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. 2015 Nov 18;197(24):3822–3833. doi: 10.1128/JB.00638-15

FIG 1.

FIG 1

Effects of croS on SXT conjugative transfer. (A) Schematic representation of the regulatory module of SXT. The dotted line indicates the region enlarged in panel B. (B) The intergenic region between croS, previously referred to as s086, and setR in SXT as represented by Beaber and Waldor (30). The PL and PR promoters, the OL, O1, O2, and O3 operators, the −10 and −35 elements, the Shine-Dalgarno (SD) sequence of croS, and the start codons of croS and setR are represented. (C) Effect of the deletion or overexpression of croS on SXT transfer. Conjugation assays were carried out with E. coli BW25113 SXT (VB17, WT) or its ΔcroS mutant (DPL353, Δ) as the donor. Overexpression assays were carried out by expressing croS from the arabinose-inducible PBAD promoter in pCroS (DPL525). E. coli CAG18439 (Tcr) was used as the recipient. Frequencies of exconjugant formation were expressed as the number of exconjugant CFU (Sur Tmr Tcr) per recipient CFU (Tcr). (D) Effect of croS deletion on the induction of SXT transfer by MC. The donor strains were VB17, DPL353, and DPL263 in which croS was expressed from its native PL promoter in pSRZ integrated in single copy in tandem with SXT ΔcroS. The recipient strain was CAG18439. The induction index corresponds to the ratio of the frequencies of exconjugant formation obtained with and without MC treatment prior to transfer. The dashed line indicates an induction index of 1, i.e., no difference between the induced and noninduced conditions. Each bar represents the mean and standard deviation of values obtained from at least three independent experiments. Statistical analyses of the logarithms of the mean values were performed with two-tailed unpaired t tests. Asterisks indicate that P values are <0.05 compared to the wild type (WT). (E) Schematic representation of the insert of the pSR, pSZR, and pSRZ plasmids site specifically integrated into the 5′ end of prfC alone or in tandem with SXT. The plasmid backbone is not represented. In pSZR and pSRZ, lacZ was translationally fused to the sixth codon of croS and setR, respectively.