From phagocytic predation to bacterial pathogenesis

Background and Working HypothesisOur laboratory studies the complex interaction between phagocytic cells and bacteria, using D. discoideum as a model phagocytic cell. Over the last four years we have mostly studied how bacteria are killed in phagosomes following their ingestion, using a combination of genetic and biochemical methods. We identified several bactericidal and bacteriolytic proteins and analyzed their mode of action. Our results demonstrate that different bacteria are killed by different mechanisms in D. discoideum phagosomes. Importantly, our ongoing studies were mostly focused on non-pathogenic bacteria, which do not actively resist phagocytosis and destruction. Specific aims and experimental designDuring the next four years, we will follow two main lines of research: (1) complete our ongoing studies of molecular mechanisms destroying bacteria in D. discoideum phagosomes. Ultimately this should culminate in a description of the main molecular mechanisms ensuring destruction of bacteria in phagosomes, and in an in vitro reconstitution of this process. (2) analyze the virulence mechanisms allowing pathogenic bacteria to escape killing by phagocytic cells. We want to identify the virulence mechanisms developed by bacteria to avoid phagocytosis and destruction, and to determine how these traits confer a pathogenic potential to opportunistic pathogens. We will study how these traits evolve during the transition of the bacteria from the environment to an infected patient. This part of our work will focus on three of the most medically important opportunistic pathogens: Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli. Expected valueOur work will generate the most complete and precise description available of bacterial destruction in phagosomes. We will use the knowledge and tools developed for this project to study the interaction of phagocytic cells with bacterial pathogens. This new porject will shed light on the emergence of opportunistic pathogenic bacteria in the environment and their transition to infected patients. Understanding the adaptive trajectory of opportunistic pathogens is essential to design appropriate therapeutic strategies.