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

Abstract

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