The activation of the master gene for motility, FlhCD, is further controlled by the quorum-sensing detector QseB, while the activity of the master regulator for biolfilm formation, CsgD, is repressed in the presence of extracellular stressing conditions, detected by CpxR. In addition, the BaeSR system controls the expression of export complexes, conferring multidrug resistance phenotypes,52 while RcsB mediates the glutamate-dependent acid resistance.53,54 QseB, CpxR, BaeR, OmpR and RcsAB are all members of two-component systems that are modified by protein–protein phosphorylation, enabling quick response in comparison to de novo protein production along transcriptional cascades. Strikingly, almost all of these two-component TFs (except OmpR) autoactivate their expression, an observation fitting the contention that positive feedback circuits are necessarily found at the core of all differentiation switches. Indeed, such TF autoactivations likely enable persistent TF expression in two stable states: “on” or “off”. Thus, they constitute a potentially robust machinery for all-or-nothing output response depending on transient exogenous signals.55–62