Characterization and functional investigations of a Staphylococcus aureus mutant which is deficient in both hemin biosynthesis and the global redox sensing regulator (rex)

  • Gunnar Sander, Institute of Medical Microbiology, University Hospital of Muenster, Germany
  • Simon Strompen, Institute of Medical Microbiology, University Hospital of Muenster, Germany
  • Karsten Becker, Institute of Medical Microbiology, University Hospital of Muenster, Germany
  • Andreas Fischer, Institute of Medical Microbiology, University Hospital of Muenster, Germany
  • Jochen Seggewiß, Institute of Medical Microbiology, University Hospital of Muenster, Germany
  • Georg Peters, Institute of Medical Microbiology, University Hospital of Muenster, Germany
  • Richard Proctor, Department of Medical Microbiology and Immunology, University of Wisconsin, School of Medicine and Public Health, Madison, United States
  • Christof von Eiff, Institute of Medical Microbiology, University Hospital of Muenster, Germany

    • The formation of small-colony variants (SCVs), a naturally occurring, slow-growing subpopulation, seems to be a strategy of Staphylococcus aureus to survive intracellularly in non-professional phagocytes. Interruption of the hemin biosynthesis of S. aureus by insertion of an ermB cassette into hemB, led to a stable hemin-auxotrophic SCV showing phenotypic features of clinical SCVs as well as anaerobically grown organisms. The operators of many genes involved in catabolism and virulence include a putative binding sequence for a regulator called Rex. This regulator is predicted to respond to oxygen limitation. To characterize the metabolic network of SCVs and to examine whether Rex is responsible for some SCV features, a rex- as well as a rex hemB double mutant were constructed. The double mutant revealed the same slow growth and reduced susceptibility to aminoglycosides as described for the hemB mutant. Using Western Blot analyses and semi-quantitative RT-PCRs, both the Rex mutant and the double mutant in contrast to the parental strain were shown to produce no message for toxins (staphylococcal enterotoxin A, alpha-toxin), no RNAIII and no SrrA (a response regulator controlling fermentation and virulence factors). Three investigated promoters (epiG, isaB, and srrA) were under direct control of Rex. The results of this study indicate that Rex might play a role in regulating virulence- and regulator genes in response to oxygen limitation and it might be in part responsible for certain biochemical and physiological characteristics observed in SCVs.