Free-living nematodes as vectors and reservoirs for Legionella pneumophila

• Applicants: Professorin Dr. Liliane Rueß; Professor Dr. Michael Steinert
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Microbial Ecology and Applied Microbiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440169731

Several virulence mechanisms of Legionella pneumophila, the causative agent of Legionnaires´ disease, exhibit a high specificity for the infection of human lung tissue. These mechanisms, which seem to be mainly relevant in a multicellular context, cannot be deduced easily from the environmental Legionella-protozoa relationship. Recently, we demonstrated that several nematode taxa, which were isolated from a thermal spring and a cooling tower, harbored L. pneumophila. These observations, taken together with infection studies in the model organism Caenorhabditis elegans, and the evidence that soil-living nematodes can act as vectors for other human pathogens, suggest that taxa from aquatic habitats may also serve as environmental reservoirs or vectors for L. pneumophila. In a follow up comprehensive field sampling campaign across natural (23 swimming lakes) and technical (1 shower, 7 cooling towers) habitats, we identified cooling towers as major environmental water bodies, where Legionella and nematodes co-occur. The respective dominant L. pneumophila strains and nematode taxa (e.g. Acrobeloides sp., Diploscapter sp., Monhystrella sp., Plectus sp.) were isolated and cultured. The proposed project will now determine the mechanisms behind the L. pneumophila-nematode interactions, for the first time taking into account free-living nematode taxa occurring in vivo with Legionella. As initial step the impact of L. pneumophila on the potential vectors/reservoir hosts is assigned, i.e. bacterial growth as well as nematode´s life cycle, biomass and food choice. Besides dominant free-living taxa from the cooling towers, C. elegans and L. pneumophila Corby are employed as “baseline models”. Next, the bacterial transport by nematodes is investigated by ingestion, colonization and shedding assays with L. pneumophila Corby mutants differing in host adherence. Another focus is on the carbon flow between L. pneumophila and nematodes. Herewith, the main question, what determines the outcome in the biotic interaction, is addressed: Is the nematode feeding on Legionella or is Legionella using nematodes as resource? Fatty acids are used as marker to disentangle transport from feeding, and the metabolic carbon fluxes are quantified by stable isotope (13C) profiling. Finally, nematode grazing and vector function is modelled under semi-natural conditions with nematode-cured biofilms inoculated with mCherry-labeled L. pneumophila. This working program offers a deep insight into the persistence, dissemination and metazoan pathogenicity of L. pneumophila. It will pave the way for improved hygienic refurbishment works in technical water systems.

• DFG Programme: Research Grants