| Summary: | Predation is a major mode of interaction in natural environments, and predators have an important impact on prey evolution, community composition and food web complexity. Bacterivorous protists are key components of aquatic and terrestrial environments, as well as major drivers of bacterial diversity and community composition. When grazing on prokaryotes, protists impact interand intraspecific interactions, biomass production and biogeochemical flows. Furthermore, the prey’s ability to develop physiological and morphological defence mechanisms affects both bacterial diversity and predatory eukaryotes’ grazing ability, survival and distribution. While theoretical work usually analyses simple to partially complex predator-prey systems, practical studies focus are often limited to one prey and one predator species. Using a variety of ecologically and physiologically diverse bacterivorous protists, this study identifies the relationship between predator-prey interactions and its impact on species diversity. While bacterial communities are closely linked to their environment characteristics, protist diversity and distribution was shown to be dependent on both biotic and abiotic factors, and community composition differences driven by few major lineages. Similarly, bacterial communities submitted to varied protist predators were distinguished only by a handful of major lineages. In parallel, protist impact on bacterial diversity was highly modulated by prey community taxonomical composition and ecological strategies. Indeed, in this study, bacteria observed genotypic changes in line with short-term phenotypic plasticity resulting on the development of defence mechanisms against predators of distinct ecological niches. Predator-prey interactions in the light of diversity are far more complex than what closed microcosm experiments can translate, but they encompass valuable information applicable to natural systems.
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