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Nicole Smits

Tuesday 6 December 2011

A Closer Look at the Transcriptome of Staphylococcus aureus

Promotor: Prof.dr Jos A.G. van Strijp
Defence: 10 January 2012

Tight regulation of genes upon changing environments is important in establishing and maintaining infections by pathogens. In Staphylococcus aureus, gene expression and particularly controlled expression of various groups of genes dependent on growth and environmental conditions is essential for survival of the pathogen. Accordingly, differential regulation of unlinked genes encoding virulence proteins, toxins and adhesins is accomplished by global regulators, like two-component systems (of which 16 are present in the genome), quorum-sensing systems, DNA-binding proteins, and the recently identified sRNAs. Also features like operon structures and untranslated regions on the 5’- and/or 3’-ends play an important role in gene regulation. This thesis describes the interaction between S. aureus and its host and in particular the pathogens’ gene responses upon interaction with the host. A better comprehension of regulation in this important human pathogen will aid in understanding its capacity to cause such diverse infections and identifying potential new targets for antimicrobial agents.
Colonization is the first step in infection. S. aureus is able to effectively colonize the human nose.. We verified the vestibulum nasi as niche and additionally identified bacteria in outer and inner parts of hair follicles, which might be an important lead to the differences in decolonization and carriership. Next, we determined important aspects in gene regulation. With the use of highly reproducible standard laboratory growth curves, we were able to accurately predict the operon structure of S. aureus. Operons play a major role in regulation of metabolic pathways. Moreover, regulation within an operon was confirmed for two innate immune evasion proteins, Efb and SCIN-B, showing the importance of operons. Small RNAs have been identified as regulators of many genes, including virulence genes, in various pathogens. In S. aureus, sRNAs were predicted and functionally characterized. An sRNA possibly regulating delta toxin, able to lyse many cells, was identified and examined further. Lastly, the altered gene expression upon exposure to human blood and IMDM both at 5% CO2 was examined. Especially the genes encoding Staphylococcal superantigen-like proteins showed a strong up-regulation in human blood, while no differential regulation was observed in IMDM with 5% CO2. Moreover, we have demonstrated that variances in gene expression between genetically similar strains can occur.
In conclusion, the exact niche of S. aureus in the human nose was determined, different regulatory elements in S. aureus depicted and the difference in gene regulation upon exposure to human blood and IMDM both at 5% CO2 was analyzed. This thesis only describes small steps in understanding gene regulation of virulence genes and regulatory elements in S. aureus. Much more research has to be done to fully understand the world of the S. aureus transcriptome.