The Secretome of Metal-Reducing Shewanella oneidensis
EMSL Project ID
34722
Abstract
The metabolic reactions catalyzed by metal- and radionuclide-reducing bacteria greatly influence the geochemistry of natural and contaminated environments. One of the more remarkable activities displayed by metal-reducing bacteria is their ability to catalyze the reductive precipitation of toxic radionuclides (uranium, technetium) that pose serious threats to human health. The reductive precipitation reactions form the basis of alternate in situ bioremediation strategies since the relative solubility (and hence mobility) of U and Tc is greatly diminished at lower oxidation states. Metal-reducing bacteria are also capable of driving electricity generation in microbial fuel cells, an activity that requires electron transfer to solid-state electrodes. Despite its fundamental importance to EMSL's mission, the molecular basis of microbial metal and radionuclide reduction is poorly understood. Metal- and radionuclide-reducing Shewanella oneidensis MR-1 catalyzes the direct enzymatic reduction of solid metal oxides via an electron transport chain postulated to terminate on the outside face of the outer membrane with a metal reduction step catalyzed by MtrC and OmcA, two decaheme c-type cytochromes. Purified MtrC and OmcA also display U(VI) and Tc(VII) reductase activities in vitro, an indication that the reductive precipitation of radionuclides also occurs on the cell surface. Identification of the S. oneidensis secretome (defined as the complement of proteins secreted to the cell surface or exterior) will therefore provide information on electron transport chain components involved in the terminal steps of metal and radionuclide reduction. The main objective of the proposed EMSL-USER research project is to determine the electron acceptor-specific secretome of metal- and radionuclide-reducing S. oneidensis. The S. oneidensis secretome will be determined via cross-comparison of proteins identified on the surface and exterior of the wild-type and protein secretion-deficient mutant strains. Identification of cell surface-associated and extracellular proteins of S. oneidensis is computationally intensive and will require the unique, high throughput proteomic capabilities available at EMSL. Genomic analysis indicates that the S. oneidensis genome harbors four protein secretion systems (Types I, IIa, IIb, and V, but not Types III, IV or VI) that may participate in protein secretion to the cell surface or exterior. We have previously constructed targeted, in-frame deletion mutants to disable the Type I, Type IIa, Type IIb, or Type V protein secretion systems of S. oneidensis. The wild-type and protein secretion-deficient mutant strains will be grown on various combinations of electron donors and electron acceptors prior to secretome analysis. The set of electron acceptors have been selected to span a wide range of redox potentials (to determine if secretome composition correlates with electron acceptor potential), and to include solid and soluble forms of metals and radionuclides (to determine if secretome composition correlates with electron acceptor solubility). Results from the Georgia Tech-EMSL collaboration will provide a wealth of information important to EMSL's mission, including identification of proteins potentially involved in the terminal step of electron transfer to extracellular metals and radionuclides, and development of strategies for electricity generation in microbial fuel cells and reductive immobilization of radionuclides at contaminated DOE sites.Project Details
Project type
Large-Scale EMSL Research
Start Date
2009-10-08
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator