Genome plasticity among related Lactococcus strains: Identification of genetic events associated with macrorestriction polymorphisms

The genomic diversity of nine strains of the Lactococcus lactis subsp. crem oris (NCDO712, NCDO505, NCDO2031, NCDO763, MMS36, C2, LM0230, LM2301, and M G1363) was studied by macrorestriction enzyme analysis using pulsed-field g el electrophoresis. These strains were considered adequate for the investig ation of genomic plasticity because they have been described as belonging t o the same genetic lineage. Comparison of ApaI and SmaI genome fingerprints of each strain revealed the presence of several macrorestriction fragment length polymorphisms (RFLPs), despite a high degree of similarity of the ge nerated restriction patterns. The physical map of the MG1363 chromosome was used to establish a genome map of the other strains and allocate the RFLPs to five regions. Southern hybridization analysis correlated the polymorphi c regions with genetic events such as chromosomal inversion, integration of prophage DNA, and location of the transposon-like structures carrying conj ugative factor or oligopeptide transport system.