Internal pH crisis, lysine decarboxylase and the acid tolerance response of Salmonella typhimurium

Mol Microbiol. 1996 May;20(3):605-11. doi: 10.1046/j.1365-2958.1996.5441070.x.


Salmonella typhimurium possesses an adaptive response to acid that increases survival during exposure to extremely low pH values. The acid tolerance response (ATR) includes both log-phase and stationary-phase systems. The log-phase ATR appears to require two components for maximum acid tolerance, namely an inducible pH homeostasis system, and a series of acid-shock proteins. We have discovered one of what appears to be a series of inducible exigency pH homeostasis systems that contribute to acid tolerance in extreme acid environments. The low pH-inducible lysine decarboxylase was shown to contribute significantly to pH homeostasis in environments as low as pH 3.0. Under the conditions tested, both lysine decarboxylase and sigma s-dependent acid-shock proteins were required for acid tolerance but only lysine decarboxylase contributed to pH homeostasis. The cadBA operon encoding lysine decarboxylase and a lysine/cadaverine antiporter were cloned from S. typhimurium and were found to be 79% homologous to the cadBA operon from Escherichia coli. The results suggest that S. typhimurium has a variety of means of fulfilling the pH homeostasis requirement of the ATR in the form of inducible amino acid decarboxylases.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acids
  • Base Sequence
  • Carboxy-Lyases / genetics
  • Carboxy-Lyases / metabolism*
  • Cloning, Molecular
  • DNA, Bacterial
  • Homeostasis
  • Hydrogen-Ion Concentration*
  • Molecular Sequence Data
  • Molecular Structure
  • Operon
  • Salmonella typhimurium / enzymology
  • Salmonella typhimurium / physiology*
  • Sequence Analysis, DNA


  • Acids
  • DNA, Bacterial
  • Carboxy-Lyases
  • lysine decarboxylase

Associated data

  • GENBANK/U37109