SPECIFIC CELL-WALL PROTEINS CONFER RESISTANCE TO NISIN UPON YEAST-CELLS

The cell wall of a yeast cell forms a barrier for various proteinaceou s and nonproteinaceous molecules. Nisin, a small polypeptide and a wel l-known preservative active against gram-positive bacteria, was tested with wild-type Saccharomyces cerevisiae. This peptide had no effect o n intact cells. However, removal of the cell wall facilitated access o f nisin to the membrane and led to cell rupture. The roles of individu al components of the cell wall in protection against nisin were studie d by using synchronized cultures. Variation in nisin sensitivity was o bserved during the cell cycle. In the S phase, which is the phase in t he cell cycle in which the permeability of the yeast wall to fluoresce in isothiocyanate dextrans is highest, the cells were most sensitive t o nisin. In contrast, the cells were most resistant to nisin after a p eak in expression of the mRNA of cell wall protein 2 (Cwp2p), which co incided with the G2 phase of the cell cycle. A mutant lacking Cwp2p ha s been shown to be more sensitive to cell wall-interfering compounds a nd Zymolyase (J. M. Van der Vaart, L. H. Care, J. W. Chapman, F. M. Kl is, and C. T. Verrips, J. Bacteriol. 177:3104-3110, 1995). Here we sho w that of the single cell wall protein knockouts, a Cwp2p-deficient mu tant is most sensitive to nisin. A mutant with a double knockout of Cw p1p and Cwp2p is hypersensitive to the peptide. Finally, in yeast muta nts with impaired cell wall structure, expression of both CWP1 and CWP 2 was modified. We concluded that Cwp2p plays a prominent role in prot ection of cells against antimicrobial peptides, such as nisin, and tha t Cwp1p and Cwp2p play a key role in the formation of a normal cell wa ll.