Transport systems for carbonate in the extremely natronophilic cyanobacterium Euhalothece sp.

The effect of carbonate concentration, pH of the medium, and illumination intensity on the major physiological characteristics (growth rate and the intensities of CO₂ assimilation and oxygen photoproduction) of the natronophilic cyanobacterium Euhalothece sp. Z-M001 have been studied. It was established that the investigated microorganism has at least two transport systems (TS) for CO₂, which differ in both the pH optimum and substrate affinity: TS I has a pH_opt 9.4–9.5 and a K _{S 0.5} of 13–17 mM, whereas TS II has a pH_opt 9.9–10.2 and a K _{S 0.5} of 600–800 mM. The substrate affinity of these transport systems is several orders of magnitude lower than the substrate affinity of the transport systems of freshwater cyanobacteria. It is suggested that they are unique for extremely alkaliphilic cyanobacteria and reflect their adaptation to the seasonal cycles of the lake hydrochemistry.