Reduction kinetics of Fe(III), Co(III), U(VI), Cr(VI), and Tc(VII) in cultures of dissimilatory metal‐reducing bacteria

Abstract

The reduction kinetics of Fe(III)citrate, Fe(III)NTA, Co(III)EDTA-, U(VI)O(2) (2+), Cr(VI)O(4) (2-), and Tc(VII)O(4) (-) 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 > or = Fe(III)NTA > Co(III)EDTA- >> UO(2)(2+) > CrO(4)(2-) > TcO(4)(-), except for CrO(4) (2-) when H(2) was used as electron donor. The metal reduction rates were also electron donor dependent with faster rates observed for H(2) than lactate- for all Shewanella species despite higher initial lactate (10 mM) than H2 (0.48 mM). The bioreduction of CrO(4) (2-) was anomalously slower compared to the other metals with H(2) as an electron donor relative to lactate and reduction ceased before all the CrO(4)(2-) 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 CrO(4)(2-), for which the Monod model had to be modified to account for incomplete reduction. However, the Monod models became statistically over-parameterized, 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.

Structural Similarities between Biogenic Uraninites Produced by Phylogenetically and Metabolically Diverse Bacteria

“…These observations complement prior observations of extracellular uraninite aggregates with individual nanometer-sized particles observed for these genera (2,3,5,23,24).…”

Speciation-Dependent Kinetics of Uranium(VI) Bioreduction

“…Hence, dependencies are expected to vary across microbial species and strains, and optimum conditions are likely to depend on the specific site conditions. Dissolved U(VI) is considerably more bioavailable for reduction than adsorbed and precipitated or solid-phase U(VI) (Liu et al 2006;Ortiz-Bernad et al 2004), which is analogous to the trend of soluble Fe(III) being more bioavailable and thus rapidly reduced by microorganisms than solid-phase Fe(III) oxides (Liu et al 2002).…”

“…Although the overall rates of microbial metal reduction may strictly follow Monod or Michaelis-Menten kinetics, at nongrowth conditions a first-order rate model approximation of Monod kinetics has been demonstrated to provide equally good fits to experimental data as Monod kinetics (Liu et al 2002). Other studies of microbial U(VI) reduction rates have also found good fits of first-order rate models to experimental data ).…”

Reduction of Selenium by Pseudomonas stutzeri Nt-I: Growth, Reduction and Kinetics

“…In the case where the reduction rate is slower due to the lower initial selenate concentration, the elemental selenium seed-nanoparticles have time to be transported out of the cell and therefore interfere less with the reduction reaction. It has been shown in another study [27] that elemental selenium seed-nanoparticles can physically get in the way of different steps in the reaction chain, for example blocking the redox enzyme or interfering with the intermediate electron transfer sites. These seed-nanoparticles can also negatively influence the porosity of the cell membrane.…”