Open AccessGenetic Analysis of Chromosomal Regions of Lactococcus lactis Acquired by Recombinant Lytic Phages
Author(s) -
Evelyn Durmaz,
Todd R. Klaenhammer
Publication year - 2000
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.66.3.895-903.2000
Subject(s) - biology , temperateness , recombinant dna , lytic cycle , plasmid , genetics , lactococcus lactis , bacteriophage , phagemid , escherichia coli , genome , dna , virology , microbiology and biotechnology , gene , bacteria , virus , lactic acid
Recombinant phages are generated whenLactococcus lactis subsp.lactis harboring plasmids encoding the abortive type (Abi) of phage resistance mechanisms is infected with small isometric phages belonging to the P335 species. These phage variants are likely to be an important source of virulent new phages that appear in dairy fermentations. They are distinguished from their progenitors by resistance to Abi defenses and by altered genome organization, including regions ofL. lactis chromosomal DNA. The objective of this study was to characterize four recombinant variants that arose from infection ofL. lactis NCK203 (Abi+ ) with phage φ31.Hin dIII restriction maps of the variants (φ31.1, φ31.2, φ31.7, and φ31.8) were generated, and these maps revealed the regions containing recombinant DNA. The recombinant region of phage φ31.1, the variant that occurred most frequently, was sequenced and revealed 7.8 kb of new DNA compared with the parent phage, φ31. This region contained numerous instances of homology with various lactococcal temperate phages, as well as homologues of the lambda recombination protein BET andEscherichia coli Holliday junction resolvase Rus, factors which may contribute to efficient recombination processes. A sequence analysis and phenotypic tests revealed a new origin of replication in the φ31.1 DNA, which replaced the φ31 origin. Three separateHin dIII fragments, accounting for most of the recombinant region of φ31.1, were separately cloned into gram-positive suicide vector pTRK333 and transformed into NCK203. Chromosomal insertions of each plasmid prevented the appearance of different combinations of recombinant phages. The chromosomal insertions did not affect an inducible prophage present in NCK203. Our results demonstrated that recombinant phages can acquire DNA cassettes from different regions of the chromosome in order to overcome Abi defenses. Disruption of these regions by insertion can alter the types and diversity of new phages that appear during phage-host interactions.