Transcriptome and proteome analysis of Clostridium ljungdahlii reveals key stress response pathways in microbial electrosynthesis

Microbial electrosynthesis (MES) allows microorganisms to utilize electrical energy (electrons) to produce value-added compounds. MES from CO₂ is based on anaerobic, electroautotrophic microorganisms that take up electrons from the cathode for CO₂ fixation and produce mainly acetate, through the Wood-Ljungdahl pathway (WLP)¹. While similar to gas fermentation, the key difference is the direct feeding of electrons rather than H₂ gas. However, the performance of acetogenic microorganisms in MES is lower, with optical densities (OD) less than 0.4, compared to higher OD in gas fermentation. MES is typically conducted in H-type bioreactors, where a cation exchange membrane separates the anode and cathode compartments. This membrane is crucial to prevent O₂ that results from the anodic water-splitting reaction from reaching the cathode. However, O₂ still intrudes through the membrane, limiting the performance of the biocatalysts ². Therefore, we hypothesize that certain stress factors, such as O₂ intrusion or electron donor limitation cause the low performance of the biocatalyst when performing MES. To elucidate and identify these stress factors, we investigated the MES and gas fermentation performance of Clostridium ljungdahlii, grown in H₂/CO₂ autotrophic gas fermenters and H-type electrobioreactors. We compared growth and acetogenic performance under both conditions, using transcriptome and proteome profiling for physiological insights. Additionally, we used transmission electron microscopy to better understand the cellular responses to the different conditions.

The contribution will present the results of this comparative analysis showing changes in the expression of the WLP, upregulation in genes of microcompartment formation, and expression of an alternative ATP-generating pathway as a stress response during MES.

Acknowledgments: The authors acknowledge support from the Deutsche Forschungsgemeinschaft (priority program SPP2240).

References:

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