Title: Methane-Linked Mechanisms of Electron Uptake from Cathodes by Methanosarcina barkeri

Abstract

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 thesemore » 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.« less

Authors:

Rowe, Annette R.  ^[1];

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Xu, Shuai ^[2]; Gardel, Emily ^[3]; Bose, Arpita ^[3]; Girguis, Peter ^[3]; Amend, Jan P. ^[2]; El-Naggar, Mohamed Y. ^[2]

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+ Show Author Affiliations

1. Univ. of Cincinnati, OH (United States); Univ. of Southern California, Los Angeles, CA (United States)
2. Univ. of Southern California, Los Angeles, CA (United States)
3. Harvard Univ., Cambridge, MA (United States)

Publication Date:

Tue Mar 12 00:00:00 EDT 2019

Research Org.:

Univ. of Southern California, Los Angeles, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1611469

Grant/Contract Number:  

SC0010609

Resource Type:

Accepted Manuscript

Journal Name:

mBio (Online)

Additional Journal Information:

Journal Name: mBio (Online); Journal Volume: 10; Journal Issue: 2; Journal ID: ISSN 2150-7511

Publisher:

American Society for Microbiology

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Microbiology