GENETIC-STUDIES OF LACTOCOCCAL BACTERIOPHAGES - TAXONOMIC DIFFERENTIATIONS AND DNA ANALYSIS - EVIDENCE FOR 3' COHESIVE ENDS

Twenty-four bacteriophages of Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris were classified. Two groups of bacteriophages m orphologically defined as prolate or isometric types by electron micro scopy were examined for their genome sizes, protein patterns and DNA h omologies. These criteria showed that prolate phages are quite homogen eous. In contrast, isometric phages exhibit more differences, particul arly in particle sizes and protein compositions. Analysis of DNA hybri dizations confirmed that prolate phages can be grouped together as can be isometric phages but for one exception, phage I52. These two famil ies were clearly defined. The unique phage which does not fit in eithe r group probably belongs to a third one which is much less represented . No obvious relationships between these criteria and the lytic spectr a were detected. Evidence of the presence of cohesive ends in phage ge nomes is also presented in this study. A more detailed analysis perfor med on one member of the prolate group revealed 3' protruding ends mad e up of around 13 nucleotides on complementary single strands.