Abstract
Enteroaggregative Escherichia coli (EAEC) strains are one of the diarrheagenic pathotypes. EAEC strains harbor a virulence plasmid (pAA2) that encodes, among other virulence determinants, the aggR gene. The expression of the AggR protein leads to the expression of several virulence determinants in both plasmids and chromosomes. In this work, we describe a novel mechanism that influences AggR expression. Because of the absence of a Rho-independent terminator in the 3′UTR, aggR transcripts extend far beyond the aggR ORF. These transcripts are prone to PNPase-mediated degradation. Structural alterations in the 3′UTR result in increased aggR transcript stability, leading to increased AggR levels. We therefore investigated the effect of increased AggR levels on EAEC virulence. Upon finding the previously described AggR-dependent virulence factors, we detected novel AggR-regulated genes that may play relevant roles in EAEC virulence. Mutants exhibiting high AggR levels because of structural alterations in the aggR 3′UTR show increased mobility and increased pAA2 conjugation frequency. Furthermore, among the genes exhibiting increased fold change values, we could identify those of metabolic pathways that promote increased degradation of arginine, fatty acids and gamma-aminobutyric acid (GABA), respectively. In this paper, we discuss how the AggR-dependent increase in specific metabolic pathways activity may contribute to EAEC virulence.
Highlights
Enteroaggregative Escherichia coli (EAEC) strains are one of the diarrheagenic pathotypes
A common genomic feature of most EAEC strains is the presence of a virulence plasmid termed pAA. pAA plasmids encode a transcriptional activator named AggR, which is a member of the AraC-XylS family of transcription factors[14]
Considering that AggR influences the expression of the AaR protein which, in turn, affects the expression of housekeeping genes[16,17], we studied whether the observed upregulation of metabolic genes in the 042 aggR + FRT3′UTR strain was detected in an aar derivative
Summary
Enteroaggregative Escherichia coli (EAEC) strains are one of the diarrheagenic pathotypes. EAEC strains harbor a virulence plasmid (pAA2) that encodes, among other virulence determinants, the aggR gene. Negative regulators of aggR expression include the nucleoid-associated protein H-NS15 and the pAA plasmidencoded member of the AraC negative family of regulators, the Aar protein[16,17]. AggR-dependent plasmid-encoded virulence factors include aggregative adherence fimbriae (AAF), of which there exist different variants[23,25,26,27,28], the Aap dispersin and its type I secretion system (TISS), the polysaccharide deacetylase encoded by the shf gene, and the Shigella flexneri virulence protein VirK13,24,29,30. The chromosomal virulence determinants regulated by AggR, including a type VI secretion system identified in strain 04224, map mainly to chromosomal islands. The aggR::lacZ transcriptional fusion generated by placing the lacZ gene after the aggR ORF in the 3′UTR ( enabling aggR promoter-dependent βgalactosidase expression in the presence of wt levels of AggR)
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