P-369 - Phage-Mediated Modulation of the Phyllosphere Microbiome and its Role in Pathogen Control in Arabidopsis thaliana

Bacteriophages shape microbial communities in diverse ecosystems, yet their role in plant microbiomes remains largely unexplored. Here, we investigated how phages isolated from wild Arabidopsis thaliana populations influence a synthetic microbial community (SynCom) that protects against Pseudomonas viridiflava, a common foliar pathogen.In vitro assays revealed that lytic phage predation on Microbacterium proteolyticum, a key SynCom member, disrupted the community’s protective function, leading to increased P. viridiflava abundance. However, in planta experiments showed that despite stable P. viridiflava colony-forming unit (CFU) counts, plants exhibited fewer disease symptoms when phages were present. This mirrors observations in natural A. thaliana populations, where even significant host colonization does not necessarily lead to severe disease, suggesting that phage-microbe interactions may influence plant immunity or pathogen behaviour beyond direct microbial competition.Our findings highlight phages as overlooked regulators of plant microbiome function. By modulating microbial interactions, they may contribute to natural disease suppression. Understanding these dynamics could open new avenues for microbiome-based plant protection strategies.