and Free-Living Nematodes: Environmental Co-Occurrence and Trophic Link.

Free-living nematodes harbor and disseminate various soil-borne bacterial pathogens. Whether they function as vectors or environmental reservoirs for the aquatic , the causative agent of Legionnaires' disease, is unknown. A survey screening of biofilms of natural (swimming lakes) and technical (cooling towers) water habitats in Germany revealed that nematodes can act as potential reservoirs, vectors or grazers of in cooling towers. Consequently, the nematode species and were isolated from the same cooling tower biofilm and taken into a monoxenic culture. Using pharyngeal pumping assays, potential feeding relationships between and different strains and mutants were examined and compared with sp., a species isolated from a -positive thermal source biofilm. The assays showed that bacterial suspensions and supernatants of the cooling tower isolate KV02 decreased pumping rate and feeding activity in nematodes. However, assays investigating the hypothesized negative impact of 's major secretory protein ProA on pumping rate revealed opposite effects on nematodes, which points to a species-specific response to ProA. To extend the food chain by a further trophic level, infected with KV02 were offered to nematodes. The pumping rates of increased when fed with -infected , while sp. pumping rates were similar when fed either infected or non-infected This study revealed that cooling towers are the main water bodies where and free-living nematodes coexist and is the first step in elucidating the trophic links between coexisting taxa from that habitat. Investigating the -nematode-amoebae interactions underlined the importance of amoebae as reservoirs and transmission vehicles of the pathogen for nematode predators.