Fermentive production of isobutanol using highly active ketol-acid reductoisomerase enzymes

1. A method for conversion of acetolactate to dihydroxy-isovalerate comprising:

a) providing a microbial host cell comprising a genetic construct encoding a polypeptide having ketol-acid reductoisomerase specific activity greater than 1.1 μmoles/min/mg

wherein the genetic construct encoding a polypeptide having ketol-acid reductoisomerase activity is isolated from Pseudomonas or Vibrio ; and

b) contacting the host cell of (a) with acetolactate wherein 2,3-dihydroxy-isovalerate is produced;

wherein the ketol-acid reductoisomerase specific activity greater than 1.1 μmoles/min/mg is based on purified protein as measured by:

A) NADPH consumption assay, run under the following conditions:

i) pH of 7.5;

ii) a temperature of 22.5° C.; and

iii) a reaction buffer comprising

a) 100 mM potassium-HEPES;

b) 10 mM MgCl 2 ;

c) 2.25 mM (R,S)-acetolactate; and

d) 200 μM NADPH; and

B) purified protein concentration as determined by absorbance at 280 nanometers.

2. A method for the production of isobutanol comprising:

a) providing a recombinant microbial host cell comprising the following genetic constructs:

1) at least one genetic construct encoding an acetolactate synthase enzyme of the conversion of pyruvate to acetolactate;

2) at least one genetic construct encoding a ketol-acid reductoisomerase enzyme having specific activity of greater than 1.1 μmoles/min/mg for the conversion of (S)-acetolactate to 2,3-dihydroxyisovalerate;

wherein the genetic construct encoding a polypeptide having ketol-acid reductoisomerase activity is isolated from Pseudomonas or Vibrio;

3) at least one genetic construct encoding an acetohydroxy acid dehydratase for the conversion of 2,3-dihydroxyisovalerate to α-ketoisovalerate;

4) at least one genetic construct encoding a branched-chain keto acid decarboxylase for the conversion of α-ketoisovalerate to isobutyraldehyde;

5) at least one genetic construct encoding a branched-chain alcohol dehydrogenase for the conversion of isobutyraldehyde to isobutanol; and

b) growing the host cell of (a) under conditions where iso-butanol is produced;

wherein the ketol-acid reductoisomerase specific activity greater than 1.1 μmoles/min/mg is based on purified protein as measured by:

A) NADPH consumption assay, run under the following conditions:

i) pH of 7.5;

ii) a temperature of 22.5° C.; and

iii) a reaction buffer comprising

a) 100 mM potassium-HEPES;

b) 10 mM MgCl 2 ;

c) 2.25 mM (R,S)-acetolactate; and

d) 200 μM NADPH; and

B) purified protein concentration as determined by absorbance at 280 nanometers.

3. The method according to claim 1 wherein the host cell is selected from the group consisting of: a bacterium, a filamentous fungus and a yeast.

4. The method according to claim 1 wherein the host cell is a member of a genus selected from the group consisting of Clostridium, Zymomonas, Escherichia, Salmonella, Rhodococcus, Pseudomonas, Bacillus, Lactobacillus, Enterococcus, Alcaligenes, Klebsiella, Paenibacillus, Arthrobacter, Corynebacterium, Brevibacterium, Pichia, Candida, Hansenula, Vibrio and Saccharomyces.

5. The method according to claim 4 wherein the host cell is Escherichia coli.

6. The method according to claim 4 wherein the cell is Lactobacillus plantarum.

7. The method according to claim 4 wherein the cell is Saccharomyces cerevisiae.

8. A recombinant host cell comprising a ketol-acid reductoisomerase enzyme having a specific activity greater than the specific activity of an E. coli ketol-acid reductoisomerase based on purified protein

wherein the genetic construct encoding a polypeptide having ketol-acid reductoisomerase activity is isolated from Pseudomonas or Vibrio ; and wherein the specific activity greater than the specific activity of an E. coli ketol-acid reductoisomerase is based on purified protein as measured by:

A) NADPH consumption assay, run under the following conditions:

i) pH of 7.5;

ii) a temperature of 22.5° C.; and

iii) a reaction buffer comprising

a) 100 mM potassium-HEPES;

b) 10 mM MgCl 2 ;

c) 2.25 mM (R,S)-acetolactate; and

d) 200 μM NADPH; and

B) purified protein concentration as determined by absorbance at 280 nanometers.

9. The recombinant host cell of claim 8 wherein the genetic construct encoding a polypeptide having ketol-acid reductoisomerase activity is isolated from Pseudomonas.

10. The recombinant host cell of claim 8 wherein the genetic construct encoding a polypeptide having ketol-acid reductoisomerase activity is isolated from Vibrio.