RELATIONSHIP BETWEEN LACTOCOCCUS-LACTIS SUBSP LACTIS 952, AN INDUSTRIAL LACTOCOCCAL STARTER CULTURE AND STRAINS 712, ML3 AND C2

Lactococcus lactis subsp. lactis 952, used as a component of a cheese starter culture, was found to be closely related to the 712/ML3/C2 gro up of strains. Plasmid profiles of the four isolates were very similar and factory phages isolated against strain 952 could produce plaques on all the other strains at the same titres. Treatment with mitomycin C failed to induce phage from strain 952 although homology was observe d between phiT712 and the chromosome of strain 952. Pulse field gel el ectrophoresis of the four strains revealed only minor differences in t heir genomic DNA. The clumping phenomenon observed during lactose tran sfer in strains 712 and ML3 was also evident in strain 952. The abilit y of strain 952 to mobilize non-conjugative vectors such as pGB301 was also examined and analysis of pGB301 transconjugants revealed that so me contained novel enlarged plasmids not present in either the donor o r the recipient. Preliminary characterization of these enlarged plasmi ds suggested the involvement of a sex factor type element in strain 95 2.