uranium enrichment, nuclear fuel processing, and disposal after pharmaceutical use ... Morrison formation of northwestern New Mexico (8). CN32 was provided.
Effect of Electron Donor and Solution Chemistry on Products of Dissimilatory Reduction of Technetium by Shewanella putrefaciens R. E. WILDUNG,* Y. A. GORBY, K. M. KRUPKA, N. J. HESS, S. W. LI, A. E. PLYMALE, J. P. MCKINLEY, AND J. K. FREDRICKSON Pacific Northwest National Laboratory, Richland, Washington 99352 Received 1 July 1999/Accepted 15 February 2000
To help provide a fundamental basis for use of microbial dissimilatory reduction processes in separating or immobilizing 99Tc in waste or groundwaters, the effects of electron donor and the presence of the bicarbonate ion on the rate and extent of pertechnetate ion [Tc(VII)O4ⴚ] enzymatic reduction by the subsurface metalreducing bacterium Shewanella putrefaciens CN32 were determined, and the forms of aqueous and solid-phase reduction products were evaluated through a combination of high-resolution transmission electron microscopy, X-ray absorption spectroscopy, and thermodynamic calculations. When H2 served as the electron donor, dissolved Tc(VII) was rapidly reduced to amorphous Tc(IV) hydrous oxide, which was largely associated with the cell in unbuffered 0.85% NaCl and with extracellular particulates (0.2 to 0.001 m) in bicarbonate buffer. Cell-associated Tc was present principally in the periplasm and outside the outer membrane. The reduction rate was much lower when lactate was the electron donor, with extracellular Tc(IV) hydrous oxide the dominant solid-phase reduction product, but in bicarbonate systems much less Tc(IV) was associated directly with the cell and solid-phase Tc(IV) carbonate may have been present. In the presence of carbonate, soluble (
