The present invention relates to processes for producing ethanol from lignocellulosic hydrolysates comprising hexoses, pentoses and acetic acid, whereby genetically modified yeast cells are use that comprise an exogenous gene encoding an acetaldehyde dehydrogenase and a bacterial gene encoding an enzyme with NAD.sup.+-linked glycerol dehydrogenase activity. The process is further characterized 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 yeast cells for use in such processes. The yeast cells advantageously comprise genetic modifications that improve glycerol utilization such as modifications that increase 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 present invention provides for a mechanism to completely replace the electron accepting function of glycerol formation with an alternative pathway to ethanol formation, thereby reducing glycerol production and increasing ethanol production. In some embodiments, the invention provides for a recombinant microorganism comprising a down-regulation in one or more native enzymes in the glycerol-production pathway. In some embodiments, the invention provides for a recombinant microorganism comprising an up-regulation in one or more enzymes in the ethanol-production pathway.

The present invention provides for a mechanism to completely replace the electron accepting function of glycerol formation with an alternative pathway to ethanol formation, thereby reducing glycerol production and increasing ethanol production. In some embodiments, the invention provides for a recombinant microorganism comprising a down-regulation in one or more native enzymes in the glycerol-production pathway. In some embodiments, the invention provides for a recombinant microorganism comprising an up-regulation in one or more enzymes in the ethanol-production pathway.

There is provided a microbial cell which is capable of producing at least one higher alcohol, wherein the microbial cell is genetically modified to include an increased expression relative to its wild type cell of at least one acyl-CoA reductase (E.sub.11). In particular, there is provided a microbial cell capable of producing at least one higher alcohol, wherein the microbial cell is genetically modified to include an increased expression relative to its wild type cell of at least one acyl-CoA reductase (E.sub.11) and wherein the cell is capable of producing a carboxylic acid and/or ester thereof using ethanol-carboxylate fermentation.

The present invention provides for a mechanism to reduce glycerol production and increase nitrogen utilization and ethanol production of recombinant microorganisms. One aspect of this invention relates to strains of S. cerevisiae with reduced glycerol productivity that get a kinetic benefit from higher nitrogen concentration without sacrificing ethanol yield. A second aspect of the invention relates tometabolic modifications resulting in altered transport and/or intracellular metabolism of nitrogen sources present in corn mash.

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.sub.+-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.

Provided herein are compositions and methods for the heterologous production of acetyl-CoA-derived isoprenoids in a host cell. In some embodiments, the host cell is genetically modified to comprise a heterologous nucleotide sequence encoding an acetaldehyde dehydrogenase, acetylating (ADA, E.C. 1.2.1.10) and an MEV pathway comprising an NADH-using HMG-CoA reductase. In some embodiments, the host cell is genetically modified to comprise a heterologous nucleotide sequence encoding an ADA and an MEV pathway comprising an acetoacetyl-CoA synthase. In some embodiments, the genetically modified host cell further comprises one or more heterologous nucleotide sequences encoding a phosphoketolase and a phosphotransacetylase. In some embodiments, the genetically modified host cell further comprises a functional disruption of the native PDH-bypass. The compositions and methods described herein provide an energy-efficient yet redox balanced route for the heterologous production of acetyl-CoA-derived isoprenoids.

The invention is intended to metabolize acetic acid and to lower acetic acid concentration in a medium at the time of xylose assimilation and ethanol fermentation by a yeast strain having xylose-metabolizing ability. To this end, a recombinant yeast strain having xylose-metabolizing ability and comprising an acetaldehyde dehydrogenase gene introduced thereinto is cultured in a medium containing cellulose, cellulase, and xylose to perform ethanol fermentation.

A combination of an electrochemical device for delivering reducing equivalents to a cell, and engineered metabolic pathways within the cell capable of utilizing the electrochemically provided reducing equivalents is disclosed. Such a combination allows the production of commodity chemicals by fermentation to proceed with increased carbon efficiency.

The present disclosure relates to methods for more efficiently recycling reduced electron carriers in a hydrogen-oxidizing microorganism with an operable Calvin-Benson cycle; synthetic carbon fixation pathways that recycle reduced electron carriers more efficiently than the Calvin-Benson cycle, such as methods for enzymatically converting carbon dioxide to formate and assimilating the resulting formate into central carbon metabolism; methods for producing biochemical products; and recombinant hosts utilizing one or more synthetic carbon fixation pathways.