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Rose ND, Regan JM. Changes in phosphorylation of adenosine phosphate and redox state of nicotinamide-adenine dinucleotide (phosphate) in Geobacter sulfurreducens in response to electron acceptor and anode potential variation. Bioelectrochemistry 2015; 106:213-20. [PMID: 25857596 DOI: 10.1016/j.bioelechem.2015.03.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 03/03/2015] [Accepted: 03/16/2015] [Indexed: 01/28/2023]
Abstract
Geobacter sulfurreducens is one of the dominant bacterial species found in biofilms growing on anodes in bioelectrochemical systems. The intracellular concentrations of reduced and oxidized forms of nicotinamide-adenine dinucleotide (NADH and NAD(+), respectively) and nicotinamide-adenine dinucleotide phosphate (NADPH and NADP(+), respectively) as well as adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) were measured in G. sulfurreducens using fumarate, Fe(III)-citrate, or anodes poised at different potentials (110, 10, -90, and -190 mV (vs. SHE)) as the electron acceptor. The ratios of CNADH/CNAD+ (0.088±0.022) and CNADPH/CNADP+ (0.268±0.098) were similar under all anode potentials tested and with Fe(III)-citrate (reduced extracellularly). Both ratios significantly increased with fumarate as the electron acceptor (0.331±0.094 for NAD and 1.96±0.37 for NADP). The adenylate energy charge (the fraction of phosphorylation in intracellular adenosine phosphates) was maintained near 0.47 under almost all conditions. Anode-growing biofilms demonstrated a significantly higher molar ratio of ATP/ADP relative to suspended cultures grown on fumarate or Fe(III)-citrate. These results provide evidence that the cellular location of reduction and not the redox potential of the electron acceptor controls the intracellular redox potential in G. sulfurreducens and that biofilm growth alters adenylate phosphorylation.
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Affiliation(s)
- Nicholas D Rose
- College of Engineering, Department of Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, State College, PA 16802, USA.
| | - John M Regan
- College of Engineering, Department of Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, State College, PA 16802, USA.
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102
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Kashima H, Regan JM. Facultative nitrate reduction by electrode-respiring Geobacter metallireducens biofilms as a competitive reaction to electrode reduction in a bioelectrochemical system. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:3195-3202. [PMID: 25622928 DOI: 10.1021/es504882f] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Alternative metabolic options of exoelectrogenic biofilms in bioelectrochemical systems (BESs) are important not only to explain the fundamental ecology and performance of these systems but also to develop reliable integrated nutrient removal strategies in BESs, which potentially involve substrates or intermediates that support/induce those alternative metabolisms. This research focused on dissimilatory nitrate reduction as an alternative metabolism to dissimilatory anode reduction. Using the exoelectrogenic nitrate reducer Geobacter metallireducens, the critical conditions controlling those alternative metabolisms were investigated in two-chamber, potentiostatically controlled BESs at various anode potentials and biofilm thicknesses and challenged over a range of nitrate concentrations. Results showed that anode-reducing biofilms facultatively reduced nitrate at all tested anode potentials (-150 to +900 mV vs Standard Hydrogen Electrode) with a rapid metabolic shift. The critical nitrate concentration that triggered a significant decrease in BES performance was a function of anode biofilm thickness but not anode potential. This indicates that these alternative metabolisms were controlled by the availability of nitrate, which is a function of nitrate concentration in bulk solution and its diffusion into an anode-reducing biofilm. Coulombic recovery decreased as a function of nitrate dose due to electron-acceptor substrate competition, and nitrate-induced suspended biomass growth decreased the effluent quality.
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Affiliation(s)
- Hiroyuki Kashima
- Department of Civil and Environmental Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
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103
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Merkley ED, Wrighton KC, Castelle CJ, Anderson BJ, Wilkins MJ, Shah V, Arbour T, Brown JN, Singer SW, Smith RD, Lipton MS. Changes in protein expression across laboratory and field experiments in Geobacter bemidjiensis. J Proteome Res 2015; 14:1361-75. [PMID: 25496566 DOI: 10.1021/pr500983v] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Bacterial extracellular metal respiration, as carried out by members of the genus Geobacter, is of interest for applications including microbial fuel cells and bioremediation. Geobacter bemidjiensis is the major species whose growth is stimulated during groundwater amendment with acetate. We have carried out label-free proteomics studies of G. bemidjiensis grown with acetate as the electron donor and either fumarate, ferric citrate, or one of two hydrous ferric oxide mineral types as electron acceptor. The major class of proteins whose expression changes across these conditions is c-type cytochromes, many of which are known to be involved in extracellular metal reduction in other, better-characterized Geobacter species. Some proteins with multiple homologues in G. bemidjiensis (OmcS, OmcB) had different expression patterns than observed for their G. sulfurreducens homologues under similar growth conditions. We also compared the proteome from our study to a prior proteomics study of biomass recovered from an aquifer in Colorado, where the microbial community was dominated by strains closely related to G. bemidjiensis. We detected an increased number of proteins with functions related to motility and chemotaxis in the Colorado field samples compared to the laboratory samples, suggesting the importance of motility for in situ extracellular metal respiration.
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Affiliation(s)
- Eric D Merkley
- Signature Sciences and Technology Division, and ‡Biological Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
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104
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Aracic S, Semenec L, Franks AE. Investigating microbial activities of electrode-associated microorganisms in real-time. Front Microbiol 2014; 5:663. [PMID: 25506343 PMCID: PMC4246885 DOI: 10.3389/fmicb.2014.00663] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 11/15/2014] [Indexed: 01/28/2023] Open
Abstract
Electrode-associated microbial biofilms are essential to the function of bioelectrochemical systems (BESs). These systems exist in a number of different configurations but all rely on electroactive microorganisms utilizing an electrode as either an electron acceptor or an electron donor to catalyze biological processes. Investigations of the structure and function of electrode-associated biofilms are critical to further the understanding of how microbial communities are able to reduce and oxidize electrodes. The community structure of electrode-reducing biofilms is diverse and often dominated by Geobacter spp. whereas electrode-oxidizing biofilms are often dominated by other microorganisms. The application of a wide range of tools, such as high-throughput sequencing and metagenomic data analyses, provide insight into the structure and possible function of microbial communities on electrode surfaces. However, the development and application of techniques that monitor gene expression profiles in real-time are required for a more definite spatial and temporal understanding of the diversity and biological activities of these dynamic communities. This mini review summarizes the key gene expression techniques used in BESs research, which have led to a better understanding of population dynamics, cell–cell communication and molecule-surface interactions in mixed and pure BES communities.
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Affiliation(s)
- Sanja Aracic
- Applied and Environmental Microbiology Laboratory, Department of Microbiology, La Trobe University , Melbourne, VIC, Australia
| | - Lucie Semenec
- Applied and Environmental Microbiology Laboratory, Department of Microbiology, La Trobe University , Melbourne, VIC, Australia
| | - Ashley E Franks
- Applied and Environmental Microbiology Laboratory, Department of Microbiology, La Trobe University , Melbourne, VIC, Australia
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105
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Shi L, Fredrickson JK, Zachara JM. Genomic analyses of bacterial porin-cytochrome gene clusters. Front Microbiol 2014; 5:657. [PMID: 25505896 PMCID: PMC4245776 DOI: 10.3389/fmicb.2014.00657] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Accepted: 11/13/2014] [Indexed: 11/13/2022] Open
Abstract
The porin-cytochrome (Pcc) protein complex is responsible for trans-outer membrane electron transfer during extracellular reduction of Fe(III) by the dissimilatory metal-reducing bacterium Geobacter sulfurreducens PCA. The identified and characterized Pcc complex of G. sulfurreducens PCA consists of a porin-like outer-membrane protein, a periplasmic 8-heme c-type cytochrome (c-Cyt) and an outer-membrane 12-heme c-Cyt, and the genes encoding the Pcc proteins are clustered in the same regions of genome (i.e., the pcc gene clusters) of G. sulfurreducens PCA. A survey of additionally microbial genomes has identified the pcc gene clusters in all sequenced Geobacter spp. and other bacteria from six different phyla, including Anaeromyxobacter dehalogenans 2CP-1, A. dehalogenans 2CP-C, Anaeromyxobacter sp. K, Candidatus Kuenenia stuttgartiensis, Denitrovibrio acetiphilus DSM 12809, Desulfurispirillum indicum S5, Desulfurivibrio alkaliphilus AHT2, Desulfurobacterium thermolithotrophum DSM 11699, Desulfuromonas acetoxidans DSM 684, Ignavibacterium album JCM 16511, and Thermovibrio ammonificans HB-1. The numbers of genes in the pcc gene clusters vary, ranging from two to nine. Similar to the metal-reducing (Mtr) gene clusters of other Fe(III)-reducing bacteria, such as Shewanella spp., additional genes that encode putative c-Cyts with predicted cellular localizations at the cytoplasmic membrane, periplasm and outer membrane often associate with the pcc gene clusters. This suggests that the Pcc-associated c-Cyts may be part of the pathways for extracellular electron transfer reactions. The presence of pcc gene clusters in the microorganisms that do not reduce solid-phase Fe(III) and Mn(IV) oxides, such as D. alkaliphilus AHT2 and I. album JCM 16511, also suggests that some of the pcc gene clusters may be involved in extracellular electron transfer reactions with the substrates other than Fe(III) and Mn(IV) oxides.
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Affiliation(s)
- Liang Shi
- Pacific Northwest National Laboratory Richland, WA, USA
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106
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107
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Enhanced uranium immobilization and reduction by Geobacter sulfurreducens biofilms. Appl Environ Microbiol 2014; 80:6638-46. [PMID: 25128347 DOI: 10.1128/aem.02289-14] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Biofilms 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 bacterium Geobacter sulfurreducens immobilized 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 of Geobacter conductive pili and, to a lesser extent, on the presence of the c cytochrome 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 of Geobacter cells 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 the in situ bioremediation of environments impacted by uranium contamination.
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108
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Research of Iron Reduction and the Iron Reductase Localization of Anammox Bacteria. Curr Microbiol 2014; 69:880-7. [DOI: 10.1007/s00284-014-0668-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Accepted: 06/15/2014] [Indexed: 10/24/2022]
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109
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Ren L, Zhang X, He W, Logan BE. High current densities enable exoelectrogens to outcompete aerobic heterotrophs for substrate. Biotechnol Bioeng 2014; 111:2163-9. [DOI: 10.1002/bit.25290] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Revised: 05/02/2014] [Accepted: 05/07/2014] [Indexed: 11/06/2022]
Affiliation(s)
- Lijiao Ren
- Department of Civil and Environmental Engineering; 212 Sackett Building, The Pennsylvania State University; University Park 16802 Pennsylvania
| | - Xiaoyuan Zhang
- Department of Civil and Environmental Engineering; 212 Sackett Building, The Pennsylvania State University; University Park 16802 Pennsylvania
| | - Weihua He
- State Key Laboratory of Urban Water Resource and Environment; Harbin Institute of Technology; Harbin P.R. China
| | - Bruce E. Logan
- Department of Civil and Environmental Engineering; 212 Sackett Building, The Pennsylvania State University; University Park 16802 Pennsylvania
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110
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Abundance of the multiheme c-type cytochrome OmcB increases in outer biofilm layers of electrode-grown Geobacter sulfurreducens. PLoS One 2014; 9:e104336. [PMID: 25090411 PMCID: PMC4121341 DOI: 10.1371/journal.pone.0104336] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 07/14/2014] [Indexed: 11/25/2022] Open
Abstract
When Geobacter sulfurreducens utilizes an electrode as its electron acceptor, cells embed themselves in a conductive biofilm tens of microns thick. While environmental conditions such as pH or redox potential have been shown to change close to the electrode, less is known about the response of G. sulfurreducens to growth in this biofilm environment. To investigate whether respiratory protein abundance varies with distance from the electrode, antibodies against an outer membrane multiheme cytochrome (OmcB) and cytoplasmic acetate kinase (AckA) were used to determine protein localization in slices spanning ∼25 µm-thick G. sulfurreducens biofilms growing on polished electrodes poised at +0.24 V (vs. Standard Hydrogen Electrode). Slices were immunogold labeled post-fixing, imaged via transmission electron microscopy, and digitally reassembled to create continuous images allowing subcellular location and abundance per cell to be quantified across an entire biofilm. OmcB was predominantly localized on cell membranes, and 3.6-fold more OmcB was detected on cells 10–20 µm distant from the electrode surface compared to inner layers (0–10 µm). In contrast, acetate kinase remained constant throughout the biofilm, and was always associated with the cell interior. This method for detecting proteins in intact conductive biofilms supports a model where the utilization of redox proteins changes with depth.
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111
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Maestro B, Ortiz JM, Schrott G, Busalmen JP, Climent V, Feliu JM. Crystallographic orientation and electrode nature are key factors for electric current generation by Geobacter sulfurreducens. Bioelectrochemistry 2014; 98:11-9. [DOI: 10.1016/j.bioelechem.2014.02.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 02/18/2014] [Accepted: 02/19/2014] [Indexed: 12/20/2022]
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112
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Nagarajan H, Embree M, Rotaru AE, Shrestha PM, Feist AM, Palsson BØ, Lovley DR, Zengler K. Characterization and modelling of interspecies electron transfer mechanisms and microbial community dynamics of a syntrophic association. Nat Commun 2014; 4:2809. [PMID: 24264237 DOI: 10.1038/ncomms3809] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 10/23/2013] [Indexed: 12/18/2022] Open
Abstract
Syntrophic associations are central to microbial communities and thus have a fundamental role in the global carbon cycle. Despite biochemical approaches describing the physiological activity of these communities, there has been a lack of a mechanistic understanding of the relationship between complex nutritional and energetic dependencies and their functioning. Here we apply a multi-omic modelling workflow that combines genomic, transcriptomic and physiological data with genome-scale models to investigate dynamics and electron flow mechanisms in the syntrophic association of Geobacter metallireducens and Geobacter sulfurreducens. Genome-scale modelling of direct interspecies electron transfer reveals insights into the energetics of electron transfer mechanisms. While G. sulfurreducens adapts to rapid syntrophic growth by changes at the genomic and transcriptomic level, G. metallireducens responds only at the transcriptomic level. This multi-omic approach enhances our understanding of adaptive responses and factors that shape the evolution of syntrophic communities.
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Affiliation(s)
- Harish Nagarajan
- Department of Bioengineering, University of California San Diego, La Jolla, California 92093-0412, USA
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113
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Microbial nanowires for bioenergy applications. Curr Opin Biotechnol 2014; 27:88-95. [DOI: 10.1016/j.copbio.2013.12.003] [Citation(s) in RCA: 202] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 11/22/2013] [Accepted: 12/06/2013] [Indexed: 11/23/2022]
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114
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Shrestha PM, Rotaru AE. Plugging in or going wireless: strategies for interspecies electron transfer. Front Microbiol 2014; 5:237. [PMID: 24904551 PMCID: PMC4032928 DOI: 10.3389/fmicb.2014.00237] [Citation(s) in RCA: 119] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 04/30/2014] [Indexed: 11/13/2022] Open
Abstract
Interspecies exchange of electrons enables a diversity of microbial communities to gain energy from reactions that no one microbe can catalyze. The first recognized strategies for interspecies electron transfer were those that relied on chemical intermediates that are recycled through oxidized and reduced forms. Well-studied examples are interspecies H2 transfer and the cycling of sulfur intermediates in anaerobic photosynthetic communities. Direct interspecies electron transfer (DIET) in which two species establish electrical contact is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions.
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Affiliation(s)
- Pravin Malla Shrestha
- Department of Microbiology, University of MassachusettsAmherst, MA, USA
- Energy Biosciences Institute, University of CaliforniaBerkeley, CA, USA
| | - Amelia-Elena Rotaru
- Nordic Center for Earth Evolution, University of Southern DenmarkOdense, Denmark
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115
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Going wireless: Fe(III) oxide reduction without pili by Geobacter sulfurreducens strain JS-1. Appl Environ Microbiol 2014; 80:4331-40. [PMID: 24814783 DOI: 10.1128/aem.01122-14] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous studies have suggested that the conductive pili of Geobacter sulfurreducens are essential for extracellular electron transfer to Fe(III) oxides and for optimal long-range electron transport through current-producing biofilms. The KN400 strain of G. sulfurreducens reduces poorly crystalline Fe(III) oxide more rapidly than the more extensively studied DL-1 strain. Deletion of the gene encoding PilA, the structural pilin protein, in strain KN400 inhibited Fe(III) oxide reduction. However, low rates of Fe(III) reduction were detected after extended incubation (>30 days) in the presence of Fe(III) oxide. After seven consecutive transfers, the PilA-deficient strain adapted to reduce Fe(III) oxide as fast as the wild type. Microarray, whole-genome resequencing, proteomic, and gene deletion studies indicated that this adaptation was associated with the production of larger amounts of the c-type cytochrome PgcA, which was released into the culture medium. It is proposed that the extracellular cytochrome acts as an electron shuttle, promoting electron transfer from the outer cell surface to Fe(III) oxides. The adapted PilA-deficient strain competed well with the wild-type strain when both were grown together on Fe(III) oxide. However, when 50% of the culture medium was replaced with fresh medium every 3 days, the wild-type strain outcompeted the adapted strain. A possible explanation for this is that the necessity to produce additional PgcA, to replace the PgcA being continually removed, put the adapted strain at a competitive disadvantage, similar to the apparent selection against electron shuttle-producing Fe(III) reducers in many anaerobic soils and sediments. Despite increased extracellular cytochrome production, the adapted PilA-deficient strain produced low levels of current, consistent with the concept that long-range electron transport through G. sulfurreducens biofilms is more effective via pili.
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116
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Liu F, Rotaru AE, Shrestha PM, Malvankar NS, Nevin KP, Lovley DR. Magnetite compensates for the lack of a pilin-associatedc-type cytochrome in extracellular electron exchange. Environ Microbiol 2014; 17:648-55. [DOI: 10.1111/1462-2920.12485] [Citation(s) in RCA: 238] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2013] [Accepted: 04/04/2014] [Indexed: 11/28/2022]
Affiliation(s)
- Fanghua Liu
- Department of Microbiology; University of Massachusetts; Amherst MA 01003 USA
- Key Laboratory of Coastal Biology and Utilization; Yantai Institute of Coastal Zone Research; Chinese Academy of Sciences; Yantai Shandong 264003 China
| | - Amelia-Elena Rotaru
- Department of Microbiology; University of Massachusetts; Amherst MA 01003 USA
| | - Pravin M. Shrestha
- Department of Microbiology; University of Massachusetts; Amherst MA 01003 USA
| | - Nikhil S. Malvankar
- Department of Microbiology; University of Massachusetts; Amherst MA 01003 USA
| | - Kelly P. Nevin
- Department of Microbiology; University of Massachusetts; Amherst MA 01003 USA
| | - Derek R. Lovley
- Department of Microbiology; University of Massachusetts; Amherst MA 01003 USA
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117
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Competitive reduction of nitrate and iron oxides by Shewanella putrefaciens 200 under anoxic conditions. Colloids Surf A Physicochem Eng Asp 2014. [DOI: 10.1016/j.colsurfa.2014.01.023] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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118
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The iron stimulon and fur regulon of Geobacter sulfurreducens and their role in energy metabolism. Appl Environ Microbiol 2014; 80:2918-27. [PMID: 24584254 DOI: 10.1128/aem.03916-13] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Iron plays a critical role in the physiology of Geobacter species. It serves as both an essential component for proteins and cofactors and an electron acceptor during anaerobic respiration. Here, we investigated the iron stimulon and ferric uptake regulator (Fur) regulon of Geobacter sulfurreducens to examine the coordination between uptake of Fe(II) and the reduction of Fe(III) at the transcriptional level. Gene expression studies across a variety of different iron concentrations in both the wild type and a Δfur mutant strain were used to determine the iron stimulon. The stimulon consists of a broad range of gene products, ranging from iron-utilizing to central metabolism and iron reduction proteins. Integration of gene expression and chromatin immunoprecipitation (ChIP) data sets assisted in the identification of the Fur transcriptional regulatory network and Fur's role as a regulator of the iron stimulon. Additional physiological and transcriptional analyses of G. sulfurreducens grown with various Fe(II) concentrations revealed the depth of Fur's involvement in energy metabolism and the existence of redundancy within the iron-regulatory network represented by IdeR, an alternative iron transcriptional regulator. These characteristics enable G. sulfurreducens to thrive in environments with fluctuating iron concentrations by providing it with a robust mechanism to maintain tight and deliberate control over intracellular iron homeostasis.
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119
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Zhu X, Yates MD, Hatzell MC, Ananda Rao H, Saikaly PE, Logan BE. Microbial community composition is unaffected by anode potential. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:1352-1358. [PMID: 24364567 DOI: 10.1021/es404690q] [Citation(s) in RCA: 102] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
There is great controversy on how different set anode potentials affect the performance of a bioelectrochemical system (BES). It is often reported that more positive potentials improve acclimation and performance of exoelectrogenic biofilms, and alter microbial community structure, while in other studies relatively more negative potentials were needed to achieve higher current densities. To address this issue, the biomass, electroactivity, and community structure of anodic biofilms were examined over a wide range of set anode potentials (-0.25, -0.09, 0.21, 0.51, and 0.81 V vs a standard hydrogen electrode, SHE) in single-chamber microbial electrolysis cells. Maximum currents produced using a wastewater inoculum increased with anode potentials in the range of -0.25 to 0.21 V, but decreased at 0.51 and 0.81 V. The maximum currents were positively correlated with increasing biofilm biomass. Pyrosequencing indicated biofilm communities were all similar and dominated by bacteria most similar to Geobacter sulfurreducens. Differences in anode performance with various set potentials suggest that the exoelectrogenic communities self-regulate their exocellular electron transfer pathways to adapt to different anode potentials.
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Affiliation(s)
- Xiuping Zhu
- Department of Civil and Environmental Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
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120
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Kuzume A, Zhumaev U, Li J, Fu Y, Füeg M, Estévez M, Borjas Z, Wandlowski T, Esteve-Nuñez A. An in situ surface electrochemistry approach towards whole-cell studies: the structure and reactivity of a Geobacter sulfurreducens submonolayer on electrified metal/electrolyte interfaces. Phys Chem Chem Phys 2014; 16:22229-36. [DOI: 10.1039/c4cp03357d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Characterisation of direct electron transfer processes between Geobacter sulfurreducens and the Au(111) surface was performed under electrochemical control.
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Affiliation(s)
- Akiyoshi Kuzume
- Department of Chemistry and Biochemistry
- University of Bern
- 3012 Bern, Switzerland
| | - Ulmas Zhumaev
- Department of Chemistry and Biochemistry
- University of Bern
- 3012 Bern, Switzerland
| | - Jianfeng Li
- Department of Chemistry and Biochemistry
- University of Bern
- 3012 Bern, Switzerland
| | - Yongchun Fu
- Department of Chemistry and Biochemistry
- University of Bern
- 3012 Bern, Switzerland
| | - Michael Füeg
- Department of Chemistry and Biochemistry
- University of Bern
- 3012 Bern, Switzerland
| | - Marta Estévez
- Department of Chemical Engineering
- University of Alcalá
- 28871 Alcalá de Heranes, Spain
| | - Zulema Borjas
- Department of Chemical Engineering
- University of Alcalá
- 28871 Alcalá de Heranes, Spain
- IMDEA WATER
- Parque Tecnológico de Alcalá
| | - Thomas Wandlowski
- Department of Chemistry and Biochemistry
- University of Bern
- 3012 Bern, Switzerland
| | - Abraham Esteve-Nuñez
- Department of Chemical Engineering
- University of Alcalá
- 28871 Alcalá de Heranes, Spain
- IMDEA WATER
- Parque Tecnológico de Alcalá
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121
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Semenec L, Franks AE. The microbiology of microbial electrolysis cells. MICROBIOLOGY AUSTRALIA 2014. [DOI: 10.1071/ma14065] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
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122
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Jana PS, Katuri K, Kavanagh P, Kumar A, Leech D. Charge transport in films of Geobacter sulfurreducens on graphite electrodes as a function of film thickness. Phys Chem Chem Phys 2014; 16:9039-46. [DOI: 10.1039/c4cp01023j] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Charge transport throughGeobacter sulfurreducensbiofilms increases with film thickness, as more porous films improves ion transport upon electrolysis.
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Affiliation(s)
- Partha Sarathi Jana
- School of Chemistry & Ryan Institute
- National University of Ireland Galway
- Galway, Ireland
| | - Krishna Katuri
- School of Chemistry & Ryan Institute
- National University of Ireland Galway
- Galway, Ireland
- Water Desalination and Reuse Research Center
- King Abdullah University of Science and Technology
| | - Paul Kavanagh
- School of Chemistry & Ryan Institute
- National University of Ireland Galway
- Galway, Ireland
| | - Amit Kumar
- School of Chemistry & Ryan Institute
- National University of Ireland Galway
- Galway, Ireland
| | - Dónal Leech
- School of Chemistry & Ryan Institute
- National University of Ireland Galway
- Galway, Ireland
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123
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Kuzume A, Zhumaev U, Li J, Fu Y, Füeg M, Esteve-Nuñez A, Wandlowski T. An in-situ surface electrochemistry approach toward whole-cell studies: Charge transfer between Geobacter sulfurreducens and electrified metal/electrolyte interfaces through linker molecules. Electrochim Acta 2013. [DOI: 10.1016/j.electacta.2013.02.073] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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124
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Yong XY, Shi DY, Chen YL, Feng J, Xu L, Zhou J, Wang SY, Yong YC, Sun YM, OuYang PK, Zheng T. Enhancement of bioelectricity generation by manipulation of the electron shuttles synthesis pathway in microbial fuel cells. BIORESOURCE TECHNOLOGY 2013; 152:220-224. [PMID: 24292201 DOI: 10.1016/j.biortech.2013.10.086] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2013] [Revised: 10/24/2013] [Accepted: 10/28/2013] [Indexed: 06/02/2023]
Abstract
Microbial fuel cells (MFCs) are promising for generating bioenergy and treating organic waste simultaneously. However, low extracellular electron transfer (EET) efficiency between electrogens and anodes remains one of the major bottlenecks in practical applications of MFCs. In this paper, pyocyanin (PYO) synthesis pathway was manipulated to improve the EET efficiency in Pseudomonas aeruginosa-inoculated MFCs. By overexpression of phzM (methyltransferase encoding gene), the maximum power density of P. aeruginosa-phzM-inoculated MFC was enhanced to 166.68 μW/cm(2), which was four folds of the original strain. In addition, the phzM overexpression strain exhibited an increase of 1.6 folds in PYO production and about a onefold decrease in the total internal resistance than the original strain, which should underlie the enhancement of the EET efficiency and the electricity power output (EPT). On the basis of these results, the manipulation of electron shuttles synthesis pathways could be an efficient approach to improve the EPT of MFCs.
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Affiliation(s)
- Xiao-Yu Yong
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China; Bioenergy Research Institute, Nanjing University of Technology, Nanjing 210095, China.
| | - Dong-Yan Shi
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China
| | - Yi-Lu Chen
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China
| | - Jiao Feng
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China
| | - Lin Xu
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China
| | - Jun Zhou
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China; Bioenergy Research Institute, Nanjing University of Technology, Nanjing 210095, China
| | - Shu-Ya Wang
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China; Bioenergy Research Institute, Nanjing University of Technology, Nanjing 210095, China
| | - Yang-Chun Yong
- Biofuels Institute, School of the Environment, Jiangsu University, Zhenjiang 212013, China
| | - Yong-Ming Sun
- Guangzhou Institute of Energy Conversion, Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Ping-Kai OuYang
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China; Bioenergy Research Institute, Nanjing University of Technology, Nanjing 210095, China
| | - Tao Zheng
- College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210095, China; Bioenergy Research Institute, Nanjing University of Technology, Nanjing 210095, China.
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125
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Meng J, Xu Z, Guo J, Yue Y, Sun X. Analysis of enhanced current-generating mechanism of Geobacter sulfurreducens strain via model-driven metabolism simulation. PLoS One 2013; 8:e73907. [PMID: 24058500 PMCID: PMC3773087 DOI: 10.1371/journal.pone.0073907] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 07/23/2013] [Indexed: 12/04/2022] Open
Abstract
Microbial fuel cells (MFCs) are a class of ideal technologies that function via anaerobic respiration of electricigens, which bring current generation and environmental restoration together. An in-depth understanding of microbial metabolism is of great importance in engineering microbes to further improve their respiration. We employed flux balance analysis and selected Fe(iii) as a substitute for the electrode to simulate current-generating metabolism of Geobacter sulfurreducens PCA with a fixed acetate uptake rate. Simulation results indicated the fluxes of reactions directing acetate towards dissimilation to generate electrons increased under the suboptimal growth condition, resulting in an increase in the respiration rate and a decrease in the growth rate. The results revealed the competitive relationship between oxidative respiration and cell growth during the metabolism of microbe current generation. The results helped us quantitatively understand why microbes growing slowly have the potential to make good use of fuel in MFCs. At the same time, slow growth does not necessarily result in speedy respiration. Alternative respirations may exist under the same growth state due to redundant pathways in the metabolic network. The big difference between the maximum and minimum respiration mainly results from the total formate secretion. With iterative flux variability analysis, a relatively ideal model of variant of G. sulfurreducens PCA was reconstructed by deleting several enzymes in the wild model, which could reach simultaneous suboptimal growth and maximum respiration. Under this ideal condition, flux towards extracellular electron transfer rather than for biosynthesis is beneficial for the conversion of organic matter to electricity without large accumulations of biomass and electricigens may maximize utilization of limited fuel. Our simulations will provide an insight into the enhanced current-generating mechanism and identify theoretical range of respiration rates for guiding strain improvement in MFCs.
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Affiliation(s)
- Jing Meng
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing, China
| | - Zixiang Xu
- Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, China
| | - Jing Guo
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing, China
| | - Yunxia Yue
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing, China
| | - Xiao Sun
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing, China
- * E-mail:
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126
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U(VI) reduction by diverse outer surface c-type cytochromes of Geobacter sulfurreducens. Appl Environ Microbiol 2013; 79:6369-74. [PMID: 23934497 DOI: 10.1128/aem.02551-13] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Early studies with Geobacter sulfurreducens suggested that outer-surface c-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain of G. sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surface c-type cytochromes of G. sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83% ± 10% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89% ± 10% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested that G. sulfurreducens requires outer-surface c-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors.
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127
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A long way to the electrode: how do Geobacter cells transport their electrons? Biochem Soc Trans 2013; 40:1274-9. [PMID: 23176467 DOI: 10.1042/bst20120046] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The mechanism of electron transport in Geobacter sulfurreducens biofilms is a topic under intense study and debate. Although some proteins were found to be essential for current production, the specific role that each one plays in electron transport to the electrode remains to be elucidated and a consensus on the mechanism of electron transport has not been reached. In the present paper, to understand the state of the art in the topic, electron transport from inside of the cell to the electrode in Geobacter sulfurreducens biofilms is analysed, reviewing genetic studies, biofilm conductivity assays and electrochemical and spectro-electrochemical experiments. Furthermore, crucial data still required to achieve a deeper understanding are highlighted.
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128
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Long-range electron transport to Fe(III) oxide via pili with metallic-like conductivity. Biochem Soc Trans 2013; 40:1186-90. [PMID: 23176452 DOI: 10.1042/bst20120131] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The mechanisms for Fe(III) oxide reduction by Geobacter species are of interest because Geobacter species have been shown to play an important role in Fe(III) oxide reduction in a diversity of environments in which Fe(III) reduction is a geochemically significant process. Geobacter species specifically express pili during growth on Fe(III) oxide compared with growth on soluble chelated Fe(III), and mutants that cannot produce pili are unable to effectively reduce Fe(III) oxide. The pili of Geobacter sulfurreducens are electrically conductive along their length under physiologically relevant conditions and exhibit a metallic-like conductivity similar to that observed previously in synthetic organic metals. Metallic-like conductivity in a biological protein filament is a previously unrecognized mechanism for electron transport that differs significantly from the more well-known biological strategy of electron hopping/tunnelling between closely spaced redox-active proteins. The multihaem c-type cytochrome OmcS is specifically associated with pili and is necessary for Fe(III) oxide reduction. However, multiple lines of evidence, including the metallic-like conductivity of the pili and the fact that OmcS molecules are spaced too far apart for electron hopping/tunnelling, indicate that OmcS is not responsible for long-range electron conduction along the pili. The role of OmcS may be to facilitate electron transfer from the pili to Fe(III) oxide. Long-range electron transport via pili with metallic-like conductivity is a paradigm shift that has important implications not only for Fe(III) oxide reduction, but also for interspecies electron exchange in syntrophic microbial communities as well as microbe-electrode interactions and the emerging field of bioelectronics.
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129
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Characterizing the interplay between multiple levels of organization within bacterial sigma factor regulatory networks. Nat Commun 2013; 4:1755. [DOI: 10.1038/ncomms2743] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 03/15/2013] [Indexed: 12/11/2022] Open
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130
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Bonanni PS, Bradley DF, Schrott GD, Busalmen JP. Limitations for current production in Geobacter sulfurreducens biofilms. CHEMSUSCHEM 2013; 6:711-720. [PMID: 23417889 DOI: 10.1002/cssc.201200671] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Revised: 11/15/2012] [Indexed: 06/01/2023]
Abstract
Devices that exploit electricity produced by electroactive bacteria such as Geobacter sulfurreducens have not yet been demonstrated beyond the laboratory scale. The current densities are far from the maximum that the bacteria can produce because fundamental properties such as the mechanism of extracellular electron transport and factors limiting cell respiration remain unclear. In this work, a strategy for the investigation of electroactive biofilms is presented. Numerical modeling of the response of G. sulfurreducens biofilms cultured on a rotating disk electrode has allowed for the discrimination of different limiting steps in the process of current production within a biofilm. The model outputs reveal that extracellular electron transport limits the respiration rate of the cells furthest from the electrode to the extent that cell division is not possible. The mathematical model also demonstrates that recent findings such as the existence of a redox gradient in actively respiring biofilms can be explained by an electron hopping mechanism but not when considering metallic-like conductivities.
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Affiliation(s)
- P Sebastian Bonanni
- Lab. de bioelectroquímica, Area de electroquímica y corrosíón INTEMA, Juan B. Justo 4302, Mar del Plata, Argentina.
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131
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Zhang F, Xia X, Luo Y, Sun D, Call DF, Logan BE. Improving startup performance with carbon mesh anodes in separator electrode assembly microbial fuel cells. BIORESOURCE TECHNOLOGY 2013; 133:74-81. [PMID: 23425580 DOI: 10.1016/j.biortech.2013.01.036] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Revised: 12/29/2012] [Accepted: 01/05/2013] [Indexed: 06/01/2023]
Abstract
In a separator electrode assembly microbial fuel cell, oxygen crossover from the cathode inhibits current generation by exoelectrogenic bacteria, resulting in poor reactor startup and performance. To determine the best approach for improving startup performance, the effect of acclimation to a low set potential (-0.2V, versus standard hydrogen electrode) was compared to startup at a higher potential (+0.2 V) or no set potential, and inoculation with wastewater or pre-acclimated cultures. Anodes acclimated to -0.2 V produced the highest power of 1330±60 mW m(-2) for these different anode conditions, but unacclimated wastewater inocula produced inconsistent results despite the use of this set potential. By inoculating reactors with transferred cell suspensions, however, startup time was reduced and high power was consistently produced. These results show that pre-acclimation at -0.2 V consistently improves power production compared to use of a more positive potential or the lack of a set potential.
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Affiliation(s)
- Fang Zhang
- Department of Civil and Environmental Engineering, Penn State University, University Park, PA 16802, USA
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132
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Aklujkar M, Coppi MV, Leang C, Kim BC, Chavan MA, Perpetua LA, Giloteaux L, Liu A, Holmes DE. Proteins involved in electron transfer to Fe(III) and Mn(IV) oxides by Geobacter sulfurreducens and Geobacter uraniireducens. MICROBIOLOGY-SGM 2013; 159:515-535. [PMID: 23306674 DOI: 10.1099/mic.0.064089-0] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Whole-genome microarray analysis of Geobacter sulfurreducens grown on insoluble Fe(III) oxide or Mn(IV) oxide versus soluble Fe(III) citrate revealed significantly different expression patterns. The most upregulated genes, omcS and omcT, encode cell-surface c-type cytochromes, OmcS being required for Fe(III) and Mn(IV) oxide reduction. Other electron transport genes upregulated on both metal oxides included genes encoding putative menaquinol : ferricytochrome c oxidoreductase complexes Cbc4 and Cbc5, periplasmic c-type cytochromes Dhc2 and PccF, outer membrane c-type cytochromes OmcC, OmcG and OmcV, multicopper oxidase OmpB, the structural components of electrically conductive pili, PilA-N and PilA-C, and enzymes that detoxify reactive oxygen/nitrogen species. Genes upregulated on Fe(III) oxide encode putative menaquinol : ferricytochrome c oxidoreductase complexes Cbc3 and Cbc6, periplasmic c-type cytochromes, including PccG and PccJ, and outer membrane c-type cytochromes, including OmcA, OmcE, OmcH, OmcL, OmcN, OmcO and OmcP. Electron transport genes upregulated on Mn(IV) oxide encode periplasmic c-type cytochromes PccR, PgcA, PpcA and PpcD, outer membrane c-type cytochromes OmaB/OmaC, OmcB and OmcZ, multicopper oxidase OmpC and menaquinone-reducing enzymes. Genetic studies indicated that MacA, OmcB, OmcF, OmcG, OmcH, OmcI, OmcJ, OmcM, OmcV and PccH, the putative Cbc5 complex subunit CbcC and the putative Cbc3 complex subunit CbcV are important for reduction of Fe(III) oxide but not essential for Mn(IV) oxide reduction. Gene expression patterns for Geobacter uraniireducens were similar. These results demonstrate that the physiology of Fe(III)-reducing bacteria differs significantly during growth on different insoluble and soluble electron acceptors and emphasize the importance of c-type cytochromes for extracellular electron transfer in G. sulfurreducens.
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Affiliation(s)
- M Aklujkar
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - M V Coppi
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - C Leang
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - B C Kim
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - M A Chavan
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - L A Perpetua
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - L Giloteaux
- Department of Microbiology, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - A Liu
- Department of Mathematics and Statistics, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - D E Holmes
- Department of Physical and Biological Sciences, Western New England University, Springfield, MA 01119, USA
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133
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Bonanni PS, Massazza D, Busalmen JP. Stepping stones in the electron transport from cells to electrodes in Geobacter sulfurreducens biofilms. Phys Chem Chem Phys 2013; 15:10300-6. [DOI: 10.1039/c3cp50411e] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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134
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Genomic plasticity enables a secondary electron transport pathway in Shewanella oneidensis. Appl Environ Microbiol 2012; 79:1150-9. [PMID: 23220953 DOI: 10.1128/aem.03556-12] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Microbial dissimilatory iron reduction is an important biogeochemical process. It is physiologically challenging because iron occurs in soils and sediments in the form of insoluble minerals such as hematite or ferrihydrite. Shewanella oneidensis MR-1 evolved an extended respiratory chain to the cell surface to reduce iron minerals. Interestingly, the organism evolved a similar strategy for reduction of dimethyl sulfoxide (DMSO), which is reduced at the cell surface as well. It has already been established that electron transfer through the outer membrane is accomplished via a complex in which β-barrel proteins enable interprotein electron transfer between periplasmic oxidoreductases and cell surface-localized terminal reductases. MtrB is the β-barrel protein that is necessary for dissimilatory iron reduction. It forms a complex together with the periplasmic decaheme c-type cytochrome MtrA and the outer membrane decaheme c-type cytochrome MtrC. Consequently, mtrB deletion mutants are unable to reduce ferric iron. The data presented here show that this inability can be overcome by a mobile genomic element with the ability to activate the expression of downstream genes and which is inserted within the SO4362 gene of the SO4362-to-SO4357 gene cluster. This cluster carries genes similar to mtrA and mtrB and encoding a putative cell surface DMSO reductase. Expression of SO4359 and SO4360 alone was sufficient to complement not only an mtrB mutant under ferric citrate-reducing conditions but also a mutant that furthermore lacks any outer membrane cytochromes. Hence, the putative complex formed by the SO4359 and SO4360 gene products is capable not only of membrane-spanning electron transfer but also of reducing extracellular electron acceptors.
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135
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Patil SA, Hägerhäll C, Gorton L. Electron transfer mechanisms between microorganisms and electrodes in bioelectrochemical systems. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/s12566-012-0033-x] [Citation(s) in RCA: 146] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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136
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137
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Outer cell surface components essential for Fe(III) oxide reduction by Geobacter metallireducens. Appl Environ Microbiol 2012. [PMID: 23183974 DOI: 10.1128/aem.02954-12] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Geobacter species are important Fe(III) reducers in a diversity of soils and sediments. Mechanisms for Fe(III) oxide reduction have been studied in detail in Geobacter sulfurreducens, but a number of the most thoroughly studied outer surface components of G. sulfurreducens, particularly c-type cytochromes, are not well conserved among Geobacter species. In order to identify cellular components potentially important for Fe(III) oxide reduction in Geobacter metallireducens, gene transcript abundance was compared in cells grown on Fe(III) oxide or soluble Fe(III) citrate with whole-genome microarrays. Outer-surface cytochromes were also identified. Deletion of genes for c-type cytochromes that had higher transcript abundance during growth on Fe(III) oxides and/or were detected in the outer-surface protein fraction identified six c-type cytochrome genes, that when deleted removed the capacity for Fe(III) oxide reduction. Several of the c-type cytochromes which were essential for Fe(III) oxide reduction in G. metallireducens have homologs in G. sulfurreducens that are not important for Fe(III) oxide reduction. Other genes essential for Fe(III) oxide reduction included a gene predicted to encode an NHL (Ncl-1-HT2A-Lin-41) repeat-containing protein and a gene potentially involved in pili glycosylation. Genes associated with flagellum-based motility, chemotaxis, and pili had higher transcript abundance during growth on Fe(III) oxide, consistent with the previously proposed importance of these components in Fe(III) oxide reduction. These results demonstrate that there are similarities in extracellular electron transfer between G. metallireducens and G. sulfurreducens but the outer-surface c-type cytochromes involved in Fe(III) oxide reduction are different.
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138
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On the road to improve the bioremediation and electricity-harvesting skills of Geobacter sulfurreducens: functional and structural characterization of multihaem cytochromes. Biochem Soc Trans 2012; 40:1295-301. [DOI: 10.1042/bst20120099] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Extracellular electron transfer is one of the physiological hallmarks of Geobacter sulfurreducens, allowing these bacteria to reduce toxic and/or radioactive metals and grow on electrode surfaces. Aiming to functionally optimize the respiratory electron-transfer chains, such properties can be explored through genetically engineered strains. Geobacter species comprise a large number of different multihaem c-type cytochromes involved in the extracellular electron-transfer pathways. The functional characterization of multihaem proteins is particularly complex because of the coexistence of several microstates in solution, connecting the fully reduced and oxidized states. NMR spectroscopy has been used to monitor the stepwise oxidation of each individual haem and thus to obtain information on each microstate. For the structural study of these proteins, a cost-effective isotopic labelling of the protein polypeptide chains was combined with the comparative analysis of 1H-13C HSQC (heteronuclear single-quantum correlation) NMR spectra obtained for labelled and unlabelled samples. These new methodological approaches allowed us to study G. sulfurreducens haem proteins functionally and structurally, revealing functional mechanisms and key residues involved in their electron-transfer capabilities. Such advances can now be applied to the design of engineered haem proteins to improve the bioremediation and electricity-harvesting skills of G. sulfurreducens.
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139
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Long-range electron transport in Geobacter sulfurreducens biofilms is redox gradient-driven. Proc Natl Acad Sci U S A 2012; 109:15467-72. [PMID: 22955881 DOI: 10.1073/pnas.1209829109] [Citation(s) in RCA: 153] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Geobacter spp. can acquire energy by coupling intracellular oxidation of organic matter with extracellular electron transfer to an anode (an electrode poised at a metabolically oxidizing potential), forming a biofilm extending many cell lengths away from the anode surface. It has been proposed that long-range electron transport in such biofilms occurs through a network of bound redox cofactors, thought to involve extracellular matrix c-type cytochromes, as occurs for polymers containing discrete redox moieties. Here, we report measurements of electron transport in actively respiring Geobacter sulfurreducens wild type biofilms using interdigitated microelectrode arrays. Measurements when one electrode is used as an anode and the other electrode is used to monitor redox status of the biofilm 15 μm away indicate the presence of an intrabiofilm redox gradient, in which the concentration of electrons residing within the proposed redox cofactor network is higher farther from the anode surface. The magnitude of the redox gradient seems to correlate with current, which is consistent with electron transport from cells in the biofilm to the anode, where electrons effectively diffuse from areas of high to low concentration, hopping between redox cofactors. Comparison with gate measurements, when one electrode is used as an electron source and the other electrode is used as an electron drain, suggests that there are multiple types of redox cofactors in Geobacter biofilms spanning a range in oxidation potential that can engage in electron transport. The majority of these redox cofactors, however, seem to have oxidation potentials too negative to be involved in electron transport when acetate is the electron source.
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140
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Set potential regulation reveals additional oxidation peaks of Geobacter sulfurreducens anodic biofilms. Electrochem commun 2012. [DOI: 10.1016/j.elecom.2012.06.013] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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141
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Fine Tuning of Redox Networks on Multiheme Cytochromes from Geobacter sulfurreducens Drives Physiological Electron/Proton Energy Transduction. Bioinorg Chem Appl 2012; 2012:298739. [PMID: 22899897 PMCID: PMC3415244 DOI: 10.1155/2012/298739] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 06/11/2012] [Indexed: 02/03/2023] Open
Abstract
The bacterium Geobacter sulfurreducens (Gs) can grow in the presence of extracellular terminal acceptors, a property that is currently explored to harvest electricity from aquatic sediments and waste organic matter into microbial fuel cells. A family composed of five triheme cytochromes (PpcA-E) was identified in Gs. These cytochromes play a crucial role by bridging the electron transfer from oxidation of cytoplasmic donors to the cell exterior and assisting the reduction of extracellular terminal acceptors. The detailed thermodynamic characterization of such proteins showed that PpcA and PpcD have an important redox-Bohr effect that might implicate these proteins in the e(-)/H(+) coupling mechanisms to sustain cellular growth. The physiological relevance of the redox-Bohr effect in these proteins was studied by determining the fractional contribution of each individual redox-microstate at different pH values. For both proteins, oxidation progresses from a particular protonated microstate to a particular deprotonated one, over specific pH ranges. The preferred e(-)/H(+) transfer pathway established by the selected microstates indicates that both proteins are functionally designed to couple e(-)/H(+) transfer at the physiological pH range for cellular growth.
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142
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Abstract
Electromicrobiology deals with the interactions between microorganisms and electronic devices and with the novel electrical properties of microorganisms. A diversity of microorganisms can donate electrons to, or accept electrons from, electrodes without the addition of artificial electron shuttles. However, the mechanisms for microbe-electrode electron exchange have been seriously studied in only a few microorganisms. Shewanella oneidensis interacts with electrodes primarily via flavins that function as soluble electron shuttles. Geobacter sulfurreducens makes direct electrical contacts with electrodes via outer-surface, c-type cytochromes. G. sulfurreducens is also capable of long-range electron transport along pili, known as microbial nanowires, that have metallic-like conductivity similar to that previously described in synthetic conducting polymers. Pili networks confer conductivity to G. sulfurreducens biofilms, which function as a conducting polymer, with supercapacitor and transistor functionalities. Conductive microorganisms and/or their nanowires have a number of potential practical applications, but additional basic research will be necessary for rational optimization.
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Affiliation(s)
- Derek R Lovley
- Department of Microbiology, University of Massachusetts, Amherst, 01003, USA.
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143
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Liu Y, Bond DR. Long-distance electron transfer by G. sulfurreducens biofilms results in accumulation of reduced c-type cytochromes. CHEMSUSCHEM 2012; 5:1047-53. [PMID: 22577055 PMCID: PMC3500873 DOI: 10.1002/cssc.201100734] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Revised: 03/06/2012] [Indexed: 05/12/2023]
Abstract
So close, but yet so far: G. sulfurreducens c-type cytochromes become reduced as biofilms grow on electrodes beyond a few cell thicknesses, even if the electrode is poised well above the potential required to oxidize all cytochromes. Cytochrome redox state also lags behind rapid potential changes during voltammetry, but only when the films are multiple cell layers thick, as would be expected if diffusional or exchange-based kinetics controls electron transfer between cytochromes.
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Affiliation(s)
- Ying Liu
- BioTechnology Institute and Department of Microbiology, University of Minnesota, 140 Gortner Laboratory, 1479 Gortner Ave St. Paul MN 55108, USA
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144
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Malvankar NS, Lovley DR. Microbial nanowires: a new paradigm for biological electron transfer and bioelectronics. CHEMSUSCHEM 2012; 5:1039-1046. [PMID: 22614997 DOI: 10.1002/cssc.201100733] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Revised: 03/06/2012] [Indexed: 06/01/2023]
Abstract
The discovery that Geobacter sulfurreducens can produce protein filaments with metallic-like conductivity, known as microbial nanowires, that facilitate long-range electron transport is a paradigm shift in biological electron transfer and has important implications for biogeochemistry, microbial ecology, and the emerging field of bioelectronics. Although filaments in a wide diversity of microorganisms have been called microbial nanowires, the type IV pili of G. sulfurreducens and G. metallireducens are the only filaments that have been shown to be required for extracellular electron transport to extracellular electron acceptors or for conduction of electrons through biofilms. Studies of G. sulfurreducens pili preparations and intact biofilms under physiologically relevant conditions have provided multiple lines of evidence for metallic-like conduction along the length of pili and for the possibility of pili networks to confer high conductivity within biofilms. This mechanism of electron conduction contrasts with the previously known mechanism for biological electron transfer via electron tunneling or hopping between closely associated molecules, a strategy unlikely to be well adapted for long-range electron transport outside the cell. In addition to promoting electron exchange with abiotic electron acceptors, microbial nanowires have recently been shown to be involved in direct interspecies electron transfer between syntrophic partners. An improved understanding of the mechanisms for metallic-like conductivity in microbial nanowires, as well as engineering microorganisms with desirable catalytic abilities with nanowires, could lead to new applications in microbial electrosynthesis and bioelectronics.
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Affiliation(s)
- Nikhil S Malvankar
- Department of Microbiology, University of Massachusetts, Amherst, 203, Morrill Science Center IVN, 639 North Pleasant Street, Amherst, MA 01003, USA
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145
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Franks AE, Glaven RH, Lovley DR. Real-time spatial gene expression analysis within current-producing biofilms. CHEMSUSCHEM 2012; 5:1092-1098. [PMID: 22577044 DOI: 10.1002/cssc.201100714] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2011] [Revised: 03/06/2011] [Indexed: 05/31/2023]
Abstract
The expression of genes involved in central metabolism and extracellular electron transfer was examined in real-time in current-producing anode biofilms of Geobacter sulfurreducens. Strains of G. sulfurreducens were generated, in which the expression of the gene for a short half-life fluorescent protein was placed under control of the promoter of the genes of interest. Anode biofilms were grown in a chamber that permitted direct examination of the cell fluorescence with confocal scanning laser microscopy. Studies on nifD and citrate synthase expression in response to environmental changes demonstrated that the reporter system revealed initiation and termination of gene transcription. Uniform expression throughout the biofilms was noted for the genes for citrate synthase; PilA, the structural protein of the conductive pili; and OmcZ, a c-type cytochrome essential for optimal current production, which was localized at the anode-biofilm interface. These results demonstrate that even cells at great distance from the anode, or within expected low-pH zones, are metabolically active and likely to contribute to current production and that there are factors other than gene expression differences influencing the distribution of OmcZ. This real-time reporter approach is likely to be a useful tool in optimizing the design of technologies relying on microbe-electrode interactions.
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Affiliation(s)
- Ashley E Franks
- Department of Microbiology, University of Massachusetts, Morrill IVN, 639 North Pleasant Street, Amherst, MA, USA.
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146
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Bond DR, Strycharz-Glaven SM, Tender LM, Torres CI. On electron transport through Geobacter biofilms. CHEMSUSCHEM 2012; 5:1099-1105. [PMID: 22615023 DOI: 10.1002/cssc.201100748] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 12/14/2011] [Indexed: 06/01/2023]
Abstract
Geobacter spp. can form a biofilm that is more than 20 μm thick on an anode surface by utilizing the anode as a terminal respiratory electron acceptor. Just how microbes transport electrons through a thick biofilm and across the biofilm/anode interface, and what determines the upper limit to biofilm thickness and catalytic activity (i.e., current, the rate at which electrons are transferred to the anode), are fundamental questions attracting substantial attention. A significant body of experimental evidence suggests that electrons are transferred from individual cells through a network of cytochromes associated with cell outer membranes, within extracellular polymeric substances, and along pili. Here, we describe what is known about this extracellular electron transfer process, referred to as electron superexchange, and its proposed role in biofilm anode respiration. Superexchange is able to account for many different types of experimental results, as well as for the upper limit to biofilm thickness and catalytic activity that Geobacter biofilm anodes can achieve.
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Affiliation(s)
- Daniel R Bond
- BioTechnology Institute and Department of Microbiology, University of Minnesota, St. Paul, MN 55108, USA
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147
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Katuri KP, Rengaraj S, Kavanagh P, O'Flaherty V, Leech D. Charge transport through Geobacter sulfurreducens biofilms grown on graphite rods. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:7904-7913. [PMID: 22524560 DOI: 10.1021/la2047036] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Biofilms of the electroactive bacterium Geobacter sulfurreducens were induced to grow on graphite-rod electrodes under a potential of 0 V (vs Ag/AgCl) in the presence of acetate as an electron donor. Increased anodic currents for bioelectrocatalytic oxidation of acetate were obtained when the electrodes were incubated for longer periods with periodic electron-donor feeding. The maximum current density for acetate oxidation increased 2.8-fold, and the biofilm thickness increased by 4.25-fold, over a time period of 83-147 h. Cyclic voltammetry in the presence of acetate supports a model of heterogeneous electron transfer, one electron at time, from biofilm to electrode through a dominant redox species centered at -0.41 V vs Ag/AgCl. Voltammetry performed under nonturnover conditions provided an estimate of the surface coverage of the redox species of 25 nmol/cm(2). This value was used to estimate a redox species concentration of 7.3 mM within the 34-μm-thick biofilm and a charge-transport diffusion coefficient of 3.6 × 10(-7) cm(2)/s. This value of diffusion coefficient is greater than that observed in traditional thin-film voltammetric studies with redox polymer films containing much higher surface concentrations of redox species and might be associated with proton transport to ensure electroneutrality within the biofilm upon electrolysis.
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Affiliation(s)
- Krishna P Katuri
- School of Chemistry, National University of Ireland Galway, University Road, Galway, Ireland
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148
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Two isoforms of Geobacter sulfurreducens PilA have distinct roles in pilus biogenesis, cytochrome localization, extracellular electron transfer, and biofilm formation. J Bacteriol 2012; 194:2551-63. [PMID: 22408162 DOI: 10.1128/jb.06366-11] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type IV pili of Geobacter sulfurreducens are composed of PilA monomers and are essential for long-range extracellular electron transfer to insoluble Fe(III) oxides and graphite anodes. A previous analysis of pilA expression indicated that transcription was initiated at two positions, with two predicted ribosome-binding sites and translation start codons, potentially producing two PilA preprotein isoforms. The present study supports the existence of two functional translation start codons for pilA and identifies two isoforms (short and long) of the PilA preprotein. The short PilA isoform is found predominantly in an intracellular fraction. It seems to stabilize the long isoform and to influence the secretion of several outer-surface c-type cytochromes. The long PilA isoform is required for secretion of PilA to the outer cell surface, a process that requires coexpression of pilA with nine downstream genes. The long isoform was determined to be essential for biofilm formation on certain surfaces, for optimum current production in microbial fuel cells, and for growth on insoluble Fe(III) oxides.
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149
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Dissimilatory reduction of extracellular electron acceptors in anaerobic respiration. Appl Environ Microbiol 2011; 78:913-21. [PMID: 22179232 DOI: 10.1128/aem.06803-11] [Citation(s) in RCA: 158] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
An extension of the respiratory chain to the cell surface is necessary to reduce extracellular electron acceptors like ferric iron or manganese oxides. In the past few years, more and more compounds were revealed to be reduced at the surface of the outer membrane of Gram-negative bacteria, and the list does not seem to have an end so far. Shewanella as well as Geobacter strains are model organisms to discover the biochemistry that enables the dissimilatory reduction of extracellular electron acceptors. In both cases, c-type cytochromes are essential electron-transferring proteins. They make the journey of respiratory electrons from the cytoplasmic membrane through periplasm and over the outer membrane possible. Outer membrane cytochromes have the ability to catalyze the last step of the respiratory chains. Still, recent discoveries provided evidence that they are accompanied by further factors that allow or at least facilitate extracellular reduction. This review gives a condensed overview of our current knowledge of extracellular respiration, highlights recent discoveries, and discusses critically the influence of different strategies for terminal electron transfer reactions.
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150
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Jain A, Gazzola G, Panzera A, Zanoni M, Marsili E. Visible spectroelectrochemical characterization of Geobacter sulfurreducens biofilms on optically transparent indium tin oxide electrode. Electrochim Acta 2011. [DOI: 10.1016/j.electacta.2011.02.073] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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