Exposure of Escherichia colito acid habituation conditions sensitizes it to alkaline stress

Abstract

Escherichia coli transferred from pHo 7.0 to pHo 5.5 or 6.0 became alkali-sensitive by a rapidly induced phenotypic response. Alkali sensitization was reduced at pHo 5.0 and virtually abolished at pHo 6.5. The response was triggered by cytoplasmic rather than external or periplasmic acidification and de novo protein synthesis was needed. Alkali sensitivity failed to appear at pHo 5.5 plus DNA gyrase inhibitors and was markedly reduced by himA, himD, hns, ompC and nhaA lesions. A tonB deletion mutant showed alkali sensitivity at pHo 7.0. Alkali sensitivity induction was not subject to catabolite repression nor was it appreciably affected by a relA lesion. Acid-induced cells were more sensitive to alkali damage to both DNA and beta-galactosidase and to alkali inhibition of beta-galactosidase induction. Alkali sensitization induced at pHo 5.5 may involve NhaB loss.

Habituation of Foodborne Pathogens Exposed to Extreme pH Conditions: Genetic Basis and Implications in Foods and Food Processing Environments

“…Alkali sensitization after exposure to acidic conditions is also thought to be an EIC-mediated process (Rowbury & Hussain, 1996). Cells of E. coli that were transferred from broth at pH 7.0 to broth at pH 5.5 and then challenged at pH 9.5 or 9.75 for 30 min survived in lower numbers than cells not exposed to pH 5.5 before exposure to alkaline pH.…”

“…Chloramphenicol inhibited the development of alkali sensitivity, indicating that protein synthesis is needed to generate alkali-sensitive ESC. There may also be a role for the sodium/hydrogen ion transporter protein, NhaA, because E. coli mutants not expressing NhaA have very little alkali sensitivity (Rowbury & Hussain, 1996). Alkali sensitivity of cells after exposure to acidic conditions may be unexpected because genes that express tolerance to both acidic and alkaline conditions are dependent upon the same sigma factor (Slonczewski & Foster, 1996).…”

The role of regulatory gene products in alkali sensitization by extracellular medium components in Escherichia coli

“…The bacterial strains used here were derivatives of Escherichia coli K12 and have been described previously by Rowbury and Hussain (1996). They were as follows: strain 1829 (trp, lac), strain 1829-Amp R1 (1829 hns), strain 1829-Kan R1 (1829 fur) and strain 1829-Tet R1 (1829 himA).…”

“…In addition, however, the levels of alkali tolerance of cultures are also influenced by prior growth at acidic pH. Over a narrow pH range (5·5-6·0), exposure to acidity rapidly leads to alkali sensitization, a process dependent on H-NS, IHF and Fur (Rowbury and Hussain 1996). The present study is on such alkali sensitization and it is reported here that extracellular components needed for sensitization, including a very heat-resistant protein, accumulate at pH 5·5; effects of lesions in himA, hns and fur on the formation of these components are described.…”

“…In both cases, incubation was for 60 min at pH 5·5. All cells being incubated for sensitization were then washed and alkali challenged at pH 9·75 for 30 min as described by Rowbury and Hussain (1996).…”