DISRUPTION OF PHOSPHOLIPASE-B GENE, PLB1, INCREASES THE SURVIVAL OF BAKERS-YEAST TORULASPORA-DELBRUECKII

An uracil auxotrophic mutant of baker's yeast Torulaspora delbrueckii, which is resitant to 5-fluoro-orotic acid, was complemented by transf ormation with YEp24 which harbors 2 mu m origin and URA3 derived from Saccharomyces cerevisiae. The phospholipase B in T. delbrueckii cells is active in both acidic and alkaline conditions. However, activity of phospholipase B gene (PLB1) in cells of disruption mutant (plb1:: URA 3) was lost in both conditions, which indicates that all phospholipase B activity is encoded by a single gene (or a single polypeptide) in t hese yeast cells. Over-expression of PLB1 with YEp plasmid vector in T . delbrueckii cells showed approximate to 2.5-fold increase in phospho lipase B activity, comparing with that in wild-type cells. Cells of pl bl Delta mutant showed increased survival when cells of plbl Delta mut ant and wild-type strain were incubated in water at 30 degrees C. Cell s of PLBI-over-expressed strain died rapidly even during the cultivati on period, indicating that phospholipase B activity may be a determina nt for the survival of this yeast.