MEMBRANE-RECEPTOR FOR PROLATE PHAGES IS NOT REQUIRED FOR INFECTION OFLACTOCOCCUS-LACTIS BY SMALL OR LARGE ISOMETRIC PHAGES

Lactococcus Lactis contains a chromosomal gene (pip) for a membrane pr otein that serves as a receptor for the prolate bacteriophage c2 and o ther phages of the c2 species. A mutated allele of this receptor gene was used to replace the wild-type allele in L. Lactis strains MM210, N CK 203, and C2. Allele replacement was confirmed by the presence of a restriction site marker in a polymerase chain reaction product from th e mutated allele. The mutated pip derivative of strain C2 was complete ly resistant to phages of the c2 species but was fully sensitive to th e small isometric phage ski of the 936 species, as expected. The mutat ed derivatives of MM210 and NCK203 were fully sensitive to the small i sometric phages mm210b and 31 (p335 species) and to the large isometri c phage 949 (949 species). These results show that pip is not required for infection by phages of species 936, p335, or 949. The resultant m utants grew as well as the parental strains in liquid media. The mutat ed derivatives of MM210 and C2 acidified and clotted milk as readily a s the wild-type strains. These results show that phage receptor replac ement in a commercial strain of L. Lactis does not affect growth and a cid production in milk.