FIG. 1.

Percent survival of stationary-phase (16 h) E. coli during acid challenge. (A) ▪, DH1; ⋄, DH1/pJB3TA; ▴, DH1/pJB3TA grown with 12 μg tetracycline ml⁻¹; ⧫, DH1/pJB3TA grown with 36 μg tetracycline ml⁻¹. (B) Strain K-12/pJB3TA was used. Except for the control experiment (⋄), where no antibiotic selection was used, all experiments used cells that were cultured with 36 μg tetracycline ml⁻¹ during overnight growth. The acid challenge medium had been supplemented with the following compounds: ⋄ and ⧫, none; ▴, 5 mM KCl; ×, 50 mM KCl; •, 75 mM KCl; ▪, 85 mM sucrose; □, 400 mM sucrose.