The uptake of mercury by microorganisms is a key step in the production of methylmercury, a biomagnifiable toxin. Mercury complexation by low molecular weight (LMW) thiols can affect its bioavailability and thus the production of methylmercury. Freshwater biofilms were sampled in the summer using artificial Teflon substrates submerged for over a year to allow natural community colonization in the littoral zone of a Boreal Shield lake. Inside biofilms, concentrations of different extracellular thiol species (thioglycolic acid, L-cysteine-L-glycine, cysteine, and glutathione) were up to three orders of magnitude greater than in the surrounding water column, potentially more readily controlling mercury speciation than in water column. All biofilm thiols except thioglycolic acid were highly correlated to chlorophyll <i>a</i>, likely indicating an algal origin. Extracellular total mercury was preferentially found in the capsular fraction. Levels of LMW thiols of presumed algal origins were highly correlated with total mercury in the mobile colloidal fraction of biofilms. We propose that phototrophic microorganisms such as algae affect the bioavailability of mercury inside natural biofilms through the exudation of LMW thiols, and thus they may play a key role in the production and accumulation of methylmercury in aquatic food webs.<br/>

Are algae playing a role in mercury methylation through the production of thiols in aquatic biofilms?

250th National Meeting (2015)

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