103 - Uptake of Mercury Species by model Cyanobacterium is Mitigated by the Presence of Bioligands

"Bioligands present in the aquatic environment are known to play a central role in the modulation of mercury uptake by phytoplankton species. However, controversial information exist showing a decrease, increase or no effect of the bioligands on Hg uptake.

The present study explores the role of low- and high-molecular mass bioligands on the uptake of inorganic (iHg) and monomethyl mercury (MMHg) by cyanobacterium Synechocystis sp. PCC6803. The biouptake was characterized in terms of intracellular (DMPS non-extractable) and adsorbed (DMPS-extractable) Hg contents. To assess the role of different bioligands on Hg uptake, Synechocystis sp. was exposed for 2h to 3.0 nM of iHg or MMHg in the presence of L-cysteine, D-penicillamine, glutathione, 2,3-dimercapto-1-propanesulfonic acid (DMPS), and extracellular polymeric substances (EPS) released by this cyanobacterium. The results were compared with the uptake of iHg or MMHg in the absence of bioligands, as well as in the presence of dissolved organic matter (DOM) of pedogenic origin (SR-DOM, SR-HA, SR-FA and PL-FA). The results showed that low molar mass bioligands (Hg/thiol ratio = 60) decreased significantly the Hg biouptake by cyanobacteria when exposed to iHg or MMHg. This reduction was proportional to the strength of the formed complexes: the stronger the iHg-thiol complex was, the bigger reduction of the uptake was observed. 0.8 mg C L-1 of cyanobacterium EPS decreased by ≈ 50 % the Hg uptake, whereas different DOM of pedogenic origin induced more than 98% reduction of iHg or MMHg uptake, when compared with the uptake in the absence of bioligands. The results confirm that different bioligands can reduce the uptake of Hg species by cyanobacteria and protect them from Hg stress and entry into the bottom of the food webs."

Authors: Thibaut Cossart, Isabelle A. M. Worms, Kevin Trindade, Arin Kantarciyan, David Amouroux, Vera Slaveykova