EFFECT OF IRRADIANCE ON FATTY-ACID, CAROTENOID, TOTAL PROTEIN-COMPOSITION AND GROWTH OF MICROCYSTIS-AERUGINOSA

The cyanobacterium, Microcystis aeruginosa, was-grown under low, stand ard and high irradiance intensities (20, 40 and 70 mu mol m(-1) s(-1)) to determine whether irradiance affected pigment, lipid and protein c omposition, growth yields and the total dry weights of the cell cultur es. The components detected in the saponified lipid extracts included C-14 to C-20 fatty acids with various levels of saturation, odd chain- length fatty acids and long-chain alcohols. 16:0 was the main fatty ac id detected in all samples and its percentage abundance was significan tly higher in cells from the lower and standard irradiance intensities compared with the high irradiance cells. Conversely, the proportions of the 14:0, 15:0, 17:0, 18:0 and 20:0 fatty acids were higher in the high irradiance cells compared with the low and standard irradiance ce lls. Polyunsaturated fatty acid concentrations were reduced and those of monounsaturated fatty acids were increased in the high irradiance c ells compared with the low and standard irradiance cells. Chlorophyll a, zeaxanthin and beta-carotene were the most abundant pigments detect ed. Cells exposed to the standard irradiance treatment had substantial ly higher amounts of carotenoid, chlorophyll a and total protein after 15 days of growth compared with cells exposed to either the low or hi gh irradiance intensities. The ratios of the zeaxanthin, echinenone an d beta-carotene with respect to chlorophyll a from the high irradiance cells were approximately double those observed in the low and standar d irradiance regimes. It was concluded that the changes in the fatty a cid composition occurred as a cellular response to reduce the suscepti bility of the cyanobacterial membranes to photo-oxidation. Copyright ( C) 1997 Elsevier Science Ltd.