GENETICALLY-ENGINEERED YEAST AND METHODS OF MAKING AND USING

1 . A yeast comprising a first heterologous nucleic acid, a second heterologous nucleic acid, a third heterologous nucleic acid, and a fourth heterologous nucleic acid,

wherein expression of said first nucleic acid results in an increase in the amount or activity of a first polypeptide that is able to transport glycerol into the yeast cell;

wherein expression of said second nucleic acid results in an increase in the amount or activity of a second polypeptide that is able to convert glycerol into dihydroxyacetone (DHA);

wherein expression of said third nucleic acid results in an increase in the amount or activity of a third polypeptide that is able to phosphorylate DHA to produce dihydroxyacetone phosphate (DHAP); and

wherein expression of said fourth nucleic acid results in an increase in the amount or activity of a fourth polypeptide that is able to convert DHAP into glycereroldehyde-3-phosphase (GAP).

2 . The yeast of claim 1 , wherein said first polypeptide is a polyol transporter, a sugar transporter or a glycerol transporter, wherein said second polypeptide is a polypeptide from Enzyme Classification (EC) 1.1.99.22, wherein said third polypeptide is a polypeptide from EC 2.7.1.29, wherein said fourth polypeptide is a polypeptide from EC 5.3.1.1.

3 . The yeast of claim 1 ,

wherein said first polypeptide is a polyol transporter, a sugar transporter or a glycerol transporter;

wherein said second polypeptide has glycerol dehydrogenase activity;

wherein said third polypeptide has dihydroxyacetone kinase activity; and

wherein said fourth polypeptide has triose-phosphate isomerase activity.

4 . The yeast of claim 3 , wherein said polypeptide having glycerol dehydrogenase activity has at least 85% sequence identity to SEQ ID NO:13.

5 . The yeast of claim 3 , wherein said polypeptide having a polyol transporter that has at least 85% sequence identity to SEQ ID NO:23.

6 . The yeast of claim 3 , wherein said polypeptide having dihydroxyacetone kinase activity has at least 85% sequence identity to SEQ ID NO: 16 or SEQ ID NO:17.

7 . The yeast of claim 2 , wherein said polypeptide having triosephosphate isomerase activity has at least 85% sequence identity to SEQ ID NO:14.

8 . The yeast of claim 1 , wherein said yeast is S. cerevisiae.

9 . The yeast of claim 1 , wherein, under fermentation conditions, said yeast produces reduced amounts of glycerol and increased amounts of ethanol compared to a yeast lacking a corresponding first, second, third, and/or fourth nucleic acid.

10 . A method of producing ethanol, comprising: contacting the yeast of claim 1 , with biomass, glycerol, carbohydrates and/or saccharides.

11 .- 12 . (canceled)

13 . A method of making the yeast of claim 1 , the method comprising introducing the first nucleic acid, the second nucleic acid, the third nucleic acid, and the fourth nucleic acid into a yeast.

14 . The method of claim 13 , wherein said first nucleic acid encodes a polyol transporter, a sugar transporter or a glycerol transporter, wherein said second nucleic acid encodes a polypeptide having glycerol dehydrogenase activity, wherein said third nucleic acid encodes a polypeptide having dihydroxyacetone kinase activity, and wherein said fourth nucleic acid encodes a polypeptide having triose-phosphate isomerase activity.

15 . The method of claim 13 , wherein the yeast produces less glycerol and more ethanol than a corresponding yeast lacking the first, second, third and fourth nucleic acids.

16 . The method of claim 13 , wherein said first, second, third, or fourth nucleic acid sequences are integrated into the yeast chromosome.