Response of antioxidant defences of Microcystis aeruginosa (Cyanobacteria) to increased temperature

Cyanobacteria have different defence mechanisms, which have improved over time, to avoid or mitigate oxidative stress by using antioxidants as reactive species scavengers. The objective of the present study was to evaluate the effects of increased temperature, over several days of exposure, on biomass, lipid damage, oxygen and nitrogen reactive species, and different antioxidants on Microcystis aeruginosa (harmful cyanobacteria). Unicellular cultures were exposed to elevated (29 degrees C) and control (26 degrees C) temperatures for 10 d. The temperature shift induced activation of enzymatic antioxidant system and changes in content of non-enzymatic antioxidants after 2 d of exposure to 29 degrees C. This was responsible for a lower content of reactive species during the subsequent days. An increase in enzymatic antioxidant activity, depending on the exposure time, was observed. In addition, there was a differential non-enzymatic antioxidant response that was also time dependent, which could be important to counteract oxidative stress induced by increases in temperature. Overall, the initial increase in beta carotene and astaxanthin content followed by an increased activity of catalase together with superoxide dismutase and glutathione S transferase activities allowed the cyanobacteria to counteract the oxidative stress induced, and improved their growth at the increased temperature. Our results increase the understanding of different antioxidant responses, integrating enzymatic and non-enzymatic protection mechanisms over time when exposing M. aeruginosa to heatwaves. The survival capacity of Cyanobacteria in drinking water supplies can have serious implications for the environment and human health.