Different responses to high light stress of toxic and non-toxicMicrocystis aeruginosaacclimated under two light intensities and zinc concentrations

Abstract

In this study, interaction effects of high light (HL) and zinc on two Microcystis aeruginosa strains (toxic CPCC299 and non-toxic CPCC632) were investigated. Our results suggested that CPCC632 was more sensitive to high zinc (HZn; 7.8 Â 10 À6 M) concentration than CPCC299 when acclimated to HL (500 mmol photons m À2 s À1 ). When M. aeruginosa strains were treated 20 min to HL (2000 mmol photons m À2 s À1 ), the maximal and the operational PSII quantum yields (F M and F 0 M ) of the two strains decreased, but CPCC632 (50 mmol photons m À2 s À1 (low light (LL)) þ HZn) has the biggest decrease among the four growth conditions. Under LL growth conditions, CPCC632 was more sensitive to HL stress than CPCC299. However, these differences disappeared when they were grown under HL condition. These results suggested that CPCC632 had the lowest ability to acclimate HL stress under LL þ HZn conditions. We also showed that the response mechanisms to HL stress of M. aeruginosa were linked to the change of pigments, energy dissipation processes, and microcystin content (for the toxic strain). Our data indicated that different effects of HL and zinc on M. aeruginosa strains may influence the dominance of different strains in aquatic system.

Combined Effects of Trace Metals and Light on Photosynthetic Microorganisms in Aquatic Environment

“…High intensity visible light per se represents a stressor for C. reinhardtii and the addition of Cu exacerbated the experienced stress e.g., by disturbing a cellular homeostasis that was already at its operating limit. The current results agree with what previously observed for the cyanobacterium M. aeruginosa [72][73][74], suggesting that similar interaction between metals and light irradiation occur in prokaryotic and eukaryotic phytoplankton. Interestingly different results were obtained when C. reinhardtii cells acclimated to low-intensity light (45 µmol phot m −2 s −1 ) were simultaneously exposed to a combination of high-intensity light (395 µmol phot m −2 s −1 ) and copper.…”

“…These results shed some light on the role of visible light on metal toxicokinetics, however although environmentally relevant these low-light irradiation conditions do not represent a stress for photosynthetic organisms. Zn uptake was also determined in three cyanobacterial species acclimated to low (50 µmol photons m −2 s −1 ) and high-visible light (300 µmol photons m −2 s −1 ) [73,74]. For the two strains of M. aeruginosa a significant increase in the intracellular Zn was observed under high-light irradiation, whereas no significant differences were found in Synechocystis sp.…”

“…Only one work focused on periphytic communities [103]. Most of the studies performed with isolated species revealed an enhancement of the metal effects on photosynthetic yield and growth inhibition under increased visible light radiation [72][73][74]99]. Similarly the intracellular ROS generation, lipid peroxidation and enzymatic antioxidant response increased upon exposure of cyanobacterium Nostoc muscorum to Hg with increase of the visible light radiation from 10 to 130 µmol photons m −2 s −1 [99].…”

“…The research focused on different metals including Zn [72][73][74]103], Cd [7,64,72,98,100,102], Hg [100], Cu [62,75,76,97], Ni [64], Pb [64] and on different light radiation components: visible [72][73][74][75]99,102] and UV radiation [7,75,76,97,98,100,101]. Most of the work explored these combined effects on model organisms, mainly cyanobacterial species [72][73][74]99], but the results are rather contrasting. Only one work focused on periphytic communities [103].…”

“…A significant number of studies explored the combined effects of metals and light on different eukaryotic algae and cyanobacteria [7,[72][73][74][75][76][97][98][99][100][101], as well as periphytic communities [102,103] ( Table 1). The research focused on different metals including Zn [72][73][74]103], Cd [7,64,72,98,100,102], Hg [100], Cu [62,75,76,97], Ni [64], Pb [64] and on different light radiation components: visible [72][73][74][75]99,102] and UV radiation [7,75,76,97,98,100,101].…”