Coexistence ecology of pathogen-inhibiting microbes in the phytobiome

Certain microbes have considerable potential as biocontrol agents against various pathogens, but they coexist with other microbial species in complex networks of interactions that influence their function in a host-dependent manner. These interactions and underlying mechanisms are still largely unknown. In this review we focus on Pseudomonas, a versatile genus of bacteria with adaptable physiological and metabolic traits, functioning as both symbionts and pathogens. We review the direct antagonism pathways Pseudomonas uses to inhibit different pathotypes and its role in indirectly inducing systemic defense responses in plants. We provide insights into bacterial coexistence and interactions in host plant–microbe and microbe–microbe relationships, considering pairwise and community dynamics. Understanding these interactions will help optimize synthetic communities and improve practices for sustainable agriculture.