Conjugal transfer and characterization of bacteriocin plasmids in group N (lactic acid) streptococci

Publisher Website
Google Scholar
Abstract
Thirteen bacteriocin-producing strains of group N (lactic acid) streptococci were screened for their potential to transfer this property by conjugation to Steptococcus lactis ssp. diacetylactis Bu2-60. Bacteriocin production in 3 strains was plasmid encoded as shown by conjugal transfer and by analysis of cured, bacteriocin-negative derivatives of the donor strains and transconjugants. With S. cremoris strains 9B4 and 4G6 and S. lactis ssp. diacetylactis 6F7 as donors, bacteriocin-producing transconjugants were isolated with frequencies ranging from .apprx. 2 .times. 10-2 to 2 .times. 10-1 per recipient cell. Bacteriocin-producing transconjugants had acquired a 39.6-megadalton plasmid from the donor strains 9B4 and 4G6 and a 75-megadalton plasmid from the donor strain 6F7. As shown by restriction endonuclease analysis, the plasmids from strains 9B4 and 4G6 were almost identical. The plasmid from strain 6F7 yielded some additional fragments not present in the 2 other plasmids. In hybridization experiments, the 3 plasmids strongly hybridized with each other and with some nontransmissible bacteriocin plasmids from other S. cremoris strains. Homology was also detected to a variety of cryptic plasmids in lactic acid streptococci.