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Gene expression related to the synthesis of microcystin in cyanobacteria submitted to physiological stress: implications of global climate change.


Because of recurring events associated with global climate changes, several combined factors have been favored formation of toxic cyanobacteria blooms and increase of cyanotoxins production. Microcystins (MC) are cyanotoxins widely distributed in drinking water sources all over the world, with a story of several human intoxication cases and deaths. In this regard, it is endowed with great scientific interest the investigation of processes driven by circadian rhythms and ecophysiological processes, both involved in microcystins production and release. In this sense, the results could be used to establish mitigating measures for aquatic ecosystems, as well as help in formulating management and accident prevention strategies. The goal of this study is the evaluation of interfering effects related to light intensity, temperature and exposure to ultraviolet radiation (UV-B), all of them driven by climate change conditions, on circadian rhythms of microcystin production and release. Additionally, expression of mcyE genes, oxidative stress and growth of Microcystis aeruginosa (BCCUSP232) and Sphaerospermopsis aphanizomenoides (BCCUSP55) will be examined. Experiments will be performed under controlled conditions, simulating several climate change scenarios at 24h cycles (light:dark, 12:12h) along the exponential growth phase of cyanobacteria. Samples will be collected at 4 h intervals during the cycles. Data will be analyzed by taking into account combined effects associated with circadian rhythms in MC production and release per cell-quota, mcyE gene expression, oxidative stress (oxygen reactive species production, catalase, superoxide dismutase and peroxidase activities), free CO2 and cyanobacteria growth. Statistical tests will be employed according with data normality and homogeneity. (AU)