3/7/2023 0 Comments Cardinal chains level 61Surprisingly, time lapse fluorescence microscopy revealed that ttss-1-expressing S. TTSS-1, the cardinal virulence factor for eliciting Salmonella diarrhea, is expressed by just a fraction of the clonal S. Here, we have analyzed for the first time the fitness costs of virulence factor expression in a simple in vitro culture experiment using the diarrheal pathogen Salmonella enterica subspecies I serovar Typhimurium ( S. However, most studies of pathogen fitness have been performed by averaging the phenotypes over large pathogen populations. Therefore, virulence factor expression is generally assumed to enhance the pathogen's fitness. Pathogenic bacteria require virulence factors to foster growth and survival of the pathogen within the host. This raises important questions about compensating mechanisms during host infection which ensure successful propagation of the genotype. Our data demonstrated that virulence factor expression imposes a growth penalty in a non-host environment. Finally, hilA and hilD mutants, which form only fast-growing TTSS-1 − cells, outcompeted wild type S. This was attributable to an increasing initiation rate of ttss-1 expression, in response to environmental cues accumulating during this growth phase, as shown by experimental data and mathematical modeling. 60% during the late logarithmic growth phase of an LB batch culture. In spite of this growth penalty, the TTSS-1 + subpopulation increased from <10% to approx. The growth retardation was at least partially attributable to the expression of TTSS-1 effector and/or translocon proteins. Strikingly, cells of the TTSS-1 + phenotype grew slower than cells of the TTSS-1 − phenotype. The regulator hilA controlled the fraction of TTSS-1+ individuals and their ttss-1 expression level. Here, we studied in vitro the TTSS-1 + phenotype at the single cell level using fluorescent protein reporters. Typhimurium population, yielding a mixture of cells that either express ttss-1 (TTSS-1 + phenotype) or not (TTSS-1 − phenotype). The type III secretion system ttss-1, a cardinal virulence factor for eliciting Salmonella diarrhea, is expressed by just a fraction of the S. Here, we have analyzed the fitness costs of virulence factor expression by Salmonella enterica subspecies I serovar Typhimurium in simple culture experiments. However, most studies of pathogen fitness have been performed by averaging the phenotypes over large populations. Virulence factors generally enhance a pathogen's fitness and thereby foster transmission.
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