Bacterial inoculation elicits changes to the coral epigenome

Environmental shifts can cause epigenetic modifications in corals, which are associated with changes in 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 show that pathogen exposure led to distinct DNA methylation changes compared to the control, probiotic, and co-inoculation groups. We also demonstrate that DNA methylation correlates with coral gene expression and highlight genes altered by pathogen inoculation that showed similar responses in their expression and methylation. Notably, the coral probiotic was able to mitigate specific epigenetic changes, which correlated with increased stress resilience and higher coral survival rates. Thus, bacterial-induced changes to the coral epigenome may instigate long-term changes in host resilience.