electrochemical-detection-deuterium-kinetic-isotope-effect-on

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in <em>Shewanella oneidensis</em> MR-1

Direct electrochemical detection of c-type cytochrome complexes embedded in the bacterial outer membrane (outer membrane c-type cytochrome complexes; OM ...

self-standing-electrochemical-set-up-to-enrich-anode-respiring

Self-standing Electrochemical Set-up to Enrich Anode-respiring Bacteria On-site

Anaerobic respiration coupled with electron transport to insoluble minerals (referred to as extracellular electron transport [EET]) is thought to be ...

National Institute for Materials Science

Outer-membrane -type cytochrome (OM Cyt) complexes in several genera of iron-reducing bacteria, such as  and , are capable of transporting electrons from the cell interior to extracellular solids as a terminal step of anaerobic respiration. The kinetics of this electron transport has implications for controlling the rate of microbial electron transport during bioenergy or biochemical production, iron corrosion, and natural mineral cycling. Herein, we review the findings from  and  studies examining electron transport kinetics through single OM Cyt complexes in  MR-1.  electron flux via a purified OM -Cyt complex, comprised of MtrA, B, and C proteins from  MR-1, embedded in a proteoliposome system is reported to be 10- to 100-fold faster compared with  estimates based on measurements of electron flux per cell and OM -Cyts density. As the proteoliposome system is estimated to have 10-fold higher cation flux via potassium channels than electrons, we speculate that the slower rate of electron-coupled cation transport across the OM is responsible for the significantly lower electron transport rate that is observed . As most studies to date have primarily focused on the energetics or kinetics of interheme electron hopping in OM -Cyts in this microbial electron transport mechanism, the proposed model involving cation transport provides new insight into the rate detemining step of EET, as well as the role of self-secreted flavin molecules bound to OM -Cyt and proton management for energy conservation and production in  MR-1.

Cation-limited kinetic model for microbial extracellular electron transport via an outer membrane cytochrome  complex.

Bacterial reduction of oxidized sulfur species (OSS) is critical for energy production in anaerobic marine subsurfaces. In organic-poor sediments, H has been considered as a major energy source for bacterial respiration. We identified outer-membrane cytochromes (OMCs) that are broadly conserved in sediment OSS-respiring bacteria and enable cells to directly use electrons from insoluble minerals via extracellular electron transport. Biochemical, transcriptomic, and microscopic analyses revealed that the identified OMCs were highly expressed on the surface of cells and nanofilaments in response to electron donor limitation. This electron uptake mechanism provides sufficient but minimum energy to drive the reduction of sulfate and other OSS. These results suggest a widespread mechanism for survival of OSS-respiring bacteria via electron uptake from solid minerals in energy-poor marine sediments.

Multi-heme cytochromes provide a pathway for survival in energy-limited environments.

While typically investigated as a microorganism capable of extracellular electron transfer to minerals or anodes,  MR-1 can also facilitate electron flow from a cathode to terminal electron acceptors, such as fumarate or oxygen, thereby providing a model system for a process that has significant environmental and technological implications. This work demonstrates that cathodic electrons enter the electron transport chain of  when oxygen is used as the terminal electron acceptor. The effect of electron transport chain inhibitors suggested that a proton gradient is generated during cathode oxidation, consistent with the higher cellular ATP levels measured in cathode-respiring cells than in controls. Cathode oxidation also correlated with an increase in the cellular redox (NADH/FMNH) pool determined with a bioluminescence assay, a proton uncoupler, and a mutant of proton-pumping NADH oxidase complex I. This work suggested that the generation of NADH/FMNH under cathodic conditions was linked to reverse electron flow mediated by complex I. A decrease in cathodic electron uptake was observed in various mutant strains, including those lacking the extracellular electron transfer components necessary for anodic-current generation. While no cell growth was observed under these conditions, here we show that cathode oxidation is linked to cellular energy acquisition, resulting in a quantifiable reduction in the cellular decay rate. This work highlights a potential mechanism for cell survival and/or persistence on cathodes, which might extend to environments where growth and division are severely limited. The majority of our knowledge of the physiology of extracellular electron transfer derives from studies of electrons moving to the exterior of the cell. The physiological mechanisms and/or consequences of the reverse processes are largely uncharacterized. This report demonstrates that when coupled to oxygen reduction, electrode oxidation can result in cellular energy acquisition. This respiratory process has potentially important implications for how microorganisms persist in energy-limited environments, such as reduced sediments under changing redox conditions. From an applied perspective, this work has important implications for microbially catalyzed processes on electrodes, particularly with regard to understanding models of cellular conversion of electrons from cathodes to microbially synthesized products.

ArticleTotal : 2	Year
Publication title	2018
Publication title	2018

Article	Year
Cation-limited kinetic model for microbial extracellular electron transport via an outer membrane cytochrome complex. Biophysics and physicobiology\| PubMed ID: 27924259	2016
Multi-heme cytochromes provide a pathway for survival in energy-limited environments. Science advances\| PubMed ID: 29464208	2018
Tracking Electron Uptake from a Cathode into Cells: Implications for Energy Acquisition from Solid-Substrate Electron Donors. mBio\| PubMed ID: 29487241	2018

Akihiro Okamoto

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