Glucose-induced acid tolerance appearing at neutral pH in log-phase Escherichia coli and its reversal by cyclic AMP.

Escherichia coli shifted from broth at external pH (pH0) 7.0 to pH0 7.0 broth plus glucose rapidly induced marked acid tolerance which also appeared, albeit to a lesser extent, plus maltose, sucrose or lactose. Tolerance appeared without the medium pH becoming acidic. Tolerance was most substantial when glucose was added at pH0 7.0 but was also appreciable at pH0 7.5, 8.0 and 8.5. Induction of tolerance by glucose was markedly reduced by cyclic AMP and essentially abolished plus NaCl or sucrose; the induction process was also reduced but not fully inhibited by chloramphenicol, tetracycline and nalidixic acid. Glucose-induced organisms showed less acid damage to DNA and beta-galactosidase and it is likely that this is because glucose induces a new pH homeostatic mechanism which keeps internal pH close to neutrality at acidic pH0. In conclusion, it is clear that glucose induces a novel acid tolerance response in log-phase E. coli at pH0 7.0; it is now known that induction of this response involves the functioning of extracellular induction components including an extracellular induction protein.