Fig. 1.

Transcriptional activity of a bhuA-lacZ reporter in B. abortus 2308, BEA2(2308 Δirr), and BEA2.C [BEA2(pKHS2)]. Gray bars show β-galactosidase production in Miller units (12) by B. abortus strains carrying pbhuA-lacZ following 96 h of growth in low-iron minimal medium (low iron). The crosshatched bars show β-galactosidase levels produced by these strains following 96 h of growth in low-iron medium supplemented with 50 μM FeCl₃ (high iron). The results presented are means and standard deviations from a single experiment that is representative of multiple (≥3) experiments performed from which equivalent results were obtained. The average β-galactosidase level produced by the parental plasmid pMR15 in B. abortus 2308 during growth in low-iron minimal medium or this medium supplemented with 50 μM FeCl₃ was subtracted from each data set to account for background activity. **, P ≤ 0.001.