Clostridium autoethanogenum alters cofactor synthesis, redox metabolism, and lysine-acetylation in response to elevated H(2):CO feedstock ratios for enhancing carbon capture efficiency.

BACKGROUND: Clostridium autoethanogenum is an acetogenic bacterium that autotrophically converts carbon monoxide (CO) and carbon dioxide (CO(2)) gases into bioproducts and fuels via the Wood-Ljungdahl pathway (WLP). To facilitate overall carbon capture efficiency, the reaction stoichiometry requires supplementation of hydrogen at an increased ratio of H(2):CO to maximize CO(2) utilization; however, the molecular details and thus the ability to understand the mechanism of this supplementation are largely unknown. RESULTS: In order to elucidate the microbial physiology and fermentation where at least 75% of the carbon in ethanol comes from CO(2), we established controlled chemostats that facilitated a novel and high (11:1) H(2):CO uptake ratio. We compared and contrasted proteomic and metabolomics profiles to replicate continuous stirred tank reactors (CSTRs) at the same growth rate from a lower (5:1) H(2):CO condition where ~ 50% of the carbon in ethanol is derived from CO(2). Our hypothesis was that major changes would be observed in the hydrogenases and/or redox-related proteins and the WLP to compensate for the elevated hydrogen feed gas. Our analyses did reveal protein abundance differences between the two conditions largely related to reduction-oxidation (redox) pathways and cofactor biosynthesis, but the changes were more minor than we would have expected. While the Wood-Ljungdahl pathway proteins remained consistent across the conditions, other post-translational regulatory processes, such as lysine-acetylation, were observed and appeared to be more important for fine-tuning this carbon metabolism pathway. Metabolomic analyses showed that the increase in H(2):CO ratio drives the organism to higher carbon dioxide utilization resulting in lower carbon storages and accumulated fatty acid metabolite levels. CONCLUSIONS: This research delves into the intricate dynamics of carbon fixation in C. autoethanogenum, examining the influence of highly elevated H(2):CO ratios on metabolic processes and product outcomes. The study underscores the significance of optimizing gas feed composition for enhanced industrial efficiency, shedding light on potential mechanisms, such as post-translational modifications (PTMs), to fine-tune enzymatic activities and improve desired product yields.