REDUCTION IN OMEGA-3-FATTY-ACIDS BY UV-B IRRADIATION IN MICROALGAE

UV-B irradiation reduced the levels of omega-3 fatty acid, eicosapentaenoic acid (EPA, 20:5omega3) and docosahexaenoic acid (DHA, 22:6omega3), in microalgae; the degree of reduction varied with species. Chaetoceros calcitrans and Skeletonema costatum were high UV-B tolerant species, followed by Phaeodactylum tricornutum, Chroomonas salina, Pavlova lutheri, and Thalassiosira pseudonana. Isochrysis galbana (T.ISO) and Prorocentrum micans were UV- B sensitive. Cells in logarithmic phase were most sensitive to UV- B irradiation. Nitrate-, phosphate-, or sulphate-starved cells were more UV-B sensitive than non-starved cells grown in a complete basal medium. A relatively short exposure to high UV-B was more damaging than a longer exposure to lower irradiance. Visible light intensity levels had a profound impact on the sensitivity of microalgal cultures to UV-B, with high levels decreasing UV-B dependent damage. Addition of polyamines (putrescine, spermidine or spermine) or an amino acid (cysteine) to the culture medium minimized the reduction of omega-3 fatty acid content in microalgae caused by UV-B irradiation.