Bacterial inoculation manipulates the coral epigenome

Environmental shifts can elicit epigenetic modifications in corals, which regulate gene expression and physiology, though it remains unclear if associated bacteria can also induce such changes. Here, we inoculated nubbins of the coral Pocillopora verrucosa with an opportunistic pathogen, Vibrio coralliilyticus , and/or a coral probiotic, Cobetia sp., and subjected the nubbins to heat stress. We discovered that the epigenomes responded already after 19 days to heat stress and 28 days to bacterial inoculation. Pathogen stress led to DNA methylation changes not seen in other treatments. Notably, the coral probiotic was able to mitigate specific epigenetic changes in a glutamate receptor pathway, and this correlated with increased stress resilience and higher survival rates of the corals. Importantly, epigenetic marks persisted even after the temperature stress was removed, suggesting epigenome acclimation. Thus, bacterial-induced changes to the coral epigenome may instigate long-term changes in host resilience.