Abstract Increasing occurrences of mass heat-induced coral bleaching around the globe have propelled research effort into enhancing coral resilience. Yet, significant progress in this space is hampered by an incomplete understanding of the inter-cellular processes sustaining the delicate, animal-algal symbiosis that underlie coral health. To elucidate links between changes in the symbiotic algal physiology and bleaching, we measured metabolic fingerprints of 1500 endosymbiotic algal cells from four coral species exposed to control and heat-stress conditions. We detected four co-occurring endosymbiont metabolomes based on spectral features, finding strong parallels across species. Clear temporal shifts in the dominance of each metabolome helped link metabolic profiles to cellular physiological states within the coral colony endosymbiotic landscape. We found two profiles common to healthy endosymbionts and two profiles reflective of physiological stress. In the absence of heat-stress, the most prevalent metabolic profiles were differentiated by high protein, high nucleic acid content and low carbon (lipid and/or carbohydrate) content. Whereas during late-stage bleaching, the dominant metabolic profiles exhibited comparatively low protein, but high carbon content. This work has uncovered the existence of endosymbiont metabolic sub-populations within coral colonies and shown their dynamic yet predictable reproportioning during heat stress conditions across different coral species. In identifying a physiological cascade of single-cell metabolomes in response to heat stress, this research highlights promising metabolic markers for detecting the onset of heat stress and dysbiosis within individual endosymbiotic coral cells.
Nielsen et al. (Sat,) studied this question.