Symbiont photosynthesis supplies carbohydrates whereas osmotrophy provides osmolytes in Collodaria photosymbiotic association

ABSTRACT:

Collodaria (Radiolaria) are widespread marine planktonic protists that host photosynthetic microalgal symbionts. Within this photosymbiosis, they can contribute substantially to primary production, particularly in oligotrophic ocean regions. Despite their ecological importance, the mechanisms underlying the formation and maintenance of the photosymbiosis are poorly understood. To uncover the metabolic dependencies within this photosymbiotic system, we developed a stable isotope labeling strategy that allows us to investigate the assimilation and exchange of inorganic and organic carbon within the Collodaria holobiont. By integrating metabolomic profiling with isotopic labeling analyses, we demonstrate that algal photosynthesis makes a substantial contribution to the holobiont carbohydrate pool. In particular, we observed the incorporation of inorganic carbon into glucose and fructose, followed by the enrichment of other metabolites including ribose. In contrast, osmotrophic uptake of labeled algal lysate did not lead to the incorporation of any of these carbohydrates, suggesting no significant contribution of osmotrophy to the holobiont's carbohydrate pool. In contrast, specialized metabolites, such as dimethylsulfoniopropionate (DMSP) and betaines, were primarily acquired through osmotrophy implying a minor contribution of photosymbionts. Our findings thus reveal defined roles of phototrophic and osmotrophic metabolism for the formation of distinct metabolites in the Collodaria holobiont with consequences for our understanding of element fluxes in the plankton. 

INSTRUMENT(S): Liquid Chromatography MS - positive - hilic, Gas Chromatography MS - positive, Gas Chromatography MS -

PROVIDER: MTBLS12592 | MetaboLights | 2026-05-26

REPOSITORIES: MetaboLights