Mark J.J.B. Sibbald and Jan Maarten van Dijl

Contact: Drs. M.J.J.B. Sibbald

Laboratory of Molecular Bacteriology

Department of Medical Microbiology

University Medical Center Groningen (UMCG)

Hanzeplein 1 Building 3217 "de Brug", room 2.036

P.O. Box 30 001

9700 RB Groningen, the Netherlands

Tel. +31-50-3610429

Fax. +31-50-3619105

Email: m.j.j.b.sibbald@med.umcg.nl

S. aureus is a part of the normal human flora and is present in 30-40% of the population in moist environments (e.g. the nose). However, it can turn into a dangerous pathogen, thereby capable of infecting almost every tissue and organ in the human body. Although most staphylococcal infections are nosocomial (i.e. hospital-acquired), an increase in the number of cases of community-acquired antibiotic (methicillin) resistant infections is currently observed world-wide. The pathogenicity of S. aureus is caused by the expression of an arsenal of virulence factors. The virulence factors that S. aureus employs to cause these diseases are displayed at the surface of the staphylococcal cell or secreted into the host milieu. Specifically, these virulence factors include (a) surface proteins that promote adhesion to and colonization of host tissues; (b) invasins that are exported to an extracytoplasmic location and promote bacterial spread in tissues (leukocidin, kinases, hyaluronidase); (c) surface molecules that inhibit phagocytic engulfment (capsule, Protein A); (d) molecules that enhance staphylococcal survival in phagocytes (carotenoids, catalase); (e) molecules for immunological disguises (Protein A, coagulase, clotting factor); (f) membrane-damaging toxins that disrupt eukaryotic cell membranes (hemolysins, leukotoxin); (g) superantigens that contribute to the symptoms of septic shock  (SEA-G, TSST, ET); and (h) determinants for inherent and acquired resistance to antimicrobial agents.

            Although the process of protein transport has been extensively described for various bacteria, such as Escherichia coli and Bacillus subtilis (Tjalsma et al., 2000, 2004), relatively little is known about the process of transport of extracellular proteins, like virulence factors, across the membrane in S. aureus. Therefore, our studies are aimed at mapping the secretome of S. aureus. By definition, the secretome includes both the machinery for protein export from the cytoplasm and the exported proteins. Our first approach was to predict the protein transport machinery as well as the secreted and cell wall-associated proteins using genome data from twelve sequenced strains of S. aureus. The results indicate that S. aureus has the potential to export 137-156 proteins with signal peptides, which are either retained at the membrane/cell wall or are released into the medium (Sibbald et al., 2006; unpublished results). To study the transport systems in S. aureus, knock-out mutants have been created in S. aureus for several components of the Sec pathway, as well as for some components of other transport pathways present in S. aureus. 2D-gelelectrophoresis and MALDITOFF analyses showed that some of these components are important for the transport of several secreted proteins. These mutants will be characterized further by analyzing growth curves, Scanning Electron Microscopy, antibiotic resistance (antibiogram) and essays for binding of S. aureus to biomaterials. Students will be involved in our ongoing research on the S. aureus secretome and its roles in virulence.

References:

- Sibbald, M. J., Ziebandt, A. K., Engelmann, S., Hecker, M., de Jong, A., Harmsen, H. J., Raangs, G. C., Stokroos, I., Arends, J. P., Dubois, J. Y., and van Dijl, J. M. (2006). Mapping the pathways to staphylococcal pathogenesis by comparative secretomics. Microbiol Mol Biol Rev 70, 755-788.

- Tjalsma, H., A. Bolhuis, J. D. Jongbloed, S. Bron, and J. M. van Dijl. 2000. Signal peptide-dependent protein transport in Bacillus subtilis: a genome-based survey of the secretome. Microbiol. Mol. Biol. Rev. 64:515-547.

- Tjalsma, H., H. Antelmann, J. D. Jongbloed, P. G. Braun, E. Darmon, R. Dorenbos, J. Y. Dubois, H. Westers, G. Zanen, W. J. Quax, O. P. Kuipers, S. Bron, M. Hecker, and J. M. van Dijl. 2004. Proteomics of protein secretion by Bacillus subtilis: separating the "secrets" of the secretome. Microbiol. Mol. Biol. Rev. 68:207-233.