Methods and materials for the production of L-lactic acid in yeast

A recombinant cell of a yeast species, wherein the yeast species contains a target gene at a locus in its genome, the cell having an exogenous lactase dehydrogenase gene integrated into its genome under the transcriptional control of functional portions of promoter and terminator sequences of the target gene, the LDH gene is integrated at the locus of the target gene and the target gene is deleted from the genome of the cell.

A process for integrating an exogenous lactate dehydrogenase gene into a cell, wherein prior to the integration the cell has a targeted gene at a locus in its genome, comprising the steps of (a) transforming the cell with a recombinant nucleic acid having a lactate dehydrogenase (LDH) gene, flanking sequences upstream and downstream of the LDH gene, and at least one selection marker gene, said flanking sequences being homologous to flanking sequences upstream and downstream of the targeted gene, such that the LDH gene is inserted into the genome of the cell adjacent to the locus of the targeted gene in a single crossover event, (b) selecting for first transformants containing the LDH gene and the selection marker gene, (c) nonselectively growing said first transformants and (d) selecting among such first transformants for second transformants that contain the LDH gene but have deleted the selection marker gene and the targeted gene.

A cell of the species K. marxianus having multiple exogenous lactate dehydrogenase genes integrated into its genome, each under the control of functional promoter and terminator sequences, wherein the genome of the K. marxianus cell further contains a functional pyruvate decarboxylase gene.