FIG. 2.
Genetic dissection of AR. Various mutants of E. coli K-12 were tested for the three AR systems. The test for the oxidative system (open bars) involved overnight growth in LB-MES (pH 5.5) followed by dilution to 1 × 106 to 3 × 106 CFU per ml in EG (pH 2.5). Survival (viable counts) was measured after 2 h at 37°C. The glutamate (shaded bars) and arginine (hatched bars) systems required overnight LBG (glutamate system) or BHIG (arginine system) cultures, which were diluted to 1 × 106 to 3 × 106 CFU/ml in EG (pH 2.5) containing 1.5 mM glutamate and 0.6 mM arginine, respectively. Percent survival is calculated as the number of CFU per milliliter remaining after the acid treatment divided by the initial CFU per milliliter at time zero. Initial cell densities ranged from 1 × 106 to 3 × 106 CFU/ml. Experiments were repeated two or three times. Variations were within 50% of the stated value.