Changes in the non-protein thiol pool and production of dissolved gaseous mercury in the marine diatom Thalassiosira weissflogii under mercury exposure

Morelli, Elisabetta and Ferrara, Romano and Bellini, Barbara and Dini, Fernando and Di Giuseppe, Graziano and Fantozzi, Laura (2009) Changes in the non-protein thiol pool and production of dissolved gaseous mercury in the marine diatom Thalassiosira weissflogii under mercury exposure. Science of the Total Environment, 408/20 (2). pp. 286-293. ISSN 0048-9697

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Abstract

SUMMARY Two detoxification mechanisms working in the marine diatom Thalassiosira weissfloggii to cope with mercury toxicity were investigated. Initially, the effect of mercury on the intracellular pool of non-protein thiols was studied in exponentially growing cultures exposed to sub-toxic HgCl2 concentrations. T. weissfloggii cells responded by synthesizing metalbinding peptides, named phytochelatins (PCs), besides increasing the intracellular pool of glutathione and g-glutamylcysteine (g-EC). Intracellular Hg and PC concentrations increased with the Hg concentration in the culture medium, exhibiting a distinct dose-response relationship. However, considerations of the PCs-SH:Hg molar ratio suggest that also glutathione could be involved in the intracellular mercury sequestration. The time course of the non-protein thiol pool and Hg intracellular concentration shows that PCs, glutathione and g-EC represent a rapid cellular response to mercury, although their role in Hg detoxification seems to lose importance at longer incubation times. The occurrence of a process of reduction of Hg(II) to Hg° and subsequent production of dissolved gaseous mercury (DGM) was also investigated at lower Hg concentrations, at which the PC synthesis doesn’t seem to be involved. The significant (P<0.01) correlation between the cellular density in solution and the production of DGM suggests that this diatom is capable of directly producing DGM, both in light and dark conditions. This finding has been confirmed by the absence of DGM production in the culture media containing formaldehyde-killed cells. Finally, the relationship between these two different pathways of Hg detoxification is discussed.

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