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 art ificial illumination at low (1 mu M) and high (31 mu M) iron concentra tions over a 9 h period. With sunlight and low iron, cellular caroteno id and chlorophyll a concentrations decreased linearly with time, and membrane polyunsaturated fatty acids were reduced after 9 h. With sunl ight and high iron, there was near-complete loss of all pigments and r educed concentrations of all major fatty acids within 3 h, presumably due to photooxidation; almost all phytol, poly- and monounsaturated fa tty acids were absent after 9 h exposure in the high iron medium, indi cating 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 irra diance can influence the composition of cyanobacterial membranes durin g natural surface blooms. The subsequent survival and regeneration of cyanobacterial cells may be affected under the high iron concentration s which can occur in Australian inland lakes and rivers.