Figure 1. Anaerobic glove box: A glove box where we manipulate samples which need to be protected from the toxicity of oxygen. A mixture of gases such as nitrogen or argon and hydrogen is flushed through the glove box to assure that the interior of the chamber is maintained anoxic. Shown is Heather manipulating her samples in the glove box.

We are interested in microbe-mercury interactions in subsurface environments, which usually have low nutrients and little or no oxygen. Recently, our colleagues at the US Geological Survey have discovered the presence of elemental mercury (Hg[0]) in well water in southern New Jersey. They suggest that this could be due to microbial activity in groundwater. This discovery highlighted our lack of knowledge regarding the interactions between microbes and mercury in this environment. While production of Hg(0) from ionic Hg(II), a reduction process, by mercury resistant aerobic bacteria has been well documented, it remains unknown how mercury is reduced by subsurface microorganisms in anoxic environments.

Some microorganisms that live in subsurface environments are capable of “breathing” metals instead of oxygen. These organisms, called dissimilatory metal reducing bacteria, are of great interest with regards to the bioremediation of toxic metals and radionuclides. A postdoctoral fellow in our lab Heather Wiatrowski has been investigating interactions between mercury and the dissimilatory metal reducing bacteria. In her previous work she discovered that pure cultures of these microorganisms such as Shewanella oneidensis MR-1, Geobacter sulfurreducens PCA, and Geobacter metallireducens GS-15 are capable of reducing Hg(II) to Hg(0), despite the fact that they are sensitive to mercury. This activity occurs at low concentrations of mercury and it is constitutive, i.e., genetic induction is not necessary for reduction to occur.

Current research by Heather examines the role of this process in intact subsurface samples from the DOE's Field Research Center in Oak Ridge, TN. Another postdoctoral fellow in the lab, Yanping Wang is performing microbial community analysis on the enrichment cultures that Heather is setting up for mercury reduction studies. Together, the results from their work will provide an assessment of the pathways that are involved in the reduction of Hg(II) to Hg(0) in the anoxic zones of groundwater aquifers.