Fig 4.

Loss of CzcS/CzcR signaling induces pyochelin production and promotes cell growth under Fe depletion and Zn excess conditions. (A) Three gene clusters involved in pyochelin (PCH) biosynthesis (pchE/pchF/pchG/PA4223/PA4222 and pchD/pchC/pchB/pchA) and pyoverdine (PVD) transportation (pvdR/pvdT/opmQ) were shown. Values underneath gene names indicate Log₂Fold changes of gene expression in the ΔczcR mutant relative to that in the WT strain. Red and green colors indicated the upregulated and downregulated gene expression in the ΔczcR mutant, respectively. (B and C) Expression of PpchD-lux, PpchE-lux, and PpvdR-lux was measured in the WT and ΔczcR strains when they were cultured in the absence (B) or presence (C) of Zn. (D) Production of PCH was measured in WT and ΔczcR strains when they were cultured in the absence or presence of Zn. (E) Growth of the WT strain, ΔczcR mutant, and the ΔczcR mutant with the complementation of czcR in the presence of 1.0 mM 2,2’-dipyridyl (DIP) when the strains were pretreated or not pretreated with Zn. (F) Growth of WT and ΔczcR strains with or without Zn pretreatment in the minimal medium without Fe supplementation. Statistical significance was calculated compared to the WT group based on Student’s t-test (B and C) and two-way ANOVA (D and E) (n.s., not significant; **, P < 0.01; ***, P < 0.001).