Figure 4. Characterization of the transcriptional fusion Pasr::gfp in acidified M9 medium.

Fluorescence produced by WT pPasr::gfp was monitored with a fluorometer and expressed proportionally to the bacterial population (GFP/OD₆₀₀). A. WT pPasr::gfp was grown overnight in M9 medium complemented with 0.1% casamino acids, 0.2% glucose pH 7.2, diluted 1/50 and grown in the same medium adjusted to the desired pH with HCl. B. Bacteria were prepared as in A and grown in M9 medium adjusted to pH 4.5 or left at pH 7.2 with addition of different stresses: amino acids, magnesium or iron starvations (a.a._-less, Mg²⁺ _-less and Fe²⁺ _-less, respectively), oxidative stress (hydrogen peroxide : H₂O₂) and antimicrobial peptide (polymixin B : PB). C. WT pPasr::gfp and ΔadiAΔcadAΔspeF pPasr::gfp were grown overnight in the same medium as in A, diluted 1/50 and grown in the same medium containing, when indicated, 5 mM L-lysine and 5 mM L-ornithine and adjusted to pH 4.5. Cultures were performed in anoxic conditions.