Effects of high irradiance and iron concentration on pigment and fatty acid composition in the cyanobacterium Microcystis aeruginosa

Microcystis aeruginosa Kuetzing emend. was exposed to sunlight and artificial illumination at low (1 µM) and high (31 µM) iron concentrations over a 9 h period. With sunlight and low iron, cellular carotenoid and chlorophyll a concentrations decreased linearly with time, and membrane polyunsaturated fatty acids were reduced after 9 h. With sunlight and high iron, there was near-complete loss of all pigments and reduced concentrations of all major fatty acids within 3 h, presumably due to photooxidation; almost all phytol, poly- and monounsaturated fatty acids were absent after 9 h exposure in the high iron medium, indicating total destruction of membranes by iron-enhanced photooxidation. Although caution is required in extrapolating results from laboratory grown cultures to field populations, it is conceivable that high irradiance can influence the composition of cyanobacterial membranes during natural surface blooms. The subsequent survival and regeneration of cyanobacterial cells may be affected under the high iron concentrations which can occur in Australian inland lakes and rivers.