Results demonstrated a pronounced concentration-dependent biphasic effect: high concentrations (100 mg·L−1) suppressed algal growth, reducing cell density to 8% of the control group, whereas low concentrations (0.01 mg·L−1) markedly stimulated algal proliferation (47% cell density increase) through photosynthetic system activation (51% chlorophyll-a elevation), metabolic enhancement (98% ATP content increase), and mild oxidative stress induction. Regarding microcystin regulation, low-concentration exposure upregulated microcystin synthesis genes (mcyA, mcyB), elevating intracellular microcystin production to 1.6-fold of controls. Conversely, high concentrations triggered microcystin release via severe membrane integrity disruption (>80% membrane damage). Risk assessment demonstrated that environmentally relevant malathion levels (0.01 mg·L−1) pose dual threats: exacerbating ecological risks by promoting algal blooms and amplifying health hazards through intensified microcystin synthesis and release. These findings provide critical theoretical insights for evaluating OPP ecotoxicity and formulating cyanobacterial bloom control strategies in agricultural non-point source pollution management.