GLUCOSE-METABOLISM AND ETHANOL-PRODUCTION IN ADH MULTIPLE AND NULL MUTANTS OF KLUYVEROMYCES-LACTIS

Four genes coding for alcohol dehydrogenase (ADH) activities were iden tified in Kluyveromyces lactis. Due to the presence in this yeast of m ultiple ADH isozymes, mutants in the individual genes constructed by g ene replacement yielded no clear phenotype. We crossed these mutants a nd developed a screening procedure which allowed us to identify strain s lacking several ADH activities. The analysis of the adh triple mutan ts revealed that each activity confers to the cell the ability to grow on ethanol as the sole carbon source. On the contrary, adh null strai ns failed to grow on this substrate, indicating that no other importan t ADH activities are present in K. lactis cells. In the ndh null mutan ts we also found a residual production of ethanol, as has been reporte d to be the case in Saccharomyces cerevisiae. This production showed a ten-fold increase when the K1ADHI activity was reintroduced in the nu ll mutant and cells were cultivated under oxygen-limiting conditions. Differently from S. cerevisiae, glycerol is poorly accumulated in K. l actis ndh null mutants.