Comparison of genes regulated by TviA in S. Typhi and Typhimurium

Bacterial pathogens causing systemic disease commonly evolve from organisms associated with localized infections but differ from their close relatives in their ability to overcome mucosal barriers by mechanisms that remain incompletely understood. Here we investigated whether acquisition of a regulatory gene, tviA, contributed to the ability of Salmonella enterica serotype Typhi to disseminate from the intestine to systemic sites of infection during typhoid fever. To study the consequences of acquiring a new regulator by horizontal gene transfer, tviA was introduced into the chromosome of S. enterica serotype Typhimurium, a closely related pathogen causing a localized gastrointestinal infection in immunocompetent individuals. Modulation of gene expression by TviA in serotype Typhi and Typhimurium was determined by profiling and found to be very comparable. Expression of flagellin, a pathogen associated molecular pattern (PAMP), was repressed by TviA when bacteria were grown at osmotic conditions encountered in tissue, but not at higher osmolarity present in the intestinal lumen. TviA-mediated flagellin repression enabled bacteria to evade sentinel functions of human model epithelia and resulted in increased bacterial dissemination to the spleen in a chicken model. The effect of tviA on gene expression profiles in S. Typhimurium was determined by comparing a tviA expressing strain (IR715(pTVIA1) with a control strain harboring the empty cloning plasmid (IR715 (WSK29). S. Typhimurium strains were cultured in SOB broth (low salt), a condition known to induce expression of TviA. Total RNA was extracted from one cultures of each strain. cDNA was differentially labeled with Alexa Fluor 555 and 648 (including a technical replicate in which the labeling of the samples was inversed [flip dye]), respectively and competitively hybridized on S.Typhimurium arrays (PFGRC, version 4). GSM509223 has 4 GPR files which are technical replicates of a competitive hybridization of cDNA from IR715(pWSK29) and IR715(pTVIA1). The profiles obtained from S. Typhimurium was compared with the corresponding data set for S. Typhi (comparing a (delta)tviB-vexE (tviBCDEvexABCDE) mutant and a (delta)viaB (tviABCDEvexABCDE) mutant) from GEO accession number GSE15752.