STRUCTURAL SIMILARITY AND GENETIC HOMOLOGY BETWEEN LACTOBACILLUS-CASEI BACTERIOPHAGES ISOLATED IN JAPAN AND IN FINLAND

Three Lactobacillus casei bacteriophages, LC-Nu, PL-1, and phiFSW, were compared. Phage LC-Nu, which has not been previously characterized, originated from a local cheese plant in Finland. Phages PL-1 and phiFSW (isolated in Japan) represent the most thoroughly studied L. casei phages so far. All three phages had similar morphotypes, but still had different patterns of structural proteins, as analyzed by SDS-PAGE. The phages differed also in types of genome organization: LC-Nu and PL-1 had cohesive ends in their DNAs, and the DNA of phiFSW was circularly permuted. The initiation site and orientation of packaging of phiFSW DNA were identified. The homologies between the phage genomes were analyzed by Southern hybridization. About one-third of each phage genome was highly homologous with other phages (homology over 85%), and two-thirds were slightly homologous (homology between 65% and 76%). DNAs from five industrial L. casei strains were also tested for homology with phage LC-Nu DNA. Phage LC-Nu related sequences were present in all the L. casei strains tested.