FIG. 2.

The ability of each strain to repress diphtheria toxin production in the presence of iron is shown on the left. The nanograms of diphtheria toxin detected in an ELISA per milliliter of culture per absorbance of the culture at a wavelength of 600 nm is indicated. The ability of each strain to repress production of siderophore in the presence of iron is shown on the right. Siderophore units detected in a CAS assay per absorbance of the culture at a wavelength of 600 nm are indicated. All strains are lysogens of corynebacteriophage β. In both charts the error bars indicate the standard deviations of the values from three independent cultures subjected to the appropriate assay.