STUDIES ON p-AMINOBENZOIC ACID : (II) GROWTH INHIBITION OF ESCHERICHIA COLI BY A SULFONAMIDE AND BY A GENETIC BLOCK

Abstract

The activity of several metabolites functionally related but structually unrelated to PABA in reversing sulfadiazine inhibition of E. coli 0-20 standard strain and in spareing PABA requirement of a mutant strain, 273-A-1,derived from 0-20,was examined. When added singly into the medium, methionine, vitamin B_<12> and to a lesser extent glycine revealed the activities. Xanthine, on the other hand, inhibited the growth of the mutant in the presence of minimal but sufficient amounts of PABA. When methionine, xanthine, serine, thymine, valine and glycine were added to the medium sequentially, the inhibitory effect of sulfadiazine for the growth of the parent and the amounts of PABA necessary for the growth of the mutant decreased. The ability to reverse sulfadiazine growth inhibition of the sequential addition of serine, thymine and valine, however, was not so apparent as that to spare PABA requirement. In a medium containing these metabolites as well as vitamin B_<12>, the mutant did not require added PABA any more. The combination of these metabolites and vitamin B_<12> was also found to be noticeably effective in reversing sulfadiazine growth inhibition, but the effect was not complete in the presence of high concentrations of sulfadiazine.