THE INFLUENCE OF IRRADIANCE ON THE BIOCHEMICAL-COMPOSITION OF THE PRYMNESIOPHYTE ISOCHRYSIS SP (CLONE T-ISO)

The effect of irradiance on the biochemical composition of the prymnesiophyte microalga, Isochrysis sp. (Parke; clone T-ISO) a popular species for mariculture, were examined. Cultures were grown under a 12:12 h light:dark (L:D) regime at five irradiances ranging from 50 to 1000 mu E.m(-2).s(-1) and harvested at late-logarithmic phase for analysis of biochemical composition. Gross composition varied over the range of irradiances. The highest levels of protein were present in cells from cultures grown at 100 and 250 mu E.m(-2).s(-1), and minimum levels of carbohydrate and lipid occurred at 50 mu E.m(-2).s(-1). Because the cell dry weight was reduced at lower irradiances, different trends were evident when results were expressed as percentage of dry weights. Protein percentages were highest at 50 and 100 mu E.m(-2).s(-1) and carbohydrate at 100 mu E.m(-2).s(-1) The composition of amino acids did not differ over the range of irradiances. Glutamate and aspartate were always present in high proportions (9.0-13.5%) histidine, methionine, tryptophan, cystine, and hydroxy-proline were minor constituents (0.0-2.6%). Glucose was the predominant sugar in all cultures, ranging from 23.0% (50 mu E.m(-2).s(-1)) to 45.0% (100 mu E.m(-2).s(-1)) of total polysaccharide. No correlation was found between the proportion of any of the sugars and irradiance. The proportions of the lipid class components and fatty acids showed little change with irradiance. The main fatty acids were 14:0, 16:0, 16:1(n-7), 18:1(n-9), 18:3(n-3), 18:4(n-3), 18:5(n-3), and 22:6(n-3). Proportions of 22:6(n-3) increased, whereas 18:3(n-3), 18:3(n-6), and 18:4(n-3) decreased, with increasing irradiance. Pigment concentrations were highest in cultures grown at 50 mu E.m(-2).s(-1), except for fucoxanthin and diadinoxanthin (100 mu E.m(-2).s(-1)). The concentrations of accessory pigments correlated with chlorophyll a, which decreased in concentration with increasing irradiance.