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1.
Biosens Bioelectron ; 141: 111444, 2019 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-31226603

RESUMO

Bioelectrochemical systems (BESs) possess a great potential for simultaneous wastewater treatment and energy recovery. Rational construction of electrode materials could significantly improve the BESs performance. Three-dimensional macroporous electrode interface with high conductivity is highly desirable but challenging. In this work, we report a hierarchically nanostructured reduced graphene oxide nanosheets-polypyrrole (rGO@PPy) electrode via one-step electrodeposition technique. The prepared electrode was comprehensively studied by scanning/transmission electron microscopy, Raman spectroscopy, X-ray diffraction and electrochemical measurements, which showed that the rGO@PPy possessed a three-dimensional macroporous interconnecting scaffold with superior conductivity. The rGO@PPy electrode was utilized in Geobacter sulfurreducens inoculated BESs, and the maximum current density was 4.10 ±â€¯0.02 mA cm-2, which is 8-fold higher than that of a rGO electrode (0.51 ±â€¯0.03 mA cm-2), and is among the best performance reported for two-dimensional electrodes. The improved performance is ascribed to ultrahigh biomass concentration induced by "best match scale" between rGO@PPy and microbes, excellent extracellular electron transfer, as well as enhanced microbial affinity through the adequate exposure of biocompatible PPy layers. This work demonstrated a synergistic effect between rGO and PPy for the BESs performance improvement, and provided a new insight to design and fabricate a high-performance bioelectrode.


Assuntos
Técnicas Eletroquímicas/instrumentação , Grafite/química , Nanoestruturas/química , Polímeros/química , Pirróis/química , Fontes de Energia Bioelétrica , Técnicas Biossensoriais/instrumentação , Catálise , Condutividade Elétrica , Eletrodos , Geobacter/fisiologia , Porosidade
2.
Adv Microb Physiol ; 74: 1-96, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31126529

RESUMO

The family Geobacteraceae, with its only valid genus Geobacter, comprises deltaproteobacteria ubiquitous in soil, sediments, and subsurface environments where metal reduction is an active process. Research for almost three decades has provided novel insights into environmental processes and biogeochemical reactions not previously known to be carried out by microorganisms. At the heart of the environmental roles played by Geobacter bacteria is their ability to integrate redox pathways and regulatory checkpoints that maximize growth efficiency with electron donors derived from the decomposition of organic matter while respiring metal oxides, particularly the often abundant oxides of ferric iron. This metabolic specialization is complemented by versatile metabolic reactions, respiratory chains, and sensory networks that allow specific members to adaptively respond to environmental cues to integrate organic and inorganic contaminants in their oxidative and reductive metabolism, respectively. Thus, Geobacteraceae are important members of the microbial communities that degrade hydrocarbon contaminants under iron-reducing conditions and that contribute, directly or indirectly, to the reduction of radionuclides, toxic metals, and oxidized species of nitrogen. Their ability to produce conductive pili as nanowires for discharging respiratory electrons to solid-phase electron acceptors and radionuclides, or for wiring cells in current-harvesting biofilms highlights the unique physiological traits that make these organisms attractive biological platforms for bioremediation, bioenergy, and bioelectronics application. Here we review some of the most notable physiological features described in Geobacter species since the first model representatives were recovered in pure culture. We provide a historical account of the environmental research that has set the foundation for numerous physiological studies and the laboratory tools that had provided novel insights into the role of Geobacter in the functioning of microbial communities from pristine and contaminated environments. We pay particular attention to latest research, both basic and applied, that has served to expand the field into new directions and to advance interdisciplinary knowledge. The electrifying physiology of Geobacter, it seems, is alive and well 30 years on.


Assuntos
Condutividade Elétrica , Geobacter/fisiologia , Biodegradação Ambiental , Biofilmes/crescimento & desenvolvimento , Biotecnologia , Grupo dos Citocromos c/genética , Grupo dos Citocromos c/metabolismo , Transporte de Elétrons/fisiologia , Fímbrias Bacterianas/genética , Fímbrias Bacterianas/metabolismo , Geobacter/classificação , Metais/metabolismo , Oxirredução
3.
Bioelectrochemistry ; 127: 145-153, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30825658

RESUMO

Geobacter sulfurreducens is a model organism for understanding the role of bacterial structures in extracellular electron transfer mechanism (EET). This kind of bacteria relies on different structures such as type IV pili and over 100 c-type cytochromes to perform EET towards soluble and insoluble electron acceptors, including electrodes. To our knowledge, this work is the first electrochemical study comparing a G. sulfurreducens PilR-deficient mutant and wild type biofilms developed on fluorine-doped tin oxide (FTO) electrodes. Open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), were used to evaluate the electroactive properties of biofilms grown without externally imposed potential. Parallel studies of Confocal Laser Scanning Microscopy (CLSM) correlated with the electrochemical results. PilR is a transcriptional regulator involved in the expression of a wide variety of genes, including pilA (pilus structural protein) relevant c-type cytochromes and some other genes involved in biofilm formation and EET processes. Our findings suggest that PilR-deficient mutant forms a thinner (CLSM analysis) and less conductive biofilm (EIS analysis) than wild type, exhibiting different and irreversible redox processes at the interface (CV analysis). Additionally, this work reinforces some of the remarkable features described in previous reports about this G. sulfurreducens mutant.


Assuntos
Proteínas de Bactérias/genética , Biofilmes , Fímbrias Bacterianas/genética , Regulação Bacteriana da Expressão Gênica , Geobacter/genética , Fatores de Transcrição/genética , Fontes de Energia Bioelétrica/microbiologia , Biofilmes/crescimento & desenvolvimento , Condutividade Elétrica , Eletrodos , Transporte de Elétrons , Flúor/química , Deleção de Genes , Geobacter/fisiologia , Oxirredução , Compostos de Estanho/química
4.
Bioresour Technol ; 283: 129-137, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30901585

RESUMO

In this study, reduced graphene oxide (rGO) was developed and employed as cathode catalyst in a membrane-less microbial fuel cell (MFC) to improve energy and metal (copper) recovery in combined with biofilms. Results showed that rGO-based cathode exhibited better characterizations in structure and electron transfer than graphene oxide (GO)-based cathode. The voltage with rGO was about 67% increased, and Cu2+ removal efficiency was 43% improved as compared to GO. Cu species on cathode demonstrated the favorable Cu2+ reduction to Cu with the catalysis of rGO. Moreover, microbial community analysis indicated that rGO-based cathode exhibited better biocompatibility for functional bacteria that related to electron transfer and Cu2+ resistance, such as Geobacter and Pseudomonas, demonstrating the interspecific synergism of microorganisms for efficient energy and copper recovery. It will be of important significance for the heavy metal and energy recovery from low concentrations wastewater by using microbial fuel cell.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Biofilmes , Cobre/metabolismo , Grafite/metabolismo , Biocatálise , Eletrodos , Transporte de Elétrons , Geobacter/fisiologia , Pseudomonas/fisiologia
5.
Nat Rev Microbiol ; 17(5): 307-319, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30846876

RESUMO

A vast array of microorganisms from all three domains of life can produce electrical current and transfer electrons to the anodes of different types of bioelectrochemical systems. These exoelectrogens are typically iron-reducing bacteria, such as Geobacter sulfurreducens, that produce high power densities at moderate temperatures. With the right media and growth conditions, many other microorganisms ranging from common yeasts to extremophiles such as hyperthermophilic archaea can also generate high current densities. Electrotrophic microorganisms that grow by using electrons derived from the cathode are less diverse and have no common or prototypical traits, and current densities are usually well below those reported for model exoelectrogens. However, electrotrophic microorganisms can use diverse terminal electron acceptors for cell respiration, including carbon dioxide, enabling a variety of novel cathode-driven reactions. The impressive diversity of electroactive microorganisms and the conditions in which they function provide new opportunities for electrochemical devices, such as microbial fuel cells that generate electricity or microbial electrolysis cells that produce hydrogen or methane.


Assuntos
Archaea/fisiologia , Bactérias/metabolismo , Fontes de Energia Bioelétrica , Eletricidade , Biofilmes , Eletrodos , Eletrólise , Transporte de Elétrons , Geobacter/fisiologia , Hidrogênio/metabolismo , Metano/metabolismo
6.
ACS Appl Mater Interfaces ; 11(9): 8961-8968, 2019 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-30730701

RESUMO

Bioelectrochemical systems (BESs) are hybrid systems using electroactive bacteria and solid electrodes, which serve as electron donor or acceptor for microorganisms. When forming a biofilm on the electrode, bacteria secrete extracellular polymeric substances (EPSs). However, EPS excretion of electroactive biofilms in BES has been rarely studied so far. Consequently, the aim of this study is to develop a routine including the electrochemical cultivation, biofilm harvesting, fractionation, and biochemical analysis of the EPS secreted by Geobacter sulfurreducens under electroactive conditions. G. sulfurreducens was cultivated in microbial fuel cell mode on graphite-based electrodes polarized to +400 mV versus Ag/AgCl for 8 d. A maximum current density of 172 ± 29 µA cm-2 was reached after 7 d. The EPS secreted from the biofilms were harvested and fractioned into soluble, loosely bound, and tightly bound EPS and biochemically analyzed. Electroactive cultures secreted significantly more EPSs compared to cells grown under standard heterotrophic conditions (fumarate respiration). With 116 pg per cell, the highest amount of EPSs was measured for the soluble EPS fraction of G. sulfurreducens using anodic respiration, followed by the tightly bound (18 pg cell-1) and loosely bound (11 pg cell-1) fractions of the EPS. Proteins were found to dominate all EPS fractions of the biofilms grown under electrochemical conditions. To the best of the authors' knowledge, these experiments are the first approach toward a complete analysis of the main EPS components of G. sulfurreducens under anode-respiring conditions.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Biofilmes/crescimento & desenvolvimento , Matriz Extracelular de Substâncias Poliméricas/química , Geobacter/fisiologia , Técnicas Eletroquímicas , Eletrodos , Grafite/química , Propriedades de Superfície
7.
J Environ Sci (China) ; 78: 193-203, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30665638

RESUMO

Microbially mediated bioreduction of iron oxyhydroxide plays an important role in the biogeochemical cycle of iron. Geobacter sulfurreducens is a representative dissimilatory iron-reducing bacterium that assembles electrically conductive pili and cytochromes. The impact of supplementation with γ-Fe2O3 nanoparticles (NPs) (0.2 and 0.6 g) on the G. sulfurreducens-mediated reduction of ferrihydrite was investigated. In the overall performance of microbial ferrihydrite reduction mediated by γ-Fe2O3 NPs, stronger reduction was observed in the presence of direct contact with γ-Fe2O3 NPs than with indirect contact. Compared to the production of Fe(II) derived from biotic modification with ferrihydrite alone, increases greater than 1.6- and 1.4-fold in the production of Fe(II) were detected in the biotic modifications in which direct contact with 0.2 g and 0.6 g γ-Fe2O3 NPs, respectively, occurred. X-ray diffraction analysis indicated that magnetite was a unique representative iron mineral in ferrihydrite when active G. sulfurreducens cells were in direct contact with γ-Fe2O3 NPs. Because of the sorption of biogenic Fe(II) onto γ-Fe2O3 NPs instead of ferrihydrite, the addition of γ-Fe2O3 NPs could also contribute to increased duration of ferrihydrite reduction by preventing ferrihydrite surface passivation. Additionally, electron microscopy analysis confirmed that the direct addition of γ-Fe2O3 NPs stimulated the electrically conductive pili and cytochromes to stretch, facilitating long-range electron transfer between the cells and ferrihydrite. The obtained findings provide a more comprehensive understanding of the effects of iron oxide NPs on soil biogeochemistry.


Assuntos
Biodegradação Ambiental , Compostos Férricos/metabolismo , Geobacter/fisiologia , Nanopartículas/metabolismo , Compostos Férricos/química , Óxido Ferroso-Férrico , Nanopartículas/química
8.
Bioresour Technol ; 276: 119-126, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30616210

RESUMO

Extracellular polymeric substances (EPS) play crucial roles in promoting biofilm formation and contribute to electrochemical activities of biofilms in bioelectrochemical systems (BES). In this study, three stratified EPS fractions were extracted from Geobacter biofilms using EDTA-, ultrasound- and heating-based protocols and characterized with chemical, spectral and electrochemical analyses. Results suggested that, for Geobacter biofilms, ultrasound-based extraction protocol was more effective in EPS yield (62.1-66.5 mg C/g dry cell) than EDTA method, and had less cell lysis than heating method. The extraction methods greatly affected the proteins composition in the extracted EPS, indicated by the varied ratios of tryptophan/tyrosine protein-like substances. Electrochemical measurements demonstrated a good correlation between protein concentration and extracellular electron transfer function for both tightly-bound EPS and total EPS. This is the first study to extract and characterize stratified EPS fractions from Geobacter biofilms, and helpful for better understanding the function of EPS in BESs predominated by Geobacter.


Assuntos
Biofilmes , Matriz Extracelular de Substâncias Poliméricas/metabolismo , Geobacter/fisiologia , Técnicas Eletroquímicas , Transporte de Elétrons
9.
Bioelectrochemistry ; 126: 130-136, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30590223

RESUMO

Geobacter sulfurreducens (Gs) attachment and biofilm formation on self-assembled monolayers (SAMs) of carboxyl-terminated alkanethiol linkers with varied chain length on gold (Au) was investigated by electrochemical and microscopic methods to elucidate the effect of the surface modification on the current production efficiency of Gs cells and biofilms. At the initial stage of the cell attachment, the electrochemical activity of Gs cells at a submonolayer coverage on the SAM-Au surface was independent of the linker length. Subsequently, multiple potential cyclings indicated that longer linkers provided more biocompatible conditions for Gs cells than shorter ones. For Gs biofilms, on the other hand, the turnover current decreased exponentially with the linker length. During the biofilm formation, bacteria need to adjust from the initial planktonic state to an electrode-respiring state, which was triggered by a strong electrochemical stress found for shorter linkers, resulting in the formation of mature biofilms. Our results suggest that the initial cell attachment and the biofilm formation are two inherently different processes. Therefore, the effects of linker molecules, electron transfer efficiency and biocompatibility, must be explored simultaneously to understand both processes to increase the current production of electrogenic microorganisms in microbial fuel cells.


Assuntos
Alcanos/química , Fontes de Energia Bioelétrica/microbiologia , Biofilmes/crescimento & desenvolvimento , Ácidos Carboxílicos/química , Geobacter/fisiologia , Ouro/química , Compostos de Sulfidrila/química , Aderência Bacteriana , Materiais Biocompatíveis/química , Eletrodos , Transporte de Elétrons , Propriedades de Superfície
10.
Bioelectrochemistry ; 126: 12-19, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30472567

RESUMO

Microbial fuels cells (MFCs) have been applied for the degradation of pyroligneous liquor (PL) derived from apple tree branches, at different concentrations. The substrate removal, electrochemical properties, and microbial community characteristics were analysed to evaluate the performance of MFCs. Maximum current density (1.94 A/m2), coulombic efficiency (28%), and phenol removal rate (84%) were achieved with MFCs fed with PL at the optimal concentration of 1 g chemical oxygen demand (COD)/L. The polarisation test, cyclic voltammetry, and electrochemical impedance of the electrode redox reaction further explained how the addition of PL could stimulate formation of the electrochemically active biofilm, at the optimal concentration of 1 g COD/L. The microbial community of the anodic biofilm demonstrated that MFCs fed with 1 g COD/L had the highest relative abundance of the typical electrogenic bacteria Geobacter (33%), followed by Sphaerochaeta (6%) and Clostridium (4%). The results revealed that syntrophic interaction of these functional microorganisms contributed significantly to the PL degradation and electrical current generation.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Eletricidade , Geobacter/fisiologia , Biofilmes/crescimento & desenvolvimento , Análise da Demanda Biológica de Oxigênio , Eletrodos/microbiologia , Desenho de Equipamento , Geobacter/isolamento & purificação , Microbiota
11.
Phys Chem Chem Phys ; 20(40): 25648-25656, 2018 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-30289415

RESUMO

Electrochemical surface plasmon resonance (ESPR) monitors faradaic processes optically by the change in refractive index that occurs with a change in redox state at the electrode surface. Here we apply ESPR to investigate the anode-grown Geobacter sulfurreducens biofilm (GSB), a model system used to study electroactive microbial biofilms (EABFs) which perform electrochemical reactions using electrodes as metabolic electron acceptors or donors. A substantial body of evidence indicates that electron transfer reactions among hemes of c-type cytochromes (c-Cyt) play major roles in the extracellular electron transfer (EET) pathways that connect intracellular metabolic processes of cells in an EABF to the electrode surface. The results reported here reveal that when the potential of the electrode is changed from relatively oxidizing (0.40 V vs. SHE) to reducing (-0.55 V vs. SHE) and then back to oxidizing, 70% of c-Cyt residing closest to the biofilm/electrode (within hundreds of nm from the electrode surface) appear to remain trapped in the reduced state, requiring as long as 12 hours to be re-oxidized. c-Cyt storing electrons cannot contribute to EET, yet turnover current resulting from cellular oxidation of acetate coupled with EET to the electrode surface is unaffected. This suggests that a relatively small fraction of c-Cyt residing closest to the biofilm/electrode interface is involved in EET while the majority store electrons. The results also reveal that biomass density at the biofilm/electrode interface increases rapidly during lag phase, reaching its maximum value at the onset of exponential biofilm growth when turnover current begins to rapidly increase.


Assuntos
Biofilmes , Fenômenos Eletromagnéticos , Geobacter/fisiologia , Grupo dos Citocromos c/metabolismo , Eletrodos , Elétrons , Heme/metabolismo , Oxirredução , Ressonância de Plasmônio de Superfície
12.
Anal Chim Acta ; 1035: 51-59, 2018 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-30224144

RESUMO

In this study two methods including coating carbon nanotubes (CNTs) layers on the electrode surface and adding CNTs-suspension during electrochemically active biofilms (EABs) growth were used, respectively, to develop CNTs hybrid EABs for enhancing electricity generation capability of EABs. EABs growth on the CNTs with functional groups of hydroxyl (CNTs-OH) or carboxyl (CNTs-COOH) and pristine CNTs without functionalization (P-CNTs) modified electrode was investigated. The maximum current densities of EABs growth on the P-CNTs, CNTs-OH and CNTs-COOH coated electrode were respective 1300 ±â€¯117, 1082 ±â€¯54 and 1124 ±â€¯78 µA cm-2, which were much higher than unmodified electrode (663 µA cm-2). Meanwhile, EABs growth in doping CNTs-COOH or CNTs-OH suspensions system also produced twice higher current density than that on unmodified electrode. These results indicated that the current production of EABs can be significantly enhanced by coating P-CNTs, CNTs-OH, CNTs-COOH layers on the electrode surface or doping CNTs-OH and CNTs-COOH suspension into EABs. Furthermore, morphology analysis of as-obtained EABs had also been studied. It was found that there was no significant difference of the morphological characteristic for EABs growth on different types CNTs coated electrode surface. By comparison, a nano-hybrid porous structure of CNTs and EABs was observed when CNTs-COOH or CNTs-OH suspension was added into the medium during EABs growth, which will be responsible for high current generation.


Assuntos
Biofilmes/crescimento & desenvolvimento , Eletroquímica/métodos , Geobacter/fisiologia , Nanotubos de Carbono/química , Biocatálise , Fontes de Energia Bioelétrica , Meios de Cultura , Eletroquímica/instrumentação , Eletrodos , Geobacter/química , Geobacter/ultraestrutura , Microscopia Confocal , Microscopia Eletrônica de Varredura
13.
Biosens Bioelectron ; 122: 217-223, 2018 Dec 30.
Artigo em Inglês | MEDLINE | ID: mdl-30265972

RESUMO

Microbial fuel cells (MFCs) are a promising clean energy source to directly convert waste chemicals to available electric power. However, the practical application of MFCs needs the increased power density, enhanced energy conversion efficiency and reduced electrode material cost. In this study, three-dimensional (3D) macroporous N, P and S co-doped carbon foams (NPS-CFs) were prepared by direct pyrolysis of the commercial bread and employed as free-standing anodes in MFCs. As-obtained NPS-CFs have a large specific surface area (295.07 m2 g-1), high N, P and S doping level, and excellent electrical conductivity. A maximum areal power density of 3134 mW m-2 and current density of 7.56 A m-2 are generated by the MFCs equipped with as-obtained NPS-CF anodes, which is 2.57- and 2.63-fold that of the plain carbon cloth anodes (areal power density of 1218 mW m-2 and current density of 2.87 A m-2), respectively. Such improvement is explored to mainly originate from two respects: the good biocompatibility of NPS-CFs favors the bacterial adhesion and enrichment of electroactive Geobacter species on the electrode surface, while the high conductivity and improved bacteria-electrode interaction efficiently promote the extracellular electron transfer (EET) between the bacteria and the anode. This study provides a low-cost and sustainable way to fabricate high power MFCs for practical applications.


Assuntos
Fontes de Energia Bioelétrica , Pão , Carbono/química , Pirólise , Aderência Bacteriana , Fontes de Energia Bioelétrica/economia , Fontes de Energia Bioelétrica/microbiologia , Pão/análise , Pão/economia , Condutividade Elétrica , Eletricidade , Eletrodos/economia , Geobacter/fisiologia , Nitrogênio/química , Fósforo/química , Porosidade , Enxofre/química
14.
Biosens Bioelectron ; 121: 183-191, 2018 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-30218926

RESUMO

Anodic electroactive biofilms (EABs) need to overcome low current densities for applications such as microbial fuel cells or biosensors. EABs can store charge in self-produced redox proteins when temporarily left in open circuit, and discharge them once the electrode is appropriately repolarized, thus behaving as pseudocapacitors. Here we investigated the effect of such periodic polarization on the intrinsic nature of the EABs during their entire growth (i.e. starting from inoculation and for 10 days) on glassy carbon electrodes. An optimal periodic polarization (half-period of 10 s) greatly increased the maximum steady-state current density delivered by the Geobacter-dominated EABs (up to 1.10 ±â€¯0.02 mA cm-2, n = 3 electrodes) when compared to continuously polarized EABs (0.41 ±â€¯0.04 mA cm-2); and increased the amount of electric charges produced per hour by 69 ±â€¯17% even taking into account the half-periods of open circuit. This enhancement was highly correlated with a substantial increase in charge carriers concentration (10.6 ±â€¯0.5 mMe- vs. 2.9 ±â€¯0.6 mMe-), allowing higher charge storage capacity and higher electron mobility across the EABs. Our results suggest that appropriate periodic polarizations may upregulate the expression of heme-containing redox proteins associated with the matrix, such as c-type cytochromes. The EABs grown under periodic polarization presented mushroom-like structures on their top layers, while EABs grown under continuous polarization were flat.


Assuntos
Biofilmes , Técnicas Biossensoriais , Eletrodos/microbiologia , Fenômenos Eletrofisiológicos , Geobacter/fisiologia , Fontes de Energia Bioelétrica
15.
Bioelectrochemistry ; 123: 219-226, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-29874632

RESUMO

Microbial community structure of anodic biofilms plays a key role in bioelectrochemical systems (BESs). When ecosystems are used as inocula, many bacterial species having interconnected ecological interactions are present. The aim of the present study was to identify these interactions for the conversion of single substrates into electrical current. Dual-chamber reactors were inoculated with activated sludge and fed in batch mode with acetate, lactate, butyrate and propionate at 80 mMe- equivalents in quadruplicate. Analyses of biofilms and planktonic microbial communities showed that the anodic biofilms were mainly dominated by the Geobacter genus (62.4% of the total sequences). At the species level, Geobacter sulfurreducens was dominant in presence of lactate and acetate, while Geobacter toluenoxydans and Geobacter pelophilus were dominant with butyrate and propionate as substrates. These results indicate for the first time a specificity within the Geobacter genus towards the electron donor, suggesting a competitive process for electrode colonization and the implementations of syntrophic interactions for complete oxidation of substrates such as propionate and butyrate. All together, these results provide a new insight into the ecological relationships within electroactive biofilms and suggest eco-engineering perspectives to improve the performances of BESs.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Geobacter/fisiologia , Ácido Butírico/metabolismo , Eletricidade , Eletrodos , Eletrólise , Fermentação , Consórcios Microbianos , Propionatos/metabolismo , Esgotos/microbiologia
16.
Sci Total Environ ; 642: 322-326, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29906723

RESUMO

Based on the new syntrophic methanogenesis route via direct interspecies electron transfer (DIET), a novel bioaugmentation method by adding exoelectrogenic Geobacter species to accelerate methanogenesis was developed in this study. Geobacter sulfurreducens PCA, type exoelectrogenic strain of Geobacter species was chosen for the research. To clarify the effect of G. sulfurreducens on methanogenesis, batch tests of CH4 production were carried out. Acetate, the most typical precursor of methanogenesis was chosen as the substrate of batch tests. Amendment of G. sulfurreducens accelerated CH4 production remarkably. The lag phase of CH4 production was shortened, and the maximum CH4 production rate was increased by 78%. Fluorescence in situ hybridization showed that G. sulfurreducens closely gathered with methanogens. For the archaeal communities, the high-throughput sequencing results demonstrated that Methanosaetaceae and Methanobacteriaceae were potential bioaugmented methanogens. We speculated that the accelerated methanogenesis by adding G. sulfurreducens may result from the syntrophic association between G. sulfurreducens and methanogens affiliated with Methanosaetaceae and Methanobacteriaceae. This research provides a new route to enhance methanogenesis through the utilization of G. sulfurreducens. Through this study, the role of Geobacter in the anaerobic engineering and carbon cycling of nature should be paid more attention.


Assuntos
Biodegradação Ambiental , Geobacter/fisiologia , Archaea , Ciclo do Carbono/fisiologia , Digestão , Transporte de Elétrons , Compostos Férricos , Hibridização in Situ Fluorescente , Metano/metabolismo , Oxirredução
17.
FEMS Microbiol Ecol ; 94(6)2018 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-29722806

RESUMO

Here, we describe the long-distance (multi-cell-length) extracellular electron transport (LD-EET) that occurs in an anode-grown mixed community biofilm (MCB) enriched from river sediment that contains 3%-45% Geobacter spp. High signal-to-noise temperature-dependent electrochemical gating measurements (EGM) using interdigitated microelectrode arrays reveal a peak-shaped electrical conductivity vs. potential dependency, indicating MCB acts as a redox conductor, similar to pure culture anode-grown Geobacter sulfurreducens biofilms (GSB). EGM also reveal that the maximum sustained rate of LD-EET in MCB is comparable to GSB, and the same whether under acetate-oxidizing or acetate-free conditions. Voltammetry indicated that MCB possesses 3- to 5-fold less electrode-accessible redox cofactors than GSB, suggesting that MCB may be more efficiently organized than GSB for LD-EET or that a small portion of electrode accessible redox cofactors of GSB are involved in LD-EET. The activation energy for LD-EET (0.11 ± 0.01 eV) was comparable to GSB, consistent with the possible role of c-type cytochromes as LD-EET cofactors, detected in abundance by confocal resonance Raman microscopy. Taken together, the results demonstrate LD-EET for a mixed community anode-grown microbial biofilm that is remarkably similar to GSB even though it contains many different types of microorganisms and appears to utilize far fewer EET redox cofactors.


Assuntos
Condutividade Elétrica , Transporte de Elétrons/fisiologia , Geobacter/fisiologia , Sedimentos Geológicos/microbiologia , Biofilmes/crescimento & desenvolvimento , Eletrodos , Elétrons , Geobacter/classificação , Microscopia Confocal , Oxirredução , Rios/microbiologia
18.
Microb Biotechnol ; 11(6): 979-994, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-29806247

RESUMO

The reduction of iron oxide minerals and uranium in model metal reducers in the genus Geobacter is mediated by conductive pili composed primarily of a structurally divergent pilin peptide that is otherwise recognized, processed and assembled in the inner membrane by a conserved Type IVa pilus apparatus. Electronic coupling among the peptides is promoted upon assembly, allowing the discharge of respiratory electrons at rates that greatly exceed the rates of cellular respiration. Harnessing the unique properties of these conductive appendages and their peptide building blocks in metal bioremediation will require understanding of how the pilins assemble to form a protein nanowire with specialized sites for metal immobilization. Also important are insights into how cells assemble the pili to make an electroactive matrix and grow on electrodes as biofilms that harvest electrical currents from the oxidation of waste organic substrates. Genetic engineering shows promise to modulate the properties of the peptide building blocks, protein nanowires and current-harvesting biofilms for various applications. This minireview discusses what is known about the pilus material properties and reactions they catalyse and how this information can be harnessed in nanotechnology, bioremediation and bioenergy applications.


Assuntos
Geobacter/química , Nanofios/química , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Biofilmes , Biotecnologia , Eletrodos/microbiologia , Fímbrias Bacterianas/química , Fímbrias Bacterianas/metabolismo , Geobacter/crescimento & desenvolvimento , Geobacter/fisiologia , Oxirredução
19.
Bioelectrochemistry ; 122: 213-220, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-29694942

RESUMO

Bioelectrochemical systems couple electricity demand/supply to the metabolic redox reactions of microorganisms. Generally, electrodes act not only as electron acceptors/donors, but also as physical support for an electroactive biofilm. The microorganism-electrode interface can be modified by changing the chemical and/or topographical features of the electrode surface. Thus far, studies have reported conflicting results on the impact of the electrode surface roughness on the growth and current production of biofilms. Here, the surface roughness of the glassy carbon electrodes was successfully modified at the sub-microscale using micro electrodischarge machining, while preserving the surface chemistry of the parent glassy carbon. All microbial electrodes showed similar startup time, maximum current density, charge transport ability across the biofilm and biomass production. Interestingly, an increase in the average surface cavity depth was observed for the biofilm top layer as a function of the electrode surface roughness (from 7 µm to 16 µm for a surface roughness of 5 nm to 682 nm, respectively). These results indicated that the surface roughness at a sub-microscale does not significantly impact the attachment or current production of mixed culture anodic biofilms on glassy carbon. Likely earlier observations were associated with changes in surface chemistry, rather than surface topography.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Biofilmes/crescimento & desenvolvimento , Geobacter/fisiologia , Eletricidade , Eletrodos , Desenho de Equipamento , Propriedades de Superfície
20.
Biosens Bioelectron ; 110: 225-232, 2018 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-29625330

RESUMO

Whereas the study of interfaces and thin films with the quartz crystal microbalance (QCM) is well established, biofilms have proven to be a difficult subject for the QCM. The main problem is that the shear wave emanating from the resonator surface does not usually reach to the top of the sample. This problem can be solved with torsional resonators. These have a resonance frequency in the range of tens of kHz, which is much below the frequency of the thickness-shear QCMs. The depth of penetration of the shear wave is correspondingly larger. Data acquisition and data analysis can proceed in analogy to the conventional thickness-shear QCM. Torsional resonators may also be operated as electrochemical QCMs (EQCMs), meaning that a DC electrical potential may be applied to the active electrode and that shifts of frequency and bandwidth may be acquired in parallel to the electrical current. Here we report on the formation of mixed-culture biofilms dominated by the microorganism Geobacter anodireducens. The viscoelastic analysis evidences an increase in rigidity as the films grows. Potential sweeps on electroactive biofilms reveal a softening under negative potentials, that is, under conditions, where the layer's metabolism was slowed down by insufficient oxidative activity of the substrate. For comparison, biofilms were monitored in parallel with a conventional thickness-shear QCM.


Assuntos
Acústica/instrumentação , Biofilmes/crescimento & desenvolvimento , Técnicas Biossensoriais/instrumentação , Geobacter/fisiologia , Técnicas de Microbalança de Cristal de Quartzo/instrumentação , Elasticidade , Desenho de Equipamento , Geobacter/química , Viscosidade
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