Mutations in corynephage β that affect the yield of diphtheria toxin

Abstract Lysogens carrying prophages of four recently isolated mutants (Lt, lowered toxin yields) of wild-type β phage produced 3–6, 1–2, 0.0001, and 0% as much toxin as is produced by the parent C7(β) strain. Toxin production by the mutant strains, like that by the parent strain C7(β), was stopped by the addition of iron. Superinfection of each of these lysogens with a CRM-producing (nontoxic protein or cross reacting with antitoxin) mutant, β45c, yielded similar levels of CRM and levels of toxin equal to those of the respective nonsuperinfected lysogens. These results suggest that the gene which is altered in the mutant phage does not code for a protein which affects toxin yield but that the altered gene regulates the expression of the tox gene.