Fig. 3.

Fig. 3. Viability of E. coli strains lacking GDAR system and Cue system under extremely acidic conditions. (A) Bacterial cells, which were pre-cultured overnight in pH 7.0 LBG, were adapted in pH 5.5 LBG for 18 h and transferred to pH 2.5 M9 minimal medium broth. After 2 h incubation, live cells were counted by plating onto LB agar. Bacterial survival rate was calculated by dividing the number (CFU/ml) at pH 2.5 by the number (CFU/ml) at pH 5.5 and the rate of wild-type E. coli was set to 100%. Tested bacterial strains include wild-type, ΔgadA, ΔgadB, ΔybaST, and ΔcueR strains which were transformed with pBAD30 or pBAD18 or its derivative producing GadA, GadB, YbaS, YbaST, or CueR. (B) Acid resistance of E. coli wildtype and ΔgadAB strains harboring pBAD30, pGadA, or pGadB was tested as described above. Statistical significance is indicated by *, p-value < 0.05; **, p-value < 0.01; ***, p-value < 0.001.

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