​In aquatic environments where CO₂ diffuses very slowly, algae have developed a mechanism that allows them to increase the intracellular concentration of CO₂ via an enzyme called RubisCO. Once concentrated, CO₂ can be efficiently "fixed" by RubisCO through biochemical reactions that transform the "inorganic" carbon of atmospheric CO₂ into "organic" carbon, in the form of "sugars".

Until recently, the energy source for CO₂ fixation was well known, namely the solar photons captured by photosynthesis, whereas the processes providing the energy necessary for the CO₂-concentrating mechanism (CCM) were still unexplained. Nonetheless, the actual accumulation of CO₂ can only occur if it is in its ionic (and hydrated) form, bicarbonate, which is then reconverted into CO₂ by RubisCO.

Researchers at Biam have now identified the processes involved in the production of the photosynthetic energy necessary for this conversion, using the green alga Chlamydomonas as a study model. Two electron transfer mechanisms combine to produce a proton gradient that participates in converting bicarbonate to CO₂, which is then fixed by Rubisco. This pathway provides sufficient energy to the CCM without compromising photosynthetic CO₂ fixation, which also consumes energy.

This research has uncovered a complex energy distribution network that plays an essential role in powering other components of the CCM, including bicarbonate transporters. Indeed, this discovery makes it possible to understand the fundamentals underlying efficient CO₂ capture by algae, in addition to paving the way for the functional application of CCM to crop plants in order to improve their productivity.