Biomolecular Mechanisms Controlling Metal and Radionuclide Transformations in Anaeromyxobacter dehalogenans

Research Objectives: Microbiological reduction and immobilization of U(VI) and Tc(VII) has been proposed as a strategy for remediating radionuclide-contaminated environments. Numerous studies focusing on the reduction kinetics and speciation of these metals have been carried out using contaminated sediment samples, microbial consortia, and pure bacterial cultures. While previous work with model organisms has increased the general understanding of radionuclide transformation processes, fundamental questions regarding radionuclide reduction mechanisms by indigenous microorganisms are poorly understood, especially under the commonly encountered scenario where multiple electron acceptors are present. Therefore, the overall goal of the proposed research is to elucidate the molecular mechanisms of radionuclide biotransformation by Anaeromyxobacter dehalogenans, a predominant member of indigenous microorganism commonly found in contaminated subsurface environments, and to assess the effects of relevant environmental factors affecting these transformation reactions. The following specific scientific questions are being addressed: • What are the mechanisms of metal and radionuclide reduction in organisms indigenous to contaminated FRC sediments? Specifically, what genes and pathways contributes to Fe(III), U(VI) and Tc(VII) reduction in A. dehalogenans 2CP-C? Are membraneassociated high-molecular weight c-type cytochromes involved in metal/radionuclide reduction in this organism? • How are genes involved in metal/radionuclide reduction in A. dehalogenans strain 2CP-C regulated under different redox conditions? What are the global gene expression patterns in A. dehalogenans 2CP-C under Fe(III), U(VI), Tc(VII), nitrate-, and 2-chlorophenolreducing conditions? • What are the key environmental factors specific to FRC subsurface environments that affect the expression of A. dehalogenans genes involved in metal/radionuclide reduction? In particular, how do low pH and the presence of co-contaminants (such as nitrate and chlorinated compounds) impact the gene expression and radionuclide transformation rates in A. dehalogenans?