Publications

Gene duplications occur in prokaryotic genomes at a detectable frequency. In many instances, the biological function of the duplicates is unknown, and hence, the significance of the presence of multiple copies of these genes remains unclear.; Gene duplications significantly impact the gene repertoires of both eukaryotic and prokaryotic microorganisms. The genomes of pathogenic Escherichia coli strains share a group of duplicated genes whose function is mostly unknown. The irmA gene is one of the duplicates encoded in several pathogenic E. coli strains. The function of its gene product was investigated in the uropathogenic E. coli strain CFT073, which contains a single functional copy. The IrmA protein structure mimics that of human interleukin receptors and likely plays a role during infection. The enteroaggregative E. coli strain 042 contains two functional copies of the irmA gene. In the present work, we investigated their biological roles. The irmA_4509 allele is expressed under several growth conditions. Its expression is modulated by the global regulators OxyR and Hha, with optimal expression at 37 degrees C and under nutritional stress conditions. Expression of the irmA_2244 allele can only be detected when the irmA_4509 allele is knocked out. Differences in the promoter regions of both alleles account for their differential expression. Our results show that under several environmental conditions, the expression of the IrmA protein in strain 042 is dictated by the irmA_4509 allele. The irmA_2244 allele appears to play a backup role to ensure IrmA expression when the irmA_4509 allele loses its function. IMPORTANCE Gene duplications occur in prokaryotic genomes at a detectable frequency. In many instances, the biological function of the duplicates is unknown, and hence, the significance of the presence of multiple copies of these genes remains unclear. In pathogenic E. coli isolates, the irmA gene can be present either as a single copy or in two or more copies. We focused our work on studying why a different pathogenic E. coli strain encodes two functional copies of the irmA gene. We show that under several environmental conditions, one of the alleles dictates IrmA expression, and the second remains silent. The latter allele is only expressed when the former is silenced. The presence of more than one functional copy of the irmA gene in some pathogenic E. coli strains can result in sufficient expression of this virulence factor during the infection process.

JTD Keywords: 042, aec69, enteroaggregative e. coli, gene duplications, 042, Adaptation, Aec69, Aggregative adherence, Chromosomal genes, Coli, Duplication, Enteroaggregative e, Escherichia-coli, Evolution, Gene duplications, Hha/ymoa, Irma, Mechanism, Outer-membrane, Protein

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.

JTD Keywords: aggregative adherence, arginine metabolism, biofilm formation, escherichia-coli, gene-expression, messenger-rna, operon, persistent diarrhea, untranslated region, Fimbria-i expression