Abstract
R. raciborskii is known for growing under wide ranges of temperature and light. In temperate regions, however, low temperature and high light may serve as a stressful condition for invading tropical populations. The genetic basis of R. raciborskii’s adaptation to this combination of stresses are unknown. In this study, the growth rate and the expression of genes that may be crucial in the response to the chill/light stress of two R. raciborskii strains (differing in their climatic origin and toxicity) exposed to low temperature and high light were examined. Results showed that AMU-DH-30, a non CYN (cylindrospermopsin) producing strain isolated from the temperate region, exhibited under stress the upregulation of genes involved in the protein translation (rbp1, nusG, hflX), membrane fluidity (desA), photosynthetic activity (ccr2 and ftsH), and the accumulation of compatible solutes (asd). In contrast, a CYN producing Australian strain CS-505 was not able to adapt quickly and to continue growth during stress conditions. Intriguingly, CS-505 and AMU-DH-30 had a similar ability to resume growth when the stress conditions subsided. Moreover, in strain CS-505 the cyrB gene was significantly upregulated under the stress conditions. The presented results shed new light on the possible mechanisms involved in the response of R.raciborskii to chill/light stress.
Highlights
Increased eutrophication of surface water results in a common occurrence of toxic or potentially toxic cyanobacterial blooms
Our results suggest that the upregulation of rbp1 in R. raciborskii may allow the initiation of other processes necessary for adaptation, mainly those responsible for enhanced membrane fluidity and photosynthesis maintenance
The increased level of desA was observed only in AMU-DH-30 strain after 1 h and five days of acclimation to chill/light stress whereas in CS-505 strain this gene was not upregulated. These results suggest that cells of R. raciborskii AMU-DH-30 exposed to chill/light stress were induced to a rapid increase in the desaturation of fatty acids chains and this process is prolonged for several days, indicating the mechanism of chill/light adaptation
Summary
Increased eutrophication of surface water results in a common occurrence of toxic or potentially toxic cyanobacterial blooms. Sci. 2020, 10, 5437 a cyanobacterium well adapted to different conditions is Raphidiopsis (formerly Cylindrospermopsis) raciborskii which has considerable flexibility with respect to light and nutrients [2]. The successful expansion of this taxa from subtropical regions toward colder temperate regions has been explained by its ability to rapidly adapt to new environments through high intraspecific variability. These so-called ecotypes vary in their ecophysiology with respect to factors driving their occurrence including temperature, light, and nutrients. Recent studies have shown high degree of strain variability within populations of this cyanobacterium originating from different geographic regions [3].
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