FIG. 5.

Functional requirements for secretion by the TTSS of SPI2. (A) The S. enterica serovar Typhimurium wild type (wt) and various strains harboring mutations in the ssc, sse, or ssa gene were grown in low-Mg²⁺ minimal medium at pH 7.0 or pH 5.0 to induce expression or expression and secretion, respectively, of SPI2 substrate proteins. Lysates of equal amounts of bacteria were adjusted by OD₆₀₀ (total cell fraction), or protein recovered from equal amounts of bacteria (detached fraction) was analyzed as described in the legend for Fig. 2. n.d., not done. (B) Role of SseB for secretion of SseC and SseD. Various strains were grown in low-Mg²⁺ minimal medium at pH 5.0. Protein from culture supernatants was prepared as described in Materials and Methods. Equal amounts of bacterial cells (total cell fraction) and protein prepared from equal amounts of culture supernatants were subjected to Western blot analysis with antibodies raised against rSseC (α SseC) or rSseD.