Taxonomic Differentiation of Bacteriophages of Lactococcus lactis by Electron Microscopy, DNA-DNA Hybridization, and Protein Profiles

Abstract

Thirty-seven virulent and 19 temperate bacteriophages of Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris were classified in a taxonomic system on the basis of morphology, DNA-DNA hybridization, and protein composition. As judged from electron microscopy and susceptibility to cleavage by restriction endonucleases, the genome of all the bacteriophages investigated is composed of double stranded DNA. Seven virulent phage groups were recognized: types P034 (genome size 18·1 kilobase pairs, kb), P001 (20·2 kb), P008 (29·7 kb), P335 (36·4 kb), P026 (51·5 kb), P107 (51·5 kb), and P087 (54·5 kb). In addition, two temperate phage groups were established: types TP-40-3 (genome size 42·1 kb) and TP-936-1 (37·8 kb). Phages within each group revealed strong DNA homology and similar protein compositions, whereas no significant DNA homology and different proteins were found in phages of different groups. Virulent phages of group P335 exhibited strong DNA homology with the temperate phages of group TP-936-1.