Microbial Electrosynthesis Reshapes Energy Metabolism and Physiology in Clostridium ljungdahlii

Microbial electrosynthesis (MES) enables a variety of microorganisms, particularly acetogens, to utilize electrical energy in the form of electrons to produce valuable compounds from CO₂. In the closely related process of gas fermentation, hydrogen gas (H₂) is provided as the energy source, whereas in MES, H₂ is produced in situ via water electrolysis. Despite the potential of MES for energy and carbon storage, it still faces major limitations, like low efficiency and low-value products. Here, we identify key limitations of the model MES biocatalyst Clostridium ljungdahlii through comparative transcriptomics, proteomics, and electron microscopy in both processes. We show that cell integrity is severely impaired in MES, consistent with membrane depolarization hampering ATP synthesis. The struggle for ATP is compensated for by activating arginine catabolism to produce ATP, a reaction that is likely fueled by cyanophycin degradation. Diversion of the Wood-Ljungdahl pathway toward the glycine synthase-reductase pathway (GSRP) resulted in a broader spectrum of reduced products, including the two amino compounds ethanolamine and glycine, which appeared exclusively under the electrochemical environment. Additionally, we observed strong induction of bacterial microcompartments, raising questions about their role during MES. This work demonstrates that MES drives C. ljungdahlii into a distinct physiological state that challenges cellular fitness and expands our understanding of MES.