Conjugal transfer of a plasmid encoding bacteriocin production and immunity in Pediococcus acidilactici H

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 (Gm r Nm r ) 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 + Bac r 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.