The influence of symbiont identity on the proteomic and metabolomic responses of the model cnidarian Aiptasia to thermal stress

We examined the effect of symbiont identity and heat stress on host metabolome and proteome in the cnidarian-dinoflagellate symbiosis. Exaiptasia diaphana (‘Aiptasia’) was inoculated with its native symbiont (Breviolum minutum) or a non-native symbiont (Symbiodinium microadriaticum; Durusdinium trenchii) and subjected to thermal stress. Host metabolomes were partially distinct at control temperature, however thermal stress caused profiles of anemones containing the two non-native symbionts to become more similar to each other and more distinct from those containing B. minutum. This may reflect symbiont densities; under control conditions, D. trenchii attained 60% and S. microadriaticum 15% of the density attained by B. minutum. At elevated temperature, only D. trenchii-colonised anemones experienced bleaching (60% loss). Combined metabolome and proteome analyses revealed the compounds that make up the thermal response of each symbiosis, either reflecting innate symbiont-specific differences or host-symbiont interactions. We show clear evidence of enhanced nutritional deprivation and cellular stress in hosts harbouring a novel symbiont following temperature stress, independent of the symbiont’s putative thermal resilience. Our findings highlight the physiological limits of partner switching as a means of adaptation to increased temperatures. However, we also offer preliminary evidence suggesting that metabolic functioning of the D. trenchii-Aiptasia association improves over the long-term.