<i>Shewanella oneidensis</i>
            MR-1 Restores Menaquinone Synthesis to a Menaquinone-Negative Mutant

Myers, Charles R.; Myers, Judith M.

doi:10.1128/aem.70.9.5415-5425.2004

Cited by 46 publications

(35 citation statements)

References 38 publications

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“…Consistent with previous reports (39,48,54), menaquinone biosynthesis was required for significant reduction of any of these compounds. CymA was also absolutely required for significant reduction of Fe compounds, as previously described (36), although the extent of AQDS reduction in a cymA mutant was not reported previously. However, the abilities of the omcB and mtrB mutants to reduce the three compounds differed depending on the substrate.…”

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confidence: 48%

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Shewanella oneidensis MR-1 Uses Overlapping Pathways for Iron Reduction at a Distance and by Direct Contact under Conditions Relevant for Biofilms

Lies¹,

Hernández

Kappler³

et al. 2005

Appl Environ Microbiol

301

199

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We developed a new method to measure iron reduction at a distance based on depositing Fe(III) (hydr)oxide within nanoporous glass beads. In this "Fe-bead" system, Shewanella oneidensis reduces at least 86.5% of the iron in the absence of direct contact. Biofilm formation accompanies Fe-bead reduction and is observable both macro-and microscopically. Fe-bead reduction is catalyzed by live cells adapted to anaerobic conditions, and maximal reduction rates require sustained protein synthesis. The amount of reactive ferric iron in the Fe-bead system is available in excess such that the rate of Fe-bead reduction is directly proportional to cell density; i.e., it is diffusion limited. Addition of either lysates prepared from anaerobic cells or exogenous electron shuttles stimulates Fe-bead reduction by S. oneidensis, but iron chelators or additional Fe(II) do not. Neither dissolved Fe(III) nor electron shuttling activity was detected in culture supernatants, implying that the mediator is retained within the biofilm matrix. Strains with mutations in omcB or mtrB show about 50% of the wild-type levels of reduction, while a cymA mutant shows less than 20% of the wild-type levels of reduction and a menF mutant shows insignificant reduction. The Fe-bead reduction defect of the menF mutant can be restored by addition of menaquinone, but menaquinone itself cannot stimulate Fe-bead reduction. Because the menF gene encodes the first committed step of menaquinone biosynthesis, no intermediates of the menaquinone biosynthetic pathway are used as diffusible mediators by this organism to promote iron reduction at a distance. CymA and menaquinone are required for both direct and indirect mineral reduction, whereas MtrB and OmcB contribute to but are not absolutely required for iron reduction at a distance.

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Section: Downloaded Fromsupporting

confidence: 48%

“…Whether S. oneidensis strain MR-1 itself reduces iron oxides at a distance has never been directly demonstrated, and the capacity of strain MR-1 for this process has been called into question (36). Because this strain is an important model system in geomicrobiology, we set out to determine whether in fact it could perform iron reduction at a distance.…”

mentioning

confidence: 99%

Shewanella oneidensis MR-1 Uses Overlapping Pathways for Iron Reduction at a Distance and by Direct Contact under Conditions Relevant for Biofilms

Lies¹,

Hernández

Kappler³

et al. 2005

Appl Environ Microbiol

301

199

View full text Add to dashboard Cite

show abstract

“…oneidensis MR-1 was also reported to secrete compounds that could rescue menaquinone biosynthesis mutants (6). Later experiments supported the hypothesis that these compounds were intermediates of quinone biosynthesis released by lysed cells, rather than intentionally secreted shuttles (7). Recent analysis of Shewanella putrefaciens 200 provided new evidence for an unidentified organic Fe(III) chelator, which was required for maximal rates of Fe(III) reduction (8).…”

mentioning

confidence: 71%

Shewanella secretes flavins that mediate extracellular electron transfer

Marsili¹,

Baron²,

Shikhare³

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

1,702

1,507

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Bacteria able to transfer electrons to metals are key agents in biogeochemical metal cycling, subsurface bioremediation, and corrosion processes. More recently, these bacteria have gained attention as the transfer of electrons from the cell surface to conductive materials can be used in multiple applications. In this work, we adapted electrochemical techniques to probe intact biofilms of Shewanella oneidensis MR-1 and Shewanella sp. MR-4 grown by using a poised electrode as an electron acceptor. This approach detected redox-active molecules within biofilms, which were involved in electron transfer to the electrode. A combination of methods identified a mixture of riboflavin and riboflavin-5 -phosphate in supernatants from biofilm reactors, with riboflavin representing the dominant component during sustained incubations (>72 h). Removal of riboflavin from biofilms reduced the rate of electron transfer to electrodes by >70%, consistent with a role as a soluble redox shuttle carrying electrons from the cell surface to external acceptors. Differential pulse voltammetry and cyclic voltammetry revealed a layer of flavins adsorbed to electrodes, even after soluble components were removed, especially in older biofilms. Riboflavin adsorbed quickly to other surfaces of geochemical interest, such as Fe(III) and Mn(IV) oxy(hydr)oxides. This in situ demonstration of flavin production, and sequestration at surfaces, requires the paradigm of soluble redox shuttles in geochemistry to be adjusted to include binding and modification of surfaces. Moreover, the known ability of isoalloxazine rings to act as metal chelators, along with their electron shuttling capacity, suggests that extracellular respiration of minerals by Shewanella is more complex than originally conceived.bioelectrochemistry ͉ biogeochemistry ͉ redox mediator ͉ riboflavin

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“…It has been hypothesized that one reason why Geobacter species predominate over other Fe(III)-reducing microorganisms in many subsurface environments is that Geobacter species expend less energy to reduce Fe(III) oxides than other Fe(III)-reducing organisms (58). Current evidence suggests that Geobacter species directly contact Fe(III) oxides (68), whereas other species, such as Geothrix (67) and possibly Shewanella (40,68,69) species, secrete a quinone-like water-soluble compound that serves as an electron shuttle between the surface of the cell and Fe(III), although this possibility is not without controversy (63).…”

Section: Resultsmentioning

confidence: 98%

Characterization of Metabolism in the Fe(III)-Reducing Organism Geobacter sulfurreducens by Constraint-Based Modeling

Mahadevan

Bond

Butler

et al. 2006

Appl Environ Microbiol

288

304

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Geobacter sulfurreducens is a well-studied representative of the Geobacteraceae, which play a critical role in organic matter oxidation coupled to Fe(III) reduction, bioremediation of groundwater contaminated with organics or metals, and electricity production from waste organic matter. In order to investigate G. sulfurreducens central metabolism and electron transport, a metabolic model which integrated genome-based predictions with available genetic and physiological data was developed via the constraint-based modeling approach. Evaluation of the rates of proton production and consumption in the extracellular and cytoplasmic compartments revealed that energy conservation with extracellular electron acceptors, such as Fe(III), was limited relative to that associated with intracellular acceptors. This limitation was attributed to lack of cytoplasmic proton consumption during reduction of extracellular electron acceptors. Model-based analysis of the metabolic cost of producing an extracellular electron shuttle to promote electron transfer to insoluble Fe(III) oxides demonstrated why Geobacter species, which do not produce shuttles, have an energetic advantage over shuttleproducing Fe(III) reducers in subsurface environments. In silico analysis also revealed that the metabolic network of G. sulfurreducens could synthesize amino acids more efficiently than that of Escherichia coli due to the presence of a pyruvate-ferredoxin oxidoreductase, which catalyzes synthesis of pyruvate from acetate and carbon dioxide in a single step. In silico phenotypic analysis of deletion mutants demonstrated the capability of the model to explore the flexibility of G. sulfurreducens central metabolism and correctly predict mutant phenotypes. These results demonstrate that iterative modeling coupled with experimentation can accelerate the understanding of the physiology of poorly studied but environmentally relevant organisms and may help optimize their practical applications.

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Shewanella oneidensis MR-1 Restores Menaquinone Synthesis to a Menaquinone-Negative Mutant

Cited by 46 publications

References 38 publications

Shewanella oneidensis MR-1 Uses Overlapping Pathways for Iron Reduction at a Distance and by Direct Contact under Conditions Relevant for Biofilms

Shewanella oneidensis MR-1 Uses Overlapping Pathways for Iron Reduction at a Distance and by Direct Contact under Conditions Relevant for Biofilms

Shewanella secretes flavins that mediate extracellular electron transfer

Characterization of Metabolism in the Fe(III)-Reducing Organism Geobacter sulfurreducens by Constraint-Based Modeling

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