Microalgae, tiny yet essential for the proper functioning of our climate, have just revealed a new secret.
A team of scientists led by BIAM (CEA/CNRS/Aix-Marseille University) has discovered that two key photosynthesis processes - the CO2 concentration mechanism and photorespiration - work hand in hand rather than in opposition as previously believed. This crucial discovery helps us better understand carbon fluxes related to climate change and could benefit the bioeconomy.
These microscopic photosynthetic organisms play a vital role in climate regulation by absorbing nearly half of the atmospheric carbon dioxide (CO₂) that enters ecosystems annually. Through photosynthesis, they fix CO₂ and convert it into biomass using light as an energy source. However, on geological timescales when CO₂ became scarcer, CO2 concentration mechanisms evolved in these organisms to limit photorespiration. Yet the precise mechanisms enabling this adaptation remained poorly understood until now.
Published in Nature Communications, a study challenges our understanding of the relationship between these two phenomena. Until now, it was assumed that microalgae concentrated CO₂ to optimize photosynthesis while "deactivating" photorespiration. However, a research team from CEA, in collaboration with the Max Planck Institute in Potsdam, Germany, and four other laboratories, has shown that these two supposedly opposing mechanisms actually cooperate, allowing microalgae to survive when CO2 becomes scarce or depleted.
A protein at the heart of the process
Researchers have identified a protein (LCI20) as central to this regulation. Present in the chloroplast envelope (a cellular organelle fundamental to photosynthesis), this protein facilitates the balance between the two metabolic pathways and enables algae to eliminate toxic byproducts from photorespiration. Without this protein, microalgae cannot adapt during a sudden transition to a very low CO₂ environment. Researchers observed a toxic accumulation of metabolites that inhibits growth, highlighting LCI20's importance in overall metabolic balance.
"This dialogue between photosynthesis and photorespiration demonstrates microalgae's remarkable ability to finely adapt to their environment. It's an acclimatization strategy far more complex than we imagined,"
explain Yonghua Li-Beisson and Gilles Peltier, co-authors of the discovery.
Implications for climate and bioeconomy
This research reshapes our understanding of the carbon cycle in oceans. Beyond environmental implications, these findings could benefit:
- The bioeconomy, by accounting for the CO₂/O₂ balance in bioreactors to improve biomass production yields or valuable compounds (biofuels, proteins, pharmaceutical molecules);
- Climate modeling, by better integrating microalgae's contribution to the global carbon cycle;
Next step? Explore this metabolic coexistence in other ecologically or industrially significant marine microalgae species to better understand their response to environmental fluctuations - a major challenge in our era of climate change.