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Yee MO, Ottosen LDM, Rotaru A. Electrical current disrupts the electron transfer in defined consortia. Microb Biotechnol 2024; 17:e14373. [PMID: 38070192 PMCID: PMC10832552 DOI: 10.1111/1751-7915.14373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 11/03/2023] [Accepted: 11/05/2023] [Indexed: 02/03/2024] Open
Abstract
Improving methane production through electrical current application to anaerobic digesters has garnered interest in optimizing such microbial electrochemical technologies, with claims suggesting direct interspecies electron transfer (DIET) at the cathode enhances methane yield. However, previous studies with mixed microbial communities only reported interspecies interactions based on species co-occurrence at the cathode, lacking insight into how a poised cathode influences well-defined DIET-based partnerships. To address this, we investigated the impact of continuous and discontinuous exposure to a poised cathode (-0.7 V vs. standard hydrogen electrode) on a defined consortium of Geobacter metallireducens and Methanosarcina barkeri, known for their DIET capabilities. The physiology of DIET consortia exposed to electrical current was compared to that of unexposed consortia. In current-exposed incubations, overall metabolic activity and cell numbers for both partners declined. The consortium, receiving electrons from the poised cathode, accumulated acetate and hydrogen, with only 32% of the recovered electrons allocated to methane production. Discontinuous exposure intensified these detrimental effects. Conversely, unexposed control reactors efficiently converted ethanol to methane, transiently accumulating acetate and recovering 88% of electrons in methane. Our results demonstrate the overall detrimental effect of electrochemical stimulation on a DIET consortium. Besides, the data indicate that the presence of an alternative electron donor (cathode) hinders efficient electron retrieval by the methanogen from Geobacter, and induces catabolic repression of oxidative metabolism in Geobacter. This study emphasizes understanding specific DIET-based interactions to enhance methane production during electrical stimulation, providing insights for optimizing tailored interspecies partnerships in microbial electrochemical technologies.
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Affiliation(s)
- Mon Oo Yee
- Nordcee, Department of BiologyUniversity of Southern DenmarkOdenseDenmark
- Nature EnergyOdenseDenmark
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Ao Z, Li Y, Li Y, Zhao Z, Zhang Y. Facilitating direct interspecies electron transfer in anaerobic digestion via speeding up transmembrane transport of electrons and CO 2 reduction in methanogens by Na + adjustment. WASTE MANAGEMENT (NEW YORK, N.Y.) 2023; 170:252-260. [PMID: 37729842 DOI: 10.1016/j.wasman.2023.09.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Revised: 08/08/2023] [Accepted: 09/15/2023] [Indexed: 09/22/2023]
Abstract
The possibility of facilitating direct interspecies electron transfer (DIET) in anaerobic digestion with different concentrations of NaCl was explored. Additional NaCl at 2 or 4 g/L strengthened anaerobic digestion to resist the high-organic loading rate impacts, whereas the higher concentrations of NaCl (6 or 8 g/L) suppressed methanogenesis. Additional MgCl2 with the same ion strength as NaCl at 2 g/L had no effect on performances. Additional NaCl at 2 or 4 g/L dramatically increased the abundance of Methanosarcina species (20.7%/23.4% vs 8.6%) and stimulated the growth of Sphaerochaeta and Petrimonas species that could transfer electrons to the soluble Fe(III) or elemental sulfur. Electrochemical evidences showed that, additional NaCl at 2 or 4 g/L increased capacitances and decreased charge transfer resistances of Methanosarcina-dominant communities. Metagenomic evidences showed that, additional NaCl at 2 or 4 g/L increased the abundance of genes that encoded the type IV pilus assembly proteins (1.98E-04/1.87E-04 vs 1.85E-04) and cytochrome c-like proteins (5.51E-04/5.60E-04 vs 5.31E-04). In addition, additional NaCl at 2 or 4 g/L increased the abundance of genes for methanophenazine (MP)/MPH2 transformation (1.04E-05/1.24E-05 vs 8.06E-06) and CO2 reduction (1.64E-03/1.86E-03 vs 1.06E-03), suggesting a rapid transmembrane transport of electrons and CO2 reduction in methanogens. Both processes were closely associated with F420/F420H2 transformation that required ATP. Additional NaCl at 2 or 4 g/L increased the yield of ATP (256.0/249.3 vs 231.8 nmol/L) that might promote F420/F420H2 transformation in methanogens, which overcame the thermodynamic limitations of combining electrons with protons for the reduction of CO2 to methane and facilitated DIET.
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Affiliation(s)
- Zhipeng Ao
- Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Yuan Li
- Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Yang Li
- School of Ocean Science and Technology, Dalian University of Technology, Panjin 124221, China
| | - Zhiqiang Zhao
- Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
| | - Yaobin Zhang
- Key Laboratory of Industrial Ecology and Environmental Engineering (Dalian University of Technology), Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China
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Duan H, He P, Zhang H, Shao L, Lü F. Metabolic Regulation of Mesophilic Methanosarcina barkeri to Ammonium Inhibition. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:8897-8907. [PMID: 35588324 DOI: 10.1021/acs.est.2c01212] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Undesirable ammonium concentrations can lead to unstable anaerobic digestion processes, and Methanosarcina spp. are the representative methanogens under inhibition. However, no known work seems to exist for directly exploring the detailed metabolic regulation of pure cultured representative Methanosarcina spp. to ammonium inhibition. We used transcriptomics and proteomics to profile the metabolic regulation of Methanosarcina barkeri to 1, 4, and 7 g N/L of total ammoniacal nitrogen (TAN), where free ammonia concentrations were between 1.5 and 36.1 mg N/L. At the initial stages of ammonium inhibition, the genes participating in the acquisition and assimilation of reduced nitrogen sources showed significant upregulation where the minimal fold change of gene transcription was about 2. Apart from nitrogen metabolism, the transcription of some genes in methanogenesis also significantly increased at the initial stages. For example, the genes encoding alternative heterodisulfide reductase subunits (HdrAB), energy-converting hydrogenase subunit (EchC), and methanophenazine-dependent hydrogenase subunits (VhtAC) were significantly upregulated by at least 2.05 times. For the element translocation at the initial stages, the genes participating in the uptake of ferrous iron, potassium ion, and molybdate were significantly upregulated with a minimal fold change of 2.10. As the cultivation proceeded, the gene encoding the cell division protein subunit (FtsH) was significantly upregulated by 13.0 times at 7 g N/L of TAN; meanwhile, an increment in OD600 was observed at the terminal sampling point of 7 g N/L of TAN. The present study explored the metabolic regulation of M. barkeri in stress response, protein synthesis, signal transduction, nitrogen metabolism, methanogenesis, and element translocation. The results would contribute to the understanding of the metabolic effects of ammonium inhibition on methanogens and have significant practical implication in inhibited anaerobic digestion.
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Affiliation(s)
- Haowen Duan
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China
| | - Pinjing He
- Institute of Waste Treatment and Reclamation, Tongji University, Shanghai 200092, China
- Shanghai Multi-Source Solid Waste Collaborative Treatment and Energy Engineering Technology Research Center, Shanghai 200092, China
| | - Hua Zhang
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
| | - Liming Shao
- Institute of Waste Treatment and Reclamation, Tongji University, Shanghai 200092, China
| | - Fan Lü
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China
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Jin Q, Wu Q, Shapiro BM, McKernan SE. Limited Mechanistic Link Between the Monod Equation and Methanogen Growth: a Perspective from Metabolic Modeling. Microbiol Spectr 2022; 10:e0225921. [PMID: 35238612 PMCID: PMC9045329 DOI: 10.1128/spectrum.02259-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Accepted: 02/06/2022] [Indexed: 11/20/2022] Open
Abstract
The Monod equation has been widely applied as the general rate law of microbial growth, but its applications are not always successful. By drawing on the frameworks of kinetic and stoichiometric metabolic models and metabolic control analysis, the modeling reported here simulated the growth kinetics of a methanogenic microorganism and illustrated that different enzymes and metabolites control growth rate to various extents and that their controls peak at either very low, intermediate, or very high substrate concentrations. In comparison, with a single term and two parameters, the Monod equation only approximately accounts for the controls of rate-determining enzymes and metabolites at very high and very low substrate concentrations, but neglects the enzymes and metabolites whose controls are most notable at intermediate concentrations. These findings support a limited link between the Monod equation and methanogen growth, and unify the competing views regarding enzyme roles in shaping growth kinetics. The results also preclude a mechanistic derivation of the Monod equation from methanogen metabolic networks and highlight a fundamental challenge in microbiology: single-term expressions may not be sufficient for accurate prediction of microbial growth. IMPORTANCE The Monod equation has been widely applied to predict the rate of microbial growth, but its application is not always successful. Using a novel metabolic modeling approach, we simulated the growth of a methanogen and uncovered a limited mechanistic link between the Monod equation and the methanogen's metabolic network. Specifically, the equation provides an approximation to the controls by rate-determining metabolites and enzymes at very low and very high substrate concentrations, but it is missing the remaining enzymes and metabolites whose controls are most notable at intermediate concentrations. These results support the Monod equation as a useful approximation of growth rates and highlight a fundamental challenge in microbial kinetics: single-term rate expressions may not be sufficient for accurate prediction of microbial growth.
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Affiliation(s)
- Qusheng Jin
- Geobiology Group, University of Oregon, Eugene, Oregon, USA
| | - Qiong Wu
- Geobiology Group, University of Oregon, Eugene, Oregon, USA
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Sadler JC, Dennis JA, Johnson NW, Wallace S. Interfacing non-enzymatic catalysis with living microorganisms. RSC Chem Biol 2021; 2:1073-1083. [PMID: 34458824 PMCID: PMC8341791 DOI: 10.1039/d1cb00072a] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 05/27/2021] [Indexed: 12/04/2022] Open
Abstract
Interfacing non-enzymatic catalysis with cellular metabolism is emerging as a powerful approach to produce a range of high value small molecules and polymers. In this review, we highlight recent examples from this promising young field. Specifically, we discuss demonstrations of living cells mediating redox processes for biopolymer production, interfacing solar-light driven chemistry with microbial metabolism, and intra- and extracellular non-enzymatic catalysis to generate high value molecules. This review highlights the vast potential of this nascent field to bridge the two disciplines of synthetic chemistry and synthetic biology for a sustainable chemical industry.
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Affiliation(s)
- Joanna C Sadler
- Institute of Quantitative Biology, Biochemistry and Biotechnology, School of Biological Sciences, University of Edinburgh Roger Land Building, Alexander Crum Brown Road, King's Buildings Edinburgh, EH9 3FF UK
| | - Jonathan A Dennis
- Institute of Quantitative Biology, Biochemistry and Biotechnology, School of Biological Sciences, University of Edinburgh Roger Land Building, Alexander Crum Brown Road, King's Buildings Edinburgh, EH9 3FF UK
- School of Chemistry, University of Edinburgh Joseph Black Building, David Brewster Road, King's Buildings Edinburgh, EH9 3F UK
| | - Nick W Johnson
- Institute of Quantitative Biology, Biochemistry and Biotechnology, School of Biological Sciences, University of Edinburgh Roger Land Building, Alexander Crum Brown Road, King's Buildings Edinburgh, EH9 3FF UK
| | - Stephen Wallace
- Institute of Quantitative Biology, Biochemistry and Biotechnology, School of Biological Sciences, University of Edinburgh Roger Land Building, Alexander Crum Brown Road, King's Buildings Edinburgh, EH9 3FF UK
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Chen J, Wade MJ, Dolfing J, Soyer OS. Increasing sulfate levels show a differential impact on synthetic communities comprising different methanogens and a sulfate reducer. J R Soc Interface 2020; 16:20190129. [PMID: 31064258 PMCID: PMC6544901 DOI: 10.1098/rsif.2019.0129] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Methane-producing microbial communities are of ecological and biotechnological interest. Syntrophic interactions among sulfate reducers and aceto/hydrogenotrophic and obligate hydrogenotrophic methanogens form a key component of these communities, yet, the impact of these different syntrophic routes on methane production and their stability against sulfate availability are not well understood. Here, we construct model synthetic communities using a sulfate reducer and two types of methanogens representing different methanogenesis routes. We find that tri-cultures with both routes increase methane production by almost twofold compared to co-cultures and are stable in the absence of sulfate. With increasing sulfate, system stability and productivity decreases and does so faster in communities with aceto/hydrogenotrophic methanogens despite the continued presence of acetate. We show that this is due to a shift in the metabolism of these methanogens towards co-utilization of hydrogen with acetate. These findings indicate the important role of hydrogen dynamics in the stability and productivity of syntrophic communities.
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Affiliation(s)
- Jing Chen
- 1 School of Life Sciences, University of Warwick , Coventry CV4 7AL , UK
| | - Matthew J Wade
- 3 School of Engineering, Newcastle University , Newcastle NE1 7RU , UK.,4 School of Mathematics and Statistics, McMaster University , Hamilton, Ontario , Canada L8S 4K1
| | - Jan Dolfing
- 3 School of Engineering, Newcastle University , Newcastle NE1 7RU , UK
| | - Orkun S Soyer
- 1 School of Life Sciences, University of Warwick , Coventry CV4 7AL , UK.,2 Warwick Integrative Synthetic Biology Centre (WISB), University of Warwick , Coventry CV4 7AL , UK
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He P, Duan H, Han W, Liu Y, Shao L, Lü F. Responses of Methanosarcina barkeri to acetate stress. BIOTECHNOLOGY FOR BIOFUELS 2019; 12:289. [PMID: 31890017 PMCID: PMC6913021 DOI: 10.1186/s13068-019-1630-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 12/05/2019] [Indexed: 05/30/2023]
Abstract
BACKGROUND Anaerobic digestion of easily degradable biowaste can lead to the accumulation of volatile fatty acids, which will cause environmental stress to the sensitive methanogens consequently. The metabolic characteristics of methanogens under acetate stress can affect the overall performance of mixed consortia. Nevertheless, there exist huge gaps in understanding the responses of the dominant methanogens to the stress, e.g., Methanosarcinaceae. Such methanogens are resistant to environmental deterioration and able to utilize multiple carbon sources. In this study, transcriptomic and proteomic analyses were conducted to explore the responses of Methanosarcina barkeri strain MS at different acetate concentrations of 10, 25, and 50 mM. RESULTS The trend of OD600 and the regulation of the specific genes in 50 mM acetate, indicated that high concentration of acetate promoted the acclimation of M. barkeri to acetate stress. Acetate stress hindered the regulation of quorum sensing and thereby eliminated the advantages of cell aggregation, which was beneficial to resist stress. Under acetate stress, M. barkeri allocated more resources to enhance the uptake of iron to maintain the integrities of electron-transport chains and other essential biological processes. Comparing with the initial stages of different acetate concentrations, most of the genes participating in acetoclastic methanogenesis did not show significantly different expressions except hdrB1C1, an electron-bifurcating heterodisulfide reductase participating in energy conversion and improving thermodynamic efficiency. Meanwhile, vnfDGHK and nifDHK participating in nitrogen fixation pathway were upregulated. CONCLUSION In this work, transcriptomic and proteomic analyses are combined to reveal the responses of M. barkeri to acetate stress in terms of central metabolic pathways, which provides basic clues for exploring the responses of other specific methanogens under high organics load. Moreover, the results can also be used to gain insights into the complex interactions and geochemical cycles among natural or engineered populations. Furthermore, these findings also provide the potential for designing effective and robust anaerobic digesters with high organic loads.
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Affiliation(s)
- Pinjing He
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, 200092 China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092 China
- Institute of Waste Treatment and Reclamation, Tongji University, Shanghai, 200092 China
| | - Haowen Duan
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, 200092 China
| | - Wenhao Han
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, 200092 China
| | - Yang Liu
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, 200092 China
| | - Liming Shao
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, 200092 China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092 China
- Institute of Waste Treatment and Reclamation, Tongji University, Shanghai, 200092 China
| | - Fan Lü
- State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, 200092 China
- Institute of Waste Treatment and Reclamation, Tongji University, Shanghai, 200092 China
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Xia X, Zhang J, Song T, Lu Y. Stimulation of Smithella-dominating propionate oxidation in a sediment enrichment by magnetite and carbon nanotubes. ENVIRONMENTAL MICROBIOLOGY REPORTS 2019; 11:236-248. [PMID: 30790444 DOI: 10.1111/1758-2229.12737] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 01/29/2019] [Indexed: 06/09/2023]
Abstract
Recent studies have shown that application of conductive materials including magnetite and carbon nanotubes (CNTs) can promote the methanogenic decomposition of short-chain fatty acids and even more complex organic matter in anaerobic digesters and natural habitats. The linkage to microbial identity and the mechanisms, however, remain poorly understood. Here, we evaluate the effects of nanoscale magnetite (nanoFe3 O4 ) and multiwalled CNTs on the syntrophic oxidation of propionate in an enrichment obtained from lake sediment. The microbial populations were composed mainly of Smithella, Syntrophomonas, Methanosaeta, Methanosarcina and Methanoregula. In addition to acetate, butyrate was transiently accumulated indicating that propionate was oxidized by Smithella via the dismutation pathway and part of the leaked butyrate was oxidized by Syntrophomonas. Propionate oxidation and CH4 production were significantly accelerated in the presence of nanoFe3 O4 and CNTs. While propionate oxidation was suppressed upon H2 application and suspended completely upon formate application in the control, this suppressive effect was substantially compromised in the presence of nanoFe3 O4 and CNTs. The tests on hydrogenotrophic methanogenesis of a pure culture methanogen and of the enrichment culture without propionate showed negative effect by both materials. The positive effect of nanoFe3 O4 disappeared when it was insulated by surface-coating with silica. Observations made with fluorescence in situ hybridization and scanning electron microscope indicated the extensive formation of microbial cell-conductive material mixture aggregates. Our results suggest that direct interspecies electron transfer is likely activated by the conductive materials and operates in concert with H2 /formate-dependent electron transfer for syntrophic propionate oxidation in the sediment enrichment.
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Affiliation(s)
- Xingxuan Xia
- Urban and Environmental Sciences, Peking University, Beijing, 100871, China
| | - Jianchao Zhang
- Institute of Surface-Earth System Science, Tianjin University, 300072, China
| | - Tianze Song
- Urban and Environmental Sciences, Peking University, Beijing, 100871, China
| | - Yahai Lu
- Urban and Environmental Sciences, Peking University, Beijing, 100871, China
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Fu L, Zhou T, Wang J, You L, Lu Y, Yu L, Zhou S. NanoFe 3O 4 as Solid Electron Shuttles to Accelerate Acetotrophic Methanogenesis by Methanosarcina barkeri. Front Microbiol 2019; 10:388. [PMID: 30891017 PMCID: PMC6411705 DOI: 10.3389/fmicb.2019.00388] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 02/13/2019] [Indexed: 12/13/2022] Open
Abstract
Magnetite nanoparticles (nanoFe3O4) have been reported to facilitate direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens thereby improving syntrophic methanogenesis. However, whether or how nanoFe3O4 affects acetotrophic methanogenesis remain unknown. Herein, we demonstrate the unique role of nanoFe3O4 in accelerating methane production from direct acetotrophic methanogenesis in Methanosarcina-enriched cultures, which was further confirmed by pure cultures of Methanosarcina barkeri. Compared with other nanomaterials of higher electrical conductivity such as carbon nanotubes and graphite, nanoFe3O4 with mixed valence Fe(II) and Fe(III) had the most significant stimulatory effect on methane production, suggesting its redox activity rather than electrical conductivity led to enhanced methanogenesis by M. barkeri. Cell morphology and spectroscopy analysis revealed that nanoFe3O4 penetrated into the cell membrane and cytoplasm of M. barkeri. These results provide the unprecedented possibility that nanoFe3O4 in the cell membrane of methanogens serve as electron shuttles to facilitate intracellular electron transfer and thus enhance methane production. This work has important implications not only for understanding the mechanisms of mineral-methanogen interaction but also for optimizing engineered methanogenic processes.
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Affiliation(s)
- Li Fu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China.,College of Urban and Environmental Sciences, Peking University, Beijing, China
| | - Ting Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Jingyuan Wang
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Lexing You
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Yahai Lu
- College of Urban and Environmental Sciences, Peking University, Beijing, China
| | - Linpeng Yu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
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Abstract
Hydrogenases are metal-containing biocatalysts that reversibly convert protons and electrons to hydrogen gas. This reaction can contribute in different ways to the generation of the proton motive force (PMF) of a cell. One means of PMF generation involves reduction of protons on the inside of the cytoplasmic membrane, releasing H2 gas, which being without charge is freely diffusible across the cytoplasmic membrane, where it can be re-oxidized to release protons. A second route of PMF generation couples transfer of electrons derived from H2 oxidation to quinone reduction and concomitant proton uptake at the membrane-bound heme cofactor. This redox-loop mechanism, as originally formulated by Mitchell, requires a second, catalytically distinct, enzyme complex to re-oxidize quinol and release the protons outside the cell. A third way of generating PMF is also by electron transfer to quinones but on the outside of the membrane while directly drawing protons through the entire membrane. The cofactor-less membrane subunits involved are proposed to operate by a conformational mechanism (redox-linked proton pump). Finally, PMF can be generated through an electron bifurcation mechanism, whereby an exergonic reaction is tightly coupled with an endergonic reaction. In all cases the protons can be channelled back inside through a F1F0-ATPase to convert the 'energy' stored in the PMF into the universal cellular energy currency, ATP. New and exciting discoveries employing these mechanisms have recently been made on the bioenergetics of hydrogenases, which will be discussed here and placed in the context of their contribution to energy conservation.
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Affiliation(s)
- Constanze Pinske
- Institute of Biology/Microbiology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle/Saale, Germany
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Abstract
Two recent studies (T. D. Mand, G. Kulkarni, and W. W. Metcalf, J. Bacteriol 200:e00342-18, 2018, https://doi.org/10.1128/JB.00342-18, and G. Kulkarni, T. D. Mand, and W. W. Metcalf, mBio 9:e01256-18, 2018, https://doi.org/10.1128/mBio.01256-18) analyzed an impressive array of hydrogenase-deficient mutant strains of Methanosarcina barkeri not only to describe H2-based growth but also to demonstrate the conservation of energy with intracellular hydrogen cycling, a novel strategy for creating a proton motive force to support ATP synthesis.
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