Small unicellular marine organisms known as diatoms are responsible for nearly 20% of carbon dioxide fixation (CO₂) by photosynthesis on our planet. But how do these microalgae come to dominate the world of photosynthetic marine organisms ?  An international research collaboration involving the participation of the Laboratory of Genetics and Physiology of Microalgae of the University of Liege, has demonstrated a cellular mechanisms behind the impressive photosynthetic activity of diatoms. This research was the subject of a published article in the American journal Nature(1).

When we speak of photosynthesis, the first image that comes to mind is that of a leaf or a tree bathed in sunlight. This is normal because the traditional explanation given for photosynthesis is that of a plant whose leaves capture solar energy in order to synthesise organic matter from carbon dioxide (CO₂) while releasing oxygen (O₂). It is a little-known fact, however, that there is a very high level of photosynthetic activity in the oceans too. In fact, the oceans play a role equivalent to the continents by supplying 50% of photosynthetic production on a global scale! It is largely phytoplankton, all the photosynthetic organisms living in the pelagic zone of the oceans which do the bulk of the work.   

Despite the ecological importance of these marine organisms, the functioning of their photosynthetic activity has been less studied than that of terrestrial plants. This type of situation tends to change when international experts press the alarm bell. What will happen to the oxygen production supplied by the oceans in the case of rising temperatures? Will these organisms still be capable of fixing atmospheric carbon dioxide in the same way? What will be the impact of global warming on oceanic flora? Do the oceans run the risk of becoming acidic?

20% of world production

It was in the context of finding answers to these questions that the study took another direction, that of understanding the photosynthetic mechanisms of diatoms. Dominant among the wider phytoplankton community, diatoms alone account for 20% of world primary photosynthetic production.

“It should be noted that, in terms of carbon fixing capacity and biomass, generation, the production levels of diatoms are equivalent to the amounts produced by tropical forests ”, says Pierre Cardol, a researcher at the Laboratory of Genetics and Physiology of Microalgae, at the University of Liege”. And yet, few studies have been conducted regarding these essentially marine organisms that have become of major interest to researchers all over the world. In fact, diatoms are key organisms with regard to understanding marine ecosystems.  

Diatoms are a class of the most successful photosynthetic eukaryotes from an ecological point of view. They are yellow-brown unicellular organisms, essentially found in the sea. They are completely surrounded by an external skeleton in the form of a silica shell. Diatoms are autotrophic and use the energy from the light absorbed by the pigments of their chloroplast to carry out photosynthesis. Like most other microalgae, diatoms also possess an asexual method of reproduction. For more than 30 million years they have contributed to the moderation of the Earth’s climate by absorbing great quantities of CO2 present in the atmosphere.

(1) Benjamin Bailleul, Nicolas Berne, Omer Murik, Dimitris Petroutsos, Judit Prihoda, Atsuko Tanaka, Valeria Villanova, Richard Bligny, Serena Flori, Denis Falconet, Anja Krieger-Liszkay, Stefano Santabarbara, Fabrice Rappaport,  Pierre Joliot, Leila Tirichine, Paul G. Falkowski, Pierre Cardol, Chris Bowler & Giovanni Finazzi, Energetic coupling between plastids and mitochondria drives CO2 assimilation in diatoms,  Nature, Juilly 2015, DOI: 10.1038/nature14599