Pathogen priming reveals host immune training and microbiome conditioning in corals

Abstract

In several species, vaccine-like approaches, where hosts are primed through controlled pathogen exposure, have proven effective in enhancing responses to subsequent infections. This principle remains unexplored in corals. Here, we demonstrate that chronic exposure to non-lethal concentrations of live or inactivated Vibrio coralliilyticus primes the coral holobiont to counter subsequent infections under heat stress. Non-primed corals experienced greater heat stress pathogen-driven bleaching and a significant decline in their photosynthetic efficiency compared to primed samples. These results were linked to microbiome conditioning and the host gene expression modulation, including a layered, fine-tuned immune and cellular response to microbial invasion. This proof-of-concept challenges the view that coral immune responses are strictly innate, fixed, and positions immune priming and microbiome conditioning as integrated mechanisms of coral holobiont resilience. Together, these findings can contribute to redefining coral immunity concepts and lay the groundwork for developing new microbiome-based strategies to enhance coral health for reef conservation under climate change.