Menaquinone biosynthesis potentiates haem toxicity in Staphylococcus aureus

Mol Microbiol. 2012 Dec;86(6):1376-92. doi: 10.1111/mmi.12063. Epub 2012 Oct 24.


Staphylococcus aureus is a pathogen that infects multiple anatomical sites leading to a diverse array of diseases. Although vertebrates can restrict the growth of invading pathogens by sequestering iron within haem, S. aureus surmounts this challenge by employing high-affinity haem uptake systems. However, the presence of excess haem is highly toxic, necessitating tight regulation of haem levels. To overcome haem stress, S. aureus expresses the detoxification system HrtAB. In this work, a transposon screen was performed in the background of a haem-susceptible, HrtAB-deficient S. aureus strain to identify the substrate transported by this putative pump and the source of haem toxicity. While a recent report indicates that HrtAB exports haem itself, the haem-resistant mutants uncovered by the transposon selection enabled us to elucidate the cellular factors contributing to haem toxicity. All mutants identified in this screen inactivated the menaquinone (MK) biosynthesis pathway. Deletion of the final steps of this pathway revealed that quinone molecules localizing to the cell membrane potentiate haem-associated superoxide production and subsequent oxidative damage. These data suggest a model in which membrane-associated haem and quinone molecules form a redox cycle that continuously generates semiquinones and reduced haem, both of which react with atmospheric oxygen to produce superoxide.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / deficiency
  • Biosynthetic Pathways / genetics
  • DNA Transposable Elements
  • Gene Deletion
  • Heme / toxicity*
  • Mutagenesis, Insertional
  • Oxidative Stress
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics
  • Staphylococcus aureus / growth & development
  • Staphylococcus aureus / metabolism*
  • Superoxides / metabolism
  • Vitamin K 2 / metabolism*


  • DNA Transposable Elements
  • Vitamin K 2
  • Superoxides
  • Heme
  • Adenosine Triphosphatases
  • HrtA protein, Staphylococcus aureus