FRAGMENTATION OF THE LACTOSE-PROTEASE PLASMID OF LACTOSE-NEGATIVE VARIANTS IN STREPTOCOCCUS-LACTIS AND STREPTOCOCCUS-LACTIS SSP DIACETYLACTIS

  • 1 January 1983
    • journal article
    • research article
    • Vol. B134  (3) , 387-399
Abstract
DNA synthesis showed the presence of plasmids in all 29 strains of mesophilic lactic streptococci. Their numbers ranged from 1-9 and their MW extended from 1.8 to 45 megadaltons (Md). Comparison of the plasmid profiles from 9 strains of S. lactis, 3 strains of S. lactis ssp. diacetylactis and from their Lac-, Prt- variants was carried out. In most of the strains, a single plasmid of 27-45 Md carried both the lactose and protease (lac and prt) determinants. In Lac- variants, this composite plasmid may at times be lost; in most derivatives, this plasmid was fragmented into several smaller plasmids. Fragmentation resulted in the inactivation of lac genes and often of prt genes; sometimes prt genes remained intact in 1 of these new plasmids. Fragmentation of the plasmid may also take place without inactivation of these metabolic genes. Restriction analysis of the lactose-protease plasmid from 3 strains of S. lactis and from 1 Lac- variant confirmed the plasmid fragmentation phenomenon, and led to a proposal for physical mapping of the plasmid and preliminary localization of the lac-prt genes.

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