scholarly journals Mechanistic stratification in electroactive biofilms of Geobacter sulfurreducens mediated by pilus nanowires

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Rebecca J. Steidl ◽  
Sanela Lampa-Pastirk ◽  
Gemma Reguera
Keyword(s):  
Electricity Generation ◽  
Geobacter Sulfurreducens ◽  
Deficient Mutant ◽  
Threshold Distance ◽  
Cytochrome Pathway ◽  
Inactivating Mutation ◽  
Electron Carriers ◽  
Biofilm Matrix ◽  
Pilus Assembly

Abstract Electricity generation by Geobacter sulfurreducens biofilms grown on electrodes involves matrix-associated electron carriers, such as c-type cytochromes. Yet, the contribution of the biofilm’s conductive pili remains uncertain, largely because pili-defective mutants also have cytochrome defects. Here we report that a pili-deficient mutant carrying an inactivating mutation in the pilus assembly motor PilB has no measurable defects in cytochrome expression, yet forms anode biofilms with reduced electroactivity and is unable to grow beyond a threshold distance (∼10 μm) from the underlying electrode. The defects are similar to those of a Tyr3 mutant, which produces poorly conductive pili. The results support a model in which the conductive pili permeate the biofilms to wire the cells to the conductive biofilm matrix and the underlying electrode, operating coordinately with cytochromes until the biofilm reaches a threshold thickness that limits the efficiency of the cytochrome pathway but not the functioning of the conductive pili network.

Insights into genes involved in electricity generation in Geobacter sulfurreducens via whole genome microarray analysis of the OmcF-deficient mutant

2008 ◽  
Vol 73 (1) ◽  
pp. 70-75 ◽  
Author(s):  
Byoung-Chan Kim ◽  
Bradley L. Postier ◽  
Raymond J. DiDonato ◽  
Swades K. Chaudhuri ◽  
Kelly P. Nevin ◽  
...  
Keyword(s):  
Microarray Analysis ◽  
Electricity Generation ◽  
Geobacter Sulfurreducens ◽  
Whole Genome ◽  
Deficient Mutant ◽  
Whole Genome Microarray

scholarly journals OmcB, a c-Type Polyheme Cytochrome, Involved in Fe(III) Reduction in Geobacter sulfurreducens

2003 ◽  
Vol 185 (7) ◽  
pp. 2096-2103 ◽  
Author(s):  
Ching Leang ◽  
M. V. Coppi ◽  
D. R. Lovley
Keyword(s):  
Electron Transport ◽  
Outer Membrane ◽  
Gene Clusters ◽  
Growth Conditions ◽  
Gene Replacement ◽  
Geobacter Sulfurreducens ◽  
Deficient Mutant ◽  
Subsurface Environments ◽  
The Family

ABSTRACT Microorganisms in the family Geobacteraceae are the predominant Fe(III)-reducing microorganisms in a variety of subsurface environments in which Fe(III) reduction is an important process, but little is known about the mechanisms for electron transport to Fe(III) in these organisms. The Geobacter sulfurreducens genome was found to contain a 10-kb chromosomal duplication consisting of two tandem three-gene clusters. The last genes of the two clusters, designated omcB and omcC, encode putative outer membrane polyheme c-type cytochromes which are 79% identical. The role of the omcB and omcC genes in Fe(III) reduction in G. sulfurreducens was investigated. OmcB and OmcC were both expressed during growth with acetate as the electron donor and either fumarate or Fe(III) as the electron acceptor. OmcB was ca. twofold more abundant under both conditions. Disrupting omcB or omcC by gene replacement had no impact on growth with fumarate. However, the OmcB-deficient mutant was greatly impaired in its ability to reduce Fe(III) both in cell suspensions and under growth conditions. In contrast, the ability of the OmcC-deficient mutant to reduce Fe(III) was similar to that of the wild type. When omcB was reintroduced into the OmcB-deficient mutant, the capacity for Fe(III) reduction was restored in proportion to the level of OmcB production. These results indicate that OmcB, but not OmcC, has a major role in electron transport to Fe(III) and suggest that electron transport to the outer membrane is an important feature in Fe(III) reduction in this organism.

scholarly journals Development of Electroactive and Anaerobic Ammonium-Oxidizing (Anammox) Biofilms from Digestate in Microbial Fuel Cells

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Enea Gino Di Domenico ◽  
Gianluca Petroni ◽  
Daniele Mancini ◽  
Alberto Geri ◽  
Luca Di Palma ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Nitrogen Removal ◽  
Microbial Fuel Cells ◽  
Energy Recovery ◽  
Electricity Generation ◽  
Geobacter Sulfurreducens ◽  
Graphite Anode ◽  
Anammox Bacteria ◽  
Ammonium Oxidation ◽  
Anodic Chamber

Microbial Fuel cells (MFCs) have been proposed for nutrient removal and energy recovery from different wastes. In this study the anaerobic digestate was used to feed H-type MFC reactors, one with a graphite anode preconditioned withGeobacter sulfurreducensand the other with an unconditioned graphite anode. The data demonstrate that the digestate acts as a carbon source, and even in the absence of anode preconditioning, electroactive bacteria colonise the anodic chamber, producing a maximum power density of 172.2 mW/m2. The carbon content was also reduced by up to 60%, while anaerobic ammonium oxidation (anammox) bacteria, which were found in the anodic compartment of the reactors, contributed to nitrogen removal from the digestate. Overall, these results demonstrate that MFCs can be used to recover anammox bacteria from natural sources, and it may represent a promising bioremediation unit in anaerobic digestor plants for the simultaneous nitrogen removal and electricity generation using digestate as substrate.

scholarly journals Adaptation to Disruption of the Electron Transfer Pathway for Fe(III) Reduction in Geobacter sulfurreducens

2005 ◽  
Vol 187 (17) ◽  
pp. 5918-5926 ◽  
Author(s):  
Ching Leang ◽  
L. A. Adams ◽  
K.-J. Chin ◽  
K. P. Nevin ◽  
B. A. Methé ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Electron Transport ◽  
Outer Membrane ◽  
Geobacter Sulfurreducens ◽  
Significant Shift ◽  
Deficient Mutant ◽  
Wild Type ◽  
Transcript Levels ◽  
Electron Transfer Pathway

ABSTRACT Previous studies demonstrated that an outer membrane c-type cytochrome, OmcB, was involved in Fe(III) reduction in Geobacter sulfurreducens. An OmcB-deficient mutant was greatly impaired in its ability to reduce both soluble and insoluble Fe(III). Reintroducing omcB restored the capacity for Fe(III) reduction at a level proportional to the level of OmcB production. Here, we report that the OmcB-deficient mutant gradually adapted to grow on soluble Fe(III) but not insoluble Fe(III). The adapted OmcB-deficient mutant reduced soluble Fe(III) at a rate comparable to that of the wild type, but the cell yield of the mutant was only ca. 60% of that of the wild type under steady-state culturing conditions. Analysis of proteins and transcript levels demonstrated that expression of several membrane-associated cytochromes was higher in the adapted mutant than in the wild type. Further comparison of transcript levels during steady-state growth on Fe(III) citrate with a whole-genome DNA microarray revealed a significant shift in gene expression in an apparent attempt to adapt metabolism to the impaired electron transport to Fe(III). These results demonstrate that, although there are many other membrane-bound c-type cytochromes in G. sulfurreducens, increased expression of these cytochromes cannot completely compensate for the loss of OmcB. The concept that outer membrane cytochromes are promiscuous reductases that are interchangeable in function appears to be incorrect. Furthermore, the results indicate that there may be different mechanisms for electron transfer to soluble Fe(III) and insoluble Fe(III) oxides in G. sulfurreducens, which emphasizes the importance of studying electron transport to the environmentally relevant Fe(III) oxides.

scholarly journals Enhanced Uranium Immobilization and Reduction by Geobacter sulfurreducens Biofilms

2014 ◽  
Vol 80 (21) ◽  
pp. 6638-6646 ◽  
Author(s):  
Dena L. Cologgi ◽  
Allison M. Speers ◽  
Blair A. Bullard ◽  
Shelly D. Kelly ◽  
Gemma Reguera
Keyword(s):  
Cell Envelope ◽  
Geobacter Sulfurreducens ◽  
Planktonic Cells ◽  
Cellular Functions ◽  
Content Type ◽  
Uranium Toxicity ◽  
Toxic Concentrations ◽  
Catalytic Capacity ◽  
Biofilm Matrix

ABSTRACTBiofilms formed by dissimilatory metal reducers are of interest to develop permeable biobarriers for the immobilization of soluble contaminants such as uranium. Here we show that biofilms of the model uranium-reducing bacteriumGeobacter sulfurreducensimmobilized substantially more U(VI) than planktonic cells and did so for longer periods of time, reductively precipitating it to a mononuclear U(IV) phase involving carbon ligands. The biofilms also tolerated high and otherwise toxic concentrations (up to 5 mM) of uranium, consistent with a respiratory strategy that also protected the cells from uranium toxicity. The enhanced ability of the biofilms to immobilize uranium correlated only partially with the biofilm biomass and thickness and depended greatly on the area of the biofilm exposed to the soluble contaminant. In contrast, uranium reduction depended on the expression ofGeobacterconductive pili and, to a lesser extent, on the presence of theccytochrome OmcZ in the biofilm matrix. The results support a model in which the electroactive biofilm matrix immobilizes and reduces the uranium in the top stratum. This mechanism prevents the permeation and mineralization of uranium in the cell envelope, thereby preserving essential cellular functions and enhancing the catalytic capacity ofGeobactercells to reduce uranium. Hence, the biofilms provide cells with a physically and chemically protected environment for the sustained immobilization and reduction of uranium that is of interest for the development of improved strategies for thein situbioremediation of environments impacted by uranium contamination.

scholarly journals OmcF, a Putative c-Type Monoheme Outer Membrane Cytochrome Required for the Expression of Other Outer Membrane Cytochromes in Geobacter sulfurreducens

2005 ◽  
Vol 187 (13) ◽  
pp. 4505-4513 ◽  
Author(s):  
Byoung-Chan Kim ◽  
Ching Leang ◽  
Yan-Huai R. Ding ◽  
Richard H. Glaven ◽  
Maddalena V. Coppi ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Critical Role ◽  
Electron Acceptors ◽  
Geobacter Sulfurreducens ◽  
Lag Phase ◽  
Membrane Association ◽  
Deficient Mutant ◽  
Wild Type ◽  
Cytochrome Content ◽  
Doubling Times

ABSTRACT Outer membrane cytochromes are often proposed as likely agents for electron transfer to extracellular electron acceptors, such as Fe(III). The omcF gene in the dissimilatory Fe(III)-reducing microorganism Geobacter sulfurreducens is predicted to code for a small outer membrane monoheme c-type cytochrome. An OmcF-deficient strain was constructed, and its ability to reduce and grow on Fe(III) citrate was found to be impaired. Following a prolonged lag phase (150 h), the OmcF-deficient strain developed the ability to grow in Fe(III) citrate medium with doubling times and yields that were ca. 145% and 70% of those of the wild type, respectively. Comparison of the c-type cytochrome contents of outer membrane-enriched fractions prepared from wild-type and OmcF-deficient cultures confirmed the outer membrane association of OmcF and revealed multiple changes in the cytochrome content of the OmcF-deficient strain. These changes included loss of expression of two previously characterized outer membrane cytochromes, OmcB and OmcC, and overexpression of a third previously characterized outer membrane cytochrome, OmcS, during growth on Fe(III) citrate. The omcB and omcC transcripts could not be detected in the OmcF-deficient mutant by either reverse transcriptase PCR or Northern blot analyses. Expression of the omcF gene in trans restored both the capacity of the OmcF-deficient mutant to reduce Fe(III) and wild-type levels of omcB and omcC mRNA and protein. Thus, elimination of OmcF may impair Fe(III) reduction by influencing expression of OmcB, which has previously been demonstrated to play a critical role in Fe(III) reduction.

scholarly journals Pili Expression in Geobacter sulfurreducens Lacking the Putative Gene for the PilB Pilus Assembly Motor

2021 ◽  
Author(s):  
Toshiyuki Ueki ◽  
David JF Walker ◽  
Kelly P Nevin ◽  
Joy E Ward ◽  
Trevor L Woodard ◽  
...  
Keyword(s):  
Electron Transport ◽  
Geobacter Sulfurreducens ◽  
Voltage Response ◽  
Wild Type ◽  
Putative Gene ◽  
Force Microscopy ◽  
His Tag ◽  
Pilin Gene ◽  
Extracellular Electron Transport ◽  
Pilus Assembly

Multiple lines of evidence suggest that electrically conductive pili (e-pili) are an important conduit for long-range electron transport in Geobacter sulfurreducens, a common model microbe for the study of extracellular electron transport mechanisms. One strategy to study the function of e-pili has been to delete the gene for PilB, the pilus assembly motor protein, in order to prevent e-pili expression. However, we found that e-pili are still expressed after the gene for PilB is deleted. Conducting probe atomic force microscopy revealed filaments with the same diameter and similar current-voltage response as e-pili harvested from wild-type G. sulfurreducens or when e-pili are heterologously expressed from the G. sulfurreducens pilin gene in E. coli. Immunogold labeling demonstrated that a G. sulfurreducens strain expressing e-pili with a His-tag continued to express His-tag labelled e-pili when the PilB gene was deleted. Strains with the PilB gene deleted produced maximum current densities comparable to wild-type controls. These results demonstrate that deleting the gene for PilB is not an appropriate strategy for constructing strains of G. sulfurreducens without e-pili, necessitating a reinterpretation of the results of previous studies that have employed this approach.

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