Environmental friendly biofuels gain great interests due to climate change and the need for renewable transportation fuels in recent years. Ethanol has been received more attention as the most widely used biofuel . However, compared to ethanol, higher alcohols have several advantages as next-generation transport fuels. And they are compatible with current infrastructure. Isobutanol exhibits superior physicochemical properties such as higher energy density and lower hygroscopicity than ethanol. Furthermore, it has higher octane number than the isomer n-butanol.
Saccharomyces cerevisiae has high tolerance to isobutanol up to 20 g/l and robustness during fermentation in harsh industrial conditions. In addition, S. cerevisiae naturally produces small amount of isobutanol as byproduct from the catabolism of amino acidsx. So S. cerevisiae has been considered as an attractive alternative host strain to produce isobutanol. Initially, glucose is converted to pyruvate via the process of glycolysis. Then pyruvate is converted to 2- ketoisovalerate (KIV) in the mitochondria by acetolactate synthase (Ilv2), acetohydroxyacid reductoisomerase (Ilv5) and dihydroxyacid dehydrates (Ilv3)