Hg is of special interest to DOE due to past use at the Oak Ridge Reservation (ORR). Its facile redox [Hg(II)/(0)] chemistry, bonding to carbon [e.g. MeHg+] and unique physical properties [e.g., Hg(0) volatility] underlie a complex global Hg cycle involving biotic and abiotic chemical and physical transport and transformations in soils, sediments, waterways and the atmosphere. Facultative and anaerobic bacteria make MeHg+ which is neurotoxic to wildlife and humans. Sustainable stewardship requires eliminating both MeHg+ and even more toxic Hg2+, which is also the substrate for methylation. The proteins encoded by the mer locus in aerobic facultative mercury resistant (HgR) bacteria convert soil or waterborne Hg2+ or MeHg+ to less toxic, gaseous Hg(0). HgR microbes live in highly Hg-contaminated sites and depress MeHg+ formation >500-fold in such zones. So, enhancing the capacity of natural HgR microbes to remove Hg(II)/MeHg+ from wetlands and waterways is a logical component of contaminated site stewardship. To apply enhancement in the field requires knowing how the HgR pathway works including the metabolic demands it makes on the cell i.e. the entire cell is the relevant catalytic unit. HgR loci occur in metabolically diverse bacteria and unique mer-host co-evolution has been found. The proteobacteria with which we have worked are abundant in high Hg areas of the ORR and here we are extending our studies to the HgR actinobacteria, which also increase in the high Hg regions of the ORR. At the molecular and sub-cellular levels, we examine mer protein interactions with each other and with specific host proteins to rapidly and completely convert Hg(II) or RHg+ to Hg(0).