Effects of salinity on cell growth and docosahexaenoic acid content of the heterotrophic marine microalga Crypthecodinium cohnii

Abstract

The effects of salinity on cell growth and docosahexaenoic acid (DHA) content of three marine microalgal strains, Crythecodinium cohnii ATCC 30556, C. cohnii ATCC 50051 and C. cohnii RJH were investigated. The lag phases of the three strains increased with increasing salinity in Porphyridium medium. The specific growth rate of C. cohnii ATCC 30556 was the highest at 9 g L-1 NaCl while the other two strains had their highest specific growth rates at 5g L-1 NaCl. The highest cell dry weight concentrations of 2.51 g L-1 and 1.56 g L-1 were achieved at 9 g L- 1 NaCl for C. cohnii ATCC 30556 and ATCC 50051, respectively, while the highest dry weight concentration of 2.49 g l-1 was achieved at 5 g L-1 NaCl for C. cohnii RJH. The highest cell growth yield coefficient on glucose was 0.5 g g-1 for both C. cohnii ATCC 30556 and C. cohnii RJH and 0.45 g g-1 for C. cohnii ATCC 50051. All three strains responded to the change of salinity by modifying their cellular fatty acid compositions. At 9 g L-1 NaCl, C. cohnii ATCC 30556 had the highest total fatty acid content and DHA (C22:6) proportion. In contrast, C. cohnii ATCC 50051 and C. cohnii RJH had the highest DHA content at 5 g L-1 NaCl. C. cohnii ATCC 30556 and ATCC 50051 had the highest DHA yield (131.55 and 68.24 mg L-1 respectively) at 9 g L-1 NaCl while C. cohnii RJH had the highest DHA yield (128.83 mg L-1) at 5 g L-1 NaCl.