Fig. 3. SrcA is not required for the secretion of the SPI-2 T3SS effectors SseL and PipB2.

(a) The indicated Salmonella strains were grown in minimal medium pH 5.0 for 4 h, then washed and transferred to minimal medium pH 7.2 for 2 h. Salmonella strains carried plasmid pWSK29 expressing either SseL-2HA under its endogenous promoter or PipB2-2HA under the SseA promoter. Bacterial lysate proteins and secreted (Sec) proteins at pH 7.2 were examined by immunoblotting with antibodies against DnaK or the HA epitope. (b) Levels of secreted HA-tagged protein were calculated by densitometry from immunoblots against HA using Image Lab software. Protein levels in ΔssaV and ΔsrcA strains are shown in relation to the wild-type strain. Mean of three independent experiments ±SD. The log₁₀ of the ratios of secreted protein levels from the ΔssaV or ΔsrcA over that of the ΔsteD strain were analysed by one sample t-test, *P<0.05. (c) Representative confo-cal immunofluorescence microscopy images of SseL localization in Mel Juso cells at 20 h p.i. with the indicated Salmonella strains. Cells were fixed and processed for immunofluorescence microscopy by labelling for SseL (anti-HA antibody, green), Salmonella cells (anti-CSA-1 antibody, red) and DNA (DAPI, blue). Scale bar, - 10 μm.