Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. Sigma-S contributes to the protection against external stress, thus playing a role in cellular fitness and survival. Autoregulated. Cells lacking this gene display a decrease in viability during heat shock, long term survival and starvation experiments. They also exhibit significantly reduced virulence in a murine model of septic arthritis infection and decreased capacity to colonize host tissues. Belongs to the sigma-70 factor family.