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 (pH(0)) 7.0 to pH(0 ) 7.0 broth plus glucose rapidly induced marked acid tolerance which a lso appeared, albeit to a lesser extent, plus maltose, sucrose or lact ose. Tolerance appeared without the medium pH becoming acidic. Toleran ce was most substantial when glucose was added at pH(0) 7.0 but was al so appreciable at pH(0) 7.5, 8.0 and 8.5. Induction of tolerance by gl ucose was markedly reduced by cyclic AMP and essentially abolished plu s NaCl or sucrose; the induction process was also reduced but not full y inhibited by chloramphenicol, tetracycline and nalidixic acid. Gluco se-induced organisms showed less acid damage to DNA and beta-galactosi dase and it is likely that this is because glucose induces a new pH ho meostatic mechanism which keeps internal pH close to neutrality at aci dic pH(0). In conclusion, it is clear that glucose induces a novel aci d tolerance response in log-phase E. coli at pH(0) 7.0; it is now know n that induction of this response involves the functioning of extracel lular induction components including an extracellular induction protei n.