FIG 3.

Ectopic csrT expression represses hydrogen peroxide resistance conferred by ICE-βox. CsrT abrogates the capacity of ICE-βox to protect L. pneumophila from hydrogen peroxide. E-phase cultures of WT Lp02 (WT, MB110), ΔcsrT mutant (MB1409), ICE-βox⁺ donor (D), ICE-βox⁻ recipient (R), and ICE-βox⁺ transconjugant (T) strains that contained IPTG-inducible plasmid pcsrT (strains MB1383, MB1384, and MB1385, respectively) were cultured overnight without (−) or with (+) IPTG and then exposed to 2 mM H₂O₂ for 1 h. The mean percent survival ± the SEM was calculated from three independent experiments as (CFU_{posttreatment}/CFU_pretreatment) × 100. Student t tests were used to determine statistically significant differences between treated, pcsrT-induced ICE-βox⁺ strains and treated uninduced strains (*, P < 0.05; **, P < 0.01). Note that after induction of pcsrT expression, the yields of D, R, and T strains were <1%, values that are not visible on this scale.