An extracellular sensor and an extracellular induction component are required for alkali induction of alkyl hydroperoxide tolerance in Escherichia coli

Escherichia coli K12 transferred from pH 7.0 to pH 9.0 gains alkylhydropero xide (AHP) tolerance. The aim here was to establish whether extracellular c omponents (ECs) are needed for such induction. Therefore, the effects of re moving ECs during incubation at pH 9.0 were tested and the abilities of cul ture filtrates to induce tolerance were examined. First, AHP tolerance did not appear, at pH 9.0, if cultures were subjected to continuous filtration or dialysis, against the same medium, suggesting that an EC might be needed . Second, neutralized filtrates from pH 9.0-grown cultures induced toleranc e at pH 7.0, and these filtrates were inactivated by dialysis, filtration o r heating but not by protease. Thus, pH 9.0 filtrates have a small non-prot ein extracellular induction component (EIC), which acts as an alarmone, 'wa rning' cells of stress and preparing them to resist it. Filtrates from pH 7 .0-grown cultures did not induce AHP tolerance at pH 7.0 but if incubated a t pH 9.0 without organisms, gained such ability. It is proposed that pH 7.0 filtrates have an EIC precursor (termed an extracellular sensing component , ESC), which senses alkaline pH, and is converted by it to the EIC. The ES C in pH 6.0 filtrates was distinct from that in pH 7.0 filtrates; there may be several oligomeric (or conformational) forms of this ESC. As the EIC is small, it can diffuse away from the alkalinized region and induce toleranc e in unstressed organisms.