Abstract：
Free-living nematodes harbor and disseminate various soil-borne bacterial pathogens. Whether they function as vectors or environmental reservoirs for the aquatic L. pneumophila, 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 L. pneumophila in cooling towers. Consequently, the nematode species Plectus similis and L. pneumophila were isolated from the same cooling tower biofilm and taken into a monoxenic culture. Using pharyngeal pumping assays, potential feeding relationships between P. similis and different L. pneumophila strains and mutants were examined and compared with Plectus sp., a species isolated from a L. pneumophila-positive thermal source biofilm. The assays showed that bacterial suspensions and supernatants of the L. pneumophila cooling tower isolate KV02 decreased pumping rate and feeding activity in nematodes. However, assays investigating the hypothesized negative impact of Legionella\'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, Acanthamoebae castellanii infected with L. pneumphila KV02 were offered to nematodes. The pumping rates of P. similis increased when fed with L. pneumophila-infected A. castellanii, while Plectus sp. pumping rates were similar when fed either infected or non-infected A. castellanii. This study revealed that cooling towers are the main water bodies where L. pneumophila and free-living nematodes coexist and is the first step in elucidating the trophic links between coexisting taxa from that habitat. Investigating the Legionella-nematode-amoebae interactions underlined the importance of amoebae as reservoirs and transmission vehicles of the pathogen for nematode predators.
摘要：
自由生活的线虫藏有并传播各种土壤传播的细菌病原体。无论它们是作为水生嗜肺乳杆菌的载体还是环境水库，军团病的病原体，是未知的。对德国自然（游泳湖泊）和技术（冷却塔）水栖息地的生物膜进行的调查筛选显示，线虫可以充当潜在的水库，冷却塔中嗜肺乳杆菌的载体或食草。因此,从同一冷却塔生物膜中分离出线虫物种Plectussimilis和嗜肺乳杆菌，并将其带入单氧培养物中。使用咽泵检测，检查了P.similis与不同的嗜肺乳杆菌菌株和突变体之间的潜在摄食关系，并将其与Plectussp。,从嗜肺乳杆菌阳性热源生物膜中分离出的物种。分析结果表明，嗜肺乳杆菌冷却塔分离物KV02的细菌悬浮液和上清液降低了线虫的泵送速率和摄食活性。然而,研究军团菌主要分泌蛋白ProA对抽水速率的假设负面影响的试验揭示了对线虫的相反影响，这指向物种对ProA的特定反应。为了将食物链延伸到进一步的营养级，向线虫提供了感染肺炎链球菌KV02的castellanii。饲喂嗜肺乳杆菌感染的卡氏A.castellanii时，P.similis的泵送率增加，而Plectussp.饲喂感染或未感染的A.castellanii时，抽水率相似。这项研究表明，冷却塔是肺炎杆菌和自由生活线虫共存的主要水体，是阐明该栖息地共存分类群之间营养联系的第一步。调查军团菌-线虫-变形虫的相互作用强调了变形虫作为线虫捕食者病原体的水库和传播媒介的重要性。
