TOXIN PRODUCTION BY MICROCYSTIS-AERUGINOSA AS A FUNCTION OF LIGHT IN CONTINUOUS CULTURES AND ITS ECOLOGICAL SIGNIFICANCE

The effects of light intensity and light quality on toxin production by Microcystis aeruginosa were examined in continuous cultures. Light intensity had a pronounced effect on toxicity and the toxin production rate. Toxicity and the toxin production rate increased with light intensity up to an intensity of about 40 microeinsteins m-2 s-1 and decreased at higher light intensities, while the ratio of toxin to protein was constant at intensities of more than 40 microeinsteins m-2 s-1. Light quality had only slight effects on toxicity. The results of our laboratory experiments were supported by the results of field work in which we examined toxin production at different depths in a lake. Our observations explain the mixed pattern of high and low toxicity found in a surface bloom of M. aeruginosa. Our findings also indicate that production of the peptide toxin can be uncoupled from general protein synthesis.