Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>

ABSTRACT The Methanosarcinales, 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...

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Autores principales:	Annette R. Rowe, Shuai Xu, Emily Gardel, Arpita Bose, Peter Girguis, Jan P. Amend, Mohamed Y. El-Naggar
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2019
Materias:	archaea Methanosarcina bioelectrochemistry cathode electrosynthesis methanogenesis Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/f6cd766450dc4b27856e4eef6ebcc720
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spelling	oai:doaj.org-article:f6cd766450dc4b27856e4eef6ebcc7202021-11-15T15:55:25ZMethane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>10.1128/mBio.02448-182150-7511https://doaj.org/article/f6cd766450dc4b27856e4eef6ebcc7202019-04-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.02448-18https://doaj.org/toc/2150-7511ABSTRACT The Methanosarcinales, 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 by Methanosarcina 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 of M. barkeri to 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 in M. 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 that M. barkeri can 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. IMPORTANCE Methanogenic 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 in Methanosarcina spp. 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 the Methanosarcinales.Annette R. RoweShuai XuEmily GardelArpita BosePeter GirguisJan P. AmendMohamed Y. El-NaggarAmerican Society for MicrobiologyarticlearchaeaMethanosarcinabioelectrochemistrycathodeelectrosynthesismethanogenesisMicrobiologyQR1-502ENmBio, Vol 10, Iss 2 (2019)
institution	DOAJ
collection	DOAJ
language	EN
topic	archaea Methanosarcina bioelectrochemistry cathode electrosynthesis methanogenesis Microbiology QR1-502
spellingShingle	archaea Methanosarcina bioelectrochemistry cathode electrosynthesis methanogenesis Microbiology QR1-502 Annette R. Rowe Shuai Xu Emily Gardel Arpita Bose Peter Girguis Jan P. Amend Mohamed Y. El-Naggar Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>
description	ABSTRACT The Methanosarcinales, 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 by Methanosarcina 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 of M. barkeri to 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 in M. 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 that M. barkeri can 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. IMPORTANCE Methanogenic 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 in Methanosarcina spp. 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 the Methanosarcinales.
format	article
author	Annette R. Rowe Shuai Xu Emily Gardel Arpita Bose Peter Girguis Jan P. Amend Mohamed Y. El-Naggar
author_facet	Annette R. Rowe Shuai Xu Emily Gardel Arpita Bose Peter Girguis Jan P. Amend Mohamed Y. El-Naggar
author_sort	Annette R. Rowe
title	Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>
title_short	Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>
title_full	Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>
title_fullStr	Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>
title_full_unstemmed	Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>
title_sort	methane-linked mechanisms of electron uptake from cathodes by <named-content content-type="genus-species">methanosarcina barkeri</named-content>
publisher	American Society for Microbiology
publishDate	2019
url	https://doaj.org/article/f6cd766450dc4b27856e4eef6ebcc720
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Methane-Linked Mechanisms of Electron Uptake from Cathodes by <named-content content-type="genus-species">Methanosarcina barkeri</named-content>

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