FIGURE 1: The absence of ppGpp reduces the MIC value of ampicillin in E. coli. (A-D) Growth curves of the three studied strains in MOPS rich medium supplemented with low (0.2 mM) phosphate (MOPSr-Lp) in the presence of two-fold serially diluted ampicillin (from 12.5 to 1.5625 μg/ml). Three biological replicates were performed and the averages and ranges were plotted. WT, E. coli MG1655; ΔrelA, E. coli MG1655 with the relA allele deleted; ppGpp⁰, ΔrelA ΔspoT207, with spoT replaced with a chloramphenicol resistance marker [7].

7. Xiao H, Kalman M, Ikehara K, Zemel S, Glaser G, Cashel M (1991). Residual guanosine 3',5'-bispyrophosphate synthetic activity of relA null mutants can be eliminated by spoT null mutations. Journal Biol Chem 266(9): 5980-5990. 10.1016/s0021-9258(19)67694-5