(96d) Ctfab and adhE2 Can Induce Acetone Production and Increase Butanol Production Yield From Glucose in Clostridium Tyrobutyricum

C. tyrobutyricum ATCC 25755 is an acidogen with butyric acid and acetic acid as two main fermentation products from glucose and xylose. In addition to the high butyric acid yield, C. tyrobutyricum also has a high butyric acid tolerance, making it an ideal candidate for industrial production of biofuels such as n-butanol. In our previous study, we introduced adhE2 gene encoding a bifunctional aldehyde/alcohol dehydrogenase from C. acetobutylicum into an ack knock-out strain of C. tyrobutyricum, and the mutant produced ~11 g/L butanol from glucose with butyric and acetic acids as two byproducts. To further improve butanol production, it is desirable to re-assimilate the butyric acid and acetic acid and convert them to corresponding alcohols. In this study, we constructed three different plasmids containing ctfAB genes which encode for a CoA-transferase together with adhE2 gene in C. tyrobutyricum. As expected, ctfAB overexpression increased butanol production to 12-14 g/L, with an improved butanol yield and productivity of ~0.24 g/g glucose and ~0.38 g/L·h, and both butyric acid and acetic acid production decreased significantly. Interestingly, ctfAB overexpression alone also induced acetone production without decarboxylation process. Batch fermentation kinetics in pH-controlled fermentors with these mutants was further investigated at different pH values, and the results will be presented in this paper.