Acid- and multistress-resistant mutants of Lactococcus lactis : identification of intracellular stress signals

Mol Microbiol. 2000 Feb;35(3):517-28. doi: 10.1046/j.1365-2958.2000.01711.x.


Lactococcus lactis growth is accompanied by lactic acid production, which results in acidification of the medium and arrest of cell multiplication. Despite growth limitation at low pH, there is evidence that lactococci do have inducible responses to an acid pH. In order to characterize the genes involved in acid tolerance responses, we selected acid-resistant insertional mutants of the L. lactis strain MG1363. Twenty-one independent characterized mutants were affected in 18 different loci, some of which are implicated in transport systems or base metabolism. None of these genes was identified previously as involved in lactococcal acid tolerance. The various phenotypes obtained by acid stress selection allowed us to define four classes of mutants, two of which comprise multistress-resistant strains. Our results reveal that L. lactis has several means of protecting itself against low pH, at least one of which results in multiple stress resistance. In particular, intracellular phosphate and guanine nucleotide pools, notably (p)ppGpp, are likely to act as signals that determine the level of lactococcal stress response induction. Our results provide a link between the physiological state of the cell and the level of stress tolerance and establish a role for the stringent response in acid stress response regulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / genetics
  • ATP-Binding Cassette Transporters / metabolism
  • Acids / pharmacology*
  • Adaptation, Physiological
  • DNA Transposable Elements
  • Drug Resistance, Microbial / genetics*
  • Escherichia coli Proteins*
  • Guanine Nucleotides / metabolism
  • Heat-Shock Response
  • Lactococcus lactis / drug effects
  • Lactococcus lactis / physiology*
  • Mutation*
  • Oxidative Stress
  • Periplasmic Binding Proteins*
  • Phosphate-Binding Proteins
  • Phosphates / metabolism
  • Purines / metabolism
  • Selection, Genetic
  • Sequence Homology, Nucleic Acid
  • Signal Transduction


  • ATP-Binding Cassette Transporters
  • Acids
  • DNA Transposable Elements
  • Escherichia coli Proteins
  • Guanine Nucleotides
  • Periplasmic Binding Proteins
  • Phosphate-Binding Proteins
  • Phosphates
  • PstS protein, E coli
  • Purines