Steering microbial communities with electricity: Towards sustainable production of medium-chain fatty acids

Scientific Context The valorization of organic waste is an essential step towards the decarbonization of the economy that the European Union has as set as objective for 2050. Such waste represents a valuable low-cost environmentally sustainable resource as its use does not compete with food production nor require dedicated agricultural land. It shows promise for large-scale production of organic molecules such as medium-chain fatty acids (MCFAs), a class of molecules widely used in industry as precursors for high-added-value products such as antimicrobials, flavorings, bioplastics, and biodiesel. However, organic waste is a complex, heterogeneous and temporally variable matrix, and these characteristics severely limit its valorization potential. Among the various technological options currently being developed for the production of higher added-value organic products for green chemistry applications, microbial electrochemical technologies are promising emerging technologies. These systems exploit a remarkable ability of some microorganisms to exchange electrons directly with a polarized electrode, using it as an electron donor or acceptor. This ability creates a direct link between microbial metabolism and an external electrical circuit, providing new opportunities to influence microbial activity and interactions. This enables the degradation/production of organic molecules, the production of hydrogen or electricity, and new options for controlling microbial communities.  This internship will contribute to Task 2 of project “ElectroMIC” (ANR, PEPR B-BEST). The work aims to explore how electrochemical and microbiological parameters can be used to improve and control MCFA production in a selected microbial community performing chain elongation (=elongation of short-chain into medium-chain fatty acids). Objectives In the context of this work, the general objective of this internship is to explore strategies to improve and control the production of medium-chain fatty acids (MCFAs) in an electro-fermentation system performing chain elongation at the biocathode. Several complementary approaches will be considered, depending on the results obtained during the internship:  Investigate the potential of a bioanode to improve the electro-fermentation process. Electroactive species will by enriched by applying an electric potential to the anode, and biofilm formation will be monitored. Metabolites in the solution will be analyzed to identify the oxidation reaction taking place at the anode (e.g.: acetate consumption by an electroactive microbe such as Geobacter sp.). The compatibility of the oxidation reaction with the chain elongation process will be assessed. If relevant, the newly enriched bioanode will be coupled with the already tested biocathode, and its impact on MCFA production will be evaluated. Explore the effect of the microbial community at the biocathode. Different microbial communities or enrichment conditions may be investigated to identify conditions promoting chain elongation and limiting competing metabolic pathways. The possibility of combining or coalescing microbial communities with complementary metabolic functions will be explored, depending on the experimental results. Investigate the influence of operating conditions on MCFA production. In addition to electrode polarization, parameters such as the nature and availability of the electron donor, substrate composition, or other relevant operating conditions may be varied to identify conditions favoring chain elongation and MCFA production. Metabolite profiles and electrochemical measurements will be used to assess the response of the microbial community. The internship will therefore combine microbial enrichment, electrochemical characterization and chemical analyses to identify conditions that favor MCFA production in the electro-fermentation system. The precise experimental strategy will be adapted according to the results obtained during the internship, with the objective of identifying promising levers for improving process performance and control. Work environment The internship will take place at the Laboratoire de Biotechnologie de l'Environnement (LBE), which is a research unit of the Occitanie-Montpellier center of Institut National de Recherche pour l’Agriculture, l’alimentation et l’Environnement (INRAE), based in Narbonne. Research carried out at the LBE aims to develop the concept of an environmental biorefinery, which involves converting residues, waste, organic effluents and certain types of biomass into products of industrial interest (bioenergy, biomolecules, soil improvers and organic fertilizers) whilst minimizing their environmental and health impacts. Its research as a whole covers a very broad spectrum of disciplinary expertise: microbiology, microbial ecology, biological engineering, process engineering, modelling, control systems and industrial transfer. INRAE is a public research organization comprising a working community