In general, cyanobacteria prefer alkaline conditions, and during a bloom, the pH may rise to more
than 9. Under these conditions, most of the inorganic carbon is in the form of carbonate and is unavailable
to many eukaryotic algae. Cyanobacteria have excellent inorganic carbon concentrating mechanisms,
with separate membrane transport systems for CO2 and for bicarbonate (HCO3). Once inside the cell, the carbon is largely present as bicarbonate, and the enzyme carbonic anhydrase catalyzes its dissociation into CO2, the substrate for ribulose 1,5-bisphosphate carboxylase/oxygenase.