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Investigating the electron uptake mechanisms of bacteria on bio-cathodes for microbial electrosynthesis

Periodic Reporting for period 1 - BioCat (Investigating the electron uptake mechanisms of bacteria on bio-cathodes for microbial electrosynthesis)

Période du rapport: 2020-09-01 au 2022-08-31

The project BioCat studied the electron uptake mechanism of Sporomusa ovata on biocathodes in microbial electrosynthesis (MES). MES is a novel technology to sustainably produce chemicals or fuels with renewable electricity by the reduction of carbon dioxide to a wanted product. In case of BioCat the aimed product is acetate, a platform chemical needed as precursor for plastics or e-fuels. So far, the acetate production rates in MES are not competitive with the state-of-the art acetate production based on fossil resources. The crucial question to further optimize MES for real world application is the electron uptake mechanism of the bacterial catalyst used. The bacteria use a cathode connected to an electrical circuit as energy source. But the mechanisms to do so, are unknown. To address this knowledge gap the electron uptake of Sporomusa ovata, the bacteria with the highest acetate production rates reported so far, was studied in the project BioCat.
The overall objective of the BioCat project was to understand the electron uptake mechanism of Sporomusa ovata to bring MES onto the path of application.

When applied, MES will contribute to decarbonize our industry and society in three ways:
1st: Carbon dioxide emissions are converted to a useful product and can be re-used. This stops us from adding new carbon dioxide emissions into the atmosphere promoting the climate crisis.
2nd: MES can replace the production of chemicals which nowadays mainly relies on fossil resources
3nd: MES converts renewable electric energy into chemical energy, exemplary in the form of E-fuels. This can be used as energy storage. The possibility of sustainable energy storage is one of the fundamental requisitions for a complete energy transition to renewable energies. The reason for its importance is the intermittent nature of solar or wind power. To make this intermittent power constantly available, we need storage systems.
Sporomusa ovata was grown in different MES reactors under different operation parameters to collect data on the effect of these on the acetate production rate. To get insights into the electron uptake mechanism, expressed proteins were analyzed starting with SDS page gelelectrophoresis. The main focus was weighted on the detection of c-type cytochromes which are known to be involved in electron transport of other well studied electroactive bacteria. The results suggest the participation of a NrfHA complex when Sporomusa ovata is grown in MES reactors. To analyze its structure and function, this NrfHA was heterologously produced. The cloning steps and production were successful, but pure batches of the proteins could not be obtained, preventing further analysis.
A thorough literature and genome study complemented the experimental work and disclosed that a direct electron transfer between cathode and c-type cytochromes of Sporomusa ovata is very unlikely. The reason for this is that there is no encoded c-type cytochrome in the genome, which is predicted to be located at the outer cell membrane of Sporomusa ovata.
Results of the project BioCat have been disseminated in two journal articles (a third one is planned), two oral presentations at international conferences (one of which by invitation), one poster presentation at an international conference and one poster presentation at a national conference.

Abhiney Jain, Anaísa Coelho, Joana Madjarov, Catarina M. Paquete Jeffrey A. Gralnick: Evidence for Quinol Oxidation Activity of ImoA, a Novel NapC/NirT Family Protein from the Neutrophilic Fe(II)-Oxidizing Bacterium Sideroxydans lithotrophicus ES-1, mBio, Vol.13 No.5 2022. https://doi.org/10.1128/mbio.02150-22
Joana Madjarov, Ricardo Soares, Catarina M. Paquete, Ricardo O. Louro: Sporomusa ovata as Catalyst for Bioelectrochemical Carbon Dioxide Reduction: A Review Across Disciplines From Microbiology to Process Engineering, Frontiers in Microbiology, Vol. 13, 2022, DOI=10.3389/fmicb.2022.913311
Joana Madjarov, Electron uptake in MES: How does Sporomusa ovata accept electrons at the cathode?, 5th European Meeting of the International Society for Microbial Electrochemistry and Technology, 13th-15th September 2021, Girona (but digital due to COVID pandemic)
Joana Madjarov, Catarina M. Paquete, Nils Rohbohm, Gonçalo Pereira, Bruno M. Fonseca, Largus T. Angenent and Ricardo O. Louro, Sporomusa ovata for bioelectrochemical acetate production, 8th Global Meeting of the International Society for Microbial Electrochemistry and Technology, Sept 19 - 23, 2022 in Chania, Crete, Greece
Joana Madjarov: Investigating the electron uptake mechanism of Sporomusa ovata for microbial electrosynthesis of acetate from CO2, Electromicrobiology 2021, Aarhus, Denmark, 3rd to 5th Nov 2021
Joana Madjarov: BioCat: Investigating the electron uptake mechanism of Sporomusa ovata for microbial electrosynthesis of acetate from CO2 XXI SPB National Congress of Biochemistry 2020, postponed to 2021, Évora, Portugal, 14-16th October 2021
The results on the fundamentals of the electron transport mechanism did not depict a clear optimization strategy for MES. But it became clear, that Sporomusa ovata cannot only fix carbon dioxide, but also nitrogen. This opens up a new area of bioelectrochemical technologies beyond state-of-the-art with the clear potential to contribute to sustainable production processes.
From a socio-economic point of view, MES is still too far from application relevance to have an impact. More research is needed on the fundamentals of MES to optimize it, so that it can be applied and have an impact on the shift to sustainable industries and societies. But alongside the research on innovations, a worldwide extensive and fast implementation of already available technologies that decarbonize our societies and industries are needed to face the progressing climate crisis.

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