Patent ID: 8133715

Claim:
A recombinant microorganism comprising: a) an isobutanol producing metabolic pathway, wherein said isobutanol producing metabolic pathway comprises at least one exogenous gene or at least one overexpressed endogenous gene encoding an enzyme that catalyzes a pathway step in the conversion of pyruvate to isobutanol; and b) at least one modification which disrupts the expression or activity of an endogenous enzyme having 3-keto acid reductase activity, wherein said modification is selected from the group consisting of: I. a mutation of an endogenous gene encoding said endogenous enzyme having 3-keto acid reductase activity; and II. a mutation of a regulatory element associated with an endogenous gene encoding said endogenous enzyme having 3-keto acid reductase activity; wherein said endogenous enzyme having 3-keto acid reductase activity catalyzes the conversion of acetolactate to 2,3-dihydroxy-2-methylbutanoic acid (DH2MB).