Characterization of Lac+ Transductants of Streptococcus lactis1

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Abstract
A phage-mediated transducing system was used in studying certain physiological characteristics of S. lactis C2 wild type, lactose-negative mutants, and lactose-positive transductants. Lac- mutants, obtained by acriflavine treatment of the wild type, were similar to the wild type in all characteristics tested except they lacked β-D-phosphogalactoside galactohydrolase (β-Pgal) and could not transport [14C]lactose; they also had approximately 10% of the proteolytic ability than wild-type cells. The lactose-fermenting characteristic was transduced from the wild type to Lac- mutants. The Lac+ transductants obtained were similar to the wild-type parent with respect to lactose fermentation and level of β-Pgal activity (0.186 U of protein per mg). These transductants, however, had not regained full proteolytic ability and were similar to the Lac- mutant in this respect. Lactic acid production of the transductants in milk was approximately two-thirds that of the wild type. Data suggest that both the lactose-fermenting and proteolytic characters are carried on extrachromasomal particles (plasmids).

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