Making protons tag along with electrons

2021 ◽  
Vol 478 (23) ◽  
pp. 4093-4097
Author(s):  
Matthew J. Guberman-Pfeffer ◽  
Nikhil S. Malvankar
Keyword(s):  
Proton Transfer ◽  
Soil Microbes ◽  
Electron Acceptors ◽  
Geobacter Sulfurreducens ◽  
Harsh Environments ◽  
Extracellular Electron Transfer ◽  
Necessary Condition ◽  
Engineering Strategy ◽  
Electron Proton Transfer

Every living cell needs to get rid of leftover electrons when metabolism extracts energy through the oxidation of nutrients. Common soil microbes such as Geobacter sulfurreducens live in harsh environments that do not afford the luxury of soluble, ingestible electron acceptors like oxygen. Instead of resorting to fermentation, which requires the export of reduced compounds (e.g. ethanol or lactate derived from pyruvate) from the cell, these organisms have evolved a means to anaerobically respire by using nanowires to export electrons to extracellular acceptors in a process called extracellular electron transfer (EET) [ 1]. Since 2005, these nanowires were thought to be pili filaments [ 2]. But recent studies have revealed that nanowires are composed of multiheme cytochromes OmcS [ 3, 4] and OmcZ [ 5] whereas pili remain inside the cell during EET and are required for the secretion of nanowires [ 6]. However, how electrons are passed to these nanowires remains a mystery ( Figure 1A). Periplasmic cytochromes (Ppc) called PpcA-E could be doing the job, but only two of them (PpcA and PpcD) can couple electron/proton transfer — a necessary condition for energy generation. In a recent study, Salgueiro and co-workers selectively replaced an aromatic with an aliphatic residue to couple electron/proton transfer in PpcB and PpcE (Biochem. J. 2021, 478 (14): 2871–2887). This significant in vitro success of their protein engineering strategy may enable the optimization of bioenergetic machinery for bioenergy, biofuels, and bioelectronics applications.

scholarly journals Rational design of electron/proton transfer mechanisms in the exoelectrogenic bacteria Geobacter sulfurreducens

2021 ◽  
Author(s):  
Marta A. Silva ◽  
Pilar C. Portela ◽  
Carlos A Salgueiro
Keyword(s):  
Proton Transfer ◽  
Rational Design ◽  
Atp Synthesis ◽  
Geobacter Sulfurreducens ◽  
Bohr Effect ◽  
Extracellular Electron Transfer ◽  
Electrochemical Gradient ◽  
Ph Range ◽  
Electron Proton Transfer ◽  
Redox Bohr Effect

The redox potential values of cytochromes can be modulated by the protonation/deprotonation of neighbor groups (redox-Bohr effect), a mechanism that permits the proteins to couple electron/proton transfer. In the respiratory chains, this effect is particularly relevant if observed in the physiological pH range, as it may contribute to the electrochemical gradient for ATP synthesis. A constitutively produced family of five triheme cytochromes (PpcA−E) from the bacterium Geobacter sulfurreducens plays a crucial role in extracellular electron transfer, a hallmark that permits this bacterium to be explored for several biotechnological applications. Two members of this family (PpcA and PpcD) couple electron/proton transfer in the physiological pH range, a feature not shared with PpcB and PpcE. That ability is crucial for G. sulfurreducens’ growth in Fe(III)-reducing habitats since extra contributors to the electrochemical gradient are needed. It was postulated that the redox-Bohr effect is determined by the nature of residue 6, a leucine in PpcA/PpcD and a phenylalanine in PpcB/PpcE. To confirm this hypothesis, Phe6 was replaced by leucine in PpcB and PpcE. The functional properties of these mutants were investigated by NMR and UV-visible spectroscopy to assess their capability to couple electron/proton transfer in the physiological pH range. The results obtained showed that the mutants have an increased redox-Bohr effect and are now capable of coupling electron/proton transfer. This confirms the determinant role of the nature of residue 6 in the modulation of the redox-Bohr effect in this family of cytochromes, opening routes to engineer Geobacter cells with improved biomass production.

scholarly journals Modulation of the Redox Potential and Electron/Proton Transfer Mechanisms in the Outer Membrane Cytochrome OmcF From Geobacter sulfurreducens

2020 ◽  
Vol 10 ◽  
Author(s):  
Liliana R. Teixeira ◽  
Cristina M. Cordas ◽  
Marta P. Fonseca ◽  
Norma E. C. Duke ◽  
Phani Raj Pokkuluri ◽  
...  
Keyword(s):  
Proton Transfer ◽  
Redox Potential ◽  
Outer Membrane ◽  
Geobacter Sulfurreducens ◽  
Electron Proton Transfer ◽  
Transfer Mechanisms

scholarly journals An Inner Membrane Cytochrome Required Only for Reduction of High Redox Potential Extracellular Electron Acceptors

mBio ◽  
2014 ◽  
Vol 5 (6) ◽  
Author(s):  
Caleb E. Levar ◽  
Chi Ho Chan ◽  
Misha G. Mehta-Kolte ◽  
Daniel R. Bond
Keyword(s):  
Electron Transfer ◽  
Electron Acceptors ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Redox Potentials ◽  
Inner Membrane ◽  
Content Type ◽  
Transfer Strategies ◽  
Reducing Bacteria ◽  
Metal Reducing Bacteria

ABSTRACTDissimilatory metal-reducing bacteria, such asGeobacter sulfurreducens, transfer electrons beyond their outer membranes to Fe(III) and Mn(IV) oxides, heavy metals, and electrodes in electrochemical devices. In the environment, metal acceptors exist in multiple chelated and insoluble forms that span a range of redox potentials and offer different amounts of available energy. Despite this, metal-reducing bacteria have not been shown to alter their electron transfer strategies to take advantage of these energy differences. Disruption ofimcH, encoding an inner membranec-type cytochrome, eliminated the ability ofG. sulfurreducensto reduce Fe(III) citrate, Fe(III)-EDTA, and insoluble Mn(IV) oxides, electron acceptors with potentials greater than 0.1 V versus the standard hydrogen electrode (SHE), but theimcHmutant retained the ability to reduce Fe(III) oxides with potentials of ≤−0.1 V versus SHE. TheimcHmutant failed to grow on electrodes poised at +0.24 V versus SHE, but switching electrodes to −0.1 V versus SHE triggered exponential growth. At potentials of ≤−0.1 V versus SHE, both the wild type and theimcHmutant doubled 60% slower than at higher potentials. Electrodes poised even 100 mV higher (0.0 V versus SHE) could not triggerimcHmutant growth. These results demonstrate thatG. sulfurreducenspossesses multiple respiratory pathways, that some of these pathways are in operation only after exposure to low redox potentials, and that electron flow can be coupled to generation of different amounts of energy for growth. The redox potentials that trigger these behaviors mirror those of metal acceptors common in subsurface environments whereGeobacteris found.IMPORTANCEInsoluble metal oxides in the environment represent a common and vast reservoir of energy for respiratory microbes capable of transferring electrons across their insulating membranes to external acceptors, a process termed extracellular electron transfer. Despite the global biogeochemical importance of metal cycling and the ability of such organisms to produce electricity at electrodes, fundamental gaps in the understanding of extracellular electron transfer biochemistry exist. Here, we describe a conserved inner membrane redox protein inGeobacter sulfurreducenswhich is required only for electron transfer to high-potential compounds, and we show thatG. sulfurreducenshas the ability to utilize different electron transfer pathways in response to the amount of energy available in a metal or electrode distant from the cell.

scholarly journals Role of Met58 in the regulation of electron/proton transfer in trihaem cytochrome PpcA from Geobacter sulfurreducens

2012 ◽  
Vol 33 (1) ◽  
Author(s):  
Leonor Morgado ◽  
Joana M. Dantas ◽  
Telma Simões ◽  
Yuri Y. Londer ◽  
P. Raj Pokkuluri ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Solvent Accessibility ◽  
Potential Gradient ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Redox States ◽  
Electron Transfer Pathways ◽  
Electron Proton Transfer ◽  
Fine Tune

The bacterium Gs (Geobacter sulfurreducens) is capable of oxidizing a large variety of compounds relaying electrons out of the cytoplasm and across the membranes in a process designated as extracellular electron transfer. The trihaem cytochrome PpcA is highly abundant in Gs and is most probably the reservoir of electrons destined for the outer surface. In addition to its role in electron transfer pathways, we have previously shown that this protein could perform e−/H+ energy transduction. This mechanism is achieved by selecting the specific redox states that the protein can access during the redox cycle and might be related to the formation of proton electrochemical potential gradient across the periplasmic membrane. The regulatory role of haem III in the functional mechanism of PpcA was probed by replacing Met58, a residue that controls the solvent accessibility of haem III, with serine, aspartic acid, asparagine or lysine. The data obtained from the mutants showed that the preferred e−/H+ transfer pathway observed for PpcA is strongly dependent on the reduction potential of haem III. It is striking to note that one residue can fine tune the redox states that can be accessed by the trihaem cytochrome enough to alter the functional pathways.

scholarly journals Identifying volatile in vitro biomarkers for oral bacteria with proton-transfer-reaction mass spectrometry and gas chromatography–mass spectrometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Kajsa Roslund ◽  
Markku Lehto ◽  
Pirkko Pussinen ◽  
Kari Hartonen ◽  
Per-Henrik Groop ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Proton Transfer ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Oral Bacteria ◽  
Gas Chromatography Mass Spectrometry ◽  
Volatile Analysis ◽  
Bacterial Volatiles

AbstractWe have measured the volatile fingerprints of four pathogenic oral bacteria connected to periodontal disease and dental abscess: Porphyromonas gingivalis (three separate strains), Prevotella intermedia, Prevotella nigrescens and Tannerella forsythia. Volatile fingerprints were measured in vitro from the headspace gas of the bacteria cultured on agar. Concrete identification of new and previously reported bacterial volatiles were performed by a combination of solid phase microextraction (SPME) and offline gas chromatography–mass spectrometry (GC–MS). We also studied the effect of the reduced electric field strength (E/N) on the fragmentation patterns of bacterial volatiles in online proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). We aimed to discover possible new biomarkers for the studied oral bacteria, as well as to validate the combination of GC–MS and PTR-MS for volatile analysis. Some of the most promising compounds produced include: 1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), indole, and a cascade of sulphur compounds, such as methanethiol, dimethyl disulphide (DMDS) and dimethyl trisulphide (DMTS). We also found that several compounds, especially alcohols, aldehydes and esters, fragment significantly with the PTR-MS method, when high E/N values are used. We conclude that the studied oral bacteria can be separated by their volatile fingerprints in vitro, which could have importance in clinical and laboratory environments. In addition, using softer ionization conditions can improve the performance of the PTR-MS method in the volatile analysis of certain compounds.

scholarly journals Comparative insights into genome signatures of ferric iron oxide- and anode-stimulated Desulfuromonas spp. strains

BMC Genomics ◽  
2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Yong Guo ◽  
Tomo Aoyagi ◽  
Tomoyuki Hori
Keyword(s):  
Iron Oxide ◽  
Genome Rearrangement ◽  
Ferric Iron ◽  
Electron Acceptors ◽  
Extracellular Electron Transfer ◽  
Redox Potentials ◽  
Bacterial Strains ◽  
Biosynthesis Gene Cluster ◽  
Genomic Signatures ◽  
Flagellar Biosynthesis

Abstract Background Halotolerant Fe (III) oxide reducers affiliated in the family Desulfuromonadaceae are ubiquitous and drive the carbon, nitrogen, sulfur and metal cycles in marine subsurface sediment. Due to their possible application in bioremediation and bioelectrochemical engineering, some of phylogenetically close Desulfuromonas spp. strains have been isolated through enrichment with crystalline Fe (III) oxide and anode. The strains isolated using electron acceptors with distinct redox potentials may have different abilities, for instance, of extracellular electron transport, surface recognition and colonization. The objective of this study was to identify the different genomic signatures between the crystalline Fe (III) oxide-stimulated strain AOP6 and the anode-stimulated strains WTL and DDH964 by comparative genome analysis. Results The AOP6 genome possessed the flagellar biosynthesis gene cluster, as well as diverse and abundant genes involved in chemotaxis sensory systems and c-type cytochromes capable of reduction of electron acceptors with low redox potentials. The WTL and DDH964 genomes lacked the flagellar biosynthesis cluster and exhibited a massive expansion of transposable gene elements that might mediate genome rearrangement, while they were deficient in some of the chemotaxis and cytochrome genes and included the genes for oxygen resistance. Conclusions Our results revealed the genomic signatures distinctive for the ferric iron oxide- and anode-stimulated Desulfuromonas spp. strains. These findings highlighted the different metabolic abilities, such as extracellular electron transfer and environmental stress resistance, of these phylogenetically close bacterial strains, casting light on genome evolution of the subsurface Fe (III) oxide reducers.

scholarly journals Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

2015 ◽  
Vol 112 (16) ◽  
pp. 4935-4940 ◽  
Author(s):  
Na Song ◽  
Javier J. Concepcion ◽  
Robert A. Binstead ◽  
Jennifer A. Rudd ◽  
Aaron K. Vannucci ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Acceptor ◽  
Half Time ◽  
X Ray ◽  
X Ray Crystallography ◽  
Buffer Base ◽  
Electron Proton Transfer ◽  
C Nmr

In aqueous solution above pH 2.4 with 4% (vol/vol) CH3CN, the complex [RuII(bda)(isoq)2] (bda is 2,2′-bipyridine-6,6′-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [RuII(CO2-bpy-CO2−)(isoq)2(NCCH3)], as shown by 1H and 13C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO43–, the calculated half-time for water oxidation is ∼7 μs. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom–proton transfer (APT) or concerted electron–proton transfer (EPT) pathways.

Geobacter sulfurreducens adapts to low electrode potential for extracellular electron transfer

2016 ◽  
Vol 191 ◽  
pp. 743-749 ◽  
Author(s):  
Luo Peng ◽  
Xiao-Ting Zhang ◽  
Jie Yin ◽  
Shuo-Yuan Xu ◽  
Yong Zhang ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electrode Potential ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer

scholarly journals Looking For Polycyclic Aromatic Hydrocarbon Metabolizing Microorganisms In The Oral Cavity of Smokers

2021 ◽  
Author(s):  
Lin Tao ◽  
M. Paul Chiarelli ◽  
Sylvia I. Pavlova ◽  
Joel L. Schwartz ◽  
James V. DeFrancesco ◽  
...  
Keyword(s):  
Oral Cavity ◽  
Large Scale ◽  
Soil Microbes ◽  
Polycyclic Aromatic ◽  
Pah Exposure ◽  
Resistant Strains ◽  
Oral Microbes ◽  
Bacteria And Fungi

Abstract Certain soil microbes resist and metabolize polycyclic aromatic hydrocarbons (PAHs). The same is true for certain skin microbes. Oral microbes have the potential to oxidize tobacco PAHs to increase their ability to cause cancer. We hypothesized that oral microbes that resist high levels of PAH in smokers exist and can be identified based on their resistance to PAHs. We isolated bacteria and fungi that survived long term in minimal media with PAHs as the sole carbon source from the oral cavity in 11 of 14 smokers and only 1 of 6 nonsmokers. Of bacteria genera that included species that survived harsh PAH exposure in vitro, all were found at trace levels on the oral mucosa, except for Staphylococcus and Actinomyces. Two PAH-resistant strains of Candida albicans (C. albicans) were isolated from smokers. C. albicans is found orally at high levels in tobacco users and some Candida species can metabolize PAHs. The two C. albicans strains were tested for metabolism of two model PAH substrates, pyrene and phenanthrene. The result showed that the PAH-resistant C. albicans strains did not metabolize the two PAHs. In conclusion, evidence for large scale oral microbial metabolism of tobacco PAHs by common oral microbes remains lacking.

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