Consequences of impaired microcystin production for light-dependent growthand pigmentation of Microcystis aeruginosa PCC 7806

Microcystis aeruginosa PCC 7806 produces potent inhibitors of eukaryotic pr otein phosphatases called microcystins, whose function to the organism is p resently unknown. Mutants with impaired microcystin biosynthesis should pro vide a useful tool for investigations of microcystin function. This study h as focused on the comparison of growth and pigment content of strain PCC 78 06 and its mcyB(-) mutant deficient in microcystin biosynthesis, under semi continuous culture conditions. Both wild-type and mutant are characterised by a very low light demand and low-maximum specific growth rates in compari son to other Microcystis strains studied. While growth of wild-type and mut ant were similar under different light conditions, the mutant cells showed significantly higher specific absorbances in the range of photosynthetic ac tive radiance 420-700 nm, under light-limiting conditions. The mutant cells possess lower contents of chlorophyll alpha, beta -carotene, zeaxanthin an d echinenone under light limitation and of myxoxanthophyll under saturated light conditions. Though microcystins are clearly not essential for growth, the observed effects of the mutation are a first indication of their invol vement in intracellular processes. (C) 2001 Federation of European Microbio logical Societies. Published by Elsevier Science B.V. All rights reserved.