Yeast organism producing isobutanol at a high yield

A recombinant yeast microorganism for producing isobutanol, the recombinant yeast microorganism comprising an isobutanol producing metabolic pathway, wherein said isobutanol producing metabolic pathway comprises the following substrate to product conversions:

• (i) pyruvate to acetolactate;
• (ii) acetolactate to 2,3-dihydroxyisovalerate;
• (iii) 2,3-dihydroxyisovalerate to α-ketoisovalerate;
• (iv) α-ketoisovalerate to isobutyraldehyde;
• and
• (v) isobutyraldehyde to isobutanol;
• wherein the recombinant yeast microorganism expresses
• (a) a heterologous acetolactate synthase (ALS) to catalyze the conversion of pyruvate to acetolactate;
• (b) a heterologous ketol-acid reductoisomerase to catalyze the conversion of acetolactate to 2,3-dihydroxyisovalerate;
• (c) a heterologous dihydroxyacid dehydratase to catalyze the conversion of 2,3-dihydroxyisovalerate to α-ketoisovalerate;
• (d) an heterologous α-ketoisovalerate decarboxylase to catalyze the conversion of α-ketoisovalerate to isobutyraldehyde;
• and
• (e) an heterologous alcohol dehydrogenase to catalyze the conversion of isobutyraldehyde to isobutanol;
• wherein the recombinant yeast microorganism has been engineered to:
• (A) disrupt, mutate, or delete one or more endogenous pyruvate decarboxylase (PDC) genes, wherein said recombinant yeast microorganism has reduced endogenous PDC activity as compared to the corresponding yeast microorganism that has not been engineered to have reduced endogenous PDC activity;
• and
• (B) disrupt, mutate, or delete one or more endogenous glycerol-3-phosphate dehydrogenase (GPD) genes, wherein said recombinant yeast microorganism has reduced endogenous GPD activity as compared to the corresponding yeast microorganism that has not been engineered to have reduced endogenous GPD activity;
• and wherein the recombinant yeast microorganism produces isobutanol at a yield which is at least 70% of the theoretical yield of isobutanol from glucose.