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 prymnes iophyte microalga, Isochrysis sp. (Parke; clone T-ISO) a popular speci es 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 m u E.m(-2).s(-1) and harvested at late-logarithmic phase for analysis o f 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 ce ll dry weight was reduced at lower irradiances, different trends were evident when results were expressed as percentage of dry weights. Prot ein percentages were highest at 50 and 100 mu E.m(-2).s(-1) and carboh ydrate 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 alw ays present in high proportions (9.0-13.5%) histidine, methionine, try ptophan, 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 pol ysaccharide. No correlation was found between the proportion of any of the sugars and irradiance. The proportions of the lipid class compone nts and fatty acids showed little change with irradiance. The main fat ty 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 irradia nce. 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 chlo rophyll a, which decreased in concentration with increasing irradiance .