FIG 2.

Iron and zinc modestly repress expression of the M. tuberculosis esx-3 locus. (A) OD₆₀₀ measurements of M. tuberculosis subcultured in chelated Sauton's medium (C.S.) with or without iron (3.67 μM ZnSO₄ present in both conditions). (B) M. tuberculosis was grown in 7H9 or CS containing iron (FeCl₃) or zinc (ZnSO₄) as indicated for 3 or 6 days. The mRNA levels of mbtI, bfrB, esxG, and ppe4 were normalized to 16S rRNA and are shown as fold changes compared to the sample without iron or zinc. Data represent the means ± the SEM from three experiments with five technical replicates each. (C) M. tuberculosis was subcultured from 7H9 into CS medium without hemin or with increasing concentrations of hemin (1, 10, and 100 μM) or iron (50 μM) as indicated for 24 h, and bacterial CFU were enumerated. Data represent the means ± the SEM from one experiment with six technical replicates. (D) M. tuberculosis was grown in CS medium without iron supplementation or with hemin (low, 3 μM; high, 30 μM) or FeCl₃ (50 μM) for 1 week. The mRNA levels of mbtI and esxG were normalized to 16S rRNA. Data represent the means ± the SEM from one experiment with five technical replicates. *, P < 0.05; **, P < 0.01; ***, P < 0.001 (unpaired Student t test). n.s., not significant.