title: Relationship between Extracellular Low-Molecular-Weight Thiols and Mercury Species in Natural Lake Periphytic Biofilms.
abstract: 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 3 orders of magnitude greater than in the surrounding water column, potentially more readily controlling mercury speciation than in the water column. All biofilm thiols except thioglycolic acid were highly correlated to chlorophyll a, likely indicating an algal origin. Extracellular total mercury represented 3 ± 1% of all biofilm mercury and 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 periphytic phototrophic microorganisms such as algae likely affect the bioavailability of mercury through the exudation of LMW thiols, and thus they may play a key role in the production of methylmercury in biofilms.
authors.affiliation: †GRIL, Département de Sciences Biologiques, Université de Montréal, C.P. 6128, Succursale Centre Ville, Montréal, Québec, Canada, H3C 3J7.
authors.forename: Maxime
authors.initials: M
authors.lastname: Leclerc
authors.affiliation: ‡GRIL, Département de Sciences Biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre Ville, Montréal, Québec, Canada H3C 3P8.
authors.forename: Dolors
authors.initials: D
authors.lastname: Planas
authors.affiliation: †GRIL, Département de Sciences Biologiques, Université de Montréal, C.P. 6128, Succursale Centre Ville, Montréal, Québec, Canada, H3C 3J7.
authors.forename: Marc
authors.initials: M
authors.lastname: Amyot
mesh_terms: D018441:Biofilms; D018533:Biomass; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D005110:Extracellular Space / Q000737:chemistry*; D060106:Lakes / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D008970:Molecular Weight; D013438:Sulfhydryl Compounds / Q000032:analysis*; D013997:Time Factors
chemical_list: D013438:Sulfhydryl Compounds; D002734:Chlorophyll; D008628:Mercury; D000077194:Chlorophyll A