Toward a low-energy bioelectrochemical fixation of N2 via mixed cultures electroactive biofilms
Comparison of enrichment methods for efficient nitrogen fixation on a biocathode
Recommendation: posted 07 August 2023, validated 11 August 2023
De Vrieze, J. (2023) Toward a low-energy bioelectrochemical fixation of N2 via mixed cultures electroactive biofilms. Peer Community in Microbiology, 100010. 10.24072/pci.microbiol.100010
Nitrogen fixation and elimination are two key microbial processes that significantly impact the release (and removal) of reactive nitrogen into natural ecosystems. Unlike global change, caused by the emission of greenhouse gasses into our atmosphere, the release of reactive nitrogen into our biosphere only recently (in the last years) received the necessary public attention. Hence, novel techniques for (1) reactive nitrogen recovery, (2) energy-effective removal, and (3) sustainable nitrogen fixation are essential to prevent the nitrogen cycle from spinning out of control without also putting an additional burden on our precious natural resources or increasing the emission of greenhouse gasses.
In this research paper by Rous et al. (2023), the authors investigated the use of a biocathode in a bioelectrochemical system (BES) for sustainable fixation of N2 into NH3, using electricity as a sustainable energy source and CO2 as the only carbon source. A critical element in their study was the enrichment of N2-fixating bacteria, starting from soil samples, in an effort to achieve effective nitrogen fixation. A comparison between the enriched culture and a pure culture of diazotrophic hydrogenotrophic bacteria confirmed comparable results for N2 fixation, indicating that the enrichment process was a viable and successful approach. Although pure culture biotechnological processes have their merits, it is clear that the usage of an enriched microbial culture allows for a more simple, robust, and open microbial process, compared to pure culture systems.
This approach does enable a sustainable way of N2 (and by extension CO2) fixation, as it relies on electricity directly (or indirectly through H2) and CO2 only, but it does suffer from low coulombic efficiencies (<5%). This indicates that, even though the results are promising, there is room for optimization, especially concerning the production of (unwanted) side products, such as acetate and other microbial metabolites. This reflects a key challenge and potential disadvantage of mixed or enriched cultures compared to pure cultures.
It is in that framework that this study provides an interesting, highly relevant view on the potential of bioelectrochemical nitrogen fixation using enriched cultures, yet, it also implies the need to either find a purpose for the byproducts, such as acetate, and/or achieve a more effective enrichment strategy to achieve an increased coulombic efficiency towards sustainable nitrogen fixation.
Rous A., Santa-Catalina G., Desmond-Le Quéméner E., Eric Trably E. and Nicolas Bernet N. (2023). Comparison of enrichment methods for efficient nitrogen fixation on a biocathode. bioRxiv, 2023.03.02.530809, ver 5, peer-reviewed and recommended by Peer Community in Microbiology. https://doi.org/10.1101/2023.03.02.530809
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article. The authors declared that they comply with the PCI rule of having no financial conflicts of interest in relation to the content of the article.
French National Research Agency (ANR, ANR-19-CE43-0013 Cathomix)
Reviewed by anonymous reviewer 1, 20 Jul 2023
Reviewed by anonymous reviewer 2, 28 Jun 2023
Evaluation round #1
DOI or URL of the preprint: https://doi.org/10.1101/2023.03.02.530809
Version of the preprint: 4
Author's Reply, 22 Jun 2023
Decision by Jo De Vrieze, posted 25 Apr 2023, validated 25 Apr 2023
Dear Dr. Bernet,
Thank you for submitting your manuscript to PCI Microbiology.
Following the evaluation of your research paper entitled "Comparison of enrichment methods for efficient nitrogen fixation on a biocathode", I have carefully considered the comments of the two highly-qualified reviewers. It is my view and decision that this manuscript has scientific value and that it is relevant for the readers of PCI Microbiology, but Major Revisions are required.
I invite you to resubmit your manuscript after addressing the comments of the two reviewers. When revising your manuscript, please consider all issues mentioned in the reviewers' comments carefully. Please outline in a separate document every change made in response to the reviewers' comments and provide suitable rebuttals for any comments not addressed. Please also not that your revised submission may need to be re-reviewed.
I'm looking forward to receiving your revised manuscript. Please don't hesitate to contact me in case of any further questions.
Prof. Jo De Vrieze