(582bx) The Effects of NADPH Reducing Power On Isopropanol Production in Clostridium Tyrobutyricum

The effects of NADPH reducing power on isopropanol production in Clostridium tyrobutyricum

Wenyan Jiang and Shang-Tian Yang

Isopropanol is one of the most widely used solvents in the world. It is also one of the secondary alcohols that can be used as a direct or partial replacement for gasoline. Since the metabolic pathways and regulation of natural isopropanol producing strains are not well known, the final isopropanol titer can not satisfy rapidly increasing industrial demand. In our previous studies, we genetically engineered Clostridium tyrobutyricum to produce isopropanol by overexpressing C. acetobutylicum ctf (acetoacetyl-CoA transferase), adc (acetoacetate decarboxylase) and C. beijerinckii adh (secondary alcohol dehydrogenase) genes. However, since one extra NADPH is required to convert acetone into isopropanol, which disrupts overall redox balance within cells, the isopropanol titers of the mutants consuming glucose cannot surpass 1.2 g/L. Therefore, in this study, two different NAD kinase genes and one transhydrogenase gene were cloned into engineered C. tyrobutyricum separately to boost NADPH formation. The enzyme activity assay was performed to confirm that the genes were successfully overexpressed and the enzymes were functionally activated. The fermentation kinetics of the mutants shown increases in isopropanol titers, yields and productivities.