Increasing temperature counteracts the negative effects of ultraviolet radiation on Microcystis aeruginosa under future climate scenarios in relation to physiological processes.

Heat waves, are a major concern related to climate change, and are projected to increase in frequency and severity. This temperature rise causes thermal stratification, exposing surface-dwelling organisms to higher levels of ultraviolet radiation (UVR). This study aims to understand how the toxic bloom-forming cyanobacterium Microcystis aeruginosa adapts to changing climatic conditions. The effects of increased temperature and UVR were evaluated in terms of cell abundance, reactive oxygen and nitrogen species (ROS/RNS), the antioxidant activity of catalase (CAT), superoxide dismutase (SOD), glutathione S transferase (GST), fatty acid (FA) content, and lipid damage. Negative UVR effects on biomass, lipid damage, and polyunsaturated fatty acids (PUFAs) were more pronounced at 26 °C compared to 29 °C. However, antioxidant responses were higher at 29 °C. The relative abundance of ω6 FAs was less affected by UVA, while ω3 FAs were highly sensitive at 29 °C but unsaturated fatty acids (UFA) did not experience peroxidation. The differential response in FA to high temperature and UVR results in differences in lipid damage and antioxidants. Changes in membrane FA may suggest an adaptation strategy at high UVR conditions. The exposure to environmental changes can alter membrane fluidity, affecting cell physiology. Thus, to survive UVR exposure, M. aeruginosa maintains a balance between damage and stress adaptation, increasing the protection of selected PUFAs at high temperatures, allowing them to effectively cope with the harmful effects of elevated temperature and UVR.