Physiological and biochemical characteristics and ecological risk assessment of Microcystis aeruginosa under Malathion stress

• • Malathion exhibits a biphasic effect on Microcystis aeruginosa: 100 mg·L−1 reduces cell density to 8% of control, while 0.01 mg·L−1 increases cell density by 47%, indicating hormesis that can exacerbate algal blooms at environmentally relevant concentrations. • • Low-dose malathion (0.01 mg·L−1) stimulates photosynthesis and metabolism, elevating chlorophyll-a by 51% and ATP content by 98%, which directly boosts algal proliferation and bloom potential in aquatic systems. • • Sub-inhibitory malathion upregulates microcystin synthesis genes (mcyA, mcyB), increasing intracellular microcystin production to 1.6-fold of controls, thereby amplifying toxin-related health risks even at low exposure levels. • • High malathion concentration (100 mg·L−1) causes >80% membrane damage, triggering microcystin release into water, which poses acute toxicity risks and complicates water treatment.