Role of Bat2p
in Saccharomyces cerevisiae grown on non-fermentable carbon source.
Sung Schoondermark-Stolk (1), Maria Tabernero (2), John Chapman (2), Theo
Verrips (1), Arie Verkleij (1), Johannes Boonstra (1)
(1) Molecular Cell Biology, Utrecht University, Padualaan 8, Utrecht, 3584 CH,
The Netherlands (S.A.Schoondermark@bio.uu.nl); (2) Unilever Research
Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands
Branched chain amino acid transaminases (BCAATs) catalyze the last step of the synthesis and the initial step of the degradation of branched chain amino acids (BCAA); leucine, isoleucine and valine. They are responsible for formation of keto acids from the corresponding BCAA and are involved in the production of fusel alcohols. S. cerevisiae posses a mitochondrial and cytosolic BCAAT, Bat1p and Bat2p, respectively. To get more insight in the role of BAT1 and BAT2, alterations in genome-wide expression of S. cerevisiae, wild type cells, bat1, bat2 single deletion mutants and a bat1bat2 double deletion mutant, were studied during fusel alcohol production. Glucose or ethanol was used as C-source and leucine as sole N-source. The wild type displayed BAT1 expression when grown on glucose. The single mutants grew similarly on glucose as the wild type. Bat1bat2 double mutant showed an inhibited growth. No significant alterations in gene-expression between strains grown on glucose could be observed. Expression of BAT2 was only found when cells were growing on ethanol. The bat2 single deletion mutant and bat1bat2 double deletion mutant failed to grow on ethanol as a carbon source. Metabolite measurements revealed that these cells, despite of the double mutation, were still able to form keto acids out of leucine. However, no formation of isoamyl alcohol was detected. This indicates that beside the transamination activity, Bat2p plays a vital role by growth on ethanol.