Fig. 1. Comparison of culture-average fluorescence of S. enterica SB300A#1 strains harboring the pET7-gfp (A), pPro7(E)-gfp (B), or pPro7(S)-gfp (C) grown in 96-well plates. Cells carrying the plasmid were grown overnight in LB medium at 37 °C and were subcultured (1:100) into fresh LB medium (5 ml) with ampicillin (100 μg/ml), grown at 37 °C in a shaking incubator until the OD₆₀₀ reached about 0.5, and then exposed to different concentrations of inducer in 96-well plates at 37 °C with shaking in a Tecan SpectraFluor Plus plate reader. The data are raw; e.g., background fluorescence intensity was not removed by using background subtraction. Symbols indicate inducer concentrations. (A) Solid diamonds, 40 mM arabinose; solid rectangles, 20 mM; solid triangles, 10 mM; open circles, 0 mM. (B) and (C) Solid diamonds, 100 mM propionate; solid rectangles, 50 mM; solid triangles, 10 mM; open circles, 0 mM. The data are representative of three independent experiments. RFU, relative fluorescence units.

Fig. 2. Comparison of cell growth and GFP expression levels between the pPro and T7 expression systems in shaking flask experiment. S. enterica SB300A#1 harboring plasmid pET7-gfp (A) and S. enterica TR6583 (B), TRB (C), or TRD (D) harboring plasmid pPro7(S)-gfp. GFP expression levels and OD₆₀₀ were determined using a Tecan SpectraFluor Plus plate reader after (1:5) dilution into LB medium. Open and solid symbols indicate cell growth and GFP production, respectively. Solid diamonds indicate GFP production in the presence of 0.4% glucose. Rectangles, 0 mM arabinose (A) or 0 mM propionate (B, C, D); circles, 15 mM arabinose (A) or 20 mM propionate (B, C, D). Error bars show the standard deviation of experiments performed in triplicate. RFU, relative fluorescence units.

Fig. 3. The culture-average fluorescence and cell growth of S. enterica strains TR6583 (A and B) and prpD mutant (C and D) harbouring pPro7(S)-gfp at various concentrations of propionate. This experiment was performed using the same culture method as described in Fig. 2. Symbols indicate propionate concentrations added into culture medium. Error bars show the standard deviation of experiments performed in triplicate.

E. coli or S. enterica strains and plasmids used in this study