Fig. 4.

Single-cell analysis of promoter activity for representative SPI1 and flagellin genes. S. Typhimurium harbouring gfp[LVA] transcriptional fusions to selected promoters were analysed by flow cytometry. (a) Activity of promoters for cultures grown with (i) or without (ii) aeration. Arrowheads indicate the time points at which aer-LL and μaer-ST bacteria were harvested. (b) Promoter activity in aer-LL (filled bars) and μaer-ST (open bars) bacteria. Comparison of SPI1 regulon genes (prgH, invF and sopB), SPI2 regulon genes (pipB and ssaG), and the flagellin gene fliC. Promoterless gfp[LVA] (null) was included as a negative control. (c) Comparison of the frequencies of high-intensity GFP (>10⁴ relative fluorescent units) expressing bacteria in aer-LL (filled bars) and μaer-ST (open bars) bacteria. Shown are means±sd from at least three independent experiments. ***P<0.001, Student's t-test.