Dissolved inorganic carbon uptake by Rhodomonas sp. and Isochrysis aff. galbana determined by a potentiometric technique

Dissolved inorganic carbon uptake (DIC) was determined in batch culture of the marine microalgae Rhodomonas sp. and Isochrysis aff. galbana (Clone T-ISO) for seven days using a simple potentiometric technique. The system used allowed the determination of small variations of the three independent parameters: pH, dissolved inorganic carbon and total alkalinity (At). The aerated cultures began with 13 μmol kg−1 of CO2 (calculated using Ct-pH), but after the third day, the concentration was almost zero. Cultures of Rhodomonas sp. continued growing in the absence of CO2 with a total DIC depletion of 1330.5 μmol kg−1 and a final pH of ∼10. Since HCO3− is the predominant form of inorganic carbon at alkaline pH, Rhodomonas sp. shows potential for direct HCO3− uptake. On the other hand, the cultures of I. aff. galbana only removed DIC during the first three days while CO2 was available, and also when the pH from culture was below 9. Nutrients (PO43−, NO3−, NO2− and NH4+) uptakes were also analyzed for the two cultures. The nutrient uptake in both microalgae did not show dependency on any specific DIC form. An extra addition of CO2 during cultivation is recommended for enhanced growth mainly in I. galbana.