Recent advances in CO2uptake and fixation mechanism of cyanobacteria and microalgae

Aquatic photosynthetic microorganisms, cyanobacteria and microalgae, account for almost half of the world's photosynthesis. They absorb carbon di oxide (CO2) as the major substrate to support photosynthesis, the beginning of energy flow into living organisms and one of the primary processes comprising the global carbon cycle. Among all photosynthetic mechanisms, inorganic carbon transport into ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is one of the major limiting steps in photosynthetic carbon fixation which involves active transport of HCO3−, CO2 and/or H+, or an energized biochemical mechanism. In fact, a unique system "carbon concentrating mechanism (CCM)" manages the inorganic carbon assimilation, accumulation of CO2 around RuBisCO, and utilization in algal cells. However, the information on mechanism of CO2 uptake and fixation inside the algal cells is limited. In order to make strategies for enhancement of CO2 fixation, understanding of CCM is crucial. Thus, this review provides an overview of advances in CCM research, the comparative state of the art and reports on the CO2 uptake model in cyanobacteria and microalgae. The review also discusses the challenges and future perspectives associated with algal CCM research.