Nutrient limitation is a critical signal in Salmonella virulence gene regulation. The katF (rpoS) gene mediates the expression of the Salmonella spv plasmid virulence genes during bacterial starvation. A katF Salmonella mutant has increased susceptibility to nutrient deprivation, oxidative stress, acid stress, and DNA damage, conditions which are relevant to the intraphagosomal environment of host macrophages. Moreover, the katF mutant has significantly reduced virulence in mice. katF encodes an alternative sigma factor of RNA polymerase which coordinately regulates Salmonella virulence.