FIG. 4.

DT production (low versus high iron). (A) The total amount of DT detected in the culture supernatant of the strain indicated under low-iron conditions was divided by the amount detected under high-iron conditions to determine the repression ratio. The average ratio for each strain was determined by using data from at least three sets of low-iron and high-iron cultures. Note that the y axis is a log scale. (B) DT production was measured in the presence or absence of a DtxR-expressing plasmid. The error bars indicate the standard deviations, with data from at least three cultures under each set of conditions.