Optimization of culture medium for the continuous cultivation of the microalga Haematococcus pluvialis

The freshwater microalga Haematococcus pluvialis is one of the best microbi al sources of the carotenoid astaxanthin. but this microalga shows low grow th rates and low final cell densities when cultured with traditional media. A single-variable optimization strategy was applied to 18 components of th e culture media in order to maximize the productivity of vegetative cells o f H. pluvialis in semicontinuous culture. The steady-state cell density obt ained with the optimized culture medium at a daily volume exchange of 20% w as 3.77 . 10(5) cells ml(-1), three times higher than the cell density obta ined with Bold basal medium and with the initial formulation. The formulati on of the optimal Haematococcus medium (OHM) is (in g l(-1)) KNO3 0.41, Na2 HPO4 0.03, MgSO4 . 7H(2)O 0.246, CaCl2 . 2H(2)O 0.11, (in mg l(-1)) Fe(III) citrate . H2O 2.62, CoCl2 . 6H(2)O 0.011, CuSO4 . 5H(2)O 0.012, Cr2O3 0.075 , MnCl2 . 4H(2)O 0.98, Na2MoO4 . 2H(2)O 0.12, SeO2 0.005 and (in yg l(-1)) biotin 25, thiamine 17.5 and B-12 15. Vanadium, iodine, boron and zinc were demonstrated to be non-essential for the growth of H. pluvialis. Higher st eady-state cell densities were obtained by a three-fold increase of all nut rient concentrations but a high nitrate concentration remained in the cultu re medium under such conditions. The high cell productivities obtained with the new optimized medium can serve as a basis for the development of a two -stage technology for the production of astaxanthin from H. pluvialis.