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Effects of bio-Au nanoparticles on electrochemical activity of Shewanella oneidensis wild type and ?omcA/mtrC mutant.

ABSTRACT: Both Shewanella oneidensis MR-1 wild type and its mutant ?omcA/mtrC are capable of transforming Au(III) into Au nanoparticles (AuNPs). Cyclic voltammetry reveals a decrease in redox current after the wild type is exposed to Au(III) but an increase in oxidation current for the mutant. The peak current of the wild type is much higher than that of the mutant before the exposure of Au(III), but lower than that of the mutant after the formation of AuNPs. This suggests that damage to the electron transfer chain in the mutant could be repaired by AuNPs to a certain extent. Spectroscopy and SDS-PAGE analysis indicate a decrease in cell protein content after the formation of AuNPs, which provides a convenient way to detect intracellular information on cells.

SUBMITTER: Wu R

PROVIDER: S-EPMC3837306 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Effects of bio-Au nanoparticles on electrochemical activity of Shewanella oneidensis wild type and ΔomcA/mtrC mutant.

Wu Ranran R Cui Li L Chen Lixiang L Wang Chao C Cao Changli C Sheng Guoping G Yu Hanqing H Zhao Feng F

Scientific reports 20131122

Both Shewanella oneidensis MR-1 wild type and its mutant ΔomcA/mtrC are capable of transforming Au(III) into Au nanoparticles (AuNPs). Cyclic voltammetry reveals a decrease in redox current after the wild type is exposed to Au(III) but an increase in oxidation current for the mutant. The peak current of the wild type is much higher than that of the mutant before the exposure of Au(III), but lower than that of the mutant after the formation of AuNPs. This suggests that damage to the electron tran ...[more]

PMID: 24264440

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Project description:The outer membrane c-type cytochromes (c-Cyts) OmcA and MtrC in Shewanella are key terminal reductases that bind and transfer electrons directly to iron (hydr)oxides. Although the amounts of OmcA and MtrC at the cell surface and their molecular structures are largely comparable, MtrC is known to play a more important role in dissimilatory iron reduction. To explore the roles of these outer membrane c-Cyts in the interaction of Shewanella oneidensis MR-1 with iron oxides, the processes of attachment of S. oneidensis MR-1 wild type and c-type cytochrome-deficient mutants (the ΔomcA, ΔmtrC, and ΔomcA ΔmtrC mutants) to goethite are compared via quartz crystal microbalance with dissipation monitoring (QCM-D). Strains with OmcA exhibit a rapid initial attachment. The quantitative model for QCM-D responses reveals that MtrC enhances the contact area and contact elasticity of cells with goethite by more than one and two times, respectively. In situ attenuated total reflectance Fourier transform infrared two-dimensional correlation spectroscopic (ATR-FTIR 2D-CoS) analysis shows that MtrC promotes the initial interfacial reaction via an inner-sphere coordination. Atomic force microscopy (AFM) analysis demonstrates that OmcA enhances the attractive force between cells and goethite by about 60%. As a result, OmcA contributes to a higher attractive force with goethite and induces a rapid short-term attachment, while MtrC is more important in the longer-term interaction through an enhanced contact area, which promotes interfacial reactions. These results reveal that c-Cyts OmcA and MtrC adopt different mechanisms for enhancing the attachment of S. oneidensis MR-1 cells to goethite. It improves our understanding of the function of outer membrane c-Cyts and the influence of cell surface macromolecules in cell-mineral interactions.IMPORTANCEShewanella species are one group of versatile and widespread dissimilatory iron-reducing bacteria, which are capable of respiring insoluble iron minerals via six multiheme c-type cytochromes. Outer membrane c-type cytochromes (c-Cyts) OmcA and MtrC are the terminal reductases in this pathway and have comparable protein structures. In this study, we elucidate the different roles of OmcA and MtrC in the interaction of S. oneidensis MR-1 with goethite at the whole-cell level. OmcA confers enhanced affinity toward goethite and results in rapid attachment. Meanwhile, MtrC significantly increases the contact area of bacterial cells with goethite and promotes the interfacial reaction, which may explain its central role in extracellular electron transfer. This study provides novel insights into the role of bacterial surface macromolecules in the interfacial interaction of bacteria with minerals, which is critical to the development of a comprehensive understanding of cell-mineral interactions.

Project description:UnlabelledOxidative stresses triggered by reactive oxygen species (ROS) that damage various cellular components are unavoidable for virtually all living organisms. In defense, microorganisms have evolved sophisticated mechanisms to sense, respond to, and battle against ROS. Shewanella oneidensis, an important research model for applied and environmental microbes, employs OxyR to mediate the response to H2O2 by derepressing the production of the major H2O2 scavenger KatB as a major means toward these goals. Surprisingly, despite enhanced H2O2 degradation, the oxyR mutant carries a viability deficiency phenotype (plating defect), which can be suppressed by the addition of exogenous iron species. Experiments showed that the defect was not due to iron starvation. Rather, multiple lines of evidence suggested that H2O2 generated abiotically in lysogeny broth (LB) is responsible for the defect by quickly killing mutant cells. We then showed that the iron species suppressed the plating defect by two distinct mechanisms, either as an H2O2 scavenger without involving living cells or as an environmental cue to stimulate an OxyR-independent response to help cells cope with oxidative stress. Based on the suppression of the plating defect by overproduction of H2O2 scavengers in vivo, we propose that cellular components that are vulnerable to H2O2 and responsible for the defect may reside outside the cytoplasm.ImportanceIn bacteria, OxyR is the major regulator controlling the cellular response to H2O2. The loss of OxyR results in reduced viability in many species, but the underlying mechanism is unknown. We showed in S. oneidensis that this defect was due to H2O2 generated abiotically in LB. We then showed that this defect could be corrected by the addition of Fe(2+) or catalase to the LB or increased intracellular production of catalase. Further analyses revealed that Fe(2+) was able not only to decompose H2O2 directly but also to stimulate the activity of OxyR-independent H2O2-scavenging enzymes. Our data indicate that iron species play a previously underappreciated role in protecting cells from H2O2 in environments.

Dataset Information

Effects of bio-Au nanoparticles on electrochemical activity of Shewanella oneidensis wild type and ?omcA/mtrC mutant.

Publications

Effects of bio-Au nanoparticles on electrochemical activity of Shewanella oneidensis wild type and ΔomcA/mtrC mutant.

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