A Novel Method to Bioaccumulate Calcium in Spirulina

To improve the calcium content of Spirulina and develop a new kind of calcium rich Spirulina, a novel bioaccumulation method, bioaccumulation in photoheterotrophic cultures, was developed to bioaccumulate calcium in Spirulina. To elucidate the mechanism of calcium bioaccumulation of Spirulina maxima in heterotrophic condition, growth and calcium contents of S.maxima in the two photoheterotrophic cultures without NaHCO₃ were measured. In the glucose culture, the best growth of S.maxima was found in the glucose concentration of 0.5g/L where the calcium content was about 5 times as high as that in photoautotrophic culture (Zarrouk). In the sodium glycerol phosphate (SGP) culture, the growth was lower than that in Zarrouk culture, but the calcium content was about 17 times higher than that of Zarrouk culture. When adding O.Olg/L CaCL₂ to the two photoheterotrophic cultures, the microorganism grew badly, but their calcium contents were about 7 and 10 times as high as those that did not add CaCl₂. Evaluation based on the Langmuire equation showed that the higher calcium contents of S.maxima in the two photoheterotrophic cultures were due to the higher binding affinities between S. maxima cells and Ca²⁺.