Microbial electrosynthesis (MES) attracts significant and increasing research interest. MES allows utilizing electric energy (electrons) by microorganisms to produce value-added compounds, most prominently using CO₂ as carbon source. This MES is based on electroautotrophic microorganisms that uptake electrons from the cathode using these for CO₂ fixation by the Wood-Ljungdahl pathway, where CO₂ serves as both, the terminal electron acceptor, and building block.

One main challenge for MES based on electroautotrophs is the design and operation of the microbial electrochemical reactors that are also known as bioelectrochemical systems (BES). BES can be one-chamber systems with anode and cathode facing the same solution or two-chambers systems, where both electrodes are separated by a membrane. In any case, oxygen evolving at the anode from water splitting that enters the cathode severely harms the obligate anaerobic bacteria. Thus, there is an urgent need to create solutions that allow future scaling and exploitation of electroautotrophic MES. ESCAPE aims to develop novel cathodic electrobioreactors to address this research need by integrating bioprocess engineering at UFZ with microbiological science at Leibniz-HKI.

In ESCAPE, in-depth electrochemical and physiological characterization of two autotrophic model species will be performed as a function of BES reaction evolution. The two cathodic obligate anaerobic bacteria, Clostridium ljungdahlii and Desulfosporosinus orientis, will be grown in established autotrophic gas fermenters (H₂/CO₂) and target electrobioreactors. Extensive performance and physiological data will be generated under the two conditions, for example, CO₂ uptake and release, pH, biomass, and metabolite production. Transcriptome and proteomics profiling will be applied to give insight into possible stress responses caused by the oxygen intrusion, insufficient hydrogen levels, or microbial electrochemical cultivation. Measures of stress response in BES will then be used for a targeted development of better MES electrobioreactors.

The main challenge for the electrochemistry and reactor engineering is the protection of the cathodic microbial environment from anodic oxygen. To create a sufficiently anoxic environment at the cathode several paths are followed in parallel. Membrane materials will be systematically characterized and improved regarding, e.g., resistance and oxygen permeability. Further, alternatives to anodic water splitting will be investigated, e.g. by using sacrificial anodes or exploiting electroorganic reactions. In parallel, design of new reactor architectures and scaling of BES for anaerobic MES using, e.g. rapid prototyping, will be performed and subsequently benchmarked with Clostridium ljungdahlii and Desulfosporosinus orientis. Finally, a scaling to bioprocess level will take place, providing a platform for the bioprocess characterization with different anaerobic MES biocatalysts.