Metazoans were proposed to host bacteriophages on their mucosal surfaces in a symbiotic relationship, where phages provide an external immunity against bacterial infections and the metazoans provide phages a medium for interacting with bacteria. However, scarce empirical evidence and model systems have left the phage-mucus interaction poorly understood. Here, we show that phages bind both to porcine mucus and to rainbow trout (Oncorhynchus mykiss) primary mucus, persist up to 7 days in the mucosa, and provide protection against Flavobacterium columnare Also, exposure to mucus changes the bacterial phenotype by increasing bacterial virulence and susceptibility to phage infections. This trade-off in bacterial virulence reveals ecological benefit of maintaining phages in the metazoan mucosal surfaces. Tests using other phage-bacterium pairs suggest that phage binding to mucus may be widespread in the biosphere, indicating its importance for disease, ecology, and evolution. This phenomenon may have significant potential to be exploited in preventive phage therapy.IMPORTANCE The mucosal surfaces of animals are habitat for microbes, including viruses. Bacteriophages-viruses that infect bacteria-were shown to be able to bind to mucus. This may result in a symbiotic relationship in which phages find bacterial hosts to infect, protecting the mucus-producing animal from bacterial infections in the process. Here, we studied phage binding on mucus and the effect of mucin on phage-bacterium interactions. The significance of our research is in showing that phage adhesion to mucus results in preventive protection against bacterial infections, which will serve as basis for the development of prophylactic phage therapy approaches. Besides, we also reveal that exposure to mucus upregulates bacterial virulence and that this is exploited by phages for infection, adding one additional layer to the metazoan-bacterium-phage biological interactions and ecology. This phenomenon might be widespread in the biosphere and thus crucial for understanding mucosal diseases, their outcome and treatment.

中文翻译：

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噬菌体粘附在粘液上介导针对病原菌的预防性保护。

后生动物被认为以共生关系在其粘膜表面宿主噬菌体，其中噬菌体提供针对细菌感染的外部免疫力，而后生动物为噬菌体提供与细菌相互作用的介质。然而，经验证据和模型系统的缺乏使得人们对噬菌体-粘液相互作用知之甚少。在这里，我们发现噬菌体既能与猪粘液和虹鳟鱼 (Oncorhynchus mykiss) 初级粘液结合，又能在粘膜中持续长达 7 天，并提供针对黄杆菌柱的保护。此外，接触粘液会通过增加细菌毒力来改变细菌表型以及对噬菌体感染的易感性。细菌毒力的这种权衡揭示了在后生动物粘膜表面维持噬菌体的生态效益。使用其他噬菌体-细菌对进行的测试表明，噬菌体与粘液的结合可能在生物圈中广泛存在，这表明它对疾病、生态和进化的重要性。这种现象可能在预防性噬菌体治疗中具有巨大的潜力。 重要性 动物的粘膜表面是微生物（包括病毒）的栖息地。噬菌体——感染细菌的病毒——被证明能够与粘液结合。这可能会导致噬菌体找到细菌宿主进行感染的共生关系，从而在此过程中保护产生粘液的动物免受细菌感染。在这里，我们研究了噬菌体在粘液上的结合以及粘蛋白对噬菌体-细菌相互作用的影响。我们研究的意义在于表明噬菌体粘附在粘液上可以预防细菌感染，这将作为开发预防性噬菌体治疗方法的基础。此外，我们还发现，接触粘液会上调细菌毒力，噬菌体利用这一点进行感染，为后生动物-细菌-噬菌体的生物相互作用和生态学增加了一层。这种现象可能在生物圈中广泛存在，因此对于了解粘膜疾病、其结果和治疗至关重要。