Isolation and Characterization of an Escherichia coli Mutant Tolerant to Colicins Ia and Ib

Two classes of spontaneous colicin I insensitive mutants of Escherichia coli have been isolated. The first class (called cir) has lost its ability to adsorb either colicin Ia or Ib, maps at 41 min on the E. coli genetic map, and retains sensitivity to all other colicins tested. The cir phenotype is probably due to an alteration in the colicin I receptor. The second class of mutant (called tolI) retains full capacity to adsorb [(125)I]colicin I and, therefore, represents the isolation of a mutant tolerant to colicin I. The tolI mutant is sensitive to all other colicins tested and has a map location of 89-1 min. The tolI mutant grows with a reduced mass yield when glucose is used as a carbon source and cannot utilize succinate or acetate for growth. The tolI mutant shows a reduced sensitivity to sodium azide and phenethylalcohol. It is suggested that tolI is deficient in some aspect of aerobic metabolism which must be operative for colicin I sensitivity.