Energy crosstalk between photosynthesis and the algal CO2-concentrating mechanisms

Microalgal photosynthesis is responsible for nearly half of the CO2 annually cap-tured by Earth's ecosystems. In aquatic environments where the CO2 availability is low, the CO2-fixing efficiency of microalgae greatly relies on mechanisms - called CO2-concentrating mechanisms (CCMs) - for concentrating CO2 at the catalytic site of the CO2-fixing enzyme ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco). While the transport of inorganic carbon (Ci) across mem-brane bilayers against a concentration gradient consumes part of the chemical energy generated by photosynthesis, the bioenergetics and cellular mechanisms involved are only beginning to be elucidated. Here, we review the current knowl-edge relating to the energy requirement of CCMs in the light of recent advances in photosynthesis regulatory mechanisms and the spatial organization of CCM components.