Phylogenetic position and expanded host range of the photosymbiont Brandtodinium nutricula (Peridiniales, Dinophyceae)

Brandtodinium nutricula is common as a free-living photosymbiont throughout the sunlit ocean in Tara Oceans metabarcode data, and its phylogeny links it to Blastodinium.

• Why it matters: The open-ocean radiolarian symbiosis with Collodaria is widespread, yet B. nutricula’s free-living presence and unclear phylogenetic placement leave its true host range unresolved.
• What they did: Using taxon-rich 18S rRNA gene phylogenetics, the study found a close association between B. nutricula and the copepod parasite lineage Blastodinium, then analyzed Tara Oceans metabarcodes for abundance and read-depth correlations.
• The result: B. nutricula was common in free-living form and did not significantly correlate with Collodaria read depth; fluorescence lifetime imaging microscopy plus fluorescence in situ hybridization also showed symbiosis within planktonic Foraminifera.