Soluble Electron Shuttles Can Mediate Energy Taxis toward Insoluble Electron Acceptors

2012 ◽  
Vol 46 (5) ◽  
pp. 2813-2820 ◽  
Author(s):  
Rui Li ◽  
James M. Tiedje ◽  
Chichia Chiu ◽  
R. Mark Worden
Keyword(s):  
Electron Acceptors ◽  
Electron Shuttles ◽  
Energy Taxis ◽  
Insoluble Electron Acceptors

Shewanella oneidensis MR-1 chemotaxis proteins and electron-transport chain components essential for congregation near insoluble electron acceptors

2012 ◽  
Vol 40 (6) ◽  
pp. 1167-1177 ◽  
Author(s):  
H. Wayne Harris ◽  
Mohamed Y. El-Naggar ◽  
Kenneth H. Nealson
Keyword(s):  
Electron Transport ◽  
Manganese Oxides ◽  
Surrounding Medium ◽  
Shewanella Oneidensis ◽  
Solid Substrate ◽  
Electron Acceptors ◽  
Energy Taxis ◽  
Signal Transduction Protein ◽  
Chemotaxis Proteins ◽  
Insoluble Electron Acceptors

Shewanella oneidensis MR-1 cells utilize a behaviour response called electrokinesis to increase their speed in the vicinity of IEAs (insoluble electron acceptors), including manganese oxides, iron oxides and poised electrodes [Harris, El-Naggar, Bretschger, Ward, Romine, Obraztsova and Nealson (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 326–331]. However, it is not currently understood how bacteria remain in the vicinity of the IEA and accumulate both on the surface and in the surrounding medium. In the present paper, we provide results indicating that cells that have contacted the IEAs swim faster than those that have not recently made contact. In addition, fast-swimming cells exhibit an enhancement of swimming reversals leading to rapid non-random accumulation of cells on, and adjacent to, mineral particles. We call the observed accumulation near IEAs ‘congregation’. Congregation is eliminated by the loss of a critical gene involved with EET (extracellular electron transport) (cymA, SO_4591) and is altered or eliminated in several deletion mutants of homologues of genes that are involved with chemotaxis or energy taxis in Escherichia coli. These genes include chemotactic signal transduction protein (cheA-3, SO_3207), methyl-accepting chemotaxis proteins with the Cache domain (mcp_cache, SO_2240) or the PAS (Per/Arnt/Sim) domain (mcp_pas, SO_1385). In the present paper, we report studies of S. oneidensis MR-1 that lend some insight into how microbes in this group can ‘sense’ the presence of a solid substrate such as a mineral surface, and maintain themselves in the vicinity of the mineral (i.e. via congregation), which may ultimately lead to attachment and biofilm formation.

scholarly journals Tactic Response ofShewanella oneidensisMR-1 toward Insoluble Electron Acceptors

mBio ◽  
2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Joseph Oram ◽  
Lars J. C. Jeuken
Keyword(s):  
Average Velocity ◽  
Cell Tracking ◽  
Reduction Potential ◽  
Electron Acceptors ◽  
Electrochemical Potential ◽  
Electrochemical Cells ◽  
Standard Hydrogen Electrode ◽  
Hydrogen Electrode ◽  
Exoelectrogenic Bacteria ◽  
Insoluble Electron Acceptors

ABSTRACTExoelectrogenic bacteria are defined by their ability to respire on extracellular and insoluble electron acceptors and have applications in bioremediation and microbial electrochemical systems (MESs), while playing important roles in biogeochemical cycling.Shewanella oneidensisMR-1, which has become a model organism for the study of extracellular respiration, is known to display taxis toward insoluble electron acceptors, including electrodes. Multiple mechanisms have been proposed for MR-1’s tactic behavior, and, here, we report on the role of electrochemical potential by video microscopy cell tracking experiments in three-electrode electrochemical cells. MR-1 trajectories were determined using a particle tracking algorithm and validated with Shannon’s entropy method. Tactic response by MR-1 in the electrochemical cell was observed to depend on the applied potential, as indicated by the average velocity and density of motile (>4 µm/s) MR-1 close to the electrode (<50 µm). Tactic behavior was observed at oxidative potentials, with a strong switch between the potentials −0.15 to −0.25 V versus the standard hydrogen electrode (SHE), which coincides with the reduction potential of flavins. The average velocity and density of motile MR-1 close to the electrode increased when riboflavin was added (2 µM), but were completely absent in a ΔmtrC/ΔomcAmutant of MR-1. Besides flavin’s function as an electron mediator to support anaerobic respiration on insoluble electron acceptors, we propose that riboflavin is excreted by MR-1 to sense redox gradients in its environment, aiding taxis toward insoluble electron acceptors, including electrodes in MESs.IMPORTANCEPrevious hypotheses of tactic behavior of exoelectrogenic bacteria are based on techniques that do not accurately control the electrochemical potential, such as chemical-in-plug assays or microscopy tracking experiments in two-electrode cells. Here, we have revisited previous experiments and, for the first time, performed microscopy cell-tracking experiments in three-electrode electrochemical cells, with defined electrode potentials. Based on these experiments, taxis toward electrodes is observed to switch at about −0.2 V versus standard hydrogen electrode (SHE), coinciding with the reduction potential of flavins.

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

2004 ◽  
Vol 70 (9) ◽  
pp. 5415-5425 ◽  
Author(s):  
Charles R. Myers ◽  
Judith M. Myers
Keyword(s):  
Shewanella Oneidensis ◽  
Electron Acceptors ◽  
Intensive Study ◽  
Feeding Experiments ◽  
Acid Analog ◽  
Previous Hypothesis ◽  
Redox Shuttle ◽  
Insoluble Electron Acceptors ◽  
Reducing Bacteria ◽  
Negative Mutant

ABSTRACT The mechanisms underlying the use of insoluble electron acceptors by metal-reducing bacteria, such as Shewanella oneidensis MR-1, are currently under intensive study. Current models for shuttling electrons across the outer membrane (OM) of MR-1 include roles for OM cytochromes and the possible excretion of a redox shuttle. While MR-1 is able to release a substance that restores the ability of a menaquinone (MK)-negative mutant, CMA-1, to reduce the humic acid analog anthraquinone-2,6-disulfonate (AQDS), cross-feeding experiments conducted here showed that the substance released by MR-1 restores the growth of CMA-1 on several soluble electron acceptors. Various strains derived from MR-1 also release this substance; these include mutants lacking the OM cytochromes OmcA and OmcB and the OM protein MtrB. Even though strains lacking OmcB and MtrB cannot reduce Fe(III) or AQDS, they still release a substance that restores the ability of CMA-1 to use MK-dependent electron acceptors, including AQDS and Fe(III). Quinone analysis showed that this released substance restores MK synthesis in CMA-1. This ability to restore MK synthesis in CMA-1 explains the cross-feeding results and challenges the previous hypothesis that this substance represents a redox shuttle that facilitates metal respiration.

scholarly journals Energy Taxis Is the Dominant Behavior in Azospirillum brasilense

2000 ◽  
Vol 182 (21) ◽  
pp. 6042-6048 ◽  
Author(s):  
Gladys Alexandre ◽  
Suzanne E. Greer ◽  
Igor B. Zhulin
Keyword(s):  
Electron Transport ◽  
Transport System ◽  
Azospirillum Brasilense ◽  
Behavioral Responses ◽  
Electron Acceptors ◽  
Electron Transport System ◽  
Microbial Species ◽  
Energy Taxis ◽  
System Energy ◽  
Type Of Behavior

ABSTRACT Energy taxis encompasses aerotaxis, phototaxis, redox taxis, taxis to alternative electron acceptors, and chemotaxis to oxidizable substrates. The signal for this type of behavior is originated within the electron transport system. Energy taxis was demonstrated, as a part of an overall behavior, in several microbial species, but it did not appear as the dominant determinant in any of them. In this study, we show that most behavioral responses proceed through this mechanism in the alpha-proteobacterium Azospirillum brasilense. First, chemotaxis to most chemoeffectors typical of the azospirilla habitat was found to be metabolism dependent and required a functional electron transport system. Second, other energy-related responses, such as aerotaxis, redox taxis, and taxis to alternative electron acceptors, were found in A. brasilense. Finally, a mutant lacking a cytochromec oxidase of the cbb 3 type was affected in chemotaxis, redox taxis, and aerotaxis. Altogether, the results indicate that behavioral responses to most stimuli inA. brasilense are triggered by changes in the electron transport system.

scholarly journals Unexpected chemoreceptors mediate energy taxis towards electron acceptors inShewanella oneidensis

2009 ◽  
Vol 73 (2) ◽  
pp. 278-290 ◽  
Author(s):  
Claudine Baraquet ◽  
Laurence Théraulaz ◽  
Chantal Iobbi-Nivol ◽  
Vincent Méjean ◽  
Cécile Jourlin-Castelli
Keyword(s):  
Electron Acceptors ◽  
Energy Taxis

scholarly journals Chemotactic Responses to Metals and Anaerobic Electron Acceptors in Shewanella oneidensis MR-1

2005 ◽  
Vol 187 (14) ◽  
pp. 5049-5053 ◽  
Author(s):  
Sira Bencharit ◽  
Mandy J. Ward
Keyword(s):  
Humic Acid ◽  
Electron Acceptor ◽  
Divalent Cations ◽  
Shewanella Oneidensis ◽  
Electron Acceptors ◽  
Anaerobic Conditions ◽  
Acid Analog ◽  
Redox Active ◽  
Insoluble Electron Acceptors ◽  
Reduced Forms

ABSTRACT Although a previous study indicated that the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 lacks chemotactic responses to metals that can be used as anaerobic electron acceptors, new results show that this bacterium responds to both Mn(III) and Fe(III). Cells were also shown to respond to another unusual electron acceptor, the humic acid analog anthraquinone-2,6-disulfonate. These results indicate that S. oneidensis is capable of moving towards a number of unusual anaerobic electron acceptors, including some that would normally be insoluble in the environment. Additionally, S. oneidensis was shown to migrate in gradients of several divalent cations under anaerobic conditions. Although responses to the reduced forms of redox-active metals, such as Mn(II) and Fe(II), might indicate that S. oneidensis uses gradients of these metals to locate the insoluble electron acceptors Mn(III/IV) and Fe(III) for dissimilatory purposes, responses to non-redox-active metals, such as Zn(II), suggest that movement towards divalent cations might serve other, potentially assimilatory, purposes.

scholarly journals Extracellular riboflavin induces anaerobic biofilm formation in Shewanella oneidensis

2021 ◽  
Author(s):  
Miriam Edel ◽  
Gunnar Sturm ◽  
Katrin Sturm-Richter ◽  
Michael Wagner ◽  
Julia Novion Ducassou ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Cell Surface ◽  
Biofilm Formation ◽  
Shewanella Oneidensis ◽  
Threshold Concentration ◽  
Electron Acceptors ◽  
Specific Response ◽  
Dependent Manner ◽  
Riboflavin Production ◽  
Electron Shuttles

AbstractSome microorganisms can respire with extracellular electron acceptors using an extended electron transport chain to the cell surface. These organisms apply flavin molecules as cofactors to facilitate one-electron transfer catalysed by the terminal reductases and as endogenous electron shuttles. In the model organism Shewanella oneidensis, riboflavin production and excretion triggers a specific biofilm formation response that is initiated at a specific threshold concentration, similar to canonical quorum sensing molecules. Riboflavin-mediated messaging is based on the overexpression of the gene encoding the putrescin decarboxylase speC which leads to posttranscriptional overproduction of proteins involved in biofilm formation. Using a model of growth-dependent riboflavin production under batch and biofilm growth conditions, the number of cells necessary to produce the threshold concentration per time was deduced. Furthermore, our results indicate that specific retention of riboflavin in the biofilm matrix leads to localized concentrations which by far exceed the necessary threshold value.ImportanceFerric iron is the fourth most abundant element of the earth crust. It occurs at neutral pH in the form insoluble iron minerals. The dissimilatory reduction of these minerals is an import part of global geological cycles and is catalyzed by microorganisms through extended respiratory chains to the cell surface. Shewanella oneidensis is one of the best understood model organisms for this kind of extracellular respiration. Flavins are important for the reduction of extracellular electron acceptors by S. oneidensis. since they have a function as (I) cofactors of the terminal reductases and (II) electron shuttles. In this study we reveal that flavin molecules are further employed as quorum sensing molecules. They are excreted by the organisms in a growth dependent manner and lead to anaerobic biofilm formation as a specific response at a certain threshold concentration. Although we know multiple examples of quorum sensing mechanisms, the use of riboflavin was so far not described and at least in S. oneidensis proceeds via a new regulatory routine that proceeds on the trancriptomic and posttranscriptomic level.

scholarly journals Novel Electrochemically Active Bacterium Phylogenetically Related to Arcobacter butzleri, Isolated from a Microbial Fuel Cell

2009 ◽  
Vol 75 (23) ◽  
pp. 7326-7334 ◽  
Author(s):  
Viatcheslav Fedorovich ◽  
Matthew C. Knighton ◽  
Eulyn Pagaling ◽  
F. Bruce Ward ◽  
Andrew Free ◽  
...  
Keyword(s):  
Microbial Fuel Cells ◽  
Electron Acceptors ◽  
Maximal Power ◽  
Electrochemically Active ◽  
Culture Independent ◽  
Arcobacter Butzleri ◽  
Active Bacterium ◽  
Insoluble Electron Acceptors ◽  
First Time ◽  
Mixed Community

ABSTRACT Exoelectrogenic bacteria are organisms that can transfer electrons to extracellular insoluble electron acceptors and have the potential to be used in devices such as microbial fuel cells (MFCs). Currently, exoelectrogens have been identified in the Alpha-, Beta-, Gamma- and Deltaproteobacteria, as well as in the Firmicutes and Acidobacteria. Here, we describe use of culture-independent methods to identify two members of the genus Arcobacter in the Epsilon p roteobacteria that are selectively enriched in an acetate-fed MFC. One of these organisms, Arcobacter butzleri strain ED-1, associates with the electrode and rapidly generates a strong electronegative potential as a pure culture when it is supplied with acetate. A mixed-community MFC in which ∼90% of the population is comprised of the two Arcobacter species generates a maximal power density of 296 mW/liter. This demonstration of exoelectrogenesis by strain ED-1 is the first time that this property has been shown for members of this genus.

Electronic structure studies of conducting polymers by electron energy-loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 160-161
Author(s):  
J. Fink
Keyword(s):  
Electronic Structure ◽  
Conducting Polymers ◽  
Conjugated Polymers ◽  
Electron Acceptors ◽  
Electron Donors ◽  
Light Emitting ◽  
One Dimensional ◽  
New Class ◽  
Electrical Conductivities ◽  
Electron Energy Loss

Conducting polymers comprises a new class of materials achieving electrical conductivities which rival those of the best metals. The parent compounds (conjugated polymers) are quasi-one-dimensional semiconductors. These polymers can be doped by electron acceptors or electron donors. The prototype of these materials is polyacetylene (PA). There are various other conjugated polymers such as polyparaphenylene, polyphenylenevinylene, polypoyrrole or polythiophene. The doped systems, i.e. the conducting polymers, have intersting potential technological applications such as replacement of conventional metals in electronic shielding and antistatic equipment, rechargable batteries, and flexible light emitting diodes.Although these systems have been investigated almost 20 years, the electronic structure of the doped metallic systems is not clear and even the reason for the gap in undoped semiconducting systems is under discussion.

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