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Title: Defining the Molecular-Cellular-Field Continuum of Mercury Detoxification

Hg is of special interest to DOE due to past use at the Oak Ridge Reservation (ORR). Its facile redox [Hg2+/0] chemistry, bonding to carbon [e.g. MeHg+] and unique physical properties [e.g., Hg0 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 and facultative mercury resistant (HgR) bacteria convert soil or waterborne Hg2+ or MeHg+ to less toxic, gaseous Hg0. 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 Hg2+/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. In thismore » project we extended our previous studies of mer enzymes in γ-proteobacteria, which are abundant in high Hg areas of the ORR to include studies of mer enzymes from HgR α-proteobacteria and HgR actinobacteria, which also increase in the high Hg regions of the ORR. Specifically, we (1) examined interactions between structural compoenents of MerA and MerB enzymes from γ-proteobacteria, (2) investigated effects of mutations on kinetic efficiency of Hg2+ reduction by γ-proteobacterial MerA, (3) cloned and performed initital characterization of MerA and MerB enzymes from Streptomyces lividans, an actinobacterium, (4) cloned and performed initial characterization of a fused MerB-MerA protein from Ochrobactrum anthropi, an α-proteobacterium, (5) investigate the extent of Hg isotope fractionation that occurs with purified γ-proteobacterial MerA.« less
  1. UCSF
Publication Date:
OSTI Identifier:
Report Number(s):
ER64984, Project ID: 0016201
DOE Contract Number:
Resource Type:
Technical Report
Research Org:
The Regents of the University of California San Francisco
Sponsoring Org:
USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Contributing Orgs:
University of California
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES bacterial mercury detoxification; mer operon; enzymes; structure/function; Hg isotope fractionation