Impact of high temperature and UVR exposure on the microcystin production and mcyB gene expression in the cyanobacterium Microcystis aeruginosa.

Toxic cyanobacterial blooms, primarily caused by Microcystis aeruginosa, are increasing globally due to climate change. These harmful organisms have adapted to high temperature and UV radiation (UVR), posing a significant threat to drinking water. While UVBR can damage cyanobacteria, they may avoid it with antioxidant defense mechanisms. Microcystins (MCs), cyclic hepatotoxic heptapeptides produced by cyanobacteria, can harm aquatic and terrestrial organisms, but their role in antioxidant protection remains unclear. This study investigated the relationship between gene expression and MC content in Microcystis aeruginosa cells pre-adapted to elevated temperatures (29 °C) exposed to natural UVR for several days. We have demonstrated a strong resilience in M. aeruginosa to high doses of UVBR, largely attributed to its enhanced antioxidant capacity following pre-exposure to elevated temperatures, as confirmed by previous studies. Moreover, our findings suggest that MCs may act as scavengers as part of the UVR protection mechanisms. This is evidenced by a temporal lack of correlation between the abundance of mcy transcripts and the cellular toxin content, where toxin quotas were lower despite increased mcy transcription. These findings are particularly relevant to the ecophysiological role of MCs, suggesting its potential involvement in increased blooms of toxic M. aeruginosa under conditions of climate change and eutrophication. This information is crucial for effective water treatment planning.