scholarly journals Methane-linked mechanisms of electron uptake from cathodes byMethanosarcina barkeri

2018 ◽  
Author(s):  
Annette R. Rowe ◽  
Shuai Xu ◽  
Emily Gardel ◽  
Arpita Bose ◽  
Peter Girguis ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Methane Production ◽  
Extracellular Enzymes ◽  
Solid Phase ◽  
Electrochemical Techniques ◽  
Extracellular Enzyme ◽  
Methanosarcina Barkeri ◽  
Extracellular Electron Transfer ◽  
Cathodic Current ◽  
Wide Range

AbstractTheMethanosarcinales, a lineage of cytochrome-containing methanogens, have recently been proposed to participate in direct extracellular electron transfer interactions within syntrophic communities. To shed light on this phenomenon, we applied electrochemical techniques to measure electron uptake from cathodes byMethanosarcina barkeri, which is an important model organism that is genetically tractable and utilizes a wide range of substrates for methanogenesis. Here we confirm the ability ofM. barkerito perform electron uptake from cathodes and show that this cathodic current is linked to quantitative increases in methane production. The underlying mechanisms we identified include, but are not limited to, a recently proposed association between cathodes and methanogen-derived extracellular enzymes (e.g. hydrogenases) that can facilitate current generation through the formation of reduced and diffusible methanogenic substrates (e.g. hydrogen). However, after minimizing the contributions of such extracellular enzymes and using a mutant lacking hydrogenases, we observe a lower potential hydrogen-independent pathway that facilitates cathodic activity coupled to methane production inM. barkeri. Our electrochemical measurements of wild-type and mutant strains point to a novel and extracellular-enzyme-free mode of electron uptake able to take up electrons at potentials lower than - 498 mV vs. SHE (over 100 mV more reduced than the observed hydrogenase midpoint potential under these conditions). These results suggest thatM. barkerican perform multiple modes (hydrogenase-mediated and free extracellular enzyme-independent) of electrode interactions on cathodes including a mechanism pointing to a direct interaction, which has significant applied and ecological implications.ImportanceMethanogenic Archaea are of fundamental applied and environmental relevance. This is largely due to their activities in a wide range of anaerobic environments, generating gaseous reduced carbon that can be utilized as a fuel source. While the bioenergetics of a wide variety of methanogens has been well studied with respect to soluble substrates, mechanistic understanding of their interaction with solid phase redox active compounds is limited. This work provides insight into solid phase redox interactions inMethanosarcinausing electrochemical methods. We highlight a previously undescribed mode of electron uptake from cathodes, that is potentially informative of direct interspecies electron transfer interactions in theMethanosarcinales.

scholarly journals Methane-Linked Mechanisms of Electron Uptake from Cathodes byMethanosarcina barkeri

mBio ◽  
2019 ◽  
Vol 10 (2) ◽  
Author(s):  
Annette R. Rowe ◽  
Shuai Xu ◽  
Emily Gardel ◽  
Arpita Bose ◽  
Peter Girguis ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Methane Production ◽  
Extracellular Enzymes ◽  
Solid Phase ◽  
Electrochemical Techniques ◽  
Methanosarcina Barkeri ◽  
Extracellular Electron Transfer ◽  
Hydrogen Electrode ◽  
Content Type ◽  
Wide Range

ABSTRACTTheMethanosarcinales, a lineage of cytochrome-containing methanogens, have recently been proposed to participate in direct extracellular electron transfer interactions within syntrophic communities. To shed light on this phenomenon, we applied electrochemical techniques to measure electron uptake from cathodes byMethanosarcina barkeri, which is an important model organism that is genetically tractable and utilizes a wide range of substrates for methanogenesis. Here, we confirm the ability ofM. barkerito perform electron uptake from cathodes and show that this cathodic current is linked to quantitative increases in methane production. The underlying mechanisms we identified include, but are not limited to, a recently proposed association between cathodes and methanogen-derived extracellular enzymes (e.g., hydrogenases) that can facilitate current generation through the formation of reduced and diffusible methanogenic substrates (e.g., hydrogen). However, after minimizing the contributions of such extracellular enzymes and using a mutant lacking hydrogenases, we observe a lower-potential hydrogen-independent pathway that facilitates cathodic activity coupled to methane production inM. barkeri. Our electrochemical measurements of wild-type and mutant strains point to a novel and hydrogenase-free mode of electron uptake with a potential near −484 mV versus standard hydrogen electrode (SHE) (over 100 mV more reduced than the observed hydrogenase midpoint potential under these conditions). These results suggest thatM. barkerican perform multiple modes (hydrogenase-mediated and free extracellular enzyme-independent modes) of electrode interactions on cathodes, including a mechanism pointing to a direct interaction, which has significant applied and ecological implications.IMPORTANCEMethanogenic archaea are of fundamental applied and environmental relevance. This is largely due to their activities in a wide range of anaerobic environments, generating gaseous reduced carbon that can be utilized as a fuel source. While the bioenergetics of a wide variety of methanogens have been well studied with respect to soluble substrates, a mechanistic understanding of their interaction with solid-phase redox-active compounds is limited. This work provides insight into solid-phase redox interactions inMethanosarcinaspp. using electrochemical methods. We highlight a previously undescribed mode of electron uptake from cathodes that is potentially informative of direct interspecies electron transfer interactions in theMethanosarcinales.

scholarly journals Single-Cell Electrophysiological Measurements Reveal Bacterial Membrane Potential Dynamics during Extracellular Electron Transfer

2020 ◽  
Author(s):  
Sahand Pirbadian ◽  
Marko S. Chavez ◽  
Mohamed Y. El-Naggar
Keyword(s):  
Electron Transfer ◽  
Membrane Potential ◽  
Single Cell ◽  
Solid Phase ◽  
Electrochemical Techniques ◽  
Model Organisms ◽  
Extracellular Electron Transfer ◽  
Single Cell Level ◽  
Cell Level ◽  
Wide Range

AbstractExtracellular electron transfer (EET) allows microorganisms to gain energy by linking intracellular reactions to external surfaces ranging from natural minerals to the electrodes of bioelectrochemical renewable energy technologies. In the past two decades, electrochemical techniques have been used to investigate EET in a wide range of microbes, with emphasis on dissimilatory metal-reducing bacteria, such as Shewanella oneidensis MR-1, as model organisms. However, due to the typically bulk nature of these techniques, they are unable to reveal the subpopulation variation in EET or link the observed electrochemical currents to energy gain by individual cells, thus overlooking the potentially complex spatial patterns of activity in bioelectrochemical systems. Here, to address these limitations, we use the cell membrane potential as a bioenergetic indicator of EET by S. oneidensis MR-1 cells. Using a fluorescent membrane potential indicator during in vivo single-cell level fluorescence microscopy in a bioelectrochemical reactor, we demonstrate that membrane potential strongly correlates with the electrode potential, produced current, and position of cells relative to the electrodes. The high spatial and temporal resolution of the reported technique can be used to study the single-cell level dynamics of EET not only on electrode surfaces, but also during respiration of other solid-phase electron acceptors.

scholarly journals Spatiotemporal mapping of bacterial membrane potential responses to extracellular electron transfer

2020 ◽  
Vol 117 (33) ◽  
pp. 20171-20179 ◽  
Author(s):  
Sahand Pirbadian ◽  
Marko S. Chavez ◽  
Mohamed Y. El-Naggar
Keyword(s):  
Electron Transfer ◽  
Membrane Potential ◽  
Single Cell ◽  
Electrochemical Techniques ◽  
Model Organisms ◽  
Extracellular Electron Transfer ◽  
Single Cell Level ◽  
Cell Level ◽  
Membrane Hyperpolarization ◽  
Wide Range

Extracellular electron transfer (EET) allows microorganisms to gain energy by linking intracellular reactions to external surfaces ranging from natural minerals to the electrodes of bioelectrochemical renewable energy technologies. In the past two decades, electrochemical techniques have been used to investigate EET in a wide range of microbes, with emphasis on dissimilatory metal-reducing bacteria, such asShewanella oneidensisMR-1, as model organisms. However, due to the typically bulk nature of these techniques, they are unable to reveal the subpopulation variation in EET or link the observed electrochemical currents to energy gain by individual cells, thus overlooking the potentially complex spatial patterns of activity in bioelectrochemical systems. Here, to address these limitations, we use the cell membrane potential as a bioenergetic indicator of EET byS. oneidensisMR-1 cells. Using a fluorescent membrane potential indicator during in vivo single-cell-level fluorescence microscopy in a bioelectrochemical reactor, we demonstrate that membrane potential strongly correlates with EET. Increasing electrode potential and associated EET current leads to more negative membrane potential. This EET-induced membrane hyperpolarization is spatially limited to cells in contact with the electrode and within a near-electrode zone (<30 μm) where the hyperpolarization decays with increasing cell-electrode distance. The high spatial and temporal resolution of the reported technique can be used to study the single-cell-level dynamics of EET not only on electrode surfaces, but also during respiration of other solid-phase electron acceptors.

scholarly journals Putative Extracellular Electron Transfer in Methanogenic Archaea

2021 ◽  
Vol 12 ◽  
Author(s):  
Kailin Gao ◽  
Yahai Lu
Keyword(s):  
Electron Transfer ◽  
Methanogenic Archaea ◽  
Methanosarcina Barkeri ◽  
Extracellular Electron Transfer ◽  
Future Research ◽  
Methanosarcina Acetivorans ◽  
Geobacter Metallireducens ◽  
Methanosarcina Mazei ◽  
Current State ◽  
Electron Transfers

It has been suggested that a few methanogens are capable of extracellular electron transfers. For instance, Methanosarcina barkeri can directly capture electrons from the coexisting microbial cells of other species. Methanothrix harundinacea and Methanosarcina horonobensis retrieve electrons from Geobacter metallireducens via direct interspecies electron transfer (DIET). Recently, Methanobacterium, designated strain YSL, has been found to grow via DIET in the co-culture with Geobacter metallireducens. Methanosarcina acetivorans can perform anaerobic methane oxidation and respiratory growth relying on Fe(III) reduction through the extracellular electron transfer. Methanosarcina mazei is capable of electromethanogenesis under the conditions where electron-transfer mediators like H2 or formate are limited. The membrane-bound multiheme c-type cytochromes (MHC) and electrically-conductive cellular appendages have been assumed to mediate the extracellular electron transfer in bacteria like Geobacter and Shewanella species. These molecules or structures are rare but have been recently identified in a few methanogens. Here, we review the current state of knowledge for the putative extracellular electron transfers in methanogens and highlight the opportunities and challenges for future research.

Extracellular electron transfer through microbial reduction of solid-phase humic substances

2010 ◽  
Vol 3 (6) ◽  
pp. 417-421 ◽  
Author(s):  
Eric E. Roden ◽  
Andreas Kappler ◽  
Iris Bauer ◽  
Jie Jiang ◽  
Andrea Paul ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Humic Substances ◽  
Solid Phase ◽  
Microbial Reduction ◽  
Extracellular Electron Transfer

Assessment of Five Electron‐Shuttling Molecules in the Extracellular Electron Transfer of Electromethanogenesis by using Methanosarcina barkeri

2020 ◽  
Vol 7 (18) ◽  
pp. 3783-3789
Author(s):  
Tian‐Tian Liang ◽  
Lei Zhou ◽  
Muhammad Irfan ◽  
Yang Bai ◽  
Xue‐Zhi Liu ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Methanosarcina Barkeri ◽  
Extracellular Electron Transfer ◽  
Electron Shuttling

scholarly journals Extracellular Enzymes Facilitate Electron Uptake in Biocorrosion and Bioelectrosynthesis

mBio ◽  
2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Jörg S. Deutzmann ◽  
Merve Sahin ◽  
Alfred M. Spormann
Keyword(s):  
Electron Transfer ◽  
Molecular Mechanisms ◽  
Solid Phase ◽  
Direct Electron Transfer ◽  
Extracellular Electron Transfer ◽  
Methane Formation ◽  
Electron Transfer Mechanism ◽  
Microbial Cells ◽  
Microbial Electrosynthesis ◽  
Microbially Influenced Corrosion

ABSTRACTDirect, mediator-free transfer of electrons between a microbial cell and a solid phase in its surrounding environment has been suggested to be a widespread and ecologically significant process. The high rates of microbial electron uptake observed during microbially influenced corrosion of iron [Fe(0)] and during microbial electrosynthesis have been considered support for a direct electron uptake in these microbial processes. However, the underlying molecular mechanisms of direct electron uptake are unknown. We investigated the electron uptake characteristics of the Fe(0)-corroding and electromethanogenic archaeonMethanococcus maripaludisand discovered that free, surface-associated redox enzymes, such as hydrogenases and presumably formate dehydrogenases, are sufficient to mediate an apparent direct electron uptake. In genetic and biochemical experiments, we showed that these enzymes, which are released from cells during routine culturing, catalyze the formation of H2or formate when sorbed to an appropriate redox-active surface. These low-molecular-weight products are rapidly consumed byM. maripaludiscells when present, thereby preventing their accumulation to any appreciable or even detectable level. Rates of H2and formate formation by cell-free spent culture medium were sufficient to explain the observed rates of methane formation from Fe(0) and cathode-derived electrons by wild-typeM. maripaludisas well as by a mutant strain carrying deletions in all catabolic hydrogenases. Our data collectively show that cell-derived free enzymes can mimic direct extracellular electron transfer during Fe(0) corrosion and microbial electrosynthesis and may represent an ecologically important but so far overlooked mechanism in biological electron transfer.IMPORTANCEThe intriguing trait of some microbial organisms to engage in direct electron transfer is thought to be widespread in nature. Consequently, direct uptake of electrons into microbial cells from solid surfaces is assumed to have a significant impact not only on fundamental microbial and biogeochemical processes but also on applied bioelectrochemical systems, such as microbial electrosynthesis and biocorrosion. This study provides a simple mechanistic explanation for frequently observed fast electron uptake kinetics in microbiological systems without a direct transfer: free, cell-derived enzymes can interact with cathodic surfaces and catalyze the formation of intermediates that are rapidly consumed by microbial cells. This electron transfer mechanism likely plays a significant role in various microbial electron transfer reactions in the environment.

scholarly journals A Membrane-Bound Cytochrome Enables Methanosarcina acetivorans To Conserve Energy from Extracellular Electron Transfer

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Dawn E. Holmes ◽  
Toshiyuki Ueki ◽  
Hai-Yan Tang ◽  
Jinjie Zhou ◽  
Jessica A. Smith ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electron Acceptor ◽  
Methane Production ◽  
Genetic Manipulation ◽  
Methanol Conversion ◽  
Extracellular Electron Transfer ◽  
Methanosarcina Acetivorans ◽  
Coenzyme M ◽  
Content Type ◽  
Expression Of Genes

ABSTRACT Extracellular electron exchange in Methanosarcina species and closely related Archaea plays an important role in the global carbon cycle and enhances the speed and stability of anaerobic digestion by facilitating efficient syntrophic interactions. Here, we grew Methanosarcina acetivorans with methanol provided as the electron donor and the humic analogue, anthraquione-2,6-disulfonate (AQDS), provided as the electron acceptor when methane production was inhibited with bromoethanesulfonate. AQDS was reduced with simultaneous methane production in the absence of bromoethanesulfonate. Transcriptomics revealed that expression of the gene for the transmembrane, multiheme, c-type cytochrome MmcA was higher in AQDS-respiring cells than in cells performing methylotrophic methanogenesis. A strain in which the gene for MmcA was deleted failed to grow via AQDS reduction but grew with the conversion of methanol or acetate to methane, suggesting that MmcA has a specialized role as a conduit for extracellular electron transfer. Enhanced expression of genes for methanol conversion to methyl-coenzyme M and the Rnf complex suggested that methanol is oxidized to carbon dioxide in AQDS-respiring cells through a pathway that is similar to methyl-coenzyme M oxidation in methanogenic cells. However, during AQDS respiration the Rnf complex and reduced methanophenazine probably transfer electrons to MmcA, which functions as the terminal reductase for AQDS reduction. Extracellular electron transfer may enable the survival of methanogens in dynamic environments in which oxidized humic substances and Fe(III) oxides are intermittently available. The availability of tools for genetic manipulation of M. acetivorans makes it an excellent model microbe for evaluating c-type cytochrome-dependent extracellular electron transfer in Archaea. IMPORTANCE The discovery of a methanogen that can conserve energy to support growth solely from the oxidation of organic carbon coupled to the reduction of an extracellular electron acceptor expands the possible environments in which methanogens might thrive. The potential importance of c-type cytochromes for extracellular electron transfer to syntrophic bacterial partners and/or Fe(III) minerals in some Archaea was previously proposed, but these studies with Methanosarcina acetivorans provide the first genetic evidence for cytochrome-based extracellular electron transfer in Archaea. The results suggest parallels with Gram-negative bacteria, such as Shewanella and Geobacter species, in which multiheme outer-surface c-type cytochromes are an essential component for electrical communication with the extracellular environment. M. acetivorans offers an unprecedented opportunity to study mechanisms for energy conservation from the anaerobic oxidation of one-carbon organic compounds coupled to extracellular electron transfer in Archaea with implications not only for methanogens but possibly also for Archaea that anaerobically oxidize methane.

A biofilm microreactor system for simultaneous electrochemical and nuclear magnetic resonance techniques

2013 ◽  
Vol 69 (5) ◽  
pp. 966-973 ◽  
Author(s):  
R. S. Renslow ◽  
J. T. Babauta ◽  
P. D. Majors ◽  
H. S. Mehta ◽  
R. J. Ewing ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Electron Transfer ◽  
Magnetic Resonance ◽  
Electrochemical Techniques ◽  
Geobacter Sulfurreducens ◽  
In Situ Monitoring ◽  
Extracellular Electron Transfer ◽  
Acetate Concentration ◽  
Nmr Techniques ◽  
Nuclear Magnetic

Nuclear magnetic resonance (NMR) techniques are ideally suited for the study of biofilms and for probing their microenvironments because these techniques allow for noninvasive interrogation and in situ monitoring with high resolution. By combining NMR with simultaneous electrochemical techniques, it is possible to sustain and study live biofilms respiring on electrodes. Here, we describe a biofilm microreactor system, including a reusable and a disposable reactor, that allows for simultaneous electrochemical and NMR techniques (EC-NMR) at the microscale. Microreactors were designed with custom radio frequency resonator coils, which allowed for NMR measurements of biofilms growing on polarized gold electrodes. For an example application of this system we grew Geobacter sulfurreducens biofilms on electrodes. EC-NMR was used to investigate growth medium flow velocities and depth-resolved acetate concentration inside the biofilm. As a novel contribution we used Monte Carlo error analysis to estimate the standard deviations of the acetate concentration measurements. Overall, we found that the disposable EC-NMR microreactor provided a 9.7 times better signal-to-noise ratio over the reusable reactor. The EC-NMR biofilm microreactor system can ultimately be used to correlate extracellular electron transfer rates with metabolic reactions and explore extracellular electron transfer mechanisms.

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