Plasmid Profiles of Lactose-Negative and Proteinase-Deficient Mutants of Streptococcus lactis C10, ML 3 , and M18

Abstract

Lactose- and proteinase-negative (Lac − Prt − ) mutants of Streptococcus lactis C10, ML3, and M18 were isolated after treatment with ethidium bromide. The Lac − Prt − mutants of C10 were missing a 40-megadalton plasmid. A 33-megadalton plasmid was absent in the ML3 mutants, and the M18 variants lacked a 45-megadalton plasmid. The results suggest a linkage of these metabolic traits to the respective plasmids. The possible complexity of the interrelationship between lactose metabolism and proteinase activity is presented.