Raja, Nazar Ullah; (1992) Inducible acid resistance in Escherichia coli. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The acid sensitivity of Escherichia coli K-12 strains was studied. The introduction of ColV, I-K94 into the cells, made them more sensitive to acid and hydrogen peroxide treatments than cells without ColV plasmids. The organisms tended to habituate when they were grown at pH 5.0, a sub-optimal value, and showed resistance when exposed to acid and whereas the non-habituated cells, which were grown at the optimal pH of 7.0, were significantly more sensitive to acid conditions. Habituation induced the synthesis of some proteins, which conferred on the cells resistance against acid treatments, and these were either synthesised in lower amounts in non-habituated cells or not at all, at 37 °C, when studied by one dimensional and two dimensional SDS polyacrylamide gel electrophoresis. Some stress-related proteins which induced at 37 °C and 44 °C were formed in very small amounts or not at all at 24 °C growth temperature. Autoradiographic studies showed that the induction of stress-related proteins occurred within 5 min of an acid shift from pH 7.0 to pH 4.3. Addition of 10 mM phosphate buffer in NB of pH 4.3 inhibited induction of habituation in P678-54 but not in P678-54 omp A. One probable site of acid injury was DNA. It was shown that for habituated organisms the DNA was less damaged and repaired better, after acid treatments, compared with non-habituated cells when examined through transformation experiments using biological activity of p BR 322 as a transformation index. The probable biochemical basis of DNA repair was studied using mutants altered in uvr A, rec A and pol A.

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