Symbiont-mediated defense of amoebae against Legionella pneumophila - molecular mechanisms and pathogen ecology

ended

Legionellae are opportunistic human pathogens infecting thousands of people annually in Europe. These bacteria are ubiquitous in many natural and man-made water systems, where they survive as free-living organisms in biofilms or intracellularly within a variety of protozoa. Free-living amoebae are the main route for spread and replication of legionellae in the environment, and infection of humans generally occurs via amoebae as vectors. Amoebae are frequently associated with bacterial endosymbionts, and recent data suggests that these symbionts interfere with replication of legionellae in amoebae thereby protecting the amoeba host from legionellae-induced lysis. The aim of this proposal is to further investigate this phenomenon of symbiont-mediated defense in protozoa, and to assess its implications for the ecology and transmission of legionellae. To shed light on the molecular and physiological interactions during infection of symbiont-containing amoebae with Legionella pneumophila, co-infection experiments will be performed and analyzed by state-of-the-art molecular methods including transcriptomics, proteomics and metabolomics, isotope profiling and chemical imaging techniques. Infection experiments will first be performed under controlled laboratory conditions to understand the interaction between amoeba, their bacterial symbionts and L. pneumophila, to analyse the molecular cross-talk, and to determine the mechanism of competition between the bacterial partners in this association. Subsequently, mesocosm experiments simulating environmental conditions will help to understand the impact of bacterial symbionts of amoebae on L. pneumophila spread and replication in the environment. Taken together, the comprehensive analysis of symbiont-mediated defense in amoebae will provide a new perspective on the ecology of L. pneumophila and lead to a better understanding of the role of amoebae and other microbes in water-borne disease outbreaks.