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Biological Methanation or (Bio/Syn)-Gas Upgrading

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Front. Energy Res. | doi: 10.3389/fenrg.2019.00029

Extracellular electron uptake by two Methanosarcina species

  • 1Nordcee, Department of Biology, University of Southern Denmark, Denmark
  • 2Department of Microbiology & Molecular Genetics, Michigan State University, United States
  • 3Department of Engineering, Aarhus University, Denmark

Direct electron uptake by prokaryotes is a recently described mechanism with a potential application for energy and CO2 storage into value added chemicals. Members of Methanosarcinales, an environmentally and biotechnologically relevant group of methanogens, were previously shown to retrieve electrons from an extracellular electrogenic partner performing Direct Interspecies Electron Transfer (DIET) and were therefore proposed to be electroactive. However, their intrinsic electroactivity has never been examined. In this study, we tested two methanogens belonging to the genus Methanosarcina, M. barkeri and M. horonobensis, regarding their ability to accept electrons directly from insoluble electron donors like other cells, conductive particles and electrodes. Both methanogens were able to retrieve electrons from Geobacter metallireducens via DIET. Furthermore, DIET was also stimulated upon addition of electrically conductive granular activated carbon (GAC) when each was co-cultured with G. metallireducens. However, when provided with a cathode poised at -400 mV (vs. SHE), only M. barkeri could perform electromethanogenesis. In contrast, the strict hydrogenotrophic methanogen, Methanobacterium formicicum, did not produce methane regardless of the type of insoluble electron donor provided (Geobacter cells, GAC or electrodes). A comparison of functional gene categories between the two Methanosarcina showed differences regarding energy metabolism, which could explain dissimilarities concerning electromethanogenesis at fixed potentials. We suggest that these dissimilarities are minimized in the presence of an electrogenic DIET partner (e.g. Geobacter), which can modulate its surface redox potentials by adjusting the expression of electroactive surface proteins.

Keywords: Extracellular electron uptake, methanogen, Methanosarcina, direct interspecies electron transfer (DIET), electromethanogenesis, GAC (Granular Activated Carbon), Geobacter

Received: 31 Oct 2018; Accepted: 05 Mar 2019.

Edited by:

Dr S Venkata Mohan, Indian Institute of Chemical Technology (CSIR), India

Reviewed by:

Sarah Glaven, United States Naval Research Laboratory, United States
Sunil A. Patil, Indian Institute of Science Education and Research Mohali, India  

Copyright: © 2019 Yee, Snoeyenbos-West, Thamdrup, Ottosen and Rotaru. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Amelia-Elena Rotaru, University of Southern Denmark, Nordcee, Department of Biology, Odense, Denmark,