Exploring microbiome engineering as a strategy for improved thermal tolerance in Exaiptasia diaphana

AIMS: Fourteen percent of all living coral, equivalent to more than all the coral on the Great Barrier Reef, has died in the past decade as a result of climate change‐driven bleaching. Inspired by the ‘oxidative stress theory of coral bleaching’, we investigated whether a bacterial consortium designed to scavenge free radicals could integrate into the host microbiome and improve thermal tolerance of the coral model, Exaiptasia diaphana. METHODS AND RESULTS: E. diaphana anemones were inoculated with a consortium of high free radical scavenging (FRS) bacteria, a consortium of congeneric low FRS bacteria, or sterile seawater as a control, then exposed to elevated temperature. Increases in the relative abundance of Labrenzia during the first 2 weeks following the last inoculation provided evidence for temporary inoculum integration into the E. diaphana microbiome. Initial uptake of other consortium members was inconsistent, and these bacteria did not persist either in E. diaphana’s microbiome over time. Given their non‐integration into the host microbiome, the ability of the FRS consortium to mitigate thermal stress could not be assessed. Importantly, there were no physiological impacts (negative or positive) of the bacterial inoculations on the holobiont. CONCLUSIONS: The introduced bacteria were not maintained in the anemone microbiome over time, thus, their protective effect is unknown. Achieving long‐term integration of bacteria into cnidarian microbiomes remains a research priority. SIGNIFICANCE AND IMPACT OF THE STUDY: Microbiome engineering strategies to mitigate coral bleaching may assist coral reefs in their persistence until climate change has been curbed. This study provides insights that will inform microbiome manipulation approaches in coral bleaching mitigation research.