The invention is intended to metabolize acetic acid in a medium at the time of culture, such as ethanol fermentation by yeast, and to reduce acetic acid concentration. Specifically, the invention relates to a recombinant yeast resulting from introduction of the acetaldehyde dehydrogenase gene (EC 1.2.1.10) and regulation of an enzyme involved with trehalose accumulation.

The present invention relates to a yeast cell that is genetically modified comprising: a) a disruption of one or more aldehyde dehydrogenase (E.C:1.2.1.4) native to the yeast; b) one or more nucleotide sequence encoding a heterologous NAD+-dependent acetylating acetaldehyde dehydrogenase (E.C. 1.2.1.10); c) one or more nucleotide sequence encoding a homologous or heterologous acetyl-CoA synthetase (E.C. 6.2.1.1); and d) a modification that leads to reduction of glycerol 3-phosphate phosphohydrolase (E.C. 3.1.3.21) and/or glycerol 3-phosphate dehydrogenase (E.C. 1.1.1.8 or E.C. 1.1.5.3) activity, native to the yeast.

The invention relates to a process for the production of ethanol from a composition comprising at least glucose comprising fermenting said composition in the presence of a recombinant yeast; and recovering the ethanol, wherein said yeast comprises one or more genes coding for an enzyme having glycerol dehydrogenase activity, one or more genes coding for an enzyme having dihydroxyacetone kinase activity (E.C. 2.7.1.28 and/or E.C. 2.7.1.29); one or more genes coding for an enzyme in an acetyl-CoA-production pathway and one or more genes coding for an enzyme having at least NAD+ dependent acetylating acetaldehyde dehydrogenase activity (EC 1.2.1.10 or EC 1.1.1.2), and optionally one or more genes coding for a glycerol transporter, wherein the composition comprises an amount of undissociated acetic acid of 10 mM or less. A recombinant yeast having the genes as described above is particularly sensitive towards acetic acid, and the ethanol yield rapidly decreases when the composition contains more than 10 mM undissociated acetic acid.

The invention provides a non-naturally occurring bacterium having decreased or eliminated activity of an enzyme that catalyzes the reaction defined by EC 1.2.7.5, such as aldehyde:ferredoxin oxidoreductase (AOR). Optionally, the bacterium also has decreased or eliminated activity of an enzyme that catalyzes the reaction defined by EC 1.2.1.10 and/or EC 1.1.1.1, such as aldehyde dehydrogenase, alcohol dehydrogenase, or bifunctional aldehyde/alcohol dehydrogenase. The invention further provides methods of producing products by culturing the bacterium in the presence of a gaseous substrate containing one or more of CO, CO.sub.2, and H.sub.2.

The present invention relates to a yeast cell, in particular a recombinant yeast cell, the cell lacking enzymatic activity needed for the NADH-dependent glycerol synthesis or the cell having a reduced enzymatic activity with respect to the NADH-dependent glycerol synthesis compared to its corresponding wild-type yeast cell, the cell comprising one or more heterologous nucleic acid sequences encoding an NAD.sup.+-dependent acetylating acetaldehyde dehydrogenase (EC 1.2.1.10) activity. The invention further relates to the use of a cell according to the invention in the preparation of ethanol.

A recombinant yeast cell, fermentation compositions, and methods of use thereof are provided. The recombinant yeast cell includes at least one heterologous nucleic acid encoding one or more polypeptide having phosphoketolase activity; phosphotransacetylase activity; and/or acetylating acetaldehyde dehydrogenase activity, wherein the cell does not include a heterologous modified xylose reductase gene, and wherein the cell is capable of increased biochemical end product production in a fermentation process when compared to a parent yeast cell.

A recombinant yeast cell, fermentation compositions, and methods of use thereof are provided. The recombinant yeast cell includes at least one heterologous nucleic acid encoding one or more polypeptide having phosphoketolase activity; phosphotransacetylase activity; and/or acetylating acetaldehyde dehydrogenase activity, wherein the cell does not include a heterologous modified xylose reductase gene, and wherein the cell is capable of increased biochemical end product production in a fermentation process when compared to a parent yeast cell.

The invention relates to a method for homo-ethanol production from lactose using a genetically modified lactic acid bacterium of the invention, where the cells are provided with a substrate comprising dairy waste supplemented with an amino nitrogen source (such as acid hydrolysed corn steep liquor). The invention further relates to genetically modified lactic acid bacterium and its use for homo-ethanol production from lactose in dairy waste. The lactic acid bacterium comprises both genes (lacABCD, LacEF, lacG) encoding enzymes catalysing the lactose catabolism pathway; and transgenes (pdc and adhB) encoding enzymes catalysing the conversion of pyruvate to ethanol. Additionally a number of genes (ldh, pta and adhE) are deleted in order to maximise homo-ethanol production as compared to production of lactate, acetoin and acetate production.

The present invention provides an engineered cyanobacterium, comprising at least one plasmid selected from three novel pathways to produce acetate, which can convert atmospheric carbon dioxide as a raw material into acetate. The present invention also constructs the expression plasmid for three different transporters specific to acetate to be expressed in cyanobacteria, which comprises putative ABC transporter (AatA), succinate/acetate: proton symporter (SatP) and acetate/glycolate: cation symporter (ActP). Therefore, the engineered cyanobacteria of the present invention can produce 0.58 mg/L to 3.54 mg/L of acetate per hour.

There is provided an acetogenic microbial cell which is capable of producing at least one higher alcohol from a carbon source, wherein the acetogenic microbial cell is genetically modified to comprise an increased expression relative to its wild type cell of at least one enzyme, E.sub.8, a butyryl-CoA:acetate CoA transferase (cat3). There is also provided a method and use of the cell to produce higher alcohols.