Figure 4.

Role of the two-component signal-transduction system cpxAR in S. typhi-mediated haemolysis. (A) Deletion of both sensor and response regulator components of the cpx system in BRD948c eliminates neuroendocrine hormone-mediated haemolysis by S. typhi. (B) Western blotting with corresponding densitometry (average of three independent experiments) indicates that levels of the sRNA chaperone protein Hfq increase on exposure of BRD948 to neuroendocrine hormones, but fail to do so in the cpx mutant BRD948c. There is no significant change in (C) expression or (D) transcript levels of the sRNA micA in BRD948c upon neuroendocrine hormone exposure, compared with the changes observed in the parent. Complementation by cpxAR on a single-copy plasmid in BRD948c cpx+ fully restored neuroendocrine hormone-mediated haemolysis in a (E) liquid or (F) blood plate assay, compared with the control BRD948c pNMD. Both neuroendocrine hormones had an identical profile; only epinephrine data are shown. Asterisk indicates significant difference (P⩽0.05) by the Student's t-test. Experiments were repeated at least three times. Standard error bars are shown. E, epinephrine; sRNA, small RNA.