Redox potential as a master variable controlling pathways of metal reduction byGeobacter sulfurreducens

AbstractGeobacter sulfurreducensuses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of −0.10 V vs. the Standard Hydrogen Electrode (SHE), while the ImcH-dependent pathway operates only above this value. Here, we provide evidence thatG. sulfurreducensalso requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)- (oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment.

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Geobacter sulfurreducens inner membrane cytochrome CbcBA controls electron transfer and growth yield near the energetic limit of respiration

10.1101/2021.04.15.440034 ◽

2021 ◽

Author(s):

Komal Joshi ◽

Chi Ho Chan ◽

Daniel R. Bond

Keyword(s):

Electron Transfer ◽

Redox Potential ◽

Growth Yield ◽

Growth Efficiency ◽

Geobacter Sulfurreducens ◽

Redox Potentials ◽

Hydrogen Electrode ◽

Highly Expressed Genes ◽

Reducing Bacteria ◽

Transfer Chain

AbstractGeobacter sulfurreducens utilizes extracellular electron acceptors such as Mn(IV), Fe(III), syntrophic partners, and electrodes that vary from +0.4 to −0.3 V vs. Standard Hydrogen Electrode (SHE), representing a potential energy span that should require a highly branched electron transfer chain. Here we describe CbcBA, a bc-type cytochrome essential near the thermodynamic limit of respiration when acetate is the electron donor. Mutants lacking cbcBA ceased Fe(III) reduction at −0.21 V vs. SHE, could not transfer electrons to electrodes between −0.21 and −0.28 V, and could not reduce the final 10% – 35% of Fe(III) minerals. As redox potential decreased during Fe(III) reduction, cbcBA was induced with the aid of the regulator BccR to become one of the most highly expressed genes in G. sulfurreducens. Growth yield (CFU/mM Fe(II)) was 112% of WT in ΔcbcBA, and deletion of cbcL (a different bc-cytochrome essential near −0.15 V) in ΔcbcBA increased yield to 220%. Together with ImcH, which is required at high redox potentials, CbcBA represents a third cytoplasmic membrane oxidoreductase in G. sulfurreducens. This expanding list shows how these important metal-reducing bacteria may constantly sense redox potential to adjust growth efficiency in changing environments.

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Isolation and Genomic Characterization of Desulfuromonas soudanensis WTL, a Metal- and Electrode-Reducing Bacterium from Anoxic Deep Subsurface Brine

10.1101/047530 ◽

2016 ◽

Author(s):

Jonathan P. Badalamenti ◽

Zarath M. Summers ◽

Chi Ho Chan ◽

Jeffrey A. Gralnick ◽

Daniel R. Bond

Keyword(s):

Single Molecule ◽

Homoserine Lactone ◽

Geobacter Sulfurreducens ◽

Iron Formation ◽

Carbon Limitation ◽

Redox Potentials ◽

Deep Biosphere ◽

Banded Iron Formation ◽

Hydrogen Electrode ◽

Wide Range

ABSTRACTReaching a depth of 713 m below the surface, the Soudan Underground Iron Mine (Soudan, Minnesota, USA) transects a massive Archaean (2.7 Ga) banded iron formation, providing a remarkably accessible window into the terrestrial deep biosphere. Despite carbon limitation, metal-reducing microbial communities are present in potentially ancient anoxic brines continuously emanating from exploratory boreholes on Level 27. Using graphite electrodes deposited in situ as bait, we enriched and isolated a novel halophilic iron-reducing Deltaproteobacterium, Desul-furomonas soudanensis strain WTL, from an acetate-fed three-electrode bioreactor poised at +0.24 V (vs. standard hydrogen electrode). Cyclic voltammetry revealed that D. soudanensis releases electrons at redox potentials approximately 100 mV more positive than the model freshwater surface isolate Geobacter sulfurreducens, suggesting that its extracellular respiration is tuned for higher potential electron acceptors. D. soudanensis contains a 3,958,620-bp circular genome, assembled to completion using single-molecule real-time (SMRT) sequencing reads, which encodes a complete TCA cycle, 38 putative multiheme c-type cytochromes, one of which contains 69 heme-binding motifs, and a LuxI/LuxR quorum sensing cassette that produces an unidentified N-acyl homoserine lactone. Another cytochrome is predicted to lie within a putative prophage, suggesting that horizontal transfer of respiratory proteins plays a role in respiratory flexibility among metal reducers. Isolation of D. soudanensis underscores the utility of electrode-based approaches for enriching rare metal reducers from a wide range of habitats.

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Electrochemical redox transformations of T1 and T2 copper sites in native Trametes hirsuta laccase at gold electrode

Biochemical Journal ◽

10.1042/bj20041015 ◽

2005 ◽

Vol 385 (3) ◽

pp. 745-754 ◽

Cited By ~ 121

Author(s):

Sergey SHLEEV ◽

Andreas CHRISTENSON ◽

Vladimir SEREZHENKOV ◽

Dosymzhan BURBAEV ◽

Alexander YAROPOLOV ◽

...

Keyword(s):

Electron Transfer ◽

Gold Electrode ◽

Direct Electron Transfer ◽

High Potential ◽

Redox Potentials ◽

Hydrogen Electrode ◽

Trametes Hirsuta ◽

Redox Transformations ◽

Copper Site ◽

Copper Sites

Mediatorless, electrochemically driven, redox transformations of T1 (type 1) and T2 copper sites in Trametes hirsuta laccase were studied by cyclic voltammetry and spectroelectrochemical redox titrations using bare gold electrode. DET (direct electron transfer) between the electrode and the enzyme was observed under anaerobic conditions. From analysis of experimental data it is concluded that the T2 copper site is in DET contact with gold. It was found that electron transfer between the gold surface and the T1 copper site progresses through the T2 copper site. From EPR measurements and electrochemical data it is proposed that the redox potential of the T2 site for high-potential ‘blue’ laccase is equal to about 400 mV versus NHE (normal hydrogen electrode) at pH 6.5. The hypothesis that the redox potentials of the T2 copper sites in low- and high-potential laccases/oxidases from totally different sources might be very similar, i.e. approx. 400 mV, is discussed.

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Effect of Sequences of the Active-Site Dipeptides of DsbA and DsbC on In Vivo Folding of Multidisulfide Proteins inEscherichia coli

Journal of Bacteriology ◽

10.1128/jb.183.3.980-988.2001 ◽

2001 ◽

Vol 183 (3) ◽

pp. 980-988 ◽

Cited By ~ 43

Author(s):

Paul H. Bessette ◽

Ji Qiu ◽

James C. A. Bardwell ◽

James R. Swartz ◽

George Georgiou

Keyword(s):

Redox Potential ◽

Active Site ◽

Active Sites ◽

Multicopy Plasmid ◽

Redox Potentials ◽

Cxxc Motif ◽

Wide Range ◽

Significant Difference ◽

Disulfide Isomerization

ABSTRACT We have examined the role of the active-site CXXC central dipeptides of DsbA and DsbC in disulfide bond formation and isomerization in the Escherichia coli periplasm. DsbA active-site mutants with a wide range of redox potentials were expressed either from the trc promoter on a multicopy plasmid or from the endogenous dsbA promoter by integration of the respective alleles into the bacterial chromosome. ThedsbA alleles gave significant differences in the yield of active murine urokinase, a protein containing 12 disulfides, including some that significantly enhanced urokinase expression over that allowed by wild-type DsbA. No direct correlation between the in vitro redox potential of dsbA variants and the urokinase yield was observed. These results suggest that the active-site CXXC motif of DsbA can play an important role in determining the folding of multidisulfide proteins, in a way that is independent from DsbA's redox potential. However, under aerobic conditions, there was no significant difference among the DsbA mutants with respect to phenotypes depending on the oxidation of proteins with few disulfide bonds. The effect of active-site mutations in the CXXC motif of DsbC on disulfide isomerization in vivo was also examined. A library of DsbC expression plasmids with the active-site dipeptide randomized was screened for mutants that have increased disulfide isomerization activity. A number of DsbC mutants that showed enhanced expression of a variant of human tissue plasminogen activator as well as mouse urokinase were obtained. These DsbC mutants overwhelmingly contained an aromatic residue at the C-terminal position of the dipeptide, whereas the N-terminal residue was more diverse. Collectively, these data indicate that the active sites of the soluble thiol- disulfide oxidoreductases can be modulated to enhance disulfide isomerization and protein folding in the bacterial periplasmic space.

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Effect of the L499M mutation of the ascomycetousBotrytis acladalaccase on redox potential and catalytic properties

Acta Crystallographica Section D Biological Crystallography ◽

10.1107/s1399004714020380 ◽

2014 ◽

Vol 70 (11) ◽

pp. 2913-2923 ◽

Cited By ~ 16

Author(s):

Evgeny Osipov ◽

Konstantin Polyakov ◽

Roman Kittl ◽

Sergey Shleev ◽

Pavel Dorovatovsky ◽

...

Keyword(s):

Redox Potential ◽

Catalytic Properties ◽

Enzymatic Reaction ◽

Copper Ion ◽

Large Family ◽

Redox Potentials ◽

Wild Type ◽

Wild Type Enzyme ◽

X Ray ◽

Wide Range

Laccases are members of a large family of multicopper oxidases that catalyze the oxidation of a wide range of organic and inorganic substrates accompanied by the reduction of dioxygen to water. These enzymes contain four Cu atoms per molecule organized into three sites: T1, T2 and T3. In all laccases, the T1 copper ion is coordinated by two histidines and one cysteine in the equatorial plane and is covered by the side chains of hydrophobic residues in the axial positions. The redox potential of the T1 copper ion influences the enzymatic reaction and is determined by the nature of the axial ligands and the structure of the second coordination sphere. In this work, the laccase from the ascomyceteBotrytis acladawas studied, which contains conserved Ile491 and nonconserved Leu499 residues in the axial positions. The three-dimensional structures of the wild-type enzyme and the L499M mutant were determined by X-ray crystallography at 1.7 Å resolution. Crystals suitable for X-ray analysis could only be grown after deglycosylation. Both structures did not contain the T2 copper ion. The catalytic properties of the enzyme were characterized and the redox potentials of both enzyme forms were determined:E0= 720 and 580 mV for the wild-type enzyme and the mutant, respectively. Since the structures of the wild-type and mutant forms are very similar, the change in the redox potential can be related to the L499M mutation in the T1 site of the enzyme.

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Role of redox-inactive metals in controlling the redox potential of heterometallic manganese–oxido clusters

Photosynthesis Research ◽

10.1007/s11120-021-00846-y ◽

2021 ◽

Author(s):

Keisuke Saito ◽

Minesato Nakagawa ◽

Manoj Mandal ◽

Hiroshi Ishikita

Keyword(s):

Photosystem Ii ◽

Redox Potential ◽

Quantum Chemical Calculations ◽

Catalytic Reaction ◽

Quantum Chemical ◽

Ionic Radius ◽

Redox Potentials ◽

Oxygen Evolving ◽

Highest Occupied Molecular Orbitals

AbstractPhotosystem II (PSII) contains Ca2+, which is essential to the oxygen-evolving activity of the catalytic Mn4CaO5 complex. Replacement of Ca2+ with other redox-inactive metals results in a loss/decrease of oxygen-evolving activity. To investigate the role of Ca2+ in this catalytic reaction, we investigate artificial Mn3[M]O2 clusters redox-inactive metals [M] ([M] = Mg2+, Ca2+, Zn2+, Sr2+, and Y3+), which were synthesized by Tsui et al. (Nat Chem 5:293, 2013). The experimentally measured redox potentials (Em) of these clusters are best described by the energy of their highest occupied molecular orbitals. Quantum chemical calculations showed that the valence of metals predominantly affects Em(MnIII/IV), whereas the ionic radius of metals affects Em(MnIII/IV) only slightly.

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Identification of different putative outer membrane electron conduits necessary for Fe(III) citrate, Fe(III) oxide, Mn(IV) oxide, or electrode reduction by Geobacter sulfurreducens

10.1101/169086 ◽

2017 ◽

Cited By ~ 1

Author(s):

Fernanda Jiménez Otero ◽

Chi Ho Chan ◽

Daniel R. Bond

Keyword(s):

Electron Transfer ◽

Outer Membrane ◽

Electron Acceptor ◽

Single Gene ◽

Gene Clusters ◽

Geobacter Sulfurreducens ◽

Transcriptional Analysis ◽

Growth Defect ◽

Redox Potentials ◽

Wild Type

AbstractAt least five gene clusters in the Geobacter sulfurreducens genome encode putative ‘electron conduits’ implicated in electron transfer across the outer membrane, each containing a periplasmic multiheme c-type cytochrome, integral outer membrane anchor, and outer membrane redox lipoprotein(s). Markerless single gene cluster deletions and all possible multiple deletion combinations were constructed and grown with soluble Fe(III) citrate, Fe(III)- and Mn(IV)-oxides, and graphite electrodes poised at +0.24 V and −0.1 V vs. SHE. Different gene clusters were necessary for reduction of each electron acceptor. During metal oxide reduction, deletion of the previously described omcBC cluster caused defects, but deletion of additional components in an ΔomcBC background, such as extEFG, were needed to produce defects greater than 50% compared to wild type. Deletion of all five gene clusters abolished all metal reduction. During electrode reduction, only the ΔextABCD mutant had a severe growth defect at both redox potentials, while this mutation did not affect Fe(III)-oxide, Mn(IV)-oxide, or Fe(III) citrate reduction. Some mutants containing only one cluster were able to reduce particular terminal electron acceptors better than wild type, suggesting routes for improvement by targeting specific electron transfer pathways. Transcriptomic comparisons between fumarate and electrode-based growth showed all of these ext clusters to be constitutive, and transcriptional analysis of the triple-deletion strain containing only extABCD detected no significant changes in expression of known redox proteins or pili components. These genetic experiments reveal new outer membrane conduit complexes necessary for growth of G. sulfurreducens, depending on the available extracellular electron acceptor.

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Detecting Redox Potentials Using Porous Boron Nitride/ATP-DNA Aptamer/Methylene Blue Biosensor to Monitor Microbial Activities

Micromachines ◽

10.3390/mi13010083 ◽

2022 ◽

Vol 13 (1) ◽

pp. 83

Author(s):

Kai Guo ◽

Zirui Song ◽

Gaoxing Wang ◽

Chengchun Tang

Keyword(s):

Methylene Blue ◽

Microbial Community ◽

Boron Nitride ◽

Redox Potential ◽

Microbial Activity ◽

Potential Change ◽

Dna Aptamer ◽

Redox Potentials ◽

Microplate Reader

Microbial activity has gained attention because of its impact on the environment and the quality of people’s lives. Most of today’s methods, which include genome sequencing and electrochemistry, are costly and difficult to manage. Our group proposed a method using the redox potential change to detect microbial activity, which is rooted in the concept that metabolic activity can change the redox potential of a microbial community. The redox potential change was captured by a biosensor consisting of porous boron nitride, ATP-DNA aptamer, and methylene blue as the fluorophore. This assembly can switch on or off when there is a redox potential change, and this change leads to a fluorescence change that can be examined using a multipurpose microplate reader. The results show that this biosensor can detect microbial community changes when its composition is changed or toxic metals are ingested.

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Identification of different putative outer membrane electron conduits necessary for Fe(III) citrate, Fe(III)-oxide, Mn(IV)-oxide, or electrode reduction by Geobacter sulfurreducens .

10.1101/350553 ◽

2018 ◽

Author(s):

Fernanda Jiménez Otero ◽

Chi Ho Chan ◽

Daniel R Bond

Keyword(s):

Electron Transfer ◽

Outer Membrane ◽

Electron Acceptor ◽

Single Gene ◽

Gene Clusters ◽

Geobacter Sulfurreducens ◽

Transcriptional Analysis ◽

Growth Defect ◽

Redox Potentials ◽

Wild Type

At least five gene clusters in the Geobacter sulfurreducens genome encode putative ‘electron conduits’ implicated in electron transfer across the outer membrane, each containing a periplasmic multiheme c -type cytochrome, integral outer membrane anchor, and outer membrane redox lipoprotein(s). Markerless single gene cluster deletions and all possible multiple deletion combinations were constructed and grown with soluble Fe(III) citrate, Fe(III)- and Mn(IV)-oxides, and graphite electrodes poised at +0.24 V and -0.1 V vs. SHE. Different gene clusters were necessary for reduction of each electron acceptor. During metal oxide reduction, deletion of the previously described omcBC cluster caused defects, but deletion of additional components in an Δ omcBC background, such as extEFG , were needed to produce defects greater than 50% compared to wild type. Deletion of all five gene clusters abolished all metal reduction. During electrode reduction, only the Δ extABCD mutant had a severe growth defect at both redox potentials, while this mutation did not affect Fe(III)-oxide, Mn(IV)-oxide, or Fe(III) citrate reduction. Some mutants containing only one cluster were able to reduce particular terminal electron acceptors better than wild type, suggesting routes for improvement by targeting specific electron transfer pathways. Transcriptomic comparisons between fumarate and electrode-based growth showed all of these ext clusters to be constitutive, and transcriptional analysis of the triple-deletion strain containing only extABCD detected no significant changes in expression of known redox proteins or pili components. These genetic experiments reveal new outer membrane conduit complexes necessary for growth of G. sulfurreducens , depending on the available extracellular electron acceptor.

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A mixed contact model for an immersed collision between two solid surfaces

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2008.0014 ◽

2008 ◽

Vol 366 (1873) ◽

pp. 2205-2218 ◽

Cited By ~ 19

Author(s):

Fu-Ling Yang ◽

Melany L Hunt

Keyword(s):

Surface Deformation ◽

Elastohydrodynamic Lubrication ◽

Solid Particles ◽

Solid Surfaces ◽

Additional Energy ◽

Collision Model ◽

Dry Granular Flow ◽

Wide Range ◽

The Impact ◽

Surrounding Liquid

Experimental evidence shows that the presence of an ambient liquid can greatly modify the collision process between two solid surfaces. Interactions between the solid surfaces and the surrounding liquid result in energy dissipation at the particle level, which leads to solid–liquid mixture rheology deviating from dry granular flow behaviour. The present work investigates how the surrounding liquid modifies the impact and rebound of solid spheres. Existing collision models use elastohydrodynamic lubrication (EHL) theory to address the surface deformation under the developing lubrication pressure, thereby coupling the motion of the liquid and solid. With EHL theory, idealized smooth particles are made to rebound from a lubrication film. Modified EHL models, however, allow particles to rebound from mutual contacts of surface asperities, assuming negligible liquid effects. In this work, a new contact mechanism, ‘mixed contact’, is formulated, which considers the interplay between the asperities and the interstitial liquid as part of a hybrid rebound scheme. A recovery factor is further proposed to characterize the additional energy loss due to asperity–liquid interactions. The resulting collision model is evaluated through comparisons with experimental data, exhibiting a better performance than the existing models. In addition to the three non-dimensional numbers that result from the EHL analysis—the wet coefficient of restitution, the particle Stokes number and the elasticity parameter—a fourth parameter is introduced to correlate particle impact momentum to the EHL deformation impulse. This generalized collision model covers a wide range of impact conditions and could be employed in numerical codes to simulate the bulk motion of solid particles with non-negligible liquid effects.

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