| abstract |
The present invention relates to genetically modified yeast cells comprising exogenous genes coding for pyruvate formate lyase and acetaldehyde dehydrogenase activities. The yeast cells further comprises genetic modifications that improve glycerol utilization such as modifications that increases NAD + -linked glycerol dehydrogenase activity, and preferably one or more of dihydroxyacetone kinase activity and transport of glycerol into the cell. The yeast cell further preferably comprises a functional exogenous xylose isomerase gene and/or functional exogenous genes which confer to the cell the ability to convert L-arabinose into D-xylulose 5-phosphate and they may comprise a genetic modification that increase acetyl-CoA synthetase activity. The process is further characterised in that glycerol is present in or fed into the culture medium, whereby the modified yeast cell ferments the hexoses, pentoses,acetic acid and glycerol to ethanol. The invention further relates to processes for producing a fermentation product and formate from carbon sources comprising glycerol and at least one of a hexose and a pentose, wherein the genetically modified yeast cells are used to ferment the carbon sources to the fermentation product and formate. A preferred fermentation product is ethanol. |