Analysis of the Patho-Metabolism of Legionella pneumophila during Intracellular Replication

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The replication of pathogenic bacteria inside the human host is a crucial event for the establishment of an infection. Despite the uniqueness of each host-microbe interaction, even phylogenetically distant bacteria developed comparable strategies to enter and to escape the host cell. However, the replication niche within host cells is quite different for major human pathogens. Whereas for example Legionella, Salmonella and Mycobacterium reside in specialized vacuoles, Francisella, Listeria and Shigella have chosen the cytosol as their replicative niche. As a consequence, intracellular bacteria have to adapt their metabolism to the available nutrients and physical conditions encountered in the respective environments. Specifically, vesicular bacteria have to cope with low pH, free-radicals, nutrient deprivation and antimicrobial compounds, whereas the cytosol seems to be a more permissive milieu. Only recently, there is emerging evidence that intracellular bacteria use multiple substrates to efficiently exploit the nutrient supply from the different and changing environments of their host cells. There is also increasing evidence that the bacterial invaders thereby trigger a major re-organization of the host cell's metabolism, especially in non-cancer primary cells. Consequently, the interactions between pathogens and hosts are highly dynamic resulting in variable nutrient and metabolic pathway usages of both organisms during the infection. This delicate metabolic interplay between host and pathogen was recently termed as patho-metabolism. Although crucial for the successful replication of intracellular bacteria, patho-metabolism is a quite unexplored and unexploited feature of bacterial infections. This also holds true for the specific topic of this proposal, namely the metabolic relationship between Legionella pneumophila (Lp) and its host cells. In order to elucidate the patho-metabolism of intracellular Lp, the metabolic compositions, pathways and fluxes of Lp and its host cells, e.g. macrophages, shall be studied for the first time by an integrative approach based on 13C-isotopologue profiling, GC-MS- and NMR-based metabolomics, whole-cell FT-IR, and growth/fitness characterization of the strains under study. On the basis of this comprehensive approach, essential metabolic patterns and reactions during the infection shall be identified as potential future targets for antimicrobial drug development. Highlighting the relevance of the general topic of this proposal, basic research on the prevention and control of bacterial infections and resistance was among the major goals of the latest G7 Summit in 2015.