Mechanistic insights into the response of Clostridium beijerinckii to hexanoic acid stress in bio-butanol fermentation

Distillers’ grain waste (DGW), a primary solid by-product in Baijiu production, holds promise as a feedstock for valuable chemicals such as bio-butanol. However, an excessive amount of hexanoic acid in DGW significantly inhibits solvent-producing clostridia during bio-butanol fermentation. This research delved into the response of Clostridium beijerinckii LY-5 to hexanoic acid stress by combining fermentation performance analysis and transcriptomics. The results indicated that hexanoic acid concentrations above 0.4 g/L could inhibit sugar consumption and butanol production. The intracellular energy status and the NADH/NAD⁺ ratio were affected, and the cell growth was decreased by 13.9 % at 1.1 g/L. Moreover, the transcriptomic analysis demonstrated that hexanoic acid affected the gene expression profiles related to the cell wall and membrane, membrane transporters, central metabolic pathways, the two-component system, and sporulation. The reduced expression of genes responsible for the phosphotransferase system and acetaldehyde-CoA/alcohol dehydrogenase may explain the decreased glucose consumption and solvent biosynthesis. These findings could provide a rational basis for constructing a tolerant strain for efficient bio-butanol production from DGW.