The Cpx envelope stress response both facilitates and inhibits elaboration of the enteropathogenic Escherichia coli bundle-forming pilus

The Cpx envelope stress response is induced by the misfolding of periplasmic proteins and restores envelope homeostasis by upregulating several periplasmic protein folding and degrading factors. The Cpx response also regulates the expression of a variety of envelope-spanning protein complexes, including flagella, secretion systems and pili, which play an important role in pathogenesis. In a previous study, we inactivated the Cpx response in enteropathogenic Escherichia coli (EPEC), a causative agent of infant diarrhoea, and observed decreased expression of its major adhesin, the bundle-forming pilus (BFP). Here, we examined the mechanism underlying this BFP expression defect, and found that this phenotype can be attributed to insufficient expression of periplasmic folding factors, such as DsbA, DegP and CpxP. Hence, a low level of Cpx pathway activity promotes BFP synthesis by upregulating factors important for folding of BFP component proteins. Conversely, we found that full induction of the Cpx response inhibits BFP expression, mainly by repressing transcription of the bfp gene cluster. In combination with a previous report examining EPEC type III secretion, our results demonstrate that the Cpx response co-ordinates the repression of cell-surface structures during periods of envelope stress

Small heat-shock protein HspL is induced by VirB protein(s) and promotes VirB/D4-mediated DNA transfer in Agrobacterium tumefaciens

Agrobacterium tumefaciens is a Gram-negative plant-pathogenic bacterium that causes crown gall disease by transferring and integrating its transferred DNA (T-DNA) into the host genome. We characterized the chromosomally encoded alpha-crystallin-type small heat-shock protein (α-Hsp) HspL, which was induced by the virulence (vir) gene inducer acetosyringone (AS). The transcription of hspL but not three other α-Hsp genes (hspC, hspAT1, hspAT2) was upregulated by AS. Further expression analysis in various vir mutants suggested that AS-induced hspL transcription is not directly activated by the VirG response regulator but rather depends on the expression of VirG-activated virB genes encoding components of the type IV secretion system (T4SS). Among the 11 virB genes encoded by the virB operon, HspL protein levels were reduced in strains with deletions of virB6, virB8 or virB11. VirB protein accumulation but not virB transcription levels were reduced in an hspL deletion mutant early after AS induction, implying that HspL may affect the stability of individual VirB proteins or of the T4S complex directly or indirectly. Tumorigenesis efficiency and the VirB/D4-mediated conjugal transfer of an IncQ plasmid RSF1010 derivative between A. tumefaciens strains were reduced in the absence of HspL. In conclusion, increased HspL abundance is triggered in response to certain VirB protein(s) and plays a role in optimal VirB protein accumulation, VirB/D4-mediated DNA transfer and tumorigenesis

Maintaining Integrity Under Stress:Envelope Stress Response Regulation of Pathogenesis in Gram-Negative Bacteria

The Gram-negative bacterial envelope is an essential interface between the intracellular and harsh extracellular environment. Envelope stress responses (ESRs) are crucial to the maintenance of this barrier and function to detect and respond to perturbations in the envelope, caused by environmental stresses. Pathogenic bacteria are exposed to an array of challenging and stressful conditions during their lifecycle and, in particular, during infection of a host. As such, maintenance of envelope homeostasis is essential to their ability to successfully cause infection. This review will discuss our current understanding of the σE- and Cpx-regulated ESRs, with a specific focus on their role in the virulence of a number of model pathogens

The Cpx Envelope Stress Response Affects Expression of the Type IV Bundle-Forming Pili of Enteropathogenic Escherichia coli

The Cpx envelope stress response mediates adaptation to potentially lethal envelope stresses in Escherichia coli. The two-component regulatory system consisting of the sensor kinase CpxA and the response regulator CpxR senses and mediates adaptation to envelope insults believed to result in protein misfolding in this compartment. Recently, a role was demonstrated for the Cpx response in the biogenesis of P pili, attachment organelles expressed by uropathogenic E. coli. CpxA senses misfolded P pilus assembly intermediates and initiates increased expression of both assembly and regulatory factors required for P pilus elaboration. In this report, we demonstrate that the Cpx response is also involved in the expression of the type IV bundle-forming pili of enteropathogenic E. coli (EPEC). Bundle-forming pili were not elaborated from an exogenous promoter in E. coli laboratory strain MC4100 unless the Cpx pathway was constitutively activated. Further, an EPEC cpxR mutant synthesized diminished levels of bundle-forming pili and was significantly affected in adherence to epithelial cells. Since type IV bundle-forming pili are very different from chaperone-usher-type P pili in both form and biogenesis, our results suggest that the Cpx envelope stress response plays a general role in the expression of envelope-localized organelles with diverse structures and assembly pathways

Strain Variation among Bordetella pertussis Isolates from Québec and Alberta Provinces of Canada from 1985 to 1994

Pulsed-field gel electrophoresis and gene typing were able to differentiate among 3,597 Bordetella pertussis isolates circulating in Alberta and Québec Provinces, Canada, from 1985 to 1994 and distinguish them from the strains used in vaccine production. This study provides a baseline for continued surveillance of prevalent and emerging strains of B. pertussis in Canada