Name: electrochemical detection of deuterium kinetic isotope effect on extracellular electron transport in shewanella oneidensis mr-1
Uploaded: 2018-04-16T14:30:00
Description: Watch this Scientific Journal Video about Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1 at JoVE.com

This work was financially supported by a Grant-in-Aid for Specially Promoted Research from the Japan Society for Promotion of Science (JSPS) KAKENHI Grant Number 24000010, 17H04969, and JP17J02602, the US Office of Naval Research Global (N62909-17-1-2038). Y.T. is a JSPS Research Fellow and supported by JSPS through the Program for Leading Graduate Schools (MERIT).

1. Formation of a Monolayer Biofilm of S. oneidensis MR-1 on an ITO Electrode (Figure 1)
NOTE: To prevent the contamination of the electrochemical reactor with other microbes, all the media, implements, and components of the electrochemical reactor should be sterilized in advance. When using S. oneidensis MR-1 cells and constructing the electrochemical reactors, all the procedures should be conducted on a clean bench.
<ol>
	<li>Cultivation of <...

<ol>
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T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Iron+corrosion+by+novel+anaerobic+microorganisms.">Iron corrosion by novel anaerobic microorganisms.</a> Nature. 427 (6977), 829-832 (2004).</li><li>McGlynn, S. E., Chadwick, G. L., Kempes, C. P., Orphan, V. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+cell+activity+reveals+direct+electron+transfer+in+methanotrophic+consortia.">Single cell activity reveals direct electron transfer in methanotrophic consortia.</a> Nature. 526 (7574), 531-535 (2015).</li><li>Okamoto, A., Nakamura, R., Nealson, K. H., Hashimoto, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bound+Flavin+Model+Suggests+Similar+Electron-Transfer+Mechanisms+in+Shewanella+and+Geobacter.">Bound Flavin Model Suggests Similar Electron-Transfer Mechanisms in Shewanella and Geobacter.</a> Chemelectrochem. 1 (11), 1808-1812 (2014).</li><li>Okamoto, A., Hashimoto, K., Nealson, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flavin+Redox+Bifurcation+as+a+Mechanism+for+Controlling+the+Direction+of+Electron+Flow+during+Extracellular+Electron+Transfer.">Flavin Redox Bifurcation as a Mechanism for Controlling the Direction of Electron Flow during Extracellular Electron Transfer.</a> Angew. Chem. Int. 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Our whole-cell electrochemical assay has several technical advantages compared with protein electrochemistry. While protein purification requires multi-step time-consuming procedures, our whole-cell method takes one day of self-organized biofilm formation after cell culture. To achieve a stable interaction between OM c-Cyts and the electrode, we need only sterilization and cleaning of the electrode surface; it does not require electrode modification for organizing the orientation of proteins4</...

Electrochemical techniques to directly characterize a redox protein in an intact bacterial cell have recently emerged since the discovery of metal-reducing microbial strains, such as S. oneidensis MR-1 or Geobacter sulfurreducens PCA, which have outer membrane c-type cytochrome complexes (OM c-Cyts) exposed to the cell exterior1,2,3,4,5. The OM c-Cyts mediate electron transport from the respiratory chain to solid substrates located extracellularly. This transport is referred to as extracellular electron transport (EET)1,6 and is a critical process for emerging biotechnologies, such as microbial fuel cells6. Therefore, to understand the underlying EET kinetics and mechanisms, and its link to microbial physiology, OM c-Cyts have been investigated using whole-cell electrochemistry4,7, combined with microscopy8,9, spectroscopy10,11, and molecular biology2,4. In contrast, methods to investigate the impact of EET-associated cation transport, e.g., protons, on EET kinetics in living cells have been scarcely established, despite proton transport across bacterial membranes having a critical role in signaling, homeostasis, and energy production12,13,14. In the present study, we describe a technique to examine the impact of proton transport on EET kinetics in the S. oneidensis MR-1 cell using whole-cell electrochemical measurements, which requires the identification of the rate-limiting step in microbial current production15.
One direct way to evaluate the contribution of proton transport on the associated EET is the deuterium kinetic isotope effect (KIE). The KIE is observable as the change in electron transfer kinetics upon the replacement of protons with deuterium ions, which represents the impact of proton transport on electron transfer kinetics16. The theory of KIE itself has been well established using electrochemical measurements with purified enzymes17. However, since current production in S. oneidensis MR-1 results from multiple, diverse, and fluctuating processes18, one cannot simply identify EET as the rate-limiting process. To observe the KIE on proton transport processes coupled with EET, we need to confirm that the microbial current production is limited by electron transport via OM c-Cyts to the electrode. For this purpose, we replaced the supernatant solution with fresh medium containing a high concentration of lactate as an electron donor at the optimal pH and temperature conditions before KIE measurement; this replacement served two roles: (1) it enhanced the rate of the upstream metabolic processes compared to the EET, and (2) omitted the swimming cells in the supernatant released from the monolayer biofilm of S. oneidensis MR-1 on the working electrode (indium tin-doped oxide (ITO) electrode). The presented detailed protocol is intended to help new practitioners maintain and confirm that the EET process is the rate-determining step.

<table>
	<tbody>
		<tr>
			<td>Glass cylinder</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Custom-made, used as the electrochemical reactor</td>
		</tr>
		<tr>
			<td>PTFE cover and base</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Custom-made, used as a cover and a foundation of the electrochemical reactor</td>
		</tr>
		<tr>
			<td>Buthyl rubber</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Custom-made, inserted between each component of electrochemical reactor</td>
		</tr>
		<tr>
			<td>Septa</td>
			<td>GL Science</td>
			<td>3007-16101</td>
			<td>Used as an injection port of electrochemical reactor</td>
		</tr>
		<tr>
			<td>Indium tin-doped oxide (ITO) electrode</td>
			<td>GEOMATEC</td>
			<td>No.0001</td>
			<td>Used as a working electrode, 5&#937;/sq</td>
		</tr>
		<tr>
			<td>Ag/AgCl KCl saturated electrode</td>
			<td>HOKUTO DENKO</td>
			<td>HX-R5</td>
			<td>Used as a reference electrode, &#934;0.30mm</td>
		</tr>
		<tr>
			<td>Platinum wire</td>
			<td>The Nilaco Cooporation</td>
			<td>PT-351325</td>
			<td>Used as a counter electrode</td>
		</tr>
		<tr>
			<td>Luria-Bertani (LB) Broth, Miller</td>
			<td>Becton, Dichkinson and Company</td>
			<td>244620</td>
			<td>Medium for precultivation of S. oneidensis MR-1</td>
		</tr>
		<tr>
			<td>Bacto agar</td>
			<td>Becton, Dichkinson and Company</td>
			<td>214010</td>
			<td></td>
		</tr>
		<tr>
			<td>Anthraquinone-1-sulfonate (&#945;-AQS)</td>
			<td>TCI</td>
			<td>A1428</td>
			<td></td>
		</tr>
		<tr>
			<td>Flavin mononucleotide (FMN)</td>
			<td>Wako</td>
			<td>184-00831</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Wako</td>
			<td>191-01305</td>
			<td>Used for defined medium (DM)</td>
		</tr>
		<tr>
			<td>CaCl2 &#183; 2H2O</td>
			<td>Wako</td>
			<td>031-00435</td>
			<td>Used for DM</td>
		</tr>
		<tr>
			<td>NH4Cl</td>
			<td>Wako</td>
			<td>011-03015</td>
			<td>Used for DM</td>
		</tr>
		<tr>
			<td>MgCl2 &#183; 6H2O</td>
			<td>Wako</td>
			<td>135-00165</td>
			<td>Used for DM</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Wako</td>
			<td>191-01665</td>
			<td>Used for DM</td>
		</tr>
		<tr>
			<td>2-[4-(2-hydroxyethyl)-1-piperazinyl] ethanesulfonic acid (HEPES)</td>
			<td>DOJINDO</td>
			<td>346-08235</td>
			<td>Used for DM</td>
		</tr>
		<tr>
			<td>Sodium Lactate Solution</td>
			<td>Wako</td>
			<td>195-02305</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Yeast Extract</td>
			<td>Becton, Dichkinson and Company</td>
			<td>212750</td>
			<td></td>
		</tr>
		<tr>
			<td>Deuterium oxide (D, 99.9%)</td>
			<td>Cambridge Isotope Laboratories, Inc.</td>
			<td>DLM-4-PK</td>
			<td>Additive for kinetic isotope effect experiments</td>
		</tr>
		<tr>
			<td>Incubator</td>
			<td>TOKYO RIKAKIKAI CO. LTD.</td>
			<td>LTI-601SD</td>
			<td>Used for precultivation</td>
		</tr>
		<tr>
			<td>Shaker</td>
			<td>TAITEC</td>
			<td>NR-3</td>
			<td>Used for precultivation</td>
		</tr>
		<tr>
			<td>Autoclave machine</td>
			<td>TOMY SEIKO CO. LTD.</td>
			<td>LSX-500</td>
			<td>Used for sterilization of the electrochemical reactor and the medium</td>
		</tr>
		<tr>
			<td>Clean bench</td>
			<td>SANYO</td>
			<td>MCV-91BNF</td>
			<td>Used to prevent the contamination of the electrochemical reactor and the medium with other microbes</td>
		</tr>
		<tr>
			<td>Centrifuge separator</td>
			<td>Eppendorf</td>
			<td>5430R</td>
			<td>Rotational speed upto 6000&#215;g is required</td>
		</tr>
		<tr>
			<td>Nitrogen gas generator</td>
			<td>Puequ CO. LTD.</td>
			<td>PNTN-2</td>
			<td>Nitrogen gas cylinder can also be used instead of gas generator</td>
		</tr>
		<tr>
			<td>UV-vis spectrometer</td>
			<td>SHIMADZU</td>
			<td>UV-1800</td>
			<td>Used for optimization of cell density</td>
		</tr>
		<tr>
			<td>Potentiostat</td>
			<td>BioLogic</td>
			<td>VMP3</td>
			<td>Used for biofilm formation and kinetic isotope effect experiments</td>
		</tr>
		<tr>
			<td>Thermal water circulator</td>
			<td>AS ONE</td>
			<td>TR-1A</td>
			<td>Used for maintanance of temperature of electrochemcial reactor</td>
		</tr>
		<tr>
			<td>Faraday cage</td>
			<td>HOKUTO DENKO</td>
			<td>HS-201S</td>
			<td>Used for electrochemical experiments</td>
		</tr>
	</tbody>
</table>

electrochemical detection of deuterium kinetic isotope effect on extracellular electron transport in shewanella oneidensis mr-1

Direct electrochemical detection of c-type cytochrome complexes embedded in the bacterial outer membrane (outer membrane c-type cytochrome complexes; OM c-Cyts) has recently emerged as a novel whole-cell analytical method to characterize the bacterial electron transport from the respiratory chain to the cell exterior, referred to as the extracellular electron transport (EET). While the pathway and kinetics of the electron flow during the EET reaction have been investigated, a whole-cell electrochemical method to examine the impact of cation transport associated with EET has not yet been established. In the present study, an example of a biochemical technique to examine the deuterium kinetic isotope effect (KIE) on EET through OM c-Cyts using a model microbe, Shewanella oneidensis MR-1, is described. The KIE on the EET process can be obtained if the EET through OM c-Cyts acts as the rate-limiting step in the microbial current production. To that end, before the addition of D2O, the supernatant solution was replaced with fresh media containing a sufficient amount of the electron donor to support the rate of upstream metabolic reactions, and to remove the planktonic cells from a uniform monolayer biofilm on the working electrode. Alternative methods to confirm the rate-limiting step in microbial current production as EET through OM c-Cyts are also described. Our technique of a whole-cell electrochemical assay for investigating proton transport kinetics can be applied to other electroactive microbial strains.

After 25 h of potential application at +0.4 V (versus SHE), a monolayer biofilm was formed on the working electrode of ITO glass, which was previously confirmed by either a scanning electron microscopy or a confocal microscopy4. The representative time course of current production from the S. oneidensis MR-1 during the formation of a monolayer biofilm is shown in Figure 2. Although the current alters in every measurement, the ...

Watch this Scientific Journal Video about Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1 at JoVE.com

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

Here we present a protocol of whole-cell electrochemical experiments to study the contribution of proton transport to the rate of extracellular electron transport via the outer-membrane cytochromes complex in Shewanella oneidensis MR-1.

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

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

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