Osmotic stress regulation and the role of cyclic di-adenosine monophosphate (c-di-AMP) in Staphylococcus aureus

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The work described in this proposal aims to provide insight into how osmotic stress is regulated in Staphylococcus aureus and what role c-di-AMP plays in this process. S. aureus is an opportunistic pathogen that causes a variety of diseases such as bacteremia, toxic shock syndrome, endocarditis and sepsis. It is also a common food borne pathogen, which is in part mediated by its ability to withstand high external concentrations of salt, a technique often used for the preservation of food. So far, the mechanism(s) behind this osmotic stress resistance is only poorly understood and the ability to impede this process could help to prevent S. aureus food borne infections. In general, S. aureus reacts to osmotic upshock with the import of potassium ions and small organic molecules called compatible solutes to counteract the efflux of water. Current data indicate that the recently discovered second messenger cyclic di-adenosine monophosphate (c-di-AMP) is involved in this process, as several c-di-AMP receptor proteins in S. aureus regulate the expression or activity of potassium transport systems. In an as yet unpublished screen for additional c-di-AMP binding proteins, a novel c-di-AMP receptor protein, likely involved in the uptake of osmolytes, was discovered. This project therefore aims to functionally characterize this osmolyte transporter in depth, elucidate the regulatory role of c-di-AMP on its function and determine its physiological role in S. aureus. In order to gain a greater understanding of how S. aureus reacts to salt stress in general, a TN-seq based approach will be used to determine on a genome wide level which genes are essential in S. aureus under salt stress conditions and how c-di-AMP is involved in this process. Promising candidate genes will then be further validated and characterized. Together, these experiments will contribute to our understanding of how S. aureus adapts and survives in high salt environments and what role c-di-AMP plays in this context.