A genetic and metabolic approach to redirection of biochemical pathways of Clostridium butyricum for enhancing hydrogen production

Clostridium butyricum, a well known H₂ producing bacterium, produces lactate, butyrate, acetate, ethanol, and CO₂ as its main by-products from glucose. The conversion of pyruvate to lactate, butyrate and ethanol involves oxidation of NADH. It was hypothesized that the NADH could be increased if the formation of these by-products could be eliminated, resulting in enhancing H₂ yield. Herein, this study aimed to establish a genetic and metabolic approach for enhancing H₂ yield via redirection of metabolic pathways of a C. butyricum strain. The ethanol formation pathway was blocked by disruption of aad (encoding aldehyde-alcohol dehydrogenase) using a ClosTron plasmid. Although elimination of ethanol formation alone did not increase hydrogen production, the resulting aad-deficient mutant showed approximately 20% enhanced performance in hydrogen production with the addition of sodium acetate. This work demonstrated the possibility of improving hydrogen yield by eliminating the unfavorable by-products ethanol and lactate.