Reduction Kinetics of Fe(III), Co(III), U(VI), Cr(VI), and Tc(VII) in Cultures of Dissimilatory Metal-Reducing Bacteria

Authors

Chongxuan Liu, Pacific Northwest National LaboratoryFollow
Yuri A. Gorby, Pacific Northwest National Laboratory
John M. Zachara, Pacific Northwest National LaboratoryFollow
James K. Fredrickson, Pacific Northwest National LaboratoryFollow
Christopher F. Brown, Pacific Northwest National Laboratory

Date of this Version

2002

Citation

Biotechnology and Bioengineering, Vol. 80, No. 6, December 20, 2002; DOI: 10.1002/bit.10430

Abstract

The reduction kinetics of Fe(III)citrate, Fe(III)NTA, Co(III)EDTA⁻, U(VI)O₂²⁺, Cr(VI)O₄²⁻, and Tc(VII)O₄⁻ were studied in cultures of dissimilatory metal reducing bacteria (DMRB): Shewanella alga strain BrY, Shewanella putrefaciens strain CN32, Shewanella oneidensis strain MR-1, and Geobacter metallireducens strain GS-15. Reduction rates were metal specific with the following rate trend: Fe (III)citrate ≥ Fe(III)NTA > Co(III)EDTA⁻ ›› UO₂ ²⁺ > CrO₄²⁻ > TcO₄⁻, except for CrO₄²⁻ when H₂ was used as electron donor. The metal reduction rates were also electron donor dependent with faster rates observed for H₂ than lactate⁻ for all Shewanella species despite higher initial lactate (10 mM) than H₂ (0.48 mM). The bioreduction of CrO₄²⁻ was anomalously slower compared to the other metals with H₂ as an electron donor relative to lactate and reduction ceased before all the CrO₄²⁻ had been reduced. Transmission electron microscopic (TEM) and energy-dispersive spectroscopic (EDS) analyses performed on selected solids at experiment termination found precipitates of reduced U and Tc in association with the outer cell membrane and in the periplasm of the bacteria. The kinetic rates of metal reduction were correlated with the precipitation of reduced metal phases and their causal relationship discussed. The experimental rate data were well described by a Monod kinetic expression with respect to the electron acceptor for all metals except CrO₄²⁻, for which the Monod model had to be modified to account for incomplete reduction. However, the Monod models became statistically over-parametrized, resulting in large uncertainties of their parameters. A first-order approximation to the Monod model also effectively described the experimental results, but the rate coefficients exhibited far less uncertainty. The more precise rate coefficients of the first-order model provided a better means than the Monod parameters, to quantitatively compare the reduction rates between metals, electron donors, and DMRB species.