Acquisition of essential nutrient lysine by Staphylococcus aureus during invasive infection

About This Grant

PROJECT SUMMARY / ABSTRACT The bacterial pathogen Staphylococcus aureus (Sa) is a serious public health threat and a leading cause of highly morbid infections such as bacteremia, endocarditis, and osteomyelitis (OM). Although Sa encodes redundant nutrient synthesis and import pathways which give the pathogen metabolic flexibility, pressures encountered in host tissues can make certain pathways essential. Work from our laboratory aimed at discovering essential metabolic pathways that support invasive infection revealed that endogenous lysine (Lys) synthesis was dispensable during OM. Since Lys is an essential nutrient, this observation indicates that Sa must obtain Lys from the host environment to survive. However, the mechanisms of Sa Lys import and how Lys import supports survival and pathogenesis remain unknown. Defining the Lys importers used by Sa to sustain invasive infections such as OM could reveal potential targets for treatment of these debilitating diseases. This proposal aims to define Sa Lys importers, transcriptional regulators of Lys importers, and the in vivo significance of Lys acquisition to OM. I hypothesize that Sa encodes two Lys importers that are essential for bacterial survival during OM and are heterogeneously expressed in vivo due to the structure of Sa tissue lesions. Further, I hypothesize that specific transcriptional regulators facilitate adaptation to nutrient limitation and the host niche through regulation of Lys import and biosynthesis. Our preliminary data suggest that Sa encodes two Lys importers, LysP and PheP. Excitingly, we have already discovered that one of these, PheP, contributes to Sa survival during OM. In addition, a screen conducted with a toxic analog of Lys revealed multiple point mutations in codY which encodes a global regulator of metabolism and virulence. However, the role of CodY in regulating Lys metabolism is incompletely characterized. Aim 1 will use isotopic Lys and mass spectrometry to determine whether LysP and PheP import Lys. Furthermore, I will define how CodY and Lys availability regulate Lys import and synthesis, and I will discover additional regulators of Lys metabolism by leveraging a cell sorting and transposon sequencing-based screen called SorTn-seq. Aim 2 will determine the contribution of Lys importers and regulators of Lys import to OM in an established mouse model. Advanced microscopy and newly developed imaging mass spectrometry techniques will define the distribution of Lys (and other metabolites) in infected bone and reveal whether expression of Lys importers is spatially restricted in Sa tissue lesions, or abscesses. Collectively, this proposal will uncover mechanisms of nutrient acquisition by Sa and their respective contributions to disease, as well as spatial patterns of nutrient abundance and importer expression. The proposed experiments could unveil host-pathogen competition for important nutrients. Further, these data could reveal nutrient importers that are expressed in host tissues and critical for Sa survival, therefore constituting potential therapeutic targets.