Properties of an L-glutamate-induced acid tolerance response which involves the functioning of extracellular induction components


Professor R.J. Rowbury, Department of Biology, University College London, Gower Street, London WC1E 6BT, UK.


Escherichia coli became more acid tolerant following incubation for 60 min in a medium containing l-glutamate at pH 7·0, 7·5 or 8·5. Several agents, including cAMP, NaCl, sucrose, SDS and DOC, prevented tolerance appearing if present with l-glutamate. Lesions in cysB, hns, fur, himA and relA, which frequently affect pH responses, failed to prevent l-glutamate-induced acid tolerance but a lesion in l-glutamate decarboxylase abolished the response. Induction of acid tolerance by l-glutamate was associated with the accumulation in the growth medium of a protein (or proteins) which was able to convert pH 7·0-grown cultures to acid tolerance, and the original l-glutamate-induced tolerance response was dependent on this component(s). Acid tolerance was also induced by l-aspartate at pH 7·0 and induction of such tolerance was dependent on an extracellular protein (or proteins). The l-glutamate and l-aspartate acid tolerance induction processes are further examples of a number of stress tolerance responses which differ from most inductions in that extracellular components, including extracellular sensors, are required.