ISOLATION FROM CORYNEBACTERIUM-DIPHTHERIAE C7(BETA) OF BACTERIAL MUTANTS THAT PRODUCE TOXIN IN MEDIUM WITH EXCESS IRON

Five mutants that produce toxin in medium with excess Fe were isolated from strain C7(.beta.). The Fe content of bacteria grown on this medium was considerably higher than that of C7(.beta.) cells grown in medium containing the minimum amount of Fe needed to inhibit toxin production. When the nonlysogenic, nontoxinogenic strain C7(-) was lysogenized with phages from each of the mutants, toxin production by all of the resulting lysogens, like that by parent strain C7(.beta.), ceased upon Fe addition. When the mutants were superinfected with .beta.45 phage, both toxin and CRM45 [45,000 MW cross reacting material] were produced in medium with excess Fe. One of the mutant strains lost its prophage as a result of treatment with UV light. When the cured strain was lysogenized with phage carrying a mutation in the tox structural gene, the lysogen produced the mutant protein at the maximum rate in medium with excess Fe. Evidently the mutant strains are not phage mutants, but are bacterial host mutants, and a host factor(s) is involved in inhibition of toxin production by Fe.