| Abstract: | Diphtherial toxin is produced in maximal yields by Corynebacterium diphtheriae (C7(beta tox+) only when iron is present in growth-limiting amounts. Toxin production is markedly decreased under high-iron conditions. We studied the role of the bacteriophage beta genome in this apparent regulation of toxin production by iron. Using a passive immune hemolysis assay to detect toxin antigen production in individual plaques, we identified rare phage mutants that were toxinogenic in high-iron medium. Lysogenic derivatives of C. diphtheriae C7 harboring such phage mutants were constructed. The lysogens were compared with wild-type strain C7(beta) for their ability to produce toxin in deferrated liquid medium containing varying amounts of added iron. Quantitative tests for extracellular toxin were performed by competitive-binding radioimmunoassays. We identified phenotypically distinct mutant strains that produced slightly, moderately, or greatly increased yields of toxin antigen under high-iron conditions. The toxin produced by the mutant lysogens was biologically active and immunochemically indistinguishable from wild-type toxin. Complementation experiments demonstrated that the phage mutation designated tox-201 had a cis-dominant effect on the expression of the toxin structural gene of phage beta. The characteristics of the tox-201 mutation suggest that it defines a regulatory locus of phage beta that is involved in control of toxinogenesis by iron in C. diphtheriae. |
