Yeast strains for ethanol production

1. A recombinant cell, optionally a recombinant yeast cell comprising:

a) a gene encoding an enzyme having glycerol-3-phosphate dehydrogenase activity, wherein said enzyme has a cofactor dependency for at least NADP and/or for NADPH;

b) a gene encoding an enzyme having at least NAD dependent acetylating acetaldehyde dehydrogenase activity (EC 1.2.1.10); and

c) a mutation or disruption in at least one gene selected from the group of GPD1 and GPD2.

2. The cell according to claim 1 wherein the enzyme having glycerol-3-phosphate dehydrogenase activity has a higher affinity and/or lower Michaelis constant and/or a higher maximum activity for NADPH than for NADH.

3. The cell according to claim 1 wherein the gene encoding an enzyme having glycerol-3-phosphate dehydrogenase activity comprises at least one exogenous gene.

4. The cell according to claim 3 wherein said gene encodes an enzyme with an amino acid sequence according to SEQ ID NO: 1 or a functional homologue thereof having a sequence identity of at least 50%.

5. The cell according to claim 1 wherein the gene encoding an enzyme having at least NAD dependent acetylating acetaldehyde dehydrogenase activity encodes an enzyme with an amino acid sequence according to SEQ ID NO: 2 or a functional homologue thereof having a sequence identity of at least 50%.

6. The cell according to claim 1 which cell is free of, or has reduced NADPH-dependent aldehyde reductase activity (EC 1.2.1.4) compared to a corresponding wildtype cell thereof.

7. The cell according to claim 1 wherein the genome of said cell comprises a mutation in ALD6 or a functional homologue thereof having a sequence identity of at least 50%.

8. The cell according to claim 1 wherein the enzyme having at least NAD + dependent acetylating acetaldehyde dehydrogenase activity catalyses the reversible conversion of acetyl-CoenzymeA to acetaldehyde and the subsequent reversible conversion of acetaldehyde to ethanol.

9. The cell according to claim 8 wherein the enzyme comprises both NAD dependent acetylating acetaldehyde dehydrogenase (EC 1.2.1.10) activity and NAD dependent alcohol dehydrogenase activity (EC 1.1.1.1).

10. The cell according to claim 1 wherein the gene encoding an enzyme having at least NAD dependent acetylating acetaldehyde dehydrogenase activity encodes an enzyme with an amino acid sequence according to SEQ ID NO: 3 or a functional homologue thereof having a sequence identity of at least 50%.

11. The cell according to claim 1 which does not comprise a gene encoding an enzyme having pyruvate formate lyase activity.

12. The cell according to claim 1 for the preparation of ethanol, butanol, lactic acid, succinic acid, a plastic, an organic acid, a solvent, an animal feed supplement, a pharmaceutical, a vitamin, an amino acid, an enzyme or a chemical feedstock, optionally ethanol.

13. A process for preparing a fermentation product, optionally ethanol, comprising preparing a fermentation product from a fermentable carbohydrate, optionally selected from the group of glucose, fructose, sucrose, maltose, xylose, arabinose, galactose, cellobiose and mannose which wherein said preparing is carried out under anaerobic conditions by contacting a cell according to claim 1 with said fermentable carbohydrate.

14. The process according to claim 13 , wherein fermentable carbohydrate is obtained from starch, lignocellulose, and/or pectin.

15. The process according to claim 13 , wherein the concentration of glucose is 80 g/L or more.