Enhancing carbon capture and utilization: mixotrophic growth of Clostridium luticellarii using methanol and hydrogen for efficient CO2 reduction

Abstract

Carbon capture and utilization remains a major challenge in mitigating climate change. Carbon dioxide (CO2) fixing microorganisms offer promising routes to convert CO2 emissions into valuable products. Clostridium luti-cellarii is a recently discovered acetogen capable of converting CO2 to acetic, butyric and isobutyric acids using H2 or methanol as electron donors. Both routes can use renewable electricity as primary energy input, but each has its limitations: While H2-based processes suffer from poor gas-to-liquid mass transfer and low product selectivity beyond acetic acid, methanol requires a preliminary energy-intensive catalytic reduction of CO2. This study investigated the growth of C. luticellarii on both substrates to compensate their respective drawbacks. Combining methanol and H2 resulted in mixotrophic growth and enhanced CO2 assimilation up to four-fold compared to conversion of methanol alone, while producing similar product spectra. Thermodynamic pathway analysis suggested that high H2 pressures inhibit the H2-producing formate oxidation, while pathways with alternative electron carriers remain favorable. Subsequently, a metabolic model of the one-carbon catabolism was constructed and used to perform flux balance analysis. This revealed that H2 oxidation during mixotrophic growth augments the intracellular pool of reducing equivalents, reducing the need for methanol oxidation and increasing net CO2 assimilation into products. These findings highlight the potential of combining methanol and H2 as electron donors to improve CO2 conversion efficiency for the sustainable production of butyric and isobutyric acids.