Extracellular proteins and other components as obligate intermediates in the induction of a range of acid tolerance and sensitisation responses in Escherichia coli.

Several acid tolerance responses of Escherichia coli were associated with secretion into the growth media of components (frequently proteins) which altered acid tolerance of other cultures. First, medium filtrates from cultures induced to acid tolerance by several conditions converted pH 7.0-grown organism to tolerance and, for most such responses, filtrate proteins were needed for full induction. Secondly, filtrates from cultures induced to acid sensitivity at alkaline pH produced sensitisation of resistant cultures. Thirdly, filtrates from inherently tolerant or sensitive strains altered tolerance or sensitivity of normal strains. In many cases, filtrate components were essential for the original response, e.g. acid habituation at pH 5.0. Extracellular components may function as intermediates only in stress tolerance responses, but other adaptive responses must be tested as such components may function in other inducible processes.