title: Effects of Incubation Conditions on Cr(VI) Reduction by c-type Cytochromes in Intact Shewanella oneidensis MR-1 Cells.
abstract: It is widely recognized that the outer membrane c-type cytochromes (OM c-Cyts) of metal-reducing bacteria play a key role in microbial metal reduction processes. However, the in situ redox status of OM c-Cyts during microbial metal reduction processes remain poorly understood. In this study, diffuse-transmission UV/Vis spectroscopy is used to investigate the in situ spectral reaction of Cr(VI) reduction by c-Cyts in intact Shewanella oneidensis MR-1 cells under different incubation conditions. The reduced c-Cyts decreased transiently at the beginning and then recovered gradually over time. The Cr(VI) reduction rates decreased with increasing initial Cr(VI) concentrations, and Cr(III) was identified as a reduced product. The presence of Cr(III) substantially inhibited Cr(VI) reduction and the recovery of reduced c-Cyts, indicating that Cr(III) might inhibit cell growth. Cr(VI) reduction rates increased with increasing cell density. The highest Cr(VI) reduction rate and fastest recovery of c-Cyts were obtained at pH 7.0 and 30°C, with sodium lactate serving as an electron donor. The presence of O2 strongly inhibited Cr(VI) reduction, suggesting that O2 might compete with Cr(VI) as an electron acceptor in cells. This study provides a case of directly examining in vivo reaction properties of an outer-membrane enzyme during microbial metal reduction processes under non-invasive physiological conditions.
authors.affiliation: School of Environment and Energy, South China University of TechnologyGuangzhou, China; Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil SciencesGuangzhou, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Han
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences Guangzhou, China.
authors.forename: Fangbai
authors.initials: F
authors.lastname: Li
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences Guangzhou, China.
authors.forename: Tongxu
authors.initials: T
authors.lastname: Liu
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences Guangzhou, China.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Li
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences Guangzhou, China.
authors.forename: Yundang
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences Guangzhou, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences Guangzhou, China.
authors.forename: Dandan
authors.initials: D
authors.lastname: Chen
keywords: Cr(VI) reduction; Shewanella oneidensis MR-1; c-type cytochromes; incubation conditions; intact cells