How Bacteria Influence Speciation (and Mobility) of Mercury in the Environment
Significant amounts of mercury have contaminated some DOE cleanup sites, such as the Oak Ridge Reservation. Mercury mobility is strongly dependent on its chemical form, with the elemental metal being volatile and hence mobile in the environment, while oxidized forms are much less mobile (though more toxic). New research at Argonne National Laboratory has provided improved understanding of the role of bacteria in controlling the chemical form of mercury in subsurface environments. The research group used x-ray absorption spectroscopy experiments at the Advanced Photon Source to study the sorption of oxidized HgII to Bacillus subtilis, a bacterium commonly found in soils. They found that HgII sorbs to bacterial cells via both high-affinity sulfhydryl binding groups and low-affinity carboxyl groups on the cell surfaces. The HgII that is sorbed to cells via the sulfhydryl groups remains unavailable for reduction by magnetite, a reactive iron-containing mineral often found in sediments, even after two months of reaction time. These results identify a mechanism by which mercury might be immobilized in the environment and help provide a clearer picture of the complex system of interactions of mercury in the subsurface.
Mishra, B., E. J. O’Loughlin, M. I. Boyanov, and K. M. Kemner. 2011. “Binding of Hg(II) to High-Affinity Sites on Bacteria Inhibits Reduction to Hg(0) by Mixed Fe(II/III) Phases,” Environmental Science and Technology 45(22), 9597–9603. DOI: 10.1021/es201820c.