Figure 1

Cation chelation by extracellular DNA induces expression of the pmr operon. (A) Expression of pmrH-lux in NM2 media (pH7.4) in final Mg²⁺ concentrations ranging from 1 mM to 0.06 mM. (B) Expression of pmrH-lux in NM2 media pH5.5 and pH7.4, in varying Mg²⁺ concentrations. (C) Expression of pmrH-lux in NM2 media (pH7.4) in varying Mg²⁺ concentrations ranging from 1 mM to 0.06 mM (white bars), media supplemented with 0.5% DNA (5 mg/ml) (grey bars) or 0.5% DNA plus excess 5 mM Mg²⁺ (black bars). (D) Expression of pmrH-lux in NM2 media (pH7.4) containing repressing levels of Mg²⁺ (1 mM) and supplemented with increasing concentrations of extracellular DNA, as indicated. Expression was measured in strains 14028, phoP, pmrAB and phoP/pmrAB mutants. In all experiments, gene expression was measured every 20 minutes for 18 hours and the maximal gene expression (t = ~7 hrs) is shown. The values shown are the means from experiments done in triplicate and the error bars represent the standard deviation.