Fermentive Production of Four Carbon Alcohols

A recombinant yeast host cell comprising an engineered isobutanol biosynthetic pathway comprising the following substrate to product conversions:

• i) pyruvate to acetolactate;
• ii) the acetolactate from i) to 2,3-dihydroxyisovalerate;
• iii) the 2,3-dihydroxyisovalerate from ii) to α-ketoisovalerate;
• iv) the α-ketoisovalerate from iii) to isobutyraldehyde;
• and
• v) the isobutyraldehyde from iv) to isobutanol;
• wherein said yeast host cell produces more isobutanol through the substrate to product conversions of steps
• iv) than a control yeast host cell not comprising the engineered isobutanol biosynthetic pathway;
• and wherein
• a) the polypeptide that catalyzes the substrate to product conversion i) is a recombinantly expressed acetolactate synthase;
• b) the polypeptide that catalyzes the substrate to product conversion iii) is a recombinantly expressed acetohydroxy acid dehydratase;
• c) the polypeptide that catalyzes the substrate to product conversion iv) is a recombinantly expressed branched-chain α-keto acid decarboxylase;
• and
• d) the polypeptide that catalyzes the substrate to product conversion v) is an alcohol dehydrogenase.