PKDl is the only circular plasmid known in the genus Kluyveromyces. Nucleotide sequence analysis has revealed that this 4757 base-pairs long plasmid contained three major open reading frames, A, B, and C, and a pair of inverted repeats of 346 base-pairs. The molecule exists in two isomeric forms generated by internal recombination at these repeats. The functional organization of pKDl genome appears to be quite analogous to that of the 2u plasmid of Saccharomyces cerevisiae. There is however little homology of sequences between these plasmids, except that the gene A has a dispersed but significant homology with the FLP recombinase gene of the 2u plasmid. S.cerevisiae cells can be transformed by derivatives of pKDl carrying URA3 gene as a selection marker.

A high yield of lactic acid per gram of glucose consumed and the absence of additional metabolites in the fermentation broth are two important goals of lactic acid production by microrganisms. Both purposes have been previously approached by using a Kluyveromyces lactis yeast strain lacking the single pyruvate decarboxylase gene ( KlPDC1 ) and transformed with the heterologous lactate dehydrogenase gene ( LDH ). The LDH gene was placed under the control the KlPDC1 promoter, which has allowed very high levels of lactate dehydrogenase (LDH) activity, due to the absence of autoregulation by KlPdc1p. The maximal yield obtained was 0.58 g g ⁻¹ , suggesting that a large fraction of the glucose consumed was not converted into pyruvate. In a different attempt to redirect pyruvate flux toward homolactic fermentation, we used K. lactis LDH transformant strains deleted of the pyruvate dehydrogenase (PDH) E1α subunit gene. A great process improvement was obtained by the use of producing strains lacking both PDH and pyruvate decarboxylase activities, which showed yield levels of as high as 0.85 g g ⁻¹ (maximum theoretical yield, 1 g g ⁻¹ ), and with high LDH activity.

Microbial lipids represent a valuable alternative feedstock for biodiesel production when oleaginous microbes are cultured with inexpensive substrates in processes exhibiting high yield and productivity. In this perspective, crude glycerol is among the most promising raw materials for lipid production, because it is the costless residual of biodiesel production. Thus, cultivation of oleaginous yeasts in glycerol-based media is attracting great interest and natural biodiversity is increasingly explored to identify novel oleaginous species recycling this carbon source for growth and lipid production.