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Article Dans Une Revue Current Biology - CB Année : 2019

Algal Remodeling in a Ubiquitous Planktonic Photosymbiosis

Benoit Gallet
Sergio Balzano
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Josselin Lupette
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Juliette Jouhet
Eric Maréchal
Rémi Tucoulou
Giovanni Finazzi

Résumé

Photosymbiosis between single-celled hosts and microalgae is common in oceanic plankton, especially in oligotrophic surface waters. However, the functioning of this ecologically important cell-cell interaction and the subcellular mechanisms allowing the host to accommodate and benefit from its microalgae remain enigmatic. Here, using a combination of quantitative single-cell structural and chemical imaging techniques (FIB-SEM, nanoSIMS, Synchrotron X-ray fluorescence), we show that the structural organization, physiology, and trophic status of the algal symbionts (the haptophyte Phaeocystis) significantly change within their acantharian hosts compared to their free-living phase in culture. In symbiosis, algal cell division is blocked, photosynthesis is enhanced, and cell volume is increased by up to 10-fold with a higher number of plastids (from 2 to up to 30) and thylakoid membranes. The multiplication of plastids can lead to a 38-fold increase of the total plastid volume in a cell. Subcellular mapping of nutrients (nitrogen and phosphorous) and their stoichiometric ratios shows that symbiotic algae are impoverished in phosphorous and suggests a higher investment in energy-acquisition machinery rather than in growth. Nanoscale imaging also showed that the host supplies a substantial amount of trace metals (e.g., iron and cobalt), which are stored in algal vacuoles at high concentrations (up to 660 ppm). Sulfur mapping reveals a high concentration in algal vacuoles that may be a source of antioxidant molecules. Overall, this study unveils an unprecedented morphological and metabolic transformation of microalgae following their integration into a host, and it suggests that this widespread symbiosis is a farming strategy wherein the host engulfs and exploits microalgae.
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hal-02083159 , version 1 (23-11-2020)

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Johan Decelle, Hryhoriy Stryhanyuk, Benoit Gallet, Giulia Veronesi, Matthias Schmidt, et al.. Algal Remodeling in a Ubiquitous Planktonic Photosymbiosis. Current Biology - CB, 2019, 29 (6), pp.968-978.e4. ⟨10.1016/j.cub.2019.01.073⟩. ⟨hal-02083159⟩
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