Lac variants ofLactobacillus casei subsp.casei DR1002 (formerly 64H) have been produced using acriflavin, ethidium bromide, mitomycin C, or combinations of these agents. Two successive transfers in the presence of acriflavin and mitomycin C or ethidium bromide and mitomycin C resulted in nearly a 100% loss of lactose fermentation. Cesium chloride-ethidium bromide isopycnic gradient ultracentrifugal analysis of purified lysates demonstrated that the 23-mdal plasmid (pDR101) found inL. casei DR1002 was consistently absent in Lac(-) clones. We concluded that, as in lactic streptococci, lactose metablism is a plasmid-mediated train inL. casei DR1002.
The transmissible plasmid pAMbeta1, which codes for erythromycin and lincomycin resistance, was conjugally transferred from a Lancefield group F Streptococcus to a strain of Streptococcus avium. Both organisms served as pAMbeta1 donors for three strains of Lactobacillus casei. Introduction of pAMbeta1 into one of the L. casei strains caused the organism to lose its native 6.7 X 10(6)-dalton plasmid. Loss of the native plasmid produced no alterations in the organism's growth characteristics or fermentation pattern.
Three strains of lactobacilli, Lactobacillus casei subsp. casei 64H, L. casei subsp. rhamnosus OC91, and L. coryniformis M34, were examined for the presence of plasmids. Plasmids of molecular weights of 23 x 10(6) and 16 x 10(6) were found in the first two strains respectively. This represents the first evidence for plasmids in lactobacilli; their function is not presently known.
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