Dissimilatory Nitrate Reduction to Ammonium (DNRA) and Denitrification Pathways Are Leveraged by Cyclic AMP Receptor Protein (CRP) Paralogues Based on Electron Donor/Acceptor Limitation in Shewanella loihica PV-4

ABSTRACT Under anoxic conditions, many bacteria, including Shewanella loihica strain PV-4, could use nitrate as an electron acceptor for dissimilatory nitrate reduction to ammonium (DNRA) and/or denitrification. Previous and current studies have shown that DNRA is favored under higher ambient carbon-to-nitrogen (C/N) ratios, whereas denitrification is upregulated under lower C/N ratios, which is consistent with our bioenergetics calculations. Interestingly, computational analyses indicate that the common cyclic AMP receptor protein (designated CRP1) and its paralogue CRP2 might both be involved in the regulation of two competing dissimilatory nitrate reduction pathways, DNRA and denitrification, in S. loihica PV-4 and several other denitrifying Shewanella species. To explore the regulatory mechanism underlying the dissimilatory nitrate reduction (DNR) pathways, nitrate reduction of a series of in-frame deletion mutants was analyzed under different C/N ratios. Deletion of crp1 could accelerate the reduction of nitrite to NO under both low and high C/N ratios. CRP1 is not required for denitrification and actually suppresses production of NO and N2O gases. Deletion of either of the NO-forming nitrite reductase genes nirK or crp2 blocked production of NO gas. Furthermore, real-time PCR and electrophoretic mobility shift assays (EMSAs) demonstrated that the transcription levels of DNRA-relevant genes such as nap-β (napDABGH), nrfA, and cymA were upregulated by CRP1, while nirK transcription was dependent on CRP2. There are tradeoffs between the different physiological roles of nitrate/lactate, as nitrogen nutrient/carbon source and electron acceptor/donor and CRPs may leverage dissimilatory nitrate reduction pathways for maximizing energy yield and bacterial survival under ambient environmental conditions. IMPORTANCE Some microbes utilize different dissimilatory nitrate reduction (DNR) pathways, including DNR to ammonia (DNRA) and denitrification pathways, for anaerobic respiration in response to ambient carbon/nitrogen ratio changes. Large-scale industrial nitrogen fixation and fertilizer application raise the concern of emission of N2O, a stable gas with potent global warming potential, as consequence of microbial respiration, thereby aggravating global warming and climate change. However, little is known about the molecular mechanism underlying the choice of two competing DNR pathways. We demonstrate that the global regulator CRP1, which is widely encoded in bacteria, is required for DNRA in S. loihica PV-4 strain, while the CRP2 paralogue is required for transcription of the nitrite reductase gene nirK for denitrification. Sufficient carbon source lead to the predominance of DNRA, while carbon source/electron donor deficiency may result in an incomplete denitrification process, raising the concern of high levels of N2O emission from nitrate-rich and carbon source-poor waters and soils.

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The Cyclic AMP Receptor Protein Regulates Quorum Sensing and Global Gene Expression in Yersinia pestis during Planktonic Growth and Growth in Biofilms

mBio ◽

10.1128/mbio.02613-19 ◽

2019 ◽

Vol 10 (6) ◽

Cited By ~ 6

Author(s):

Jeremy T. Ritzert ◽

George Minasov ◽

Ryan Embry ◽

Matthew J. Schipma ◽

Karla J. F. Satchell

Keyword(s):

Gene Expression ◽

Quorum Sensing ◽

Carbon Source ◽

Cyclic Amp ◽

Yersinia Pestis ◽

Carbon Sources ◽

Transcriptional Regulator ◽

Receptor Protein ◽

Content Type ◽

Bacterial Physiology

ABSTRACT Cyclic AMP (cAMP) receptor protein (Crp) is an important transcriptional regulator of Yersinia pestis. Expression of crp increases during pneumonic plague as the pathogen depletes glucose and forms large biofilms within lungs. To better understand control of Y. pestis Crp, we determined a 1.8-Å crystal structure of the protein-cAMP complex. We found that compared to Escherichia coli Crp, C helix amino acid substitutions in Y. pestis Crp did not impact the cAMP dependency of Crp to bind DNA promoters. To investigate Y. pestis Crp-regulated genes during plague pneumonia, we performed RNA sequencing on both wild-type and Δcrp mutant bacteria growing in planktonic and biofilm states in minimal media with glucose or glycerol. Y. pestis Crp was found to dramatically alter expression of hundreds of genes in a manner dependent upon carbon source and growth state. Gel shift assays confirmed direct regulation of the malT and ptsG promoters, and Crp was then linked to Y. pestis growth on maltose as a sole carbon source. Iron regulation genes ybtA and fyuA were found to be indirectly regulated by Crp. A new connection between carbon source and quorum sensing was revealed as Crp was found to regulate production of acyl-homoserine lactones (AHLs) through direct and indirect regulation of genes for AHL synthetases and receptors. AHLs were subsequently identified in the lungs of Y. pestis-infected mice when crp expression was highest in Y. pestis biofilms. Thus, in addition to the well-studied pla gene, other Crp-regulated genes likely have important functions during plague infection. IMPORTANCE Bacterial pathogens have evolved extensive signaling pathways to translate environmental signals into changes in gene expression. While Crp has long been appreciated for its role in regulating metabolism of carbon sources in many bacterial species, transcriptional profiling has revealed that this protein regulates many other aspects of bacterial physiology. The plague pathogen Y. pestis requires this global regulator to survive in blood, skin, and lungs. During disease progression, this organism adapts to changes within these niches. In addition to regulating genes for metabolism of nonglucose sugars, we found that Crp regulates genes for virulence, metal acquisition, and quorum sensing by direct or indirect mechanisms. Thus, this single transcriptional regulator, which responds to changes in available carbon sources, can regulate multiple critical behaviors for causing disease.

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Mannose utilization in Escherichia coli requires cyclic AMP but not an exogenous inducer

Canadian Journal of Microbiology ◽

10.1139/m80-251 ◽

1980 ◽

Vol 26 (12) ◽

pp. 1508-1511 ◽

Cited By ~ 8

Author(s):

Ann D. E. Fraser ◽

Hiroshi Yamazaki

Keyword(s):

Escherichia Coli ◽

Carbon Source ◽

Cyclic Amp ◽

Adenylyl Cyclase ◽

Sole Carbon Source ◽

Receptor Protein ◽

Deficient Mutant ◽

Phosphotransferase System ◽

Cyclic Amp Receptor Protein ◽

Cyclic Monophosphate

It has not been clarified whether the utilization of mannose by Escherichia coli requires adenosine 3′,5′-cyclic monophosphate (cyclic AMP). Using an adenylyl cyclase deficient mutant (CA8306B) and a cyclic AMP receptor protein (CRP) deficient mutant (5333B) we have shown that the utilization of mannose is dependent on the cyclic AMP–CRP complex. 2-Deoxyglucose (DG) is a nonmetabolizable glucose analog specific for the phosphotransferase system (PTS) which transports mannose (termed here PTSM). Growth of CA8306B on glycerol is unaffected by addition of the analog, whereas growth of the strain on glycerol plus cyclic AMP ceases im mediately upon addition of DG. These results suggest that the formation of PTSM is dependent on cyclic AMP. In addition, CA8306B grown on glycerol plus cyclic AMP can immediately utilize mannose when transferred to a medium containing mannose as a sole carbon source, whereas the same strain grown on glycerol without cyclic AMP cannot utilize mannose when so transferred. These results suggest that the formation of PTSM does not require an exogenous inducer.

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Diversity and Ubiquity of Bacteria Capable of Utilizing Humic Substances as Electron Donors for Anaerobic Respiration

Applied and Environmental Microbiology ◽

10.1128/aem.68.5.2445-2452.2002 ◽

2002 ◽

Vol 68 (5) ◽

pp. 2445-2452 ◽

Cited By ~ 134

Author(s):

John D. Coates ◽

Kimberly A. Cole ◽

Romy Chakraborty ◽

Susan M. O'Connor ◽

Laurie A. Achenbach

Keyword(s):

Energy Source ◽

Carbon Source ◽

Humic Substances ◽

Electron Donor ◽

Electron Acceptor ◽

Electron Donors ◽

16S Rrna Genes ◽

Rrna Genes ◽

Couple Growth ◽

Probable Number

ABSTRACT Previous studies have demonstrated that reduced humic substances (HS) can be reoxidized by anaerobic bacteria such as Geobacter, Geothrix, and Wolinella species with a suitable electron acceptor; however, little is known of the importance of this metabolism in the environment. Recently we investigated this metabolism in a diversity of environments including marine and aquatic sediments, forest soils, and drainage ditch soils. Most-probable-number enumeration studies were performed using 2,6-anthrahydroquinone disulfonate (AHDS), an analog for reduced HS, as the electron donor with nitrate as the electron acceptor. Anaerobic organisms capable of utilizing reduced HS as an electron donor were found in all environments tested and ranged from a low of 2.31 × 101 in aquifer sediments to a high of 9.33 × 106 in lake sediments. As part of this study we isolated six novel organisms capable of anaerobic AHDS oxidation. All of the isolates coupled the oxidation of AHDS to the reduction of nitrate with acetate (0.1 mM) as the carbon source. In the absence of cells, no AHDS oxidation was apparent, and in the absence of AHDS, no cell density increase was observed. Generally, nitrate was reduced to N2. Analysis of the AHDS and its oxidized form, 2,6-anthraquinone disulfonate (AQDS), in the medium during growth revealed that the anthraquinone was not being biodegraded as a carbon source and was simply being oxidized as an energy source. Determination of the AHDS oxidized and nitrate reduced accounted for 109% of the theoretical electron transfer. In addition to AHDS, all of these isolates could also couple the oxidation of reduced humic substances to the reduction of nitrate. No HS oxidation occurred in the absence of cells and in the absence of a suitable electron acceptor, demonstrating that these organisms were capable of utilizing natural HS as an energy source and that AHDS serves as a suitable analog for studying this metabolism. Alternative electron donors included simple volatile fatty acids such as propionate, butyrate, and valerate as well as simple organic acids such as lactate and pyruvate. Analysis of the complete sequences of the 16S rRNA genes revealed that the isolates were not closely related to each other and were phylogenetically diverse, with members in the alpha, beta, gamma, and delta subdivisions of the Proteobacteria. Most of the isolates were closely related to known genera not previously recognized for their ability to couple growth to HS oxidation, while one of the isolates represented a new genus in the delta subclass of the Proteobacteria. The results presented here demonstrate that microbial oxidation of HS is a ubiquitous metabolism in the environment. This study represents the first description of HS-oxidizing isolates and demonstrates that microorganisms capable of HS oxidation are phylogenetically diverse.

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Posttranscriptional Regulation of the Yersinia pestis Cyclic AMP Receptor Protein Crp and Impact on Virulence

mBio ◽

10.1128/mbio.01038-13 ◽

2014 ◽

Vol 5 (1) ◽

Cited By ~ 31

Author(s):

Wyndham W. Lathem ◽

Jay A. Schroeder ◽

Lauren E. Bellows ◽

Jeremy T. Ritzert ◽

Jovanka T. Koo ◽

...

Keyword(s):

Cyclic Amp ◽

Yersinia Pestis ◽

Posttranscriptional Regulation ◽

Transcriptional Regulator ◽

Receptor Protein ◽

Dependent Manner ◽

Content Type ◽

Cyclic Amp Receptor Protein ◽

Protein Levels ◽

Posttranscriptional Level

ABSTRACTThe cyclic AMP receptor protein (Crp) is a transcriptional regulator that controls the expression of numerous bacterial genes, usually in response to environmental conditions and particularly by sensing the availability of carbon. In the plague pathogenYersinia pestis, Crp regulates the expression of multiple virulence factors, including components of the type III secretion system and the plasminogen activator protease Pla. The regulation of Crp itself, however, is distinctly different from that found in the well-studiedEscherichia colisystem. Here, we show that at physiological temperatures, the synthesis of Crp inY. pestisis positively regulated at the posttranscriptional level. The loss of the small RNA chaperone Hfq results in decreased Crp protein levels but not in steady-state Crp transcript levels, and this regulatory effect occurs within the 5′ untranslated region (UTR) of the Crp mRNA. The posttranscriptional activation of Crp synthesis is required for the expression ofpla, and decouplingcrpfrom Hfq through the use of an exogenously controlled promoter and 5′ UTR increases Pla protein levels as well as partially rescues the growth defect associated with the loss of Hfq. Finally, we show that both Hfq and the posttranscriptional regulation of Crp contribute to the virulence ofY. pestisduring pneumonic plague. The Hfq-dependent, posttranscriptional regulation of Crp may be specific toYersiniaspecies, and thus our data help explain the dramatic growth and virulence defects associated with the loss of Hfq inY. pestis.IMPORTANCEThe Crp protein is a major transcriptional regulator in bacteria, and its synthesis is tightly controlled to avoid inappropriate induction of the Crp regulon. In this report, we provide the first evidence of Crp regulation in an Hfq-dependent manner at the posttranscriptional level. Our discovery that the synthesis of Crp inYersinia pestisis Hfq dependent adds an additional layer of regulation to catabolite repression in this bacterium. Our work provides a mechanism by which the plague pathogen links not just the sensing of glucose or other carbon sources but also other signals that influence Crp abundance via the expression of small RNAs to the induction of the Crp regulon. In turn, this allowsY. pestisto fine-tune Crp levels to optimize virulence gene expression during plague infection and may allow the bacterium to adapt to its unique environmental niches.

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Effect of high electron donor supply on dissimilatory nitrate reduction pathways in a bioreactor for nitrate removal

Bioresource Technology ◽

10.1016/j.biortech.2014.08.073 ◽

2014 ◽

Vol 171 ◽

pp. 291-297 ◽

Cited By ~ 14

Author(s):

Anna Behrendt ◽

Sheldon Tarre ◽

Michael Beliavski ◽

Michal Green ◽

Judith Klatt ◽

...

Keyword(s):

Electron Donor ◽

Nitrate Reduction ◽

Nitrate Removal ◽

High Electron ◽

Dissimilatory Nitrate Reduction

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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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Adenylate Cyclase and the Cyclic AMP Receptor Protein Modulate Stress Resistance and Virulence Capacity of Uropathogenic Escherichia coli

Infection and Immunity ◽

10.1128/iai.00796-12 ◽

2012 ◽

Vol 81 (1) ◽

pp. 249-258 ◽

Cited By ~ 29

Author(s):

Grant T. Donovan ◽

J. Paul Norton ◽

Jean M. Bower ◽

Matthew A. Mulvey

Keyword(s):

Escherichia Coli ◽

Urinary Tract ◽

Cyclic Amp ◽

Stress Resistance ◽

Nitrosative Stress ◽

Carbon Sources ◽

Receptor Protein ◽

Infection Model ◽

Content Type ◽

Tract Infections

In many bacteria, the second messenger cyclic AMP (cAMP) interacts with the transcription factor cAMP receptor protein (CRP), forming active cAMP-CRP complexes that can control a multitude of cellular activities, including expanded carbon source utilization, stress response pathways, and virulence. Here, we assessed the role of cAMP-CRP as a regulator of stress resistance and virulence in uropathogenicEscherichia coli(UPEC), the principal cause of urinary tract infections worldwide. Deletion of genes encoding either CRP or CyaA, the enzyme responsible for cAMP synthesis, attenuates the ability of UPEC to colonize the bladder in a mouse infection model, dependent on intact innate host defenses. UPEC mutants lacking cAMP-CRP grow normally in the presence of glucose but are unable to utilize alternate carbon sources like amino acids, the primary nutrients available to UPEC within the urinary tract. Relative to the wild-type UPEC isolate, thecyaAandcrpdeletion mutants are sensitive to nitrosative stress and the superoxide generator methyl viologen but remarkably resistant to hydrogen peroxide (H2O2) and acid stress. In the mutant strains, H2O2resistance correlates with elevated catalase activity attributable in part to enhanced translation of the alternate sigma factor RpoS. Acid resistance was promoted by both RpoS-independent and RpoS-dependent mechanisms, including expression of the RpoS-regulated DNA-binding ferritin-like protein Dps. We conclude that balanced input from many cAMP-CRP-responsive elements, including RpoS, is critical to the ability of UPEC to handle the nutrient limitations and severe environmental stresses present within the mammalian urinary tract.

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Involvement of a Putative Cyclic AMP Receptor Protein (CRP)-Like Binding Sequence and a CRP-Like Protein in Glucose-Mediated Catabolite Repression ofthnGenes in Rhodococcus sp. Strain TFB

Applied and Environmental Microbiology ◽

10.1128/aem.00700-12 ◽

2012 ◽

Vol 78 (15) ◽

pp. 5460-5462 ◽

Cited By ~ 5

Author(s):

Laura Tomás-Gallardo ◽

Eduardo Santero ◽

Belén Floriano

Keyword(s):

Cyclic Amp ◽

Catabolite Repression ◽

Transcriptional Regulators ◽

Receptor Protein ◽

Content Type ◽

Cyclic Amp Receptor Protein ◽

Catabolic Genes ◽

Binding Sequence ◽

Rhodococcus Sp

ABSTRACTGlucose catabolite repression of tetralin catabolic genes inRhodococcussp. strain TFB was shown to be exerted by a protein homologous to transcriptional regulators of the cyclic AMP receptor (CRP)-FNR family. The protein was detected bound to putative CRP-like boxes localized at the promoters of thethnA1andthnSgenes.

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A NovelShewanellaIsolate Enhances Corrosion by Using Metallic Iron as the Electron Donor with Fumarate as the Electron Acceptor

Applied and Environmental Microbiology ◽

10.1128/aem.01154-18 ◽

2018 ◽

Vol 84 (20) ◽

Cited By ~ 19

Author(s):

Jo Philips ◽

Niels Van den Driessche ◽

Kim De Paepe ◽

Antonin Prévoteau ◽

Jeffrey A. Gralnick ◽

...

Keyword(s):

Corrosion Rate ◽

Electron Donor ◽

Electron Acceptor ◽

Metallic Iron ◽

Hydrogen Generation ◽

Formation Rate ◽

Fold Increase ◽

Hydrogen Formation ◽

Content Type ◽

Reducing Properties

ABSTRACTThe involvement ofShewanellaspp. in biocorrosion is often attributed to their Fe(III)-reducing properties, but they could also affect corrosion by using metallic iron as an electron donor. Previously, we isolatedShewanellastrain 4t3-1-2LB from an acetogenic community enriched with Fe(0) as the sole electron donor. Here, we investigated its use of Fe(0) as an electron donor with fumarate as an electron acceptor and explored its corrosion-enhancing mechanism. Without Fe(0), strain 4t3-1-2LB fermented fumarate to succinate and CO2, as was shown by the reaction stoichiometry and pH. With Fe(0), strain 4t3-1-2LB completely reduced fumarate to succinate and increased the Fe(0) corrosion rate (7.0 ± 0.6)-fold in comparison to that of abiotic controls (based on the succinate-versus-abiotic hydrogen formation rate). Fumarate reduction by strain 4t3-1-2LB was, at least in part, supported by chemical hydrogen formation on Fe(0). Filter-sterilized spent medium increased the hydrogen generation rate only 1.5-fold, and thus extracellular hydrogenase enzymes appear to be insufficient to explain the enhanced corrosion rate. Electrochemical measurements suggested that strain 4t3-1-2LB did not excrete dissolved redox mediators. Exchanging the medium and scanning electron microscopy (SEM) imaging indicated that cells were attached to Fe(0). It is possible that strain 4t3-1-2LB used a direct mechanism to withdraw electrons from Fe(0) or favored chemical hydrogen formation on Fe(0) through maintaining low hydrogen concentrations. In coculture with anAcetobacteriumstrain, strain 4t3-1-2LB did not enhance acetogenesis from Fe(0). This work describes a strong corrosion enhancement by aShewanellastrain through its use of Fe(0) as an electron donor and provides insights into its corrosion-enhancing mechanism.IMPORTANCEShewanellaspp. are frequently found on corroded metal structures. Their role in microbial influenced corrosion has been attributed mainly to their Fe(III)-reducing properties and, therefore, has been studied with the addition of an electron donor (lactate).Shewanellaspp., however, can also use solid electron donors, such as cathodes and potentially Fe(0). In this work, we show that the electron acceptor fumarate supported the use of Fe(0) as the electron donor byShewanellastrain 4t3-1-2LB, which caused a (7.0 ± 0.6)-fold increase of the corrosion rate. The corrosion-enhancing mechanism likely involved cell surface-associated components in direct contact with the Fe(0) surface or maintenance of low hydrogen levels by attached cells, thereby favoring chemical hydrogen formation by Fe(0). This work sheds new light on the role ofShewanellaspp. in biocorrosion, while the insights into the corrosion-enhancing mechanism contribute to the understanding of extracellular electron uptake processes.

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