Faster Growth Enhances Low Carbon Fuel and Chemical Production Through Gas Fermentation

Gas fermentation offers both fossil carbon-free sustainable production of fuels and chemicals and recycling of gaseous and solid waste using gas-fermenting microbes. Bioprocess development, systems-level analysis of biocatalyst metabolism, and engineering of cell factories are advancing the widespread deployment of the commercialised technology. Acetogens are particularly attractive biocatalysts but effects of the key physiological parameter-specific growth rate (mu)-on acetogen metabolism and the gas fermentation bioprocess have not been established yet. Here, we investigate the mu-dependent bioprocess performance of the model-acetogen Clostridium autoethanogenum in CO and syngas (CO + CO2 +H-2) grown chemostat cultures and assess systems-level metabolic responses using gas analysis, metabolomics, transcriptomics, and metabolic modelling. We were able to obtain steady-states up to mu similar to 2.8 day(-1) (similar to 0.12 h(-1)) and show that faster growth supports both higher yields and productivities for reduced by-products ethanol and 2,3-butanediol. Transcriptomics data revealed differential expression of 1,337 genes with increasing p and suggest that C. autoethanogenum uses transcriptional regulation to a large extent for facilitating faster growth. Metabolic modelling showed significantly increased fluxes for faster growing cells that were, however, not accompanied by gene expression changes in key catabolic pathways for CO and H-2 metabolism. Cells thus seem to maintain sufficient baseline gene expression to rapidly respond to CO and H-2 availability without delays to kick-start metabolism. Our work advances understanding of transcriptional regulation in acetogens and shows that faster growth of the biocatalyst improves the gas fermentation bioprocess.

Automated summary

The study investigates the performance of Clostridium autoethanogenum in gas fermentation at different growth rates and evaluates the metabolic responses using various methods. The findings reveal that faster growth supports higher yields and productivities, and transcriptional regulation plays a significant role in facilitating faster growth. Additionally, the cells maintain sufficient baseline gene expression to respond rapidly to the availability of CO and H-2.