Elucidating the Molecular Basis and Regulation of Chromium(VI) Reduction by Shewanella oneidensis MR-1 and Resistance to Metal Toxicity Using Integrated Biochemical, Genomics and Proteomic Approaches

In situ bioremediation that exploits the intrinsic respiratory processes of dissimilatory metal ion-reducing bacteria is a potent, potentially cost-effective approach to the reductive immobilization or detoxification of environmental contaminants. Shewanella oneidensis strain MR-1 is a metal-reducing bacterium that can respire a wide array of organic and inorganic substrates, including Cr(VI), U(VI), and Tc(VII). Consequently, S. oneidensis can potentially be used to immobilize metals/radionuclides by reducing soluble and more mobile forms to sparingly soluble, less bioavailable forms. However, the prediction and assessment of bioremediation performance is compounded by the lack of fundamental knowledge on microbe-metal interactions and on a microorganism's ability to survive and function in relevant contaminated environments.    Images

S. oneidensis is currently the subject of a DOE Natural and Accelerated Bioremediation Research (NABIR) project that is employing an integrated functional genomics approach to characterizing the molecular basis and regulation of hexavalent chromium [Cr(VI)] stress response and reduction by MR-1. This research project takes advantage of the 5-Mbp genome sequence of S. oneidensis MR-1, which was deciphered by The Institute for Genomic Research (TIGR) under the support of the DOE (Heidelberg et al., Nature Biotechnology, 2002). Availability of whole-genome sequence information for MR-1 has enabled detailed systems biology studies involving global gene and protein expression profiling. In this project, more traditional approaches such as targeted deletion mutagenesis and physiological assays are combined with microarray hybridization and multidimensional high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) to understand the molecular mechanisms underlying Cr(VI) detoxification by S. oneidensis.

In the first phase of research, parallel transcriptomic and proteomic characterization of the molecular response of MR-1 to acute chromium stress and adaptation under aerobic growth conditions was completed. From these studies, several Cr-responsive genes were identified and targeted for deletion mutagenesis, including two ORFs encoding a putative FMN reductase and a DNA-binding response regulator. Time-series microarray experiments and dose-response studies revealed the transcriptome dynamics of the cellular response to toxic chromate concentrations. Future investigations will focus on globally defining the molecular response to chromate under anaerobic respiratory conditions, elucidating the function and protein-protein interactions of a putative protein complex involved in the chromium stress response, and characterizing the regulon and function of a Cr-responsive regulator. Together, these studies will help us understand how S. oneidensis responds and adapts to its environment.