The influence of temperature on Radiocystis fernandoi strain (cyanobacteria) growth and microcystin production

Abstract

Radiocystis fernandoi Komarek and Komarkova-Legnerova has great ecological importance in tropical regions, due to its widespread occurrence in freshwaters in the American continent, besides its ability to form blooms and to produce toxins. Global warming has a very important and positive role on cyanobacterial development considering that the growth rate of these organisms increases at temperatures above 25 °C. Considering that there is no information in the literature about the effects of temperature on the development of R. fernandoi, we performed an experimental study on its effects on growth and microcystin-LR production, employing a tropical microcystin-producer R. fernandoi. The selected strain was tested at three temperatures: 20, 25 and 30 °C and sampled at intervals of 2 days including different growth phases. Our results show that the strain presents greater growth rates and the smaller cell size at 25 and 30 °C. Differently from Microcystis aeruginosa (Kutzing) Kutzing that presents the greatest microcystin production at the end of the exponential growth phase, R. fernandoi produced microcystin only in the stationary phase. This result emphasizes the importance of monitoring Radiocystis blooms for a long period of time considering that these toxins remain in the water for up to 42 days. Thus, besides the morphological differences between M. aeruginosa and R. fernandoi, our results reveal that physiologically these cyanobacterial species also present different strategies that allow them to co-occur in nature forming long-lasting blooms.