scholarly journals Basicity of N5 in semiquinone enhances the rate of respiratory electron outflow inShewanella oneidensisMR-1

2019 ◽  
Author(s):  
Yoshihide Tokunou ◽  
Keisuke Saito ◽  
Ryo Hasegawa ◽  
Kenneth H. Nealson ◽  
Kazuhito Hashimoto ◽  
...  
Keyword(s):  
Free Energy ◽  
Electron Transport ◽  
Nitrogen Atom ◽  
Outer Membrane ◽  
Diffusion Constant ◽  
Shewanella Oneidensis ◽  
Molecular Structures ◽  
Redox Potentials ◽  
Transport Reaction ◽  
Extracellular Electron Transport

AbstractExtracellular electron transport (EET) occurs in environmental iron-reducing bacteria and is mediated by an outer membrane multi-heme cytochrome complex (Cyts). It has critical implications for global mineral cycling and electrochemical microbial catalysis. The rate of EET mediated by multiple heme redox centers significantly increases in the presence of flavins and quinones. Their electron free energy does not entirely account for the fact that differential effects on EET rate enhancement vary significantly by factors ≥100. Here, we report on whole-cell electrochemical analysis ofShewanella oneidensisMR-1 using six flavin analogs and four quinones. We demonstrated that protonation of the nitrogen atom at position 5 (N5) of the isoalloxazine ring is essential for electron outflow acceleration as a bound non-covalent cofactor of Cyts. EET mediated by Cyts was accelerated at a rate dependent on pKa(N5). The EET rate largely decreased in response to the addition of deuterated water (D2O), while low concentration of D2O (4 %) had little impact on electron free energy difference of the heme and non-covalent bound cofactors, strongly suggesting that the protonation of N5 limits the rate of EET. Our findings directly link EET kinetics to proton transport reaction via N5 and provide a basis for the development of novel strategies for controlling EET-associated biological reactions.Significance statementThe potential of various small molecules such as flavins and quinones to enhance the rate of extracellular electron transport (EET) has been exploited to develop environmental energy conversion systems. Flavins and quinones have similar molecular structures but their abilities to enhance EET vary by >100× inShewanella oneidensisMR-1. These large differences are inconsistent with conventional models, which rely on redox potentials or diffusion constant of shuttling electron mediators. In this study, we demonstrated that the basicity of the nitrogen atom of the isoalloxazine ring (N5) enhances the rate of electron outflow when a flavin or quinone is a non-covalent cofactor ofS. oneidensisMR-1 outer membranec-type cytochromes.

scholarly journals Bacterial Nanowires of Shewanella Oneidensis MR-1 are Outer Membrane and Periplasmic Extensions of the Extracellular Electron Transport Components

2015 ◽  
Vol 108 (2) ◽  
pp. 368a ◽  
Author(s):  
Sahand Pirbadian ◽  
Sarah E. Barchinger ◽  
Kar Man Leung ◽  
Hye Suk Byun ◽  
Yamini Jangir ◽  
...  
Keyword(s):  
Electron Transport ◽  
Outer Membrane ◽  
Shewanella Oneidensis ◽  
Extracellular Electron Transport ◽  
Bacterial Nanowires

scholarly journals Outer Membrane c-Type Cytochromes OmcA and MtrC Play Distinct Roles in Enhancing the Attachment of Shewanella oneidensis MR-1 Cells to Goethite

2020 ◽  
Vol 86 (23) ◽  
Author(s):  
Xinxin Jing ◽  
Yichao Wu ◽  
Liang Shi ◽  
Caroline L. Peacock ◽  
Noha Mohamed Ashry ◽  
...  
Keyword(s):  
Cell Surface ◽  
Outer Membrane ◽  
Interfacial Reaction ◽  
Contact Area ◽  
Protein Structures ◽  
Shewanella Oneidensis ◽  
Molecular Structures ◽  
Attractive Force ◽  
Extracellular Electron Transfer ◽  
Content Type

ABSTRACT 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. IMPORTANCE Shewanella 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.

scholarly journals Ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryotomography

2018 ◽  
Vol 115 (14) ◽  
pp. E3246-E3255 ◽  
Author(s):  
Poorna Subramanian ◽  
Sahand Pirbadian ◽  
Mohamed Y. El-Naggar ◽  
Grant J. Jensen
Keyword(s):  
Electron Microscopy ◽  
Electron Transport ◽  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Shewanella Oneidensis ◽  
Extracellular Electron Transfer ◽  
Field Calculation ◽  
Microscopy Imaging ◽  
Electron Cryotomography ◽  
Bacterial Nanowires

Bacterial nanowires have garnered recent interest as a proposed extracellular electron transfer (EET) pathway that links the bacterial electron transport chain to solid-phase electron acceptors away from the cell. Recent studies showed that Shewanella oneidensis MR-1 produces outer membrane (OM) and periplasmic extensions that contain EET components and hinted at their possible role as bacterial nanowires. However, their fine structure and distribution of cytochrome electron carriers under native conditions remained unclear, making it difficult to evaluate the potential electron transport (ET) mechanism along OM extensions. Here, we report high-resolution images of S. oneidensis OM extensions, using electron cryotomography (ECT). We developed a robust method for fluorescence light microscopy imaging of OM extension growth on electron microscopy grids and used correlative light and electron microscopy to identify and image the same structures by ECT. Our results reveal that S. oneidensis OM extensions are dynamic chains of interconnected outer membrane vesicles (OMVs) with variable dimensions, curvature, and extent of tubulation. Junction densities that potentially stabilize OMV chains are seen between neighboring vesicles in cryotomograms. By comparing wild type and a cytochrome gene deletion mutant, our ECT results provide the likely positions and packing of periplasmic and outer membrane proteins consistent with cytochromes. Based on the observed cytochrome packing density, we propose a plausible ET path along the OM extensions involving a combination of direct hopping and cytochrome diffusion. A mean-field calculation, informed by the observed ECT cytochrome density, supports this proposal by revealing ET rates on par with a fully packed cytochrome network.

scholarly journals Proton Transport in the Outer-Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport

2017 ◽  
Vol 56 (31) ◽  
pp. 9082-9086 ◽  
Author(s):  
Akihiro Okamoto ◽  
Yoshihide Tokunou ◽  
Shafeer Kalathil ◽  
Kazuhito Hashimoto
Keyword(s):  
Electron Transport ◽  
Outer Membrane ◽  
Proton Transport ◽  
Extracellular Electron Transport
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