(A) Cross-talk from HitRS to Phrt. B.anthracis Sterne (WT), ΔhssR, ΔhssRΔhitR, and ΔhssSΔhitR were transformed with the xylE reporter plasmid, phrt. Each strain was treated with either 50 μM ‘205 or an equivalent volume of vehicle (DMSO). (B) Cross-talk from HssRS to Phit at low heme concentrations. WT, ΔhitR, ΔhssRΔhitR, ΔhitSΔhssR, and ΔhitSΔhssR-hitR:D56N were transformed with the xylE reporter plasmid, phit. Each strain was treated with either 1 μM heme or an equivalent volume of vehicle (0.1 M NaOH). (C) Cross-talk from HssRS to Phit. WT and ΔhitR phit were treated with either 5 μM heme or an equivalent volume of vehicle (0.1 M NaOH). In all instances, cultures were grown for 24 h and XylE activity was quantified. Error bars represent ±SEM of data averaged from two independent experiments performed with biological triplicates. Significance was calculated by an unpaired Student's t-test, where ** = P≤0.001 and *** = P≤0.0001.