Membrane Receptor for Prolate Phages is Not Required for Infection of Lactococcus lactis by Small or Large Isometric Phages

Abstract

Lactococcus lactis contains a chromosomal gene (pip) for a membrane protein that serves as a receptor for the prolate bacteriophage c2 and other 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, NCK 203, and C2. Allele replacement was confirmed by the presence of a restriction site marker in a polymerase chain reaction product from the mutated allele. The mutated pip derivative of strain C2 was completely resistant to phages of the c2 species but was fully sensitive to the small isometric phage ski of the 936 species, as expected. The mutated derivatives of MM210 and NCK203 were fully sensitive to the small isometric phages mm210b and 31 (p335 species) and to the large isometric phage 949 (949 species). These results show that pip is not required for infection by phages of species 936, p335, or 949. The resultant mutants grew as well as the parental strains in liquid media The mutated derivatives of MM210 and C2 acidified and clotted milk as readily as the wild-type strains. These results show that phage receptor replacement in a commercial strain of L. lactis does not affect growth and acid production in milk.