Sebastià Puig
Ludovic Jourdin
Shafeer Kalathil- 1LEQUiA, Institute of the Environment, University of Girona, Girona, Spain
- 2Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Delft, Netherlands
- 3Hub for Biotechnology in the Built Environment, Department of Applied Sciences, Faculty of Health and Life Sciences, Northumbria University, Newcastle, United Kingdom
Editorial on the Research Topic
Microbial Electrogenesis, Microbial Electrosynthesis, and Electro-bioremediation
Microbial electrochemical technology (MET) is a bioelectrochemical platform with the potential to overcome a broad range of environmental issues (i.e., global energy, climate crises and water scarcity, among others). This emerging field of research represents an interdisciplinary approach that combines the strengths of microbial catalysis, synthetic electrodes, and analytical techniques for the production of energy and chemicals from waste carbon. The interest in METs has been growing over the years. As an example, the number of papers published in 2020 for the keywords of this Research Topic were ‘Microbial Electrogenesis (10 papers; 9 in 2017)’, ‘Microbial Electrosynthesis (83 papers; 61 in 2017)’, and ‘Electro-bioremediation (51 papers; 25 in 2017)’ according to the Scopus database (July 29th, 2021).
Of particular interest are electroactive microbes with the naturally-evolved ability to electrically interact with insoluble electron acceptors or donors (metal oxides/electrodes) for anaerobic respiration or fermentation, which promises broad applications in microbial fuel cells (Lovley and Holmes, 2021), microbial electrosynthesis (MES; Dessì et al., 2021) and electro-bioremediation (Wang et al., 2020). A key limitation of METs arises from the imperfect integration of microbes with electrode materials which limits the power output, treatment capacity, or volumetric productivity depending on the application (Domínguez-Garay et al., 2018; Fang et al., 2020; Jourdin et al., 2020). Therefore, the nexus of breakthroughs lie in the electrode architecture and microbial interfaces.
The articles published in this Research Topic represent a step forward in the development of METs. For instance, Erben et al. studied the influence of local acidification on the current production of Shewanella oneidensis MR-1/electrode composites using various buffer concentrations from 10 to 40 mM. The results suggest that proton transport associated with electron transfer dictates the rate of extracellular electron transport in S. oneidensis MR-1 in agreement with a previous report (Okamoto et al., 2017). This study concluded that current production was dictated by the chemical (micro)-environment (i.e., local acidification) and the anode material to promote biofilm growth. The electrospun anode materials proposed in this study could provide a solution for high current densities by facilitating biofilm formation while minimising media costs.
MES systems are plagued with poor-performing electrodes that limit microbial activity (Prévoteau et al., 2020; Dessì et al., 2021; Jourdin and Burdyny, 2021). Significant efforts have been given to develop improved cathodes for MES. Kracke et al. propose the use of 3D-printed custom electrodes to fine-tune H2 delivery during MES. The idea behind this is to integrate a 3D fabricated carbon aerogel cathode plated with nickel-molybdenum and Methanococcus maripaludis for electromethanogenesis. Specifically, the nickel-molybdenum coating catalysed the H2 evolution reaction catalysts that provided H2 to M. maripaludis while the 3D structure enhanced the catalytically active surface area. These modifications could mitigate the effects of bubble formation and local pH gradients within the boundary layer, hence overcoming some key constraints on in situ electron delivery in MES.
Breakthrough understanding of the process limiting steps in MES can be achieved using computational modelling tools. Cabau-Peinado et al. developed a general framework for modelling microbial kinetics in biofilm-driven MES of carboxylates (e.g., acetate, n-butyrate, and n-caproate) from CO2. The model was fitted and validated using experimental data from different research groups. The results indicate significant substrate limitation (as CO2 dissolved concentration) in existing MES systems and suggest that operating MES in continuous mode (as constant CO2 sparging and continuous flow of fresh medium) enhances microbial growth and allows higher current densities to be achieved.
Another interesting approach is the use of electro fermentation to overcome the metabolic limitations of fermentative pathways. Application of current can alter metabolic pathways in fermentative microbes and can yield energetically unfavourable products which are not commonly produced by traditional fermentation reactions (Schievano et al., 2016; Logan et al., 2019). Isipato and colleagues proposed electro fermentation to enhance propionate production via controlling lactate fermentation and to recycle the resulting CO2 into acetate, thus increasing the volatile fatty acid yield and reducing the addition of chemicals for pH control (Isipato et al.).
In summary, we believe that the collection of articles included in this Research Topic can pave the way for the development of a high-performing bioelectrochemical platform for sustainable power generation and chemical synthesis.
Author Contributions
All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.
Funding
SP is a Serra Húnter Fellow (UdG-AG-575) and acknowledges the funding from the ICREA Acadèmia award and the Spanish Ministry of Science (RTI2018-098360-B-I00). LEQUIA (http://www.lequia.udg.edu/) has been recognized as a consolidated research group by the Catalan Government (2017-SGR-1552). LJ acknowledges the funding from Shell and a PPP-allowance from Top Consortia for Knowledge and Innovation (TKI's), of the Ministry of Economic Affairs and Climate in the context of the TU Delft e-Refinery Institute. SK acknowledges Research England's Expanding Excellence in England (E3) Fund.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher's Note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
References
Dessì, P., Rovira-Alsina, L., Sánchez, C., Dinesh, G. K., Tong, W., Chatterjee, P., et al. (2021). Microbial electrosynthesis: towards sustainable biorefineries for production of green chemicals from CO2 emissions. Biotechnol. Adv. 46:107675. doi: 10.1016/j.biotechadv.2020.107675
Domínguez-Garay, A., Quejigo, J. R., Dörfler, U., Schroll, R., and Esteve-Núñez, A. (2018). Bioelectroventing: an electrochemical-assisted bioremediation strategy for cleaning-up atrazine-polluted soils. Microb. Biotechnol. 11, 50–62. doi: 10.1111/1751-7915.12687
Fang, X., Kalathil, S., Divitini, G., Wang, Q., and Reisner, E. (2020). A three-dimensional hybrid electrode with electroactive microbes for efficient electrogenesis and chemical synthesis. Proc. Natl. Acad. Sci. U.S.A. 117, 5074–5080. doi: 10.1073/pnas.1913463117
Jourdin, L., and Burdyny, T. (2021). Microbial electrosynthesis : where do we go from here? Trends Biotechnol. 39, 359–369. doi: 10.1016/j.tibtech.2020.10.014
Jourdin, L., Sousa, J., Stralen, N., and van Strik, D. P. B. T. B. (2020). Techno-economic assessment of microbial electrosynthesis from CO2 and/or organics: an interdisciplinary roadmap towards future research and application. Appl. Energy 279:115775. doi: 10.1016/j.apenergy.2020.115775
Logan, B. E., Rossi, R., Ragab, A., and Saikaly, P. E. (2019). Electroactive microorganisms in bioelectrochemical systems. Nat. Rev. Microbiol. 17, 307–319. doi: 10.1038/s41579-019-0173-x
Lovley, D. R., and Holmes, D. E. (2021). Electromicrobiology: the ecophysiology of phylogenetically diverse electroactive microorganisms. Nat. Rev. Microbiol. doi: 10.1038/s41579-021-00597-6
Okamoto, A., Tokunou, Y., Kalathil, S., and Hashimoto, K. (2017). Proton transport in the outer-membrane flavocytochrome complex limits the rate of extracellular electron transport. Angew. Chemie Int. Ed. 56, 9082–9086. doi: 10.1002/anie.201704241
Prévoteau, A., Carvajal-Arroyo, J. M., Ganigué, R., and Rabaey, K. (2020). Microbial electrosynthesis from CO2: forever a promise? Curr. Opin. Biotechnol. 62, 48–57. doi: 10.1016/j.copbio.2019.08.014
Schievano, A., Pepé Sciarria, T., Vanbroekhoven, K., De Wever, H., Puig, S., Andersen, S. J., et al. (2016). Electro-fermentation–merging electrochemistry with fermentation in industrial applications. Trends Biotechnol. 34, 866–878. doi: 10.1016/j.tibtech.2016.04.007
Keywords: microbial electrochemical technologies, 3-D printing, electro microbiology, synthetic electrodes, kinetics modelling
Citation: Puig S, Jourdin L and Kalathil S (2021) Editorial: Microbial Electrogenesis, Microbial Electrosynthesis, and Electro-bioremediation. Front. Microbiol. 12:742479. doi: 10.3389/fmicb.2021.742479
Received: 16 July 2021; Accepted: 20 August 2021;
Published: 13 September 2021.
Edited by:
Celin Acharya, Bhabha Atomic Research Centre (BARC), IndiaReviewed by:
Daniel Ross, National Energy Technology Laboratory (DOE), United StatesPratyoosh Shukla, Banaras Hindu University, India
Copyright © 2021 Puig, Jourdin and Kalathil. 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: Sebastià Puig, sebastia.puig@udg.edu