W.J. KIM, B. RAY AND M.C. JOHNSON. 1992. Plasmid profiles of wild and mutant strains of Pediococcus acidilactici M showed that a 53.7 kb plasmid (pPR72) encodes the sucrose hydrolysis trait (Suc+) and an 11.1 kb plasmid encodes the bacteriocin production trait (Pap+). Neither of these plasmids encode traits involving fermentation of other carbohydrates, antibiotic resistance or resistance to bacteriocin. Broad host‐range plasmids (pAMβ1 and pIP501) from Enterococcus faecalis and plasmid pPR72 from Ped. acidilactici were conjugally transferred by filter mating into two strains of Ped. acidilactici. Four plasmids, ranging in size from 4.4 to 53.7 kb, were also transferred into Ped. acidilactici strains by electroporation. Optimum transformation of the 4.4 kb plasmid, pGK12, was obtained at a DNA concentration of 1 μg/220 μl. The same amount of DNA gave lower transformation frequencies as the plasmid size increased. Results of these studies indicated that both conjugation and electroporation can be used to transfer plasmid‐linked traits in Ped. acidilactici strains.

Previous investigations indicated that curing of a 7.4‐Md plasmid (pSMB74) resulted in concomitant loss of bacteriocin activity and immunity in Pediococcus acidilactici H. Transfer of pSMB74 to a gentamicin‐neomycin resistant (GmrNmr) derivative of P. acidilactici LB42, which was devoid of any plasmid DNA, required cell‐to‐cell contact on a solid mating surface and converted the strain to Bac+Bacr phenotype. Gene transfer processes such as transduction and transformation were ruled out from the experiment. Treatment of donor cells with chloroform did not allow the appearance of recombinant clones, confirming that viable cells were essential for this particular mechanism of genetic transfer. Transconjugants obtained from selective agar surface were subjected to plasmid isolation and agarose gel electrophoresis. Each of them exhibited plasmid size corresponding to pSMB74 of donor strain. All results suggested this genetic transfer similar to conjugation, and provided presumptive evidence for plasmid‐encoded bacteriocin activity and immunity in P. acidilactici H.