Fermentive production of four carbon alcohols

1. A method for producing isobutanol comprising;

a. providing a fermentation media comprising carbon substrate; and

b. contacting said media with a recombinant yeast microorganism expressing an engineered isobutanol biosynthetic pathway wherein said pathway comprises the following substrate to product conversions;

i. pyruvate to acetolactate (pathway step a);

ii. acetolactate to 2,3-dihydroxyisovalerate (pathway step b);

iii. 2,3-dihydroxyisovalerate to α-ketoisovalerate (pathway step c);

iv. α-ketoisovalerate to isobutyraldehyde (pathway step d); and

v. isobutyraldehyde to isobutanol (pathway step e);

and wherein

a) the substrate to product conversion of step (i) is performed by an acetolactate synthase enzyme;

b) the substrate to product conversion of step (ii) is performed by an acetohydroxy acid isomeroreductase enzyme;

c) the substrate to product conversion of step (iii) is performed by an acetohydroxy acid dehydratase enzyme;

d) the substrate to product conversion of step (iv) is performed by a decarboxylase enzyme; and

e) the substrate to product conversion of step (v) is performed by an alcohol dehydrogenase enzyme;

whereby isobutanol is produced.

2. The method of claim 1 , wherein contacting said media with a recombinant microorganism is performed under anaerobic or microaerobic conditions.

3. The method of claim 1 , wherein contacting said media with a recombinant microorganism is performed as a batch fermentation.

4. The method of claim 1 , wherein the contacting said media with a recombinant microorganism is performed as a continuous fermentation.

5. The method of claim 1 , further comprising recovering the isobutanol from the fermentation media by distillation, liquid-liquid extraction, adsorption, decantation, pervaporation or combinations thereof.

6. The method of claim 1 , wherein the fermentation media further comprises water and wherein said isobutanol and water form a heterogeneous azeotrope.

7. The method of claim 6 , further comprising recovering the isobutanol from the azeotrope by distillation and decantation.

8. The method of claim 1 , wherein the microorganism produces isobutanol as a single product.

9. The method of claim 1 , wherein the fermentation media further comprises mixtures of carbon substrates.

10. The method of claim 1 , wherein the fermentation media further comprises unpurified carbon substrates.

11. The method of claim 1 , wherein the contacting said media with a recombinant microorganism is performed at a temperature range of about 25° C. to about 40° C.

12. The recombinant yeast microorganism of claim 1 wherein the said microorganism further comprises inactivated genes thereby reducing yield loss from competing pathways for carbon flow.

13. The recombinant yeast microorganism of claim 12 , wherein said inactivated genes reduce pyruvate decarboxylase activity.

14. The method of claim 1 , wherein one or more enzymes of said engineered isobutanol biosynthetic pathway uses NADH as an electron donor.

15. The method of claim 1 , wherein said alcohol dehydrogenase enzyme of step (e) is a native enzyme to the yeast microorganism.

16. The method of claim 1 , wherein steps (i)-(v) are performed by separate and distinct enzymes.

17. The method of claim 1 , wherein said isobutanol is produced in the fermentation media.

18. The method of claim 17 , wherein said isobutanol is produced in one or more of the following growth phases, high growth log phase, moderate through static lag phase, stationary phase, steady state growth phase, and combinations thereof.

19. The method of claim 17 , wherein the recombinant yeast microorganism is a whole cell catalyst subjected to conditions for isobutanol production.