S94: Discovery of Bioactive Small Molecules from the Human Pathogen Legionella pneumophila

Bacteria have evolved a complex secondary metabolism that serves to increase fitness in challenging environments through the production of bioactive metabolites. Bioactivity is often associated with requirements of specific environmental niches, as observed with insecticides from insect pathogens, and herbicides from plant pathogens. Recent studies indicate that human pathogens also use small molecules during infection, and that these compounds may be adapted for manipulating human systems. Among bacterial pathogens that manipulate host intracellular processes, Legionella pneumophila is perhaps the most adept, converting a hostile macrophage into a complacent food source within a few hours. Interestingly, genome inspection has revealed that Legionella possesses five biosynthetic gene clusters that may yield unique compounds evolved to affect host responses during infection. In this work we demonstrate that Legionella pneumophila can produce novel natural products that influence host biology. Initially, secondary metabolic gene clusters were identified through bioinformatics, and a series of biosynthetically deficient strains were generated. Infection studies using macrophage cell lines indicated that one gene cluster was involved in preventing phagosome-lysosome fusion, a crucial first step during intracellular infection. Comparative metabolomics studies were then conducted, and statistical data analysis software was used to detect a series of novel polyketide-derived secondary metabolites present in vanishing quantities. Our results demonstrate that human pathogens can produce novel small molecules to manipulate host cells during infection, and that these bacteria may be a valuable source of bioactive metabolites for use as probes of cell biology or for treating human diseases.