Liu Chongxuan, Zachara John M, Fredrickson James K, Kennedy David W, Dohnalkova Alice
Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Environ Sci Technol. 2002 Apr 1;36(7):1452-9. doi: 10.1021/es011159u.
Pyrolusite (beta-MnO2(s)) was used to assess the influence of a competitive electron acceptor on the kinetics of reduction of aqueous uranyl carbonate by a dissimilatory metal-reducing bacterium (DMRB), Shewanella putrefaciens strain CN32. The enzymatic reduction of U(VI) and beta-MnO2(s) and the abiotic redox reaction between beta-MnO2(s) and biogenic uraninite (UO2(s)) were independently investigated to allow for interpretation of studies of U(VI) bioreduction in the presence of beta-MnO2(s). Uranyl bioreduction to UO2(s) by CN32 with H2 as the electron donor followed Monod kinetics, with a maximum specific reduction rate of 110 M/h/10(8) cells/mL and a half-saturation constant of 370 microM. The bioreduction rate of beta-MnO2(s) by CN32 was described by a pseudo-first-order model with respect to beta-MnO2(s) surface sites, with a rate constant of 7.92 x 10(-2) h(-1)/10(8) cells/mL. Uraninite that precipitated as a result of microbial U(VI) reduction was abiotically reoxidized to U(VI) by beta-MnO2(s), with concomitant reduction to Mn(II). The oxidation of biogenic UO2(s) coupled with beta-MnO2(s) reduction was well-described by an electrochemical model. However, a simple model that coupled the bacterial reduction of U(VI) and beta-MnO2(s) with an abiotic redox reaction between UO2(s) and beta-MnO2(s) failed to describe the mass loss of U(VI) in the presence of beta-MnO2(s). Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) revealed that the particle size and spatial distribution of the biogenic UO2(s) changed dynamically in systems with, as compared to without, beta-MnO2(s)). These observations suggested that the surface properties and localization of UO2(s) in relation to the cell and beta-MnO2(s) surfaces was an important factor controlling the abiotic oxidation of UO2(s) and, thus, the overall rate and extent of U(VI) bioreduction. The coupled model that was modified to account for the "effective" contact surface area between UO2(s) and beta-MnO2(s) significantly improved the simulation of microbial reduction of U(VI) in the presence of beta-MnO2(s).
采用软锰矿（β-MnO₂(s)）评估竞争性电子受体对异化金属还原菌（DMRB）——腐败希瓦氏菌菌株CN32还原碳酸铀酰动力学的影响。分别研究了U(VI)和β-MnO₂(s)的酶促还原以及β-MnO₂(s)与生物成因的晶质铀矿（UO₂(s)）之间的非生物氧化还原反应，以便解释在β-MnO₂(s)存在下U(VI)生物还原的研究结果。以H₂作为电子供体时，CN32将铀酰生物还原为UO₂(s)遵循莫诺德动力学，最大比还原速率为110 M/h/10⁸个细胞/mL，半饱和常数为370 μM。CN32对β-MnO₂(s)的生物还原速率可用一个关于β-MnO₂(s)表面位点的准一级模型来描述，速率常数为7.92×10⁻² h⁻¹/10⁸个细胞/mL。微生物还原U(VI)过程中沉淀生成的晶质铀矿被β-MnO₂(s)非生物再氧化为U(VI)，同时β-MnO₂(s)被还原为Mn(II)。生物成因的UO₂(s)氧化与β-MnO₂(s)还原的耦合过程可用一个电化学模型很好地描述。然而，一个将U(VI)和β-MnO₂(s)的细菌还原与UO₂(s)和β-MnO₂(s)之间的非生物氧化还原反应耦合起来的简单模型未能描述在β-MnO₂(s)存在下U(VI)的质量损失情况。透射电子显微镜（TEM）和能量色散光谱（EDS）显示，与不存在β-MnO₂(s)的体系相比，在含有β-MnO₂(s)的体系中，生物成因的UO₂(s)的粒径和空间分布会动态变化。这些观察结果表明，UO₂(s)相对于细胞和β-MnO₂(s)表面的表面性质和定位是控制UO₂(s)非生物氧化以及U(VI)生物还原的总速率和程度的一个重要因素。经过修正以考虑UO₂(s)与β-MnO₂(s)之间“有效”接触表面积的耦合模型显著改善了对在β-MnO₂(s)存在下U(VI)微生物还原的模拟。
