UNRAVELING THE MECHANISM OF Hg(II) TRANSPORT IN ANAEROBIC BACTERIA
Methylmercury is a potent neurotoxic substance which poses health risks to humans consuming diets rich in fish. It is produced primarily by certain species of sulfate and iron-reducing bacteria within the delta-Proteobacteria. The specific mechanism for the uptake and methylation of Hg(II) by these bacteria is an area of great interest, as the production of methylmercury represents a key first step in the accumulation and biomagnification of methylmercury in aquatic food webs. While the exact mechanism of Hg(II) transport remains unknown, we will discuss the recent improvements for directly measuring intracellular uptake in bacteria, and how these are changing our ideas of how Hg(II) enters cells and why they might methylate Hg(II). Evidence from our lab suggests that Hg(II) enters cells accidently through heavy metal transporters, where it is methylated in the cytosol and rapidly exported out of the cell. Thus, it is possible that Hg(II) methylation is an important mechanism for maintaining low Hg(II) concentrations in anoxic environments where essential trace metals are complexed to reduced sulfur and thiol species.