Reduction of technetium by Desulfovibrio desulfuricans: Biocatalyst characterization and use in a flowthrough bioreactor

Resting cells of Desulfovibrio desulfuricans coupled the oxidation of a ran ge of electron donors to Tc(VII) reduction. The reduced technetium was prec ipitated as an insoluble low-valence oxide. The optimum electron donor for the biotransformation was hydrogen, although rapid rates of reduction were also supported when formate or pyruvate was supplied to the cells. Techneti um reduction was less efficient when the growth substrates lactate and etha nol were supplied as electron donors, while glycerol, succinate, acetate, a nd methanol supported negligible reduction. Enzyme activity was stable for several weeks and was insensitive to oxygen. Transmission electron microsco py showed that the radionuclide was precipitated at the periphery of the ce ll. Cells poisoned with Cu(II), which is selective for periplasmic but not cytoplasmic hydrogenases, were unable to reduce Tc(VII), a result consisten t with the involvement of a periplasmic hydrogenase in Tc(VII) reduction. R esting cells, immobilized in a flowthrough membrane bioreactor and supplied with Tc(VII)-supplemented solution, accumulated substantial quantities of the radionuclide when formate was supplied as the electron donor, indicatin g the potential of this organism as a biocatalyst to treat Tc-contaminated wastewater.