Adapting to succeed : Post-transcriptional gene regulation in Salmonella

Sammanfattning: Salmonella are zoonotic pathogens of worldwide economic and health importance. Both during life outside and inside the host, these pathogens are subject to continuously changing environmental conditions, such as temperature changes, acid stress, nutrient limitations, and others. In order to thrive and survive, Salmonella must respond to these changes by adapting their physiology and morphology through changes in gene expression. RNA-binding proteins (RBPs) often work in concert with small RNAs (sRNAs) to control gene expression at the post-transcriptional level. Their mode of action includes regulation of RNA translation and/or stability, either positive or negative. Recently, ProQ was discovered to be a global RBP with a large repertoire of mRNA and sRNA targets in Salmonella. However, many details regarding ProQ biology are not fully understood, including the requirements for RNA-binding, mechanisms of gene regulation, and ProQ-dependent phenotypic changes. The main purpose of this doctoral thesis was to characterize the RBP ProQ and its regulatory role in Salmonella.First, we developed a method based on saturation mutagenesis coupled to phenotypic sorting and high-throughput sequencing to chart the functionally important regions in ProQ. Our results reveal that both the N-terminal and C-terminal domains are important for ProQ’s gene regulatory function, but the underlying mechanisms differ. Second, we show that ProQ is important for flagellar-mediated motility in Salmonella. More specifically, we show that ProQ and an associated sRNA promotes flagellar gene expression and motility by affecting translation of the master flagellar regulator FlhDC. Finally, we reveal that ProQ induces persister formation in Salmonella and enables a subpopulation of cells to survive high doses of different types of antibiotics through growth arrest.In conclusion, the findings presented herein provide new insights into the role of ProQ as a global post-transcriptional regulator of gene expression in Salmonella. Together, these findings contribute to our understanding of how Salmonella shapes its lifestyle and induces pathogenesis.