N-3 POLYUNSATURATED FATTY-ACID PRODUCTIVITY OF THE MARINE MICROALGA ISOCHRYSIS-GALBANA - GROWTH-CONDITIONS AND PHENOTYPIC SELECTION

Two set of isolates were obtained in an isolation/selection programme to select eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA ) rich strains of Isochrysis galbana. EPA content was improved up to a n average of 5.3% (d.wt) for the second set of isolates. On the other hand, with the aeration rate, pH and irradiance kept at low levels, th e growth rate was slow and EPA synthesis was enhanced, but productivit y increased when growth rates were maximum. A model relating steady-st ate dilution rates in chemostat cultures of I. galbana to internal ave rage irradiance is proposed. The greatest productivities were obtained between 0.0295 h(-1) and 0.0355 h(-1) with 300 mg m(-3) h(-1) for EPA and 130 mg m(-3) h(-1) for DHA.