In the periplasmic space peptidoglycan ensures the structural integrity of the cell by preventing osmolysis. To sense and rapidly respond to environmental signals, bacteria primarily use two-component signal transduction systems, composed of an inner membrane histidine kinase and a cytoplasmic response regulator [16]. Peptidoglycan is the major structural Inhibitor Library component of the bacterial cell wall. It provides the bacterial cell structural strength and protects the osmotically sensitive membrane [17]. As expected, by targeting peptidoglycan synthesis, colicin M induced

an envelope stress response. In E. coli envelope homeostasis is monitored by several stress responses; namely, Rcs, Cpx, Psp, σE, Bae and vesicle release responses [18–20]. Our microarray analysis revealed that the Rcs regulon has a major

role in the response to envelope stress induced by colicin M. RcsC and RcsD are inner-membrane-bound proteins, with RcsC as the sensor kinase that autophosphorylates upon sensing the appropriate signal, while RcsD transfers the phosphoryl group to the transcriptional regulator RcsB. Certain promoters require the RcsA protein to act as an auxiliary regulatory protein, apparently exerting its effects by forming a heterodimer with RcsB [21]. The Rcs system controls the production of exopolysaccharides [22], biofilm formation MK 8931 cell line [23, 24], cell motility, and chemotaxis [25]. We observed induction of rcsA and a number of other Rcs-regulated genes: the exopolysaccharide operons wca for colanic acid synthesis, L-gulonolactone oxidase and yjbEFGH, as well as genes osmB, ymgG and ymgD, ivy, yfbR, ugd, yfdC, yjbJ, galU, yaaX, yggG, yegS, spy, rprA, bdm and yaiY (Table  1). Recently, perturbations to peptidoglycan by several ß-lactam antibiotics were shown to elicit shared as well as unique responses with all activating the Rcs system

[26] indicating that, the Rcs pathway elicits a global response to peptidoglycan stress [27]. Colicin M treatment also induced the expression of cpxP, which encodes the periplasmic inhibitor of the Cpx envelope stress response. The Cpx system appears to sense misfolded proteins that are synthesized for the periplasm, and it is controlled by the sensor kinase CpxA, the response regulator CpxR, and the periplasmic inhibitor CpxP. CpxP has been assumed to fine tune Cpx activation during envelope stress, by preventing its incorrect activation and enabling its rapid shut-down following envelope stress relief [28]. Treatment with colicin M also up-regulated a third cell envelope stress system, the psp genes that encode the membrane-bound phage shock proteins: PspA, PspB, PspC, PspD and PspG. The psp regulon consists of the psp operon with genes pspA, pspB, pspC, pspD and pspE, as well as genes pspF and pspG. Proteins PspB, PspC and PspD are located in the inner membrane, while PspA is on the cytoplasmic side of the inner membrane. In the absence of stress, PspA binds to protein PspF, thus selleck chemicals llc inhibiting transcription of the psp operon.