EXPRESSION OF SALMONELLA-TYPHIMURIUM RPOS AND RPOS-DEPENDENT GENES INTHE INTRACELLULAR ENVIRONMENT OF EUKARYOTIC CELLS

Adaptation to the intracellular environment of host cells is crucial f or the pathogenesis of Salmonella infections. The alternative sigma fa ctor RpoS is a global regulator of gene expression during starvation a nd stress conditions and is required for virulence in Salmonella spp. We have used lacZ reporter fusions to rpoS and rpoS-dependent genes to study rpoS regulation after entry of Salmonella typhimurium into macr ophages and epithelial cells. The results demonstrate that expression of an rpoS::lacZ translational fusion increases rapidly in S. typhimur ium after phagocytosis. Activity of RpoS also increases after bacteria l entry into both macrophages and epithelial cells, as demonstrated by the induction of the rpoS-regulated genes katE and spvB. A control rp oS-independent promoter for neomycin resistance does not show signific ant induction after cell entry. These results demonstrate that the reg ulatory system mediated by RpoS in S. typhimurium is activated by the intracellular environment of eukaryotic cells.