Metabolic pathway for purine nucleotide synthesis.

Survival of purA and purB mutants at pH 2.5. After the cells had been grown in EG medium at pH 7.5 until the OD₆₀₀ reached 0.3, the cells were harvested and suspended in EG medium at pH 5.5. After the cells had been grown for 4 h at pH 5.5 under anaerobic conditions, the cells were challenged at pH 2.5 for 1 and 2 h under anaerobic conditions, and the viable cells were counted. Adenine (0.1 mM) was added to EG medium at pH 7.5 for the growth of purA and purB mutants. Adenine also was added at pH 5.5 but not at pH 2.5 for bars labeled adenine. Isopropyl-β-d-thiogalactopyranoside (0.25 mM) was added when the cells containing plasmids were cultured. Symbols: open bars, W3110; gray bars, W3110 purA; black bars, W3110 purB; vertical striped bars, W3110 purA containing ppurA; horizontal striped bars, W3110 purB containing ppurB; gray dotted bars, W3110 purA with the addition of adenine; black dotted bars, W3110 purB with the addition of adenine. The average values and standard deviations obtained from three experiments using separate cultures are represented.

ATP content of purA and purB mutants at pH 5.5 and 2.5. The same strains as those used in Fig. 2 were cultured as described in the legend of Fig. 2. The cells were harvested at the indicated times at pH 2.5. The ATP contents were measured as described in Materials and Methods. Symbols are the same as those for Fig. 2. The average values and standard deviations obtained from three experiments using separate cultures are represented.

Survival of various mutants at pH 2.5. W3110, W3110 adk(ts), W3110 guaA, W3110 guaB, BW25113 nrdD, BW25113 nrdF, W3110 purC, W3110 purK, W3110 purL, W3110 recB, and TH1559 (recB, recC, and sbcB) were used. After the cells had been grown in EG medium at pH 7.5 until the OD₆₀₀ reached 0.3, the cells were harvested and suspended in EG medium at pH 5.5. After the cells had been grown for 4 h at pH 5.5, the cells were challenged at pH 2.5 for 1 h and the viable cells were counted. Adenine (0.1 mM) was added only to medium of pH 7.5 for the growth of the pur mutants. For the bars labeled 40°C, the cells were cultured at 30°C in medium at pH 7.5, adapted at 40°C in medium at pH 5.5, and challenged at 37°C in medium at pH 2.5. After the acidic challenge at pH 2.5, the cells were cultured on LB agar plates at 30°C. For the bars labeled 30°C, the cells were cultured at 30°C for all steps. The average values and standard deviations obtained from three experiments using separate cultures are represented.

ATP content of various mutants at pH 5.5 and 2.5. W3110, W3110 purA, W3110 purB, W3110 purL, W3110 purC, and W3110 purK were used. The cells were cultured as described in the legend to Fig. 4. They were harvested at the indicated times at pH 2.5. The ATP contents were measured as described in Materials and Methods. The average values and standard deviations obtained from three experiments using separate cultures are represented.