An activator of glutamate decarboxylase genes regulates the expression of enteropathogenic Escherichia coli virulence genes through control of the plasmid-encoded regulator, per

Citation
S. Shin et al., An activator of glutamate decarboxylase genes regulates the expression of enteropathogenic Escherichia coli virulence genes through control of the plasmid-encoded regulator, per, MOL MICROB, 41(5), 2001, pp. 1133-1150
Citations number
70
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Microbiology
Journal title
MOLECULAR MICROBIOLOGY
ISSN journal
0950-382X → ACNP
Volume
41
Issue
5
Year of publication
2001
Pages
1133 - 1150
Database
ISI
SICI code
0950-382X(200109)41:5<1133:AAOGDG>2.0.ZU;2-H
Abstract
Enteropathogenic Escherichia coil (EPEC) is a major cause of infantile diar rhoea in a number of developing countries and is the prototype of pathogeni c bacteria that cause attaching and effacing (A/E) intestinal lesions. A ch romosomal pathogenicity island, termed the locus of enterocyte effacement ( LEE), contains all the genes necessary for the A/E phenotype as well as gen es for a type III secretion system and intimate adhesion. Genes in the LEE and genes involved in the synthesis of bundle-forming pili (BFP) are positi vely regulated by the plasmid-encoded regulator (Per) and comprise the per regulon. In order to identify factors that control the per regulon, we scre ened an EPEC genomic library for clones that modulate the expression of per . A plasmid clone that decreased the expression of per was isolated using a lacZ reporter gene fused to the per promoter. Subcloning revealed that YhI X, a putative AraC/XyIR family transcriptional regulator, was the effector of per repression. Through downregulation of per, a plasmid overproducing Y hiX reduced the synthesis of intimin, BfpA, Tir, and CesT, factors importan t for EPEC virulence. yhiX is located downstream of gadA, which encodes glu tamate decarboxylase, an enzyme involved in acid resistance of E. coli. Yhi X was found to be an activator of gadA, and the cloned yhiX gene increased production of glutamate decarboxylases (GAD) and activated the transcriptio n of the gadA and gadB promoters. Therefore, yhiX was renamed gadX. Analysi s of a gadX mutant grown in the different culture media with acidic and alk aline pH showed that regulation of perA, gadA and gadB by GadX was altered by the external pH and the culture media condition. Under conditions in whi ch EPEC infects cultured epithelial cells, GadX negatively regulated perA e xpression, and the derepression in the gadX mutant increased translocation of Tir into epithelial cells relative to wild-type EPEC. DNA mobility shift experiments showed that purified GadX protein bound to the perA, gadA and gadB promoter regions in vitro, indicating that GadX is a transcriptional r egulator of these genes. On the basis of these results, we propose that Gad X may be involved in the appropriate expression of genes required for acid resistance and virulence of EPEC. Our data are consistent with a model in w hich environmental changes resulting from passage from the stomach to the p roximal small intestine induce the functional effect of GadX on per and GAD expression in order to prevent inappropriate expression of the products of these two systems.