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

Abstract

Thirteen bacteriocin-producing strains of group N (lactic acid) streptococci were screened for their potential to transfer this property by conjugation to Streptococcus lactis subsp. diacetylactis Bacteriocin production in three strains was plasmid encoded as shown by conjugal transfer and by analysis of cured, bacteriocin-tiegative derivatives of the donor strains and the transconjugants. With Streptococcus cremoris strains 9B4 and 4G6 and S. lactis subsp. diacetylactis 6F7 as donors, bacteriocin-producing transconjugants were isolated with frequencies ranging from ca. 2 x 10-2 to 2 x 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 two other plasmids. In hybridization experiments any of the three plasmids strongly hybridized with each other and with some other bacteriocin but nontransmissible plasmids from other S. cremoris strains. Homology was also detected to a variety of cryptic plasmids in lactic acid streptococci.

Liposome-enhanced transformation of streptococcus lactis and plasmid transfer by intergeneric protoplast fusion of streptococcus lactis and bacillus subtilis

“…S. lactis strains were cultured in glucose-M17 broth [20] (Difco Laboratories, East Molesey, U.K.). Chlo-/ ramphenicol was added at final concentrations of 5 /~g/ml and 2 /~g/ml for B. subtilis and E. coli, leuA8, arg15, thrA, recE4, rm, m~ [11] Mirdcell, thy, met [12] trpC2 [13] /euA8, metB5 [14] 803, supE ÷, supF +, metrk-, m~- [15] Plasmid-free strain lac-, prt- [16] Rif r IL1403 this work Plasmid-free strain lac-, prt- [17] Plasmid-free strain Str r, Rif r, lac-, bac- [18] Em r, Cm r [19] Em r, Cm r [1] respectively. Erythromycin was used at a concentration of 5 #g/ml for both B. subtilis and S. lactis, and 50/~g/ml for E. coli.…”

In vitro conjugal transfer of tetracycline resistance fromLactobacillusisolates to other Gram-positive bacteria

“…L. lactis subsp. cremoris strain AC1 was used as a plasmid size marker [15]. MIC was determined by Etest; Chr.…”

Looking backward and forward at the practical applications of genetic researches on lactic acid bacteria

“…Bacteriocin-encoding plasmids have also been found in lactic streptococci [137]. In this case, bacteriocin production was plasmid-encoded in several strains as revealed by conjugation and responsible plasmids revealed considerable homology.…”