Iron Corrosion via Direct Metal-Microbe Electron Transfer

ABSTRACTThe concept that anaerobic microorganisms can directly accept electrons from Fe(0) has been controversial because direct metal-microbe electron transfer has previously only been indirectly inferred. Fe(0) oxidation was studied withGeobacter sulfurreducensstrain ACL, an autotrophic strain that was previously shown to grow with electrons derived from a graphite cathode as the sole electron donor. Strain ACL grew with Fe(0) as the sole electron donor and fumarate as the electron acceptor. However, it appeared that at least a portion of the electron transfer was via H2produced nonenzymatically from the oxidation of Fe(0) to Fe(II). H2, which accumulated in abiotic controls, was consumed during the growth of strain ACL, the cells were predominately planktonic, and genes for the uptake hydrogenase were highly expressed. Strain ACLHFwas constructed to prevent growth on H2or formate by deleting the genes for the uptake of hydrogenase and formate dehydrogenases from strain ACL. Strain ACLHFalso grew with Fe(0) as the sole electron donor, but H2accumulated in the culture, and cells heavily colonized Fe(0) surfaces with no visible planktonic growth. Transcriptomics suggested that the outer surfacec-type cytochromes OmcS and OmcZ were important during growth of strain ACLHFon Fe(0). Strain ACLHFdid not grow on Fe(0) if the gene for either of these cytochromes was deleted. The specific attachment of strain ACLHFto Fe(0), coupled with requirements for known extracellular electrical contacts, suggest that direct metal-microbe electron transfer is the most likely option for Fe(0) serving as an electron donor.IMPORTANCEThe anaerobic corrosion of iron structures is expensive to repair and can be a safety and environmental concern. It has been known for over 100 years that the presence of anaerobic respiratory microorganisms can accelerate iron corrosion. Multiple studies have suggested that there are sulfate reducers, methanogens, and acetogens that can directly accept electrons from Fe(0) to support sulfate or carbon dioxide reduction. However, all of the strains studied can also use H2as an electron donor for growth, which is known to be abiotically produced from Fe(0). Furthermore, no proteins definitely shown to function as extracellular electrical contacts with Fe(0) were identified. The studies described here demonstrate that direct electron transfer from Fe(0) can support anaerobic respiration. They also map out a simple genetic approach to the study of iron corrosion mechanisms in other microorganisms. A better understanding of how microorganisms promote iron corrosion is expected to lead to the development of strategies that can help reduce adverse impacts from this process.

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Direct Electron Transfer between the frhAGB-Encoded Hydrogenase and Thioredoxin Reductase in the Nonmethanogenic Archaeon Thermococcus onnurineus NA1

Applied and Environmental Microbiology ◽

10.1128/aem.02630-19 ◽

2020 ◽

Vol 86 (6) ◽

Cited By ~ 1

Author(s):

Hae-Chang Jung ◽

Jae Kyu Lim ◽

Tae-Jun Yang ◽

Sung Gyun Kang ◽

Hyun Sook Lee

Keyword(s):

Electron Transfer ◽

Electron Donor ◽

Direct Electron Transfer ◽

Thioredoxin Reductase ◽

Thermococcus Onnurineus Na1 ◽

Content Type ◽

Protein Target ◽

Redox Partner ◽

Significant Step

ABSTRACT To date, NAD(P)H, ferredoxin, and coenzyme F420 have been identified as electron donors for thioredoxin reductase (TrxR). In this study, we present a novel electron source for TrxR. In the hyperthermophilic archaeon Thermococcus onnurineus NA1, the frhAGB-encoded hydrogenase, a homolog of the F420-reducing hydrogenase of methanogens, was demonstrated to interact with TrxR in coimmunoprecipitation experiments and in vitro pulldown assays. Electrons derived from H2 oxidation by the frhAGB-encoded hydrogenase were transferred to TrxR and reduced Pdo, a redox partner of TrxR. Interaction and electron transfer were observed between TrxR and the heterodimeric hydrogenase complex (FrhAG) as well as the heterotrimeric complex (FrhAGB). Hydrogen-dependent reduction of TrxR was 7-fold less efficient than when NADPH was the electron donor. This study not only presents a different type of electron donor for TrxR but also reveals new functionality of the frhAGB-encoded hydrogenase utilizing a protein as an electron acceptor. IMPORTANCE This study has importance in that TrxR can use H2 as an electron donor with the aid of the frhAGB-encoded hydrogenase as well as NAD(P)H in T. onnurineus NA1. Further studies are needed to explore the physiological significance of this protein. This study also has importance as a significant step toward understanding the functionality of the frhAGB-encoded hydrogenase in a nonmethanogen; the hydrogenase can transfer electrons derived from oxidation of H2 to a protein target by direct contact without the involvement of an electron carrier, which is distinct from the mechanism of its homologs, F420-reducing hydrogenases of methanogens.

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A Hybrid Extracellular Electron Transfer Pathway Enhances the Survival of Vibrio natriegens

Applied and Environmental Microbiology ◽

10.1128/aem.01253-20 ◽

2020 ◽

Vol 86 (19) ◽

Cited By ~ 1

Author(s):

Bridget E. Conley ◽

Matthew T. Weinstock ◽

Daniel R. Bond ◽

Jeffrey A. Gralnick

Keyword(s):

Electron Transfer ◽

Shewanella Oneidensis ◽

Anaerobic Respiration ◽

Basic Research ◽

Extracellular Electron Transfer ◽

Content Type ◽

Electron Transfer Pathway ◽

Sedimentary Environments ◽

Genetic Potential ◽

Iron And Manganese

ABSTRACT Vibrio natriegens is the fastest-growing microorganism discovered to date, making it a useful model for biotechnology and basic research. While it is recognized for its rapid aerobic metabolism, less is known about anaerobic adaptations in V. natriegens or how the organism survives when oxygen is limited. Here, we describe and characterize extracellular electron transfer (EET) in V. natriegens, a metabolism that requires movement of electrons across protective cellular barriers to reach the extracellular space. V. natriegens performs extracellular electron transfer under fermentative conditions with gluconate, glucosamine, and pyruvate. We characterized a pathway in V. natriegens that requires CymA, PdsA, and MtrCAB for Fe(III) citrate and Fe(III) oxide reduction, which represents a hybrid of strategies previously discovered in Shewanella and Aeromonas. Expression of these V. natriegens genes functionally complemented Shewanella oneidensis mutants. Phylogenetic analysis of the inner membrane quinol dehydrogenases CymA and NapC in gammaproteobacteria suggests that CymA from Shewanella diverged from Vibrionaceae CymA and NapC. Analysis of sequenced Vibrionaceae revealed that the genetic potential to perform EET is conserved in some members of the Harveyi and Vulnificus clades but is more variable in other clades. We provide evidence that EET enhances anaerobic survival of V. natriegens, which may be the primary physiological function for EET in Vibrionaceae. IMPORTANCE Bacteria from the genus Vibrio occupy a variety of marine and brackish niches with fluctuating nutrient and energy sources. When oxygen is limited, fermentation or alternative respiration pathways must be used to conserve energy. In sedimentary environments, insoluble oxide minerals (primarily iron and manganese) are able to serve as electron acceptors for anaerobic respiration by microorganisms capable of extracellular electron transfer, a metabolism that enables the use of these insoluble substrates. Here, we identify the mechanism for extracellular electron transfer in Vibrio natriegens, which uses a combination of strategies previously identified in Shewanella and Aeromonas. We show that extracellular electron transfer enhanced survival of V. natriegens under fermentative conditions, which may be a generalized strategy among Vibrio spp. predicted to have this metabolism.

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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 byGeobacter sulfurreducens

Journal of Bacteriology ◽

10.1128/jb.00347-18 ◽

2018 ◽

Vol 200 (19) ◽

Cited By ~ 17

Author(s):

Fernanda Jiménez Otero ◽

Chi Ho Chan ◽

Daniel R. Bond

Keyword(s):

Electron Transfer ◽

Outer Membrane ◽

Electron Acceptor ◽

Gene Clusters ◽

Geobacter Sulfurreducens ◽

Transcriptional Analysis ◽

Metal Reduction ◽

Wild Type ◽

Redox Proteins ◽

Content Type

ABSTRACTAt least five gene clusters in theGeobacter sulfurreducensgenome encode putative “electron conduits” implicated in electron transfer across the outer membrane, each containing a periplasmic multihemec-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 versus the standard hydrogen electrode (SHE). Different gene clusters were necessary for reduction of each electron acceptor. During metal oxide reduction, deletion of the previously describedomcBCcluster caused defects, but deletion of additional components in an ΔomcBCbackground, such asextEFG, were needed to produce defects greater than 50% compared to findings with the wild type. Deletion of all five gene clusters abolished all metal reduction. During electrode reduction, only the ΔextABCDmutant 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 the wild type, suggesting routes for improvement by targeting specific electron transfer pathways. Transcriptomic comparisons between fumarate and electrode-based growth conditions showed all of theseextclusters to be constitutive, and transcriptional analysis of the triple-deletion strain containing onlyextABCDdetected no significant changes in expression of genes encoding known redox proteins or pilus components. These genetic experiments reveal new outer membrane conduit complexes necessary for growth ofG. sulfurreducens, depending on the available extracellular electron acceptor.IMPORTANCEGram-negative metal-reducing bacteria utilize electron conduits, chains of redox proteins spanning the outer membrane, to transfer electrons to the extracellular surface. Only one pathway for electron transfer across the outer membrane ofGeobacter sulfurreducenshas been linked to Fe(III) reduction. However,G. sulfurreducensis able to respire a wide array of extracellular substrates. Here we present the first combinatorial genetic analysis of five different electron conduits via creation of new markerless deletion strains and complementation vectors. Multiple conduit gene clusters appear to have overlapping roles, including two that have never been linked to metal reduction. Another recently described cluster (ExtABCD) was the only electron conduit essential during electrode reduction, a substrate of special importance to biotechnological applications of this organism.

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A Geobacter sulfurreducens Strain Expressing Pseudomonas aeruginosa Type IV Pili Localizes OmcS on Pili but Is Deficient in Fe(III) Oxide Reduction and Current Production

Applied and Environmental Microbiology ◽

10.1128/aem.02938-13 ◽

2013 ◽

Vol 80 (3) ◽

pp. 1219-1224 ◽

Cited By ~ 67

Author(s):

Xing Liu ◽

Pier-Luc Tremblay ◽

Nikhil S. Malvankar ◽

Kelly P. Nevin ◽

Derek R. Lovley ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Electron Transfer ◽

Structural Features ◽

Geobacter Sulfurreducens ◽

Control Strain ◽

Oxide Reduction ◽

Content Type ◽

Type Iv ◽

Current Production ◽

Pilin Protein

ABSTRACTThe conductive pili ofGeobacterspecies play an important role in electron transfer to Fe(III) oxides, in long-range electron transport through current-producing biofilms, and in direct interspecies electron transfer. Although multiple lines of evidence have indicated that the pili ofGeobacter sulfurreducenshave a metal-like conductivity, independent of the presence ofc-type cytochromes, this claim is still controversial. In order to further investigate this phenomenon, a strain ofG. sulfurreducens, designated strain PA, was constructed in which the gene for the native PilA, the structural pilin protein, was replaced with the PilA gene ofPseudomonas aeruginosaPAO1. Strain PA expressed and properly assembledP. aeruginosaPilA subunits into pili and exhibited a profile of outer surfacec-type cytochromes similar to that of a control strain expressing theG. sulfurreducensPilA. Surprisingly, the strain PA pili were decorated with thec-type cytochrome OmcS in a manner similar to the control strain. However, the strain PA pili were 14-fold less conductive than the pili of the control strain, and strain PA was severely impaired in Fe(III) oxide reduction and current production. These results demonstrate that the presence of OmcS on pili is not sufficient to confer conductivity to pili and suggest that there are unique structural features of theG. sulfurreducensPilA that are necessary for conductivity.

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Geobacter soli sp. nov., a dissimilatory Fe(III)-reducing bacterium isolated from forest soil

INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY ◽

10.1099/ijs.0.066662-0 ◽

2014 ◽

Vol 64 (Pt_11) ◽

pp. 3786-3791 ◽

Cited By ~ 25

Author(s):

Shungui Zhou ◽

Guiqin Yang ◽

Qin Lu ◽

Min Wu

Keyword(s):

Forest Soil ◽

Electron Donor ◽

Electron Acceptor ◽

Type Species ◽

Geobacter Sulfurreducens ◽

Phenotypic Characterization ◽

Strictly Anaerobic ◽

Content Type ◽

Link Type ◽

Physiological Tests

A novel Fe(III)-reducing bacterium, designated GSS01T, was isolated from a forest soil sample using a liquid medium containing acetate and ferrihydrite as electron donor and electron acceptor, respectively. Cells of strain GSS01T were strictly anaerobic, Gram-stain-negative, motile, non-spore-forming and slightly curved rod-shaped. Growth occurred at 16–40 °C and optimally at 30 °C. The DNA G+C content was 60.9 mol%. The major respiratory quinone was MK-8. The major fatty acids were C16 : 0, C18 : 0 and C16 : 1ω7c/C16 : 1ω6c. Strain GSS01T was able to grow with ferrihydrite, Fe(III) citrate, Mn(IV), sulfur, nitrate or anthraquinone-2,6-disulfonate, but not with fumarate, as sole electron acceptor when acetate was the sole electron donor. The isolate was able to utilize acetate, ethanol, glucose, lactate, butyrate, pyruvate, benzoate, benzaldehyde, m-cresol and phenol but not toluene, p-cresol, propionate, malate or succinate as sole electron donor when ferrihydrite was the sole electron acceptor. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain GSS01T was most closely related to Geobacter sulfurreducens PCAT (98.3 % sequence similarity) and exhibited low similarities (94.9–91.8 %) to the type strains of other species of the genus Geobacter . The DNA–DNA relatedness between strain GSS01T and G. sulfurreducens PCAT was 41.4±1.1 %. On the basis of phylogenetic analysis, phenotypic characterization and physiological tests, strain GSS01T is believed to represent a novel species of the genus Geobacter , and the name Geobacter soli sp. nov. is proposed. The type strain is GSS01T ( = KCTC 4545T = MCCC 1K00269T).

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Uniform and Pitting Corrosion of Carbon Steel byShewanella oneidensisMR-1 under Nitrate-Reducing Conditions

Applied and Environmental Microbiology ◽

10.1128/aem.00790-18 ◽

2018 ◽

Vol 84 (12) ◽

pp. e00790-18 ◽

Cited By ~ 11

Author(s):

Robert B. Miller ◽

Kenton Lawson ◽

Anwar Sadek ◽

Chelsea N. Monty ◽

John M. Senko

Keyword(s):

Electron Transfer ◽

Carbon Steel ◽

Electron Donor ◽

Pitting Corrosion ◽

Nitrate Reduction ◽

Steel Corrosion ◽

Nitrite Accumulation ◽

Content Type ◽

Microbially Influenced Corrosion ◽

Reducing Conditions

ABSTRACTDespite observations of steel corrosion in nitrate-reducing environments, processes of nitrate-dependent microbially influenced corrosion (MIC) remain poorly understood and difficult to identify. We evaluated carbon steel corrosion byShewanella oneidensisMR-1 under nitrate-reducing conditions using a split-chamber/zero-resistance ammetry (ZRA) technique. This approach entails the deployment of two metal (carbon steel 1018 in this case) electrodes into separate chambers of an electrochemical split-chamber unit, where the microbiology or chemistry of the chambers can be manipulated. This approach mimics the conditions of heterogeneous metal coverage that can lead to uniform and pitting corrosion. The current between working electrode 1 (WE1) and WE2 can be used to determine rates, mechanisms, and, we now show, extents of corrosion. WhenS. oneidensiswas incubated in the WE1 chamber with lactate under nitrate-reducing conditions, nitrite transiently accumulated, and electron transfer from WE2 to WE1 occurred as long as nitrite was present. Nitrite in the WE1 chamber (withoutS. oneidensis) induced electron transfer in the same direction, indicating that nitrite cathodically protected WE1 and accelerated the corrosion of WE2. WhenS. oneidensiswas incubated in the WE1 chamber without an electron donor, nitrate reduction proceeded, and electron transfer from WE2 to WE1 also occurred, indicating that the microorganism could use the carbon steel electrode as an electron donor for nitrate reduction. Our results indicate that under nitrate-reducing conditions, uniform and pitting carbon steel corrosion can occur due to nitrite accumulation and the use of steel-Fe(0) as an electron donor, but conditions of sustained nitrite accumulation can lead to more-aggressive corrosive conditions.IMPORTANCEMicrobially influenced corrosion (MIC) causes damage to metals and metal alloys that is estimated to cost over $100 million/year in the United States for prevention, mitigation, and repair. While MIC occurs in a variety of settings and by a variety of organisms, the mechanisms by which microorganisms cause this damage remain unclear. Steel pipe and equipment may be exposed to nitrate, especially in oil and gas production, where this compound is used for corrosion and “souring” control. In this paper, we show uniform and pitting MIC under nitrate-reducing conditions and that a major mechanism by which it occurs is via the heterogeneous cathodic protection of metal surfaces by nitrite as well as by the microbial oxidation of steel-Fe(0).

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Concerted Ion and Electron Transfer Across Electronically Conductive Polymer Membranes

MRS Proceedings ◽

10.1557/proc-293-153 ◽

1992 ◽

Vol 293 ◽

Author(s):

Charles R. Martin ◽

Del R. Lawson ◽

Wenbin Liang

Keyword(s):

Electron Transfer ◽

Electron Donor ◽

Direct Electron Transfer ◽

Conductive Polymer ◽

Electron Transfer Reaction ◽

Reduced Form ◽

Free Standing ◽

Transfer Processes ◽

Donor Acceptor ◽

Synthetic Metal

AbstractWe describe in this paper an experiment involving an electronically conductive polymer (ECP) which, to our knowledge, has not been described previously. A free-standing ECP (polypyrrole)-based membrane separates a solution of an electron donor from a solution of an electron acceptor. Because the ECP is both electronically and anionically conductive, the membrane can transport electrons from the donor solution to the acceptor solution, and anions in the opposite direction, such that a sustainable electron-transfer reaction is driven across the ECP membrane. We demonstrate such transmembrane electron/ion-transfer processes using both an inorganic and a biochemical electron donor/acceptor system. The biochemical case is of particular interest because we show that the reduced form of the enzyme glucose oxidase can give its electrons directly to the synthetic metal. Direct electron transfer is usually not possible at inorganic metals.

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Flavin Electron Shuttles Dominate Extracellular Electron Transfer by Shewanella oneidensis

mBio ◽

10.1128/mbio.00553-12 ◽

2013 ◽

Vol 4 (1) ◽

Cited By ~ 237

Author(s):

Nicholas J. Kotloski ◽

Jeffrey A. Gralnick

Keyword(s):

Electron Transfer ◽

Direct Electron Transfer ◽

Shewanella Oneidensis ◽

Phenotypic Characterization ◽

Extracellular Electron Transfer ◽

Wild Type ◽

Content Type ◽

Electron Shuttling ◽

Electron Shuttles ◽

Set Up

ABSTRACT Shewanella oneidensis strain MR-1 is widely studied for its ability to respire a diverse array of soluble and insoluble electron acceptors. The ability to breathe insoluble substrates is defined as extracellular electron transfer and can occur via direct contact or by electron shuttling in S. oneidensis. To determine the contribution of flavin electron shuttles in extracellular electron transfer, a transposon mutagenesis screen was performed with S. oneidensis to identify mutants unable to secrete flavins. A multidrug and toxin efflux transporter encoded by SO_0702 was identified and renamed bfe (bacterial flavin adenine dinucleotide [FAD] exporter) based on phenotypic characterization. Deletion of bfe resulted in a severe decrease in extracellular flavins, while overexpression of bfe increased the concentration of extracellular flavins. Strains lacking bfe had no defect in reduction of soluble Fe(III), but these strains were deficient in the rate of insoluble Fe(III) oxide reduction, which was alleviated by the addition of exogenous flavins. To test a different insoluble electron acceptor, graphite electrode bioreactors were set up to measure current produced by wild-type S. oneidensis and the Δbfe mutant. With the same concentration of supplemented flavins, the two strains produced similar amounts of current. However, when exogenous flavins were not supplemented to bioreactors, bfe mutant strains produced significantly less current than the wild type. We have demonstrated that flavin electron shuttling accounts for ~75% of extracellular electron transfer to insoluble substrates by S. oneidensis and have identified the first FAD transporter in bacteria. IMPORTANCE Extracellular electron transfer by microbes is critical for the geochemical cycling of metals, bioremediation, and biocatalysis using electrodes. A controversy in the field was addressed by demonstrating that flavin electron shuttling, not direct electron transfer or nanowires, is the primary mechanism of extracellular electron transfer employed by the bacterium Shewanella oneidensis. We have identified a flavin adenine dinucleotide transporter conserved in all sequenced Shewanella species that facilitates export of flavin electron shuttles in S. oneidensis. Analysis of a strain that is unable to secrete flavins demonstrated that electron shuttling accounts for ~75% of the insoluble extracellular electron transfer capacity in S. oneidensis.

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Iron Corrosion Induced by Nonhydrogenotrophic Nitrate-Reducing Prolixibacter sp. Strain MIC1-1

Applied and Environmental Microbiology ◽

10.1128/aem.03741-14 ◽

2014 ◽

Vol 81 (5) ◽

pp. 1839-1846 ◽

Cited By ~ 39

Author(s):

Takao Iino ◽

Kimio Ito ◽

Satoshi Wakai ◽

Hirohito Tsurumaru ◽

Moriya Ohkuma ◽

...

Keyword(s):

Carbon Source ◽

Electron Donor ◽

Microbiologically Influenced Corrosion ◽

Rrna Gene ◽

Oil Well ◽

Metallic Materials ◽

Anaerobic Conditions ◽

Iron Corrosion ◽

Content Type ◽

Donor Acceptor

ABSTRACTMicrobiologically influenced corrosion (MIC) of metallic materials imposes a heavy economic burden. The mechanism of MIC of metallic iron (Fe0) under anaerobic conditions is usually explained as the consumption of cathodic hydrogen by hydrogenotrophic microorganisms that accelerates anodic Fe0oxidation. In this study, we describe Fe0corrosion induced by a nonhydrogenotrophic nitrate-reducing bacterium called MIC1-1, which was isolated from a crude-oil sample collected at an oil well in Akita, Japan. This strain requires specific electron donor-acceptor combinations and an organic carbon source to grow. For example, the strain grew anaerobically on nitrate as a sole electron acceptor with pyruvate as a carbon source and Fe0as the sole electron donor. In addition, ferrous ion andl-cysteine served as electron donors, whereas molecular hydrogen did not. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain MIC1-1 was a member of the genusProlixibacterin the orderBacteroidales. Thus,Prolixibactersp. strain MIC1-1 is the first Fe0-corroding representative belonging to the phylumBacteroidetes. Under anaerobic conditions,Prolixibactersp. MIC1-1 corroded Fe0concomitantly with nitrate reduction, and the amount of iron dissolved by the strain was six times higher than that in an aseptic control. Scanning electron microscopy analyses revealed that microscopic crystals of FePO4developed on the surface of the Fe0foils, and a layer of FeCO3covered the FePO4crystals. We propose that cells ofProlixibactersp. MIC1-1 accept electrons directly from Fe0to reduce nitrate.

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Adaptive Evolution of Geobacter sulfurreducens in Coculture with Pseudomonas aeruginosa

mBio ◽

10.1128/mbio.02875-19 ◽

2020 ◽

Vol 11 (2) ◽

Author(s):

Lucie Semenec ◽

Ismael A. Vergara ◽

Andrew E. Laloo ◽

Steve Petrovski ◽

Philip L. Bond ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Electron Transfer ◽

Adaptive Evolution ◽

Efflux Pump ◽

Antibiotic Production ◽

Geobacter Sulfurreducens ◽

Extracellular Electron Transfer ◽

Content Type ◽

Interaction Dynamics ◽

Syntrophic Interaction

ABSTRACT Interactions between microorganisms in mixed communities are highly complex, being either syntrophic, neutral, predatory, or competitive. Evolutionary changes can occur in the interaction dynamics between community members as they adapt to coexistence. Here, we report that the syntrophic interaction between Geobacter sulfurreducens and Pseudomonas aeruginosa coculture change in their dynamics over evolutionary time. Specifically, Geobacter sp. dominance increases with adaptation within the cocultures, as determined through quantitative PCR and fluorescence in situ hybridization. This suggests a transition from syntrophy to competition and demonstrates the rapid adaptive capacity of Geobacter spp. to dominate in cocultures with P. aeruginosa. Early in coculture establishment, two single-nucleotide variants in the G. sulfurreducens fabI and tetR genes emerged that were strongly selected for throughout coculture evolution with P. aeruginosa phenazine wild-type and phenazine-deficient mutants. Sequential window acquisition of all theoretical spectra-mass spectrometry (SWATH-MS) proteomics revealed that the tetR variant cooccurred with the upregulation of an adenylate cyclase transporter, CyaE, and a resistance-nodulation-division (RND) efflux pump notably known for antibiotic efflux. To determine whether antibiotic production was driving the increased expression of the multidrug efflux pump, we tested Pseudomonas-derived phenazine-1-carboxylic acid (PHZ-1-CA) for its potential to inhibit Geobacter growth and drive selection of the tetR and fabI genetic variants. Despite its inhibitory properties, PHZ-1-CA did not drive variant selection, indicating that other antibiotics may drive overexpression of the efflux pump and CyaE or that a novel role exists for these proteins in the context of this interaction. IMPORTANCE Geobacter and Pseudomonas spp. cohabit many of the same environments, where Geobacter spp. often dominate. Both bacteria are capable of extracellular electron transfer (EET) and play important roles in biogeochemical cycling. Although they recently in 2017 were demonstrated to undergo direct interspecies electron transfer (DIET) with one another, the genetic evolution of this syntrophic interaction has not been examined. Here, we use whole-genome sequencing of the cocultures before and after adaptive evolution to determine whether genetic selection is occurring. We also probe their interaction on a temporal level and determine whether their interaction dynamics change over the course of adaptive evolution. This study brings to light the multifaceted nature of interactions between just two microorganisms within a controlled environment and will aid in improving metabolic models of microbial communities comprising these two bacteria.

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