Manipulation of the biochemical composition of the eicosapentaenoic acid-rich microalga Isochrysis galbana in semicontinuous cultures
1997
Otero, A. | Garcia, D. | Morales, Ed | Aran, J. | Fabregas, J.
The marine microalga Isochrysis galbana was cultured semicontinuously with two nutrient concentrations [2 and 4 mmol of nitrogen (N)/litre] and five rates of daily renewal of culture medium (from 10 to 50%) in order to optimize the productivity of the valuable polyunsaturated fatty acids eicosapentaenoic acid (EPA, C20:5.n-3) and docosahexaenoic acid (DHA, C22:6,n-3). The N conversion rate and chlorophyll content indicated that a nutrient concentration of 2 mmol of N.l-1 was limiting, except for a renewal rate of 50%, while cultures maintained with 4 mmol of N.l-1 were nutrient-limited only up to a renewal rate of 20%. Carbohydrates, but not lipids, were stored by I. galbana under nutrient deficiency, but the composition of the fatty acid fraction was strongly affected by culture conditions. The degree of unsaturation of fatty acids increased with increasing renewal rate, mainly at the expense of C16:0 and C16:1 fatty acids, which decreased under the same conditions. EPA increased from 9% of total fatty acids with 2 mmol of N.l-1 and a renewal rate of 10% to values around 25% of total fatty acids achieved in nutrient saturated cultures for both nutrient concentrations. On the other hand, the percentage of DHA was not strongly affected by either renewal rate or nutrient concentration, which was reflected in very little variation in the productivity, which remained in the range 0.9-1.3 mg.day-1.l-1. Owing to the decrease of cell density with increasing renewal rates, maximal EPA productivity, 4.6 mg.day-1.l-1, was achieved with 4 mmol of N.l-1 and intermediate renewal rates.
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