Trophic modulation of endophytes by rhizosphere protists.

The plant-microbe interactions, which is crucial for plant health and productivity, mainly occur in rhizosphere: a narrow zone of soil surrounding roots of living plants. The rhizosphere hosts one of the most intense habitats for microbial prey-predator interactions, especially between predatory protists and bacteria. Here, based on two key facts, microbial predators modulate rhizobacterial community composition, and the rhizobacterial community is the primary source of root microbiome, endophytes; we hypothesized that predation upon rhizobacteria would modulate the community composition of endophytic bacteria. The effects of three taxonomically distinct axenic protist species (Acanthamoeba castellanii, Vermamoeba vermiformis, and Heteromita globosa) were tested in this study. To examine the robustness of the hypotheses, the experiments were conducted in three soil types characterized by distinct bacterial communities and physicochemical properties. The bacterial community compositions were analyzed with high throughput sequencing. Bacterial gene abundances were estimated with a real-time-PCR method. The results showed that protists modulated endophytic communities, which originated in the rhizosphere soil. The modulation of endophytic communities by protists showed chaotic patterns rather than a deterministic effect under different soil types. The observed chaotic dynamics were further confirmed with an additional experiment, in which chaos was triggered by changes in the dilution rates of soil nutrients. Furthermore, the presence of predators enhanced the root colonization of endophytes. Our findings identify a key mechanism for the modulation of root endophytes and enhance understanding of underground plant-microbe interactions, which can lead to open new avenues for modulating the root microbiome to enhance crop production.