The transcriptional regulator SsrB is involved in a molecular switch controlling virulence lifestyles of Salmonella
Fig 2
SsrB represses the secretion of SPI-1-encoded proteins and Salmonella invasion of HeLa cells.
(A) Secretion profiles of the SPI-1-encoded proteins SipA, SipB, SipC and SipD were examined in the WT S. Typhimurium strain and its isogenic ΔSPI-2 mutant containing the plasmid pK3-SsrB that constitutively expresses SsrB, or the vector pMPM-K3, grown for 9 h in LB at 37°C. As a control, the secretion profile for the ΔhilD mutant that lacks the SipA-D proteins is also shown. FliC is the major subunit of the flagellar filament. (B) HeLa cells were infected with WT S. Typhimurium or isogenic ΔhilD and ΔflhDC mutants containing either pK3-SsrB or vector control pMPM-K3, and intracellular bacteria enumerated after 1 hr. White and black columns indicate the number of bacteria from the starting inoculum and from intracellular bacteria recovered from the HeLa cells, respectively. Data represents the mean with standard deviation of three independent experiments. *Statistically different values with respect to the WT strain with or without the vector pMPM-K3, P < 0.005.