From shallow tropical seas to deep-sea vents, nutrients from symbiotic microbes allow their invertebrate hosts to dominate oligotrophic environments. Reef-building corals, as sterol auxotrophs, depend on sterols from photosynthetic dinoflagellate symbionts, yet this process is poorly understood.
We characterized sterols and their transfer machinery using lipidomics, phylogenetics, gene expression, and biochemistry in coral and the model anemone Aiptasia. We found both symbiont- and host-driven patterns of sterol transfer, mediated by atypical Niemann-Pick-Type-C2 (NPC2) proteins. Our data suggest that transfer of a unique symbiont-produced sterol mix to the host via an acid-tolerant sterol-harvesting machinery is key to symbiosis.
Future perspectives include using lipidomics, single-cell transcriptomics, and functional experimentation to understand the evolutionary conservation of lipid transfer and other key symbiosis mechanisms more broadly among photosymbiotic marine invertebrates.