Effect of restriction-modification systems on transfer of foreign DNA intoLactococcus lactissubsp.lactis

The efficiency of transfer of plasmid pIP501 DNA into Restriction/Modification (R/M) proficient strains of Lactococcus lactis subsp. lactis strongly depends on the mode of transfer. In two strains, each one containing a different R/M system, the efficiency of protoplast transformation with unmodified pIP501 DNA was restricted by more than 3 orders of magnitude when compared to pIP501 carrying the host modification. By contrast, no difference was observed when modified or unmodified DNA was introduced into the same hosts by electroporation. The pIP501 conjugation frequency between a R−/M− donor and an isogenic recipient were also unaffected whether the recipient possesses a R/M system or not.