Sulfate-reducing bacteria involvement in mercury methylation in water column and floating macrophytes rhizosphere

This study investigated the involvement of sulfate reducing bacteria (SRB) in mercury methylation in two contrasting compartments and environments. The water column of a boreal lake and the macrophyte root associated periphyton of an Amazonian oxbow lake. I also examined other groups of bacteria potentially involved in mercury methylation and how the newly produced methylmercury may enter the food web. In the Amazonian lake significant relationship between the presence and abundance of Desulfobacteraceae and mercury methylation potential was observed, suggesting that this family plays a major role in mercury methylation. However, molybdate achieved only partial inhibition of mercury methylation suggesting the involvement of non-SRB bacteria. In the boreal lake significant mercury methylation was only observed when samples were stimulated with lactate and the only viable strains isolated were Desulfovibrio, suggesting that Desulfovibrionaceae is the main mercury methylating group, which is partially in agreement with findings in sulfate rich fresh water sediments. Despite the environmental and geographical differences, SRB appear to be important mercury methylators in many compartments. This suggests that SRB may be involved in mercury methylation in most aquatic compartments, implicating that similar approaches to manage methylmercury production may work across many different aquatic ecosystems around the globe. We also found evidence that mercury methylating bacteria retain most of the methylmercury produced and that direct feeding in the mercury methylating community causes a higher incorporation of methylmercury.;Key words: Mercury methylation, methylmercury, sulfate reducing bacteria, stable isotopes, macrophytes, Amazon, DGT...