CHANGES IN THE LIPOPHILIC PHOTOSYNTHETIC PIGMENT CONTENTS OF DIFFERENT MICROCYSTIS-AERUGINOSA STRAINS IN RESPONSE TO GROWTH IRRADIANCE

In vivo absorption spectra and contents of lipophilic photosynthetic p igments were determined in three Microcystis aeruginosa strains, HUB 5 -2-4, HUB 5-3, and HUB 063 grown at different irradiances [between 12 and 150 mu mol(quantum) m(-2) s(-1)]. Besides chlorophyll (Chi) alpha, beta-carotene, echinenone, zeaxanthin, and nyxoxanthophyll, the strai ns HUB 063 and HUB 5-2-4 contained two additional carotenoids identifi ed as nostoxanthin and caloxanthin. A further carotenoid-glycoside, os cillaxanthin, could be detected only in high-irradiance grown cultures . All strains exhibited comparable pigment/Chl a ratios and similar in vivo absorption spectra measured cytophotometrically. With increasing irradiances, the cellular concentrations of Chi alpha, beta-carotene, and its hydroxylated derivatives decreased, whereas the echinenone co ntent remained constant. In contrast to that, the concentrations of th e carotenoid glycosides increased under higher irradiances.