Redox-Active Glyconanoparticles as Electron Shuttles for Mediated Electron Transfer with Bilirubin Oxidase in Solution

ABSTRACTThe current understanding of dissimilatory metal reduction is based primarily on isolates from the proteobacterial generaGeobacterandShewanella. However, environments undergoing active Fe(III) reduction often harbor less-well-studied phyla that are equally abundant. In this work, electrochemical techniques were used to analyze respiratory electron transfer by the only known Fe(III)-reducing representative of theAcidobacteria,Geothrix fermentans. In contrast to previously characterized metal-reducing bacteria, which typically reach maximal rates of respiration at electron acceptor potentials of 0 V versus standard hydrogen electrode (SHE),G. fermentansrequired potentials as high as 0.55 V to respire at its maximum rate. In addition,G. fermentanssecreted two different soluble redox-active electron shuttles with separate redox potentials (−0.2 V and 0.3 V). The compound with the lower midpoint potential, responsible for 20 to 30% of electron transfer activity, was riboflavin. The behavior of the higher-potential compound was consistent with hydrophilic UV-fluorescent molecules previously found inG. fermentanssupernatants. Both electron shuttles were also produced when cultures were grown with Fe(III), but not when fumarate was the electron acceptor. This study reveals thatGeothrixis able to take advantage of higher-redox-potential environments, demonstrates that secretion of flavin-based shuttles is not confined toShewanella, and points to the existence of high-potential-redox-active compounds involved in extracellular electron transfer. Based on differences between the respiratory strategies ofGeothrixandGeobacter, these two groups of bacteria could exist in distinctive environmental niches defined by redox potential.

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Mediated Electron Transfer at Redox Active Monolayers

Sensors ◽

10.3390/s10700215 ◽

2001 ◽

Vol 1 (7) ◽

pp. 215-228 ◽

Cited By ~ 8

Author(s):

Michael Lyons

Keyword(s):

Electron Transfer ◽

Redox Active ◽

Mediated Electron Transfer

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Extracellular DNA promotes efficient extracellular electron transfer by pyocyanin in Pseudomonas aeruginosa biofilms

10.1101/2019.12.12.872085 ◽

2019 ◽

Cited By ~ 1

Author(s):

Scott H. Saunders ◽

Edmund C.M. Tse ◽

Matthew D. Yates ◽

Fernanda Jiménez Otero ◽

Scott A. Trammell ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Electron Transfer ◽

Redox Reactions ◽

Extracellular Dna ◽

Extracellular Electron Transfer ◽

Bacterial Biofilms ◽

Active Metabolites ◽

Electron Shuttles ◽

Redox Active

SUMMARYExtracellular electron transfer (EET), the process whereby cells access electron acceptors or donors that reside many cell lengths away, enables metabolic activity by microorganisms, particularly under oxidant-limited conditions that occur in multicellular bacterial biofilms. Although different mechanisms underpin this process in select organisms, a widespread strategy involves extracellular electron shuttles, redox-active metabolites that are secreted and recycled by diverse bacteria. How these shuttles catalyze electron transfer within biofilms without being lost to the environment has been a long-standing question. Here, we show that phenazine electron shuttles mediate efficient EET through interactions with extracellular DNA (eDNA) in Pseudomonas aeruginosa biofilms, which are important in nature and disease. Retention of pyocyanin (PYO) and phenazine carboxamide in the biofilm matrix is facilitated by binding to eDNA. In vitro, different phenazines can exchange electrons in the presence or absence of DNA and phenazines can participate directly in redox reactions through DNA; the biofilm eDNA can also support rapid electron transfer between redox active intercalators. Electrochemical measurements of biofilms indicate that retained PYO supports an efficient redox cycle with rapid EET and slow loss from the biofilm. Together, these results establish that eDNA facilitates phenazine metabolic processes in P. aeruginosa biofilms, suggesting a model for how extracellular electron shuttles achieve retention and efficient EET in biofilms.

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Comparison of Direct and Mediated Electron Transfer for Bilirubin Oxidase from Myrothecium Verrucaria. Effects of Inhibitors and Temperature on the Oxygen Reduction Reaction

Catalysts ◽

10.3390/catal9121056 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1056 ◽

Cited By ~ 4

Author(s):

Riccarda Antiochia ◽

Diego Oyarzun ◽

Julio Sánchez ◽

Federico Tasca

Keyword(s):

Electron Transfer ◽

Oxygen Reduction Reaction ◽

Oxygen Reduction ◽

Direct Electron Transfer ◽

Reduction Reaction ◽

Redox Mediator ◽

Bilirubin Oxidase ◽

Myrothecium Verrucaria ◽

Physiological Conditions ◽

Mediated Electron Transfer

One of the processes most studied in bioenergetic systems in recent years is the oxygen reduction reaction (ORR). An important challenge in bioelectrochemistry is to achieve this reaction under physiological conditions. In this study, we used bilirubin oxidase (BOD) from Myrothecium verrucaria, a subclass of multicopper oxidases (MCOs), to catalyse the ORR to water via four electrons in physiological conditions. The active site of BOD, the T2/T3 cluster, contains three Cu atoms classified as T2, T3α, and T3β depending on their spectroscopic characteristics. A fourth Cu atom; the T1 cluster acts as a relay of electrons to the T2/T3 cluster. Graphite electrodes were modified with BOD and the direct electron transfer (DET) to the enzyme, and the mediated electron transfer (MET) using an osmium polymer (OsP) as a redox mediator, were compared. As a result, an alternative resting (AR) form was observed in the catalytic cycle of BOD. In the absence and presence of the redox mediator, the AR direct reduction occurs through the trinuclear site (TNC) via T1, specifically activated at low potentials in which T2 and T3α of the TNC are reduced and T3β is oxidized. A comparative study between the DET and MET was conducted at various pH and temperatures, considering the influence of inhibitors like H2O2, F−, and Cl−. In the presence of H2O2 and F−, these bind to the TNC in a non-competitive reversible inhibition of O2. Instead; Cl− acts as a competitive inhibitor for the electron donor substrate and binds to the T1 site.

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Electricity from lignocellulosic substrates by thermophilic Geobacillus species

Scientific Reports ◽

10.1038/s41598-020-72866-y ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Namita Shrestha ◽

Abhilash Kumar Tripathi ◽

Tanvi Govil ◽

Rajesh Kumar Sani ◽

Meltem Urgun-Demirtas ◽

...

Keyword(s):

Electron Transfer ◽

Cyclic Voltammetry ◽

Lignocellulosic Biomass ◽

Microbial Fuel Cells ◽

Nadh Dehydrogenase ◽

Type Ii ◽

Lignocellulosic Substrates ◽

Redox Active ◽

Mediated Electron Transfer ◽

Exogenous Enzymes

Abstract Given our vast lignocellulosic biomass reserves and the difficulty in bioprocessing them without expensive pretreatment and fuel separation steps, the conversion of lignocellulosic biomass directly into electricity would be beneficial. Here we report the previously unexplored capabilities of thermophilic Geobacillus sp. strain WSUCF1 to generate electricity directly from such complex substrates in microbial fuel cells. This process obviates the need for exogenous enzymes and redox mediator supplements. Cyclic voltammetry and chromatography studies revealed the electrochemical signatures of riboflavin molecules that reflect mediated electron transfer capabilities of strain WSUCF1. Proteomics and genomics analysis corroborated that WSUCF1 biofilms uses type-II NADH dehydrogenase and demethylmenaquinone methyltransferase to transfer the electrons to conducting anode via the redox active pheromone lipoproteins localized at the cell membrane.

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