GENETIC SCREENS IDENTIFY A HISTIDINE KINASE AND AN AMINOPEPTIDASE AS FACTORS THAT REGULATE LISTERIA MONOCYTOGENES VIRULENCE GENES EXPRESSION

Listeria monocytogenes is a Gram-positive intracellular bacterial pathogen. Once invading the host cytosol, L. monocytogenes senses various signals, which affect regulation of the bacterial virulence state. The availability of these signals serves as a niche-specific signature that informs the bacteria of its intracellular location and induces its virulence genes. We aimed at studying the role of metabolic signals in the regulation of L. monocytogenes virulence genes and the cross-regulation of metabolism and virulence during infection. In this study, we performed genetic screens of L. monocytogenes mutants searching for genes that link metabolism to virulence. A mariner Tn mutant library was generated in L. monocytogenes bacteria harboring a Luciferase reporter system fused to the hly promoter of the LLO toxin, a classic virulence factor that is regulated by the virulence activator, PrfA. The library was screened under two conditions: during bacterial growth in the presence of glucose-1-phosphate as a carbon source and under conditions of low concentrations of branched chain amino acids, both known to activate PrfA. In these screens we identified 90 mutants that differentially induce hly transcription under the tested conditions. In this report we present two mutants that exhibit altered transcription of hly, the first mutated in a gene encoding an aminopeptidase and the other in a gene encoding a histidine kinase. Both mutants demonstrate a reduced ability to infect and grow within primary macrophages and mice, as well exhibit low transcription levels of major virulence genes. Future studies of these genes` functions will provide insights into the cross-regulation of metabolism and virulence in L. monocytogenes.