Jaisi Deb P, Dong Hailiang, Liu Chongxuan
Department of Geology, Miami University, Oxford, Ohio 45056, USA.
Environ Sci Technol. 2007 Apr 1;41(7):2437-44. doi: 10.1021/es0619399.
Microbial reduction of structural Fe(III) in nontronite (NAu-2) was studied in batch cultures under non-growth condition using Shewanella putrefaciens strain CN32. The rate and extent of structural Fe(III) reduction was examined as a function of electron acceptor [Fe(III)] and bacterial concentration. Fe(ll) sorption onto NAu-2 and CN32 surfaces was independently measured and described by the Langmuir expression with the affinity constant (log K) of 3.21 and 3.30 for NAu-2 and bacteria, respectively. The Fe(II) sorption capacity of NAu-2 decreased with increasing NAu-2 concentration, suggesting a particle aggregation effect. An empirical equation for maximum sorption capacity was derived from the sorption isotherms as a function of NAu-2 concentration. The total reactive surface concentration of Fe(III) was proposed as a proxy for the "effective" or bioaccessible Fe(III) concentration. The initial rate of microbial reduction was first-order with respect to the effective Fe-(III) concentration. A kinetic biogeochemical model was assembled that incorporated the first-order rate expression with respect to the effective Fe(III) concentration, Fe(II) sorption to cell and NAu-2 surfaces, and the empirical equation for maximum sorption capacity. The model successfully described the experimental results with variable NAu-2 concentration. The initial rate of microbial reduction of Fe(III) in NAu-2 increased with increasing cell concentration from 10(2) up to approximately 10(8) cells/mL, and then leveled off with further increase. A saturation-type kinetics with respect to cell concentration was required to describe microbial reduction of Fe(III) in NAu-2 as a function of cell concentration. Overall, our results indicated that the kinetics of microbial reduction of Fe(III) in NAu-2 can be modeled at variable concentration of key variables (clay and cell concentration) by considering the surface saturation, Fe(II) production, and its sorption to NAu-2 and cell surfaces.
在非生长条件下，使用腐败希瓦氏菌菌株CN32在分批培养中研究了蒙脱石（NAu - 2）中结构态Fe(III)的微生物还原作用。研究了结构态Fe(III)还原的速率和程度与电子受体[Fe(III)]和细菌浓度的关系。分别独立测量了Fe(II)在NAu - 2和CN32表面的吸附情况，并通过Langmuir表达式进行描述，NAu - 2和细菌的亲和常数（log K）分别为3.21和3.30。NAu - 2的Fe(II)吸附容量随NAu - 2浓度增加而降低，表明存在颗粒聚集效应。从吸附等温线得出了最大吸附容量与NAu - 2浓度的经验方程。提出将Fe(III)的总反应表面浓度作为“有效”或生物可利用Fe(III)浓度的替代指标。微生物还原的初始速率相对于有效Fe(III)浓度为一级反应。构建了一个动力学生物地球化学模型，该模型纳入了相对于有效Fe(III)浓度的一级反应速率表达式、Fe(II)在细胞和NAu - 2表面的吸附以及最大吸附容量的经验方程。该模型成功描述了不同NAu - 2浓度下的实验结果。NAu - 2中Fe(III)的微生物还原初始速率随着细胞浓度从10²增加到约10⁸个细胞/毫升而增加，然后随着细胞浓度进一步增加而趋于平稳。需要用关于细胞浓度的饱和型动力学来描述NAu - 2中Fe(III)的微生物还原与细胞浓度的关系。总体而言，我们的结果表明，通过考虑表面饱和度、Fe(II)的产生及其在NAu - 2和细胞表面的吸附，可以在关键变量（粘土和细胞浓度）的可变浓度下对NAu - 2中Fe(III)的微生物还原动力学进行建模。
