Fluorescence Lifetime Imaging Microscopy (FLIM) reveals the diversity and complexities of an open ocean photosymbiosis

FLIM-FISH analysis of 92 photosymbionts across 71 open-ocean Retaria hosts shows photosymbiosis is far more complex than expected, with Brandtodinium nutricula in only 34% of hosts.

• Why it matters: Open-ocean Retaria strongly shape biogeochemical cycling through photosymbiosis, but the diversity of their algal photosymbionts is poorly resolved because these cells are hard to collect and analyze.
• What they did: The study combined FISH probes targeting common retarian photosymbiont lineages with FLIM, using fluorescence lifetime to separate chlorophyll autofluorescence from FISH probe signal in environmental plankton samples.
• The result: Retaria commonly contained multiple algal lineages per cell and also hosted algal lineages beyond the two most common ones, and FLIM is positioned as a way to distinguish chlorophyll autofluorescence from probe signal in such samples.

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