Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 986
Filtrar
1.
Water Res ; 208: 117860, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34798422

RESUMO

The present nitrogen fixation industry is usually energy-intensive and environmentally detrimental. Therefore, it is appealing to find alternatives. Here, we achieved both a synchronized biological nitrogen fixation and electric energy production by using Geobacter sulfurreducens in a microbial electrochemical system. The results showed that G. sulfurreducens was able to fix nitrogen depending on anode respiration, producing a maximum current density of 0.17 ± 0.015 mA cm-2 and a nitrogen-fixing activity of ca. 0.78 µmol C2H4 mg protein-1 h-1, thereby achieving a net total nitrogen-fixing rate of ca. 5.6 mg L-1 day-1. Specifically, nitrogen fixation did not impair coulombic efficiency. Transcriptomic and metabolic analyses demonstrated that anode respiration provided sufficient energy to drive nitrogen fixation, and in turn nitrogen fixation promoted anode respiration of the cell by increasing acetate catabolism but reducing acetate anabolism. Furthermore, we showed that G. sulfurreducens could be supplied in a bioelectrochemical system for N-deficient wastewater treatment to relieve N-deficiency stress contributing to the formation of an electroactive biofilm, thereby simultaneously achieving nitrogen fixation, current generation and dissoluble organic carbon removal. Our study revealed a synergistic effect between biological nitrogen fixation and current generation by G. sulfurreducens, providing a green nitrogen fixation alternative through shifting the nitrogen fixation field from energy consumption to energy production and having implications for N-deficient wastewater treatment.


Assuntos
Fontes de Energia Bioelétrica , Geobacter , Biofilmes , Eletrodos , Nitrogênio , Fixação de Nitrogênio , Respiração
2.
Chemosphere ; 286(Pt 3): 131943, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-34426266

RESUMO

The wide use of chloramphenicol and its residues in the environments are an increasing threat to human beings. Electroactive microorganisms were proven with the ability of biodegradation of chloramphenicol, but the removal rate and efficiency need to be improved. In this study, a model electricigens, Geobacter metallireducens, was supplied with and Fe3O4 and MnO2 nanoparticles. Five times higher chloramphenicol removal rate (0.71 d-1) and two times higher chloramphenicol removal efficiency (100%) was achieved. Fe3O4 and MnO2 nanoparticles highly increased the current density and NADH-quinone oxidoreductase expression. Fe3O4 nanoparticles enhanced the expression of alcohol dehydrogenase and c-type cytochrome, while MnO2 nanoparticles increased the transcription of pyruvate dehydrogenase and Type IV pili assembly genes. Chloramphenicol was reduced to a type of dichlorination reducing product named CPD3 which is a benzene ring containing compound. Collectively, Fe3O4 and MnO2 nanoparticles increased the chloramphenicol removal capacity in MFCs by enhancing electron transfer efficiency. This study provides new enhancing strategies for the bioremediation of chloramphenicol in the environments.


Assuntos
Geobacter , Nanopartículas Metálicas , Cloranfenicol , Geobacter/genética , Humanos , Compostos de Manganês , Oxirredução , Óxidos
3.
Environ Sci Technol ; 55(21): 14928-14937, 2021 11 02.
Artigo em Inglês | MEDLINE | ID: mdl-34676765

RESUMO

Geobacter spp. are well-known exoelectrogenic microorganisms that often predominate acetate-fed biofilms in microbial fuel cells (MFCs) and other bioelectrochemical systems (BESs). By using an amplicon sequence variance analysis (at one nucleotide resolution), we observed a succession between two closely related species (98% similarity in 16S RNA), Geobacter sulfurreducens and Geobacter anodireducens, in the long-term studies (20 months) of MFC biofilms. Geobacter spp. predominated in the near-electrode portion of the biofilm, while the outer layer contained an abundance of aerobes, which may have helped to consume oxygen but reduced the relative abundance of Geobacter. Removal of the outer aerobes by norspermidine washing of biofilms revealed a transition from G. sulfurreducens to G. anodireducens. This succession was also found to occur rapidly in co-cultures in BES tests even in the absence of oxygen, suggesting that oxygen was not a critical factor. G. sulfurreducens likely dominated in early biofilms by its relatively larger cell size and production of extracellular polymeric substances (individual advantages), while G. anodireducens later predominated due to greater cell numbers (quantitative advantage). Our findings revealed the interspecies competition in the long-term evolution of Geobacter genus, providing microscopic insights into Geobacter's niche and competitiveness in complex electroactive microbial consortia.


Assuntos
Fontes de Energia Bioelétrica , Geobacter , Biofilmes , Eletrodos , Geobacter/genética
4.
Arch Biochem Biophys ; 712: 109025, 2021 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-34506758

RESUMO

In many bacteria, the reactions of proline catabolism are catalyzed by the bifunctional enzyme known as proline utilization A (PutA). PutA catalyzes the two-step oxidation of l-proline to l-glutamate using distinct proline dehydrogenase (PRODH) and l-glutamate-γ-semialdehyde dehydrogenase (GSALDH) active sites, which are separated by over 40 Å and connected by a complex tunnel system. The tunnel system consists of a main tunnel that connects the two active sites and functions in substrate channeling, plus six ancillary tunnels whose functions are unknown. Here we used tunnel-blocking mutagenesis to probe the role of a dynamic ancillary tunnel (tunnel 2a) whose shape is modulated by ligand binding to the PRODH active site. The 1.90 Å resolution crystal structure of Geobacter sulfurreducens PutA variant A206W verified that the side chain of Trp206 cleanly blocks tunnel 2a without perturbing the surrounding structure. Steady-state kinetic measurements indicate the mutation impaired PRODH activity without affecting the GSALDH activity. Single-turnover experiments corroborated a severe impairment of PRODH activity with flavin reduction decreased by nearly 600-fold in A206W relative to wild-type. Substrate channeling is also significantly impacted as A206W exhibited a 3000-fold lower catalytic efficiency in coupled PRODH-GSALDH activity assays, which measure NADH formation as a function of proline. The structure suggests that Trp206 inhibits binding of the substrate l-proline by preventing the formation of a conserved glutamate-arginine ion pair and closure of the PRODH active site. Our data are consistent with tunnel 2a serving as an open space through which the glutamate of the ion pair travels during the opening and closing of the active site in response to binding l-proline. These results confirm the essentiality of the conserved ion pair in binding l-proline and support the hypothesis that the ion pair functions as a gate that controls access to the PRODH active site.


Assuntos
Proteínas de Bactérias/química , Glutamato-5-Semialdeído Desidrogenase/química , Proteínas de Membrana/química , Complexos Multienzimáticos/química , Prolina Oxidase/química , Proteínas de Bactérias/genética , Biocatálise , Domínio Catalítico , Cristalografia por Raios X , Geobacter/enzimologia , Glutamato-5-Semialdeído Desidrogenase/genética , Proteínas de Membrana/genética , Complexos Multienzimáticos/genética , Mutagênese Sítio-Dirigida , Mutação , Prolina Oxidase/genética , Conformação Proteica
5.
Nature ; 597(7876): 430-434, 2021 09.
Artigo em Inglês | MEDLINE | ID: mdl-34471289

RESUMO

Extracellular electron transfer by Geobacter species through surface appendages known as microbial nanowires1 is important in a range of globally important environmental phenomena2, as well as for applications in bio-remediation, bioenergy, biofuels and bioelectronics. Since 2005, these nanowires have been thought to be type 4 pili composed solely of the PilA-N protein1. However, previous structural analyses have demonstrated that, during extracellular electron transfer, cells do not produce pili but rather nanowires made up of the cytochromes OmcS2,3 and OmcZ4. Here we show that Geobacter sulfurreducens binds PilA-N to PilA-C to assemble heterodimeric pili, which remain periplasmic under nanowire-producing conditions that require extracellular electron transfer5. Cryo-electron microscopy revealed that C-terminal residues of PilA-N stabilize its copolymerization with PilA-C (to form PilA-N-C) through electrostatic and hydrophobic interactions that position PilA-C along the outer surface of the filament. PilA-N-C filaments lack π-stacking of aromatic side chains and show a conductivity that is 20,000-fold lower than that of OmcZ nanowires. In contrast with surface-displayed type 4 pili, PilA-N-C filaments show structure, function and localization akin to those of type 2 secretion pseudopili6. The secretion of OmcS and OmcZ nanowires is lost when pilA-N is deleted and restored when PilA-N-C filaments are reconstituted. The substitution of pilA-N with the type 4 pili of other microorganisms also causes a loss of secretion of OmcZ nanowires. As all major phyla of prokaryotes use systems similar to type 4 pili, this nanowire translocation machinery may have a widespread effect in identifying the evolution and prevalence of diverse electron-transferring microorganisms and in determining nanowire assembly architecture for designing synthetic protein nanowires.


Assuntos
Fímbrias Bacterianas/química , Fímbrias Bacterianas/metabolismo , Geobacter , Nanofios , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Biopolímeros , Condutividade Elétrica , Proteínas de Fímbrias/química , Proteínas de Fímbrias/metabolismo , Geobacter/citologia , Geobacter/metabolismo , Multimerização Proteica
6.
Artigo em Inglês | MEDLINE | ID: mdl-34444543

RESUMO

This paper analyzed the degradation pathways of petroleum hydrocarbon degradation bacteria, screened the main degradation pathways, and found the petroleum hydrocarbon degradation enzymes corresponding to each step of the degradation pathway. Through the Copeland method, the best inoculation program of petroleum hydrocarbon degradation bacteria in a polluted site was selected as follows: single oxygenation path was dominated by Streptomyces avermitilis, hydroxylation path was dominated by Methylosinus trichosporium OB3b, secondary oxygenation path was dominated by Pseudomonas aeruginosa, secondary hydroxylation path was dominated by Methylococcus capsulatus, double oxygenation path was dominated by Acinetobacter baylyi ADP1, hydrolysis path was dominated by Rhodococcus erythropolis, and CoA path was dominated by Geobacter metallireducens GS-15 to repair petroleum hydrocarbon contaminated sites. The Copeland method score for this solution is 22, which is the highest among the 375 solutions designed in this paper, indicating that it has the best degradation effect. Meanwhile, we verified its effect by the Cdocker method, and the Cdocker energy of this solution is -285.811 kcal/mol, which has the highest absolute value. Among the inoculation programs of the top 13 petroleum hydrocarbon degradation bacteria, the effect of the best inoculation program of petroleum hydrocarbon degradation bacteria was 18% higher than that of the 13th group, verifying that this solution has the best overall degradation effect. The inoculation program of petroleum hydrocarbon degradation bacteria designed in this paper considered the main pathways of petroleum hydrocarbon pollutant degradation, especially highlighting the degradability of petroleum hydrocarbon intermediate degradation products, and enriching the theoretical program of microbial remediation of petroleum hydrocarbon contaminated sites.


Assuntos
Petróleo , Rhodococcus , Poluentes do Solo , Acinetobacter , Biodegradação Ambiental , Geobacter , Hidrocarbonetos , Solo , Microbiologia do Solo , Poluentes do Solo/análise , Streptomyces
7.
Appl Environ Microbiol ; 87(20): e0096421, 2021 09 28.
Artigo em Inglês | MEDLINE | ID: mdl-34347518

RESUMO

The ability of some metal-reducing bacteria to produce a rough (no O-antigen) lipopolysaccharide (LPS) could facilitate surface interactions with minerals and metal reduction. Consistent with this, the laboratory model metal reducer Geobacter sulfurreducens PCA produced two rough LPS isoforms (with or without a terminal methyl-quinovosamine sugar) when growing with the soluble electron acceptor fumarate but expressed only the shorter and more hydrophilic variant when reducing iron oxides. We reconstructed from genomic data conserved pathways for the synthesis of the rough LPS and generated heptosyltransferase mutants with partial (ΔrfaQ) or complete (ΔrfaC) truncations in the core oligosaccharide. The stepwise removal of the LPS core sugars reduced the hydrophilicity of the cell and increased outer membrane vesiculation. These changes in surface charge and remodeling did not substantially impact planktonic growth but disrupted the developmental stages and structure of electroactive biofilms. Furthermore, the mutants assembled conductive pili for extracellular mineralization of the toxic uranyl cation but were unable to prevent permeation and mineralization of the radionuclide in the cell envelope. Hence, not only does the rough LPS promote cell-cell and cell-mineral interactions critical to biofilm formation and metal respiration but it also functions as a permeability barrier to toxic metal cations. In doing so, the rough LPS maximizes the extracellular reduction of soluble and insoluble metals and preserves cell envelope functions critical to the environmental survival of Geobacter bacteria in metal-rich environments and their performance in bioremediation and bioenergy applications. IMPORTANCE Some metal-reducing bacteria produce an LPS without the repeating sugars (O-antigen) that decorate the surface of most Gram-negative bacteria, but the biological significance of this adaptive feature was not previously investigated. Using the model representative Geobacter sulfurreducens strain PCA and mutants carrying stepwise truncations in the LPS core sugars, we demonstrate the importance of the rough LPS in the control of cell surface chemistry during the respiration of iron minerals and the formation of electroactive biofilms. Importantly, we describe hitherto overlooked roles for the rough LPS in metal sequestration and outer membrane vesiculation that are critical for the extracellular reduction and detoxification of toxic metals and radionuclides. These results are of interest for the optimization of bioremediation schemes and electricity-harvesting platforms using these bacteria.


Assuntos
Geobacter/metabolismo , Lipopolissacarídeos/metabolismo , Urânio/metabolismo , Biofilmes/crescimento & desenvolvimento , Geobacter/genética , Geobacter/fisiologia , Lipopolissacarídeos/genética , Oxirredução , Urânio/toxicidade
8.
Water Res ; 202: 117490, 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34364064

RESUMO

Geobacter, as a typical electroactive microorganism, is the "engine" of interspecies electron transfer (IET) between microorganisms. However, it does not have a dominant position in all natural environments. It is not known what performs a similar function as Geobacter in coastal zones. Metagenomic and metatranscriptomic analysis revealed that Desulfovibrio and Methanobacterium species were the most abundant in electrochemically active aggregates. Metatranscriptomic analysis showed that Desulfovibrio species highly expressed genes for ethanol metabolism and extracellular electron transfer involving cytochromes, pili and flagella. Methanobacterium species in the aggregates also expressed genes for enzymes involved in reducing carbon dioxide to methane. Pure cultures demonstrated that the isolated Desulfovibrio sp. strain JY contributed to aggregate conductivity and directly transferred electrons to Methanothrix harundinacea, which is unable to use H2 or formate. Most importantly, further coculture studies indicated that Methanobacterium strain YSL might directly accept electrons from the Desulfovibrio strain JY for the reduction of carbon dioxide to methane in the aggregate. This finding suggested that the possibility of DIET by Desulfovibrio similar to Geobacter species in conductive methanogenic aggregates can not be excluded.


Assuntos
Desulfovibrio , Geobacter , Desulfovibrio/genética , Transporte de Elétrons , Elétrons , Geobacter/genética , Metano , Methanobacterium/genética
9.
Bioresour Technol ; 340: 125717, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34426232

RESUMO

A microbial fuel cell-photocatalysis system with a novel photocatalytic air-cathode (MFC-PhotoCat) was proposed for synergistic degradation of 2,4,6-trichlorophenol (TCP) with simultaneous electricity generation. Stable electricity generation of 350 mV was achieved during 130 days of operation. Besides, 50 mg L-1 TCP was completely degraded within 72 h, and the rate constant of 0.050 h-1 was 1.8-fold higher than MFC with air-cathode without N-TiO2 photocatalyst. Degradation pathway was proposed based on the intermediates detected and density functional theory (DFT) calculation, with two open-chain intermediates (2-chloro-4-keto-2-hexenedioic acid and hexanoic acid) detected. Furthermore, hierarchical cluster and PCoA revealed significant shifts of microbial community structures, with enriched exoelectrogen (55.2% of Geobacter) and TCP-degrading microbe (7.1% of Thauera) on the cathode biofilm as well as 61.8% of Pseudomonas in the culture solution. This study provides a promising strategy for synergic degradation of recalcitrant contaminants by intimate-coupling of MFC and photocatalysis.


Assuntos
Fontes de Energia Bioelétrica , Poluentes Ambientais , Geobacter , Eletricidade , Eletrodos
10.
Int J Mol Sci ; 22(16)2021 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-34445739

RESUMO

Environmental changes trigger the continuous adaptation of bacteria to ensure their survival. This is possible through a variety of signal transduction pathways involving chemoreceptors known as methyl-accepting chemotaxis proteins (MCP) that allow the microorganisms to redirect their mobility towards favorable environments. MCP are two-component regulatory (or signal transduction) systems (TCS) formed by a sensor and a response regulator domain. These domains synchronize transient protein phosphorylation and dephosphorylation events to convert the stimuli into an appropriate cellular response. In this review, the variability of TCS domains and the most common signaling mechanisms are highlighted. This is followed by the description of the overall cellular topology, classification and mechanisms of MCP. Finally, the structural and functional properties of a new family of MCP found in Geobacter sulfurreducens are revisited. This bacterium has a diverse repertoire of chemosensory systems, which represents a striking example of a survival mechanism in challenging environments. Two G. sulfurreducens MCP-GSU0582 and GSU0935-are members of a new family of chemotaxis sensor proteins containing a periplasmic PAS-like sensor domain with a c-type heme. Interestingly, the cellular location of this domain opens new routes to the understanding of the redox potential sensing signaling transduction pathways.


Assuntos
Quimiotaxia/fisiologia , Geobacter/fisiologia , Proteínas Quimiotáticas Aceptoras de Metil/fisiologia , Transdução de Sinais
11.
Nat Commun ; 12(1): 4119, 2021 07 05.
Artigo em Inglês | MEDLINE | ID: mdl-34226558

RESUMO

Northern peatlands are experiencing more frequent and severe fire events as a result of changing climate conditions. Recent studies show that such a fire-regime change imposes a direct climate-warming impact by emitting large amounts of carbon into the atmosphere. However, the fires also convert parts of the burnt biomass into pyrogenic carbon. Here, we show a potential climate-cooling impact induced by fire-derived pyrogenic carbon in laboratory incubations. We found that the accumulation of pyrogenic carbon reduced post-fire methane production from warm (32 °C) incubated peatland soils by 13-24%. The redox-cycling, capacitive, and conductive electron transfer mechanisms in pyrogenic carbon functioned as an electron snorkel, which facilitated extracellular electron transfer and stimulated soil alternative microbial respiration to suppress methane production. Our results highlight an important, but overlooked, function of pyrogenic carbon in neutralizing forest fire emissions and call for its consideration in the global carbon budget estimation.


Assuntos
Carbono/metabolismo , Elétrons , Metano/biossíntese , Incêndios Florestais , Bactérias , Biomassa , Dióxido de Carbono , Clima , Mudança Climática , Ecossistema , Incêndios , Geobacter , Laboratórios , Solo
12.
Sci Rep ; 11(1): 15140, 2021 07 23.
Artigo em Inglês | MEDLINE | ID: mdl-34302023

RESUMO

Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET) are two syntrophy models for methanogenesis. Their relative importance in methanogenic environments is still unclear. Our recent discovery of a novel species Candidatus Geobacter eutrophica with the genetic potential of IHT and DIET may serve as a model species to address this knowledge gap. To experimentally demonstrate its DIET ability, we performed electrochemical enrichment of Ca. G. eutrophica-dominating communities under 0 and 0.4 V vs. Ag/AgCl based on the presumption that DIET and extracellular electron transfer (EET) share similar metabolic pathways. After three batches of enrichment, Geobacter OTU650, which was phylogenetically close to Ca. G. eutrophica, was outcompeted in the control but remained abundant and active under electrochemical stimulation, indicating Ca. G. eutrophica's EET ability. The high-quality draft genome further showed high phylogenomic similarity with Ca. G. eutrophica, and the genes encoding outer membrane cytochromes and enzymes for hydrogen metabolism were actively expressed. A Bayesian network was trained with the genes encoding enzymes for alcohol metabolism, hydrogen metabolism, EET, and methanogenesis from dominant fermentative bacteria, Geobacter, and Methanobacterium. Methane production could not be accurately predicted when the genes for IHT were in silico knocked out, inferring its more important role in methanogenesis. The genomics-enabled machine learning modeling approach can provide predictive insights into the importance of IHT and DIET.


Assuntos
Transporte de Elétrons/fisiologia , Geobacter/metabolismo , Hidrogênio/metabolismo , Teorema de Bayes , Citocromos/metabolismo , Elétrons , Aprendizado de Máquina , Redes e Vias Metabólicas/fisiologia , Metano/metabolismo , Methanobacterium/metabolismo
13.
Environ Sci Technol ; 55(14): 10142-10151, 2021 07 20.
Artigo em Inglês | MEDLINE | ID: mdl-34196176

RESUMO

Direct interspecies electron transfer (DIET) between microbial species prevails in some key microbial consortia. However, the electron transfer mechanism(s) in these consortia is controversial due to lack of efficient characterization methods. Here, we provide an in situ anaerobic spectroelectrochemical coculture cell (in situ ASCC) to induce the formation of DIET coculture biofilm on the interdigitated microelectrode arrays and characterize the electron transfer directly. Two typical Geobacter DIET cocultures, Geobacter metallireducens and wild-type Geobacter sulfurreducens (G.m&G.s) and G. metallireducens and a G. sulfurreducens strain deficient in citrate synthase (G.m&G.s-ΔgltA), were selected. In situ Raman and electrochemical Fourier transform infrared (FTIR) spectroscopy indicated that cytochromes are abundant in the electric syntrophic coculture. Cyclic voltammetry and potential step experiment revealed a diffusion-controlled electron transfer process and the electrochemical gating measurements further demonstrated a cytochrome-mediated electron transfer in the DIET coculture. Furthermore, the G.m&G.s-ΔgltA coculture displayed a higher redox conductivity than the G.m&G.s coculture, consistent with the existence of an intimate and efficient electrical connection between these two species. Our findings provide the first report of a redox-gradient-driven electron transport facilitated by c-type cytochromes in DIET coculture, supporting the model that DIET is mediated by cytochromes and suggest a platform to explore the other DIET consortia.


Assuntos
Geobacter , Técnicas de Cocultura , Citocromos/metabolismo , Transporte de Elétrons , Geobacter/metabolismo , Oxirredução
14.
Environ Sci Technol ; 55(15): 10821-10831, 2021 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-34288663

RESUMO

Microbial reduction of Fe(III) minerals is a prominent process in redoximorphic soils and is strongly affected by organic matter (OM). We herein determined the rate and extent of microbial reduction of ferrihydrite (Fh) with either adsorbed or coprecipitated OM by Geobacter sulfurreducens. We focused on OM-mediated effects on electron uptake and alterations in Fh crystallinity. The OM was obtained from anoxic soil columns (effluent OM, efOM) and included-unlike water-extractable OM-compounds released by microbial activity under anoxic conditions. We found that organic molecules in efOM had generally no or only very low electron-accepting capacity and were incorporated into the Fh aggregates when coprecipitated with Fh. Compared to OM-free Fh, adsorption of efOM to Fh decelerated the microbial Fe(III) reduction by passivating the Fh surface toward electron uptake. In contrast, coprecipitation of Fh with efOM accelerated the microbial reduction, likely because efOM disrupted the Fh structure, as noted by Mössbauer spectroscopy. Additionally, the adsorbed and coprecipitated efOM resulted in a more sustained Fe(III) reduction, potentially because efOM could have effectively scavenged biogenic Fe(II) and prevented the passivation of the Fh surface by the adsorbed Fe(II). Fe(III)-OM coprecipitates forming at anoxic-oxic interfaces are thus likely readily reducible by Fe(III)-reducing bacteria in redoximorphic soils.


Assuntos
Compostos Férricos , Solo , Geobacter , Ferro , Minerais , Oxirredução
15.
J Phys Chem B ; 125(30): 8305-8312, 2021 08 05.
Artigo em Inglês | MEDLINE | ID: mdl-34292748

RESUMO

Long-range electron transport has been widely and experimentally reported in Geobacter sulfurreducens pilus protein. However, a better understanding of the still undefined molecular arrangement can bring to light the role of key residues in this phenomenon. We propose a theoretical investigation of the electronic structure of aromatic residue groups in the protein through a classical molecular dynamics (MD) simulation, followed by a quantum mechanics/molecular mechanics (QM/MM) electronic study of different frames sampled from MD trajectories, an electrostatic potential and electron density analysis, an analysis of the density of states, and an investigation of hole formation through Dyson orbital calculations. We observe a highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap in the ranges of 1.4-2.3 eV and 2.9-3.3 eV and a less intense dipole moment along the aromatic residues in the presence of water in comparison to the system in vacuum. HOMO and LUMO electron densities highlight the occupation of one tyrosine residue in every representation for HOMO and a delocalization along two to three rings for LUMO. The results show how the electronic structure of the aromatic residues is sensitive to the ring arrangement and the surrounding environment. In our study, we observe that slight rearrangements in the fiber geometry can create temporary conditions for hole transfer.


Assuntos
Geobacter , Simulação de Dinâmica Molecular , Eletrônica , Fímbrias Bacterianas
16.
Biochemistry ; 60(23): 1853-1867, 2021 06 15.
Artigo em Inglês | MEDLINE | ID: mdl-34061493

RESUMO

Cytochrome c nitrite reductases (CcNIR or NrfA) play important roles in the global nitrogen cycle by conserving the usable nitrogen in the soil. Here, the electron storage and distribution properties within the pentaheme scaffold of Geobacter lovleyi NrfA were investigated via electron paramagnetic resonance (EPR) spectroscopy coupled with chemical titration experiments. Initially, a chemical reduction method was established to sequentially add electrons to the fully oxidized protein, 1 equiv at a time. The step-by-step reduction of the hemes was then followed using ultraviolet-visible absorption and EPR spectroscopy. EPR spectral simulations were used to elucidate the sequence of heme reduction within the pentaheme scaffold of NrfA and identify the signals of all five hemes in the EPR spectra. Electrochemical experiments ascertain the reduction potentials for each heme, observed in a narrow range from +10 mV (heme 5) to -226 mV (heme 3) (vs the standard hydrogen electrode). On the basis of quantitative analysis and simulation of the EPR data, we demonstrate that hemes 4 and 5 are reduced first (before the active site heme 1) and serve the purpose of an electron storage unit within the protein. To probe the role of the central heme 3, an H108M NrfA variant was generated where the reduction potential of heme 3 is shifted positively (from -226 to +48 mV). The H108M mutation significantly impacts the distribution of electrons within the pentaheme scaffold and the reduction potentials of the hemes, reducing the catalytic activity of the enzyme to 1% compared to that of the wild type. We propose that this is due to heme 3's important role as an electron gateway in the wild-type enzyme.


Assuntos
Grupo dos Citocromos c/metabolismo , Citocromos a1/metabolismo , Citocromos c1/metabolismo , Geobacter/metabolismo , Nitrato Redutases/metabolismo , Domínio Catalítico , Cristalografia por Raios X/métodos , Grupo dos Citocromos c/química , Citocromos a1/química , Citocromos c1/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Elétrons , Geobacter/química , Heme/química , Heme/metabolismo , Modelos Moleculares , Nitrato Redutases/química , Nitrito Redutases/química , Nitrito Redutases/metabolismo , Oxirredução , Conformação Proteica
17.
Environ Sci Technol ; 55(12): 8258-8266, 2021 06 15.
Artigo em Inglês | MEDLINE | ID: mdl-34096274

RESUMO

Anaerobic digestion (AD) and microbial electrochemical technologies (MET) can be combined in manifold ways. Recent studies show negative influences of AD effluents on the performance of pre-grown Geobacter spp.-dominated biofilm anodes. In this study, it was investigated how such biofilm anodes are affected by AD effluents. Therefore, experiments using AD effluents in different concentrations (0-100%) in combination with biofilms of different ages were performed. Furthermore, the activity of methanogens was inhibited and minimized by application of 2-bromoethanesulfonate (2-BES) and microfiltration, respectively. Biofilms pre-grown for 5 weeks show higher resistance against AD effluents compared to biofilms pre-grown for only 3 weeks. Nevertheless, adaptation of biofilms to AD effluents was not successful. Biofilm activity in terms of coulombic efficiency and maximum current density (jmax) dropped by factor 32.2 ± 3.2 and 38.9 ± 8.4, respectively. The application of 2-BES and microfiltration had positive effects on the biofilm activity. The results support the assumption that methanogens or further compounds not studied here, for example, protozoans, which may have been inhibited or removed by 2-BES application or microfiltration, have an immediate influence on the stability of Geobacter spp.-dominated biofilms and may limit their practical application in AD environments.


Assuntos
Fontes de Energia Bioelétrica , Geobacter , Anaerobiose , Biofilmes , Eletrodos
18.
Appl Environ Microbiol ; 87(17): e0070621, 2021 08 11.
Artigo em Inglês | MEDLINE | ID: mdl-34190605

RESUMO

A strain of Geobacter sulfurreducens, an organism capable of respiring solid extracellular substrates, lacking four of five outer membrane cytochrome complexes (extABCD+ strain) grows faster and produces greater current density than the wild type grown under identical conditions. To understand cellular and biofilm modifications in the extABCD+ strain responsible for this increased performance, biofilms grown using electrodes as terminal electron acceptors were sectioned and imaged using electron microscopy to determine changes in thickness and cell density, while parallel biofilms incubated in the presence of nitrogen and carbon isotopes were analyzed using NanoSIMS (nanoscale secondary ion mass spectrometry) to quantify and localize anabolic activity. Long-distance electron transfer parameters were measured for wild-type and extABCD+ biofilms spanning 5-µm gaps. Our results reveal that extABCD+ biofilms achieved higher current densities through the additive effects of denser cell packing close to the electrode (based on electron microscopy), combined with higher metabolic rates per cell compared to the wild type (based on increased rates of 15N incorporation). We also observed an increased rate of electron transfer through extABCD+ versus wild-type biofilms, suggesting that denser biofilms resulting from the deletion of unnecessary multiheme cytochromes streamline electron transfer to electrodes. The combination of imaging, physiological, and electrochemical data confirms that engineered electrogenic bacteria are capable of producing more current per cell and, in combination with higher biofilm density and electron diffusion rates, can produce a higher final current density than the wild type. IMPORTANCE Current-producing biofilms in microbial electrochemical systems could potentially sustain technologies ranging from wastewater treatment to bioproduction of electricity if the maximum current produced could be increased and current production start-up times after inoculation could be reduced. Enhancing the current output of microbial electrochemical systems has been mostly approached by engineering physical components of reactors and electrodes. Here, we show that biofilms formed by a Geobacter sulfurreducens strain producing ∼1.4× higher current than the wild type results from a combination of denser cell packing and higher anabolic activity, enabled by an increased rate of electron diffusion through the biofilms. Our results confirm that it is possible to engineer electrode-specific G. sulfurreducens strains with both faster growth on electrodes and streamlined electron transfer pathways for enhanced current production.


Assuntos
Biofilmes , Espaço Extracelular/metabolismo , Geobacter/química , Geobacter/fisiologia , Eletricidade , Eletrodos , Transporte de Elétrons , Espaço Extracelular/química , Geobacter/crescimento & desenvolvimento
19.
Biochem J ; 478(14): 2871-2887, 2021 07 30.
Artigo em Inglês | MEDLINE | ID: mdl-34190983

RESUMO

The redox potential values of cytochromes can be modulated by the protonation/deprotonation of neighbor groups (redox-Bohr effect), a mechanism that permits the proteins to couple electron/proton transfer. In the respiratory chains, this effect is particularly relevant if observed in the physiological pH range, as it may contribute to the electrochemical gradient for ATP synthesis. A constitutively produced family of five triheme cytochromes (PpcA-E) from the bacterium Geobacter sulfurreducens plays a crucial role in extracellular electron transfer, a hallmark that permits this bacterium to be explored for several biotechnological applications. Two members of this family (PpcA and PpcD) couple electron/proton transfer in the physiological pH range, a feature not shared with PpcB and PpcE. That ability is crucial for G. sulfurreducens' growth in Fe(III)-reducing habitats since extra contributors to the electrochemical gradient are needed. It was postulated that the redox-Bohr effect is determined by the nature of residue 6, a leucine in PpcA/PpcD and a phenylalanine in PpcB/PpcE. To confirm this hypothesis, Phe6 was replaced by leucine in PpcB and PpcE. The functional properties of these mutants were investigated by NMR and UV-visible spectroscopy to assess their capability to couple electron/proton transfer in the physiological pH range. The results obtained showed that the mutants have an increased redox-Bohr effect and are now capable of coupling electron/proton transfer. This confirms the determinant role of the nature of residue 6 in the modulation of the redox-Bohr effect in this family of cytochromes, opening routes to engineer Geobacter cells with improved biomass production.


Assuntos
Proteínas de Bactérias/metabolismo , Citocromos/metabolismo , Geobacter/metabolismo , Heme/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Citocromos/química , Citocromos/genética , Transporte de Elétrons/genética , Elétrons , Geobacter/genética , Heme/química , Concentração de Íons de Hidrogênio , Modelos Moleculares , Estrutura Molecular , Mutação , Oxirredução , Conformação Proteica , Isoformas de Proteínas/química , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Prótons , Espectrofotometria/métodos , Termodinâmica
20.
Chemosphere ; 283: 130983, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34153910

RESUMO

Biochar was proved as an electron shuttle to facilitate extracellular electron transfer (EET) of electrochemically active bacteria (EAB); however, its underlying mechanism was not fully understood. In this study, we aimed to further explore how the regulation of surface functional groups of biochar would affect the microbial iron reduction process of Geobacter sulfurreducens as a typical EAB. Two modified biochars were achieved after HNO3 (NBC) and NaBH4 (RBC) pretreatments, and a control biochar was produced after deionized water (WBC) washing. Results showed that WBC and RBC significantly accelerated microbial iron reduction of G. sulfurreducens PCA, while had no effect in the final Fe (II) minerals (e.g., vivianite and green rust (CO32-)). Besides, Brunauer-Emmett-Teller (BET) surface area, electron spin resonance (ESR) and electrochemical measurements showed that larger surface area, lower redox potential, and more redox-active groups (e.g., aromatic structures and quinone/hydroquinone moieties) in RBC explained its better electron transfer performance comparing to WBC. Interestingly, NBC completely suppressed the Fe (III) reduction process, mainly due to the production of reactive oxygen species which inhibited the growth of G. sulfurreducens PCA. Overall, this work paves a feasible way to regulate the surface functional groups for biochar, and comprehensively revealed its effect on EET process of microorganisms.


Assuntos
Geobacter , Carvão Vegetal , Transporte de Elétrons , Compostos Férricos , Ferro , Oxirredução
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...