Carbon concentration mechanisms in photosynthetic microorganisms

Unicellular green algae and cyanobacteria have mechanism to actively concen trate dissolved inorganic carbon into the cells, only if they are grown wit h air levels of CO2. The carbon concentration mechanisms are commonly known as "CCM" or "DIC-pumps". The DIG-pumps are environmental adaptation that f unction to actively transport and accumulate inorganic carbon (HCO3 - and C O2; C-i) within the cell and then uses this C-i pool to actively increase t he concentration of CO2 at the site of ribulose bisphosphate carboxylase-ox ygenase (Rubisco), the primary CO2-fixing enzyme. The current working model for dissolved inorganic carbon concentration mechanism in unicellular gree n algae includes several isoforms of carbonic anhydrase (CA), and ATPase dr iven active transporters at the plasmalemma and at the inner chloroplast en velopes. In the past fifteen years, significant progress has been made in i solating and characterizing the various isoforms of carbonic anhydrase at t he biochemical and molecular level. However, we have an inadequate understa nding of active transporters that are located on the plasmalemma and at the chloroplast envelopes. In this mini-review we focus on certain aspects of the induction, function and significance of the dissolved inorganic carbon concentration mechanisms in aquatic photosynthetic microorganisms.