LIGHT CAUSES SELECTION AMONG 2 PHYCOERYTHRIN-RICH SYNECHOCOCCUS ISOLATES FROM LAKE CONSTANCE

The phycoerythrin (PE)-rich unicellular cyanobacteria Synechococcus sp p. strains BO 8808 and BO 9203, from the pelagic zone of Lake Constanc e, exhibited different responses when cultured under low light and lig ht stress conditions. Under light stress caused by continuous illumina tion at elevated light intensity, strain BO 8808 ceased growth, the PE /chlorophyll ratio was slowly reduced and the zeaxanthin content was s ignificantly decreased. By contrast, strain BO 9203 grew faster under high light compared to low light intensities. This strain responded to increased light by a rapid reduction of the PE/chlorophyll ratio whil e the zeaxanthin content remained constant. Both of these alterations may have protecting effects for BO 9203 against light toxicity. In mix tures of both strains, the predominance of the light-tolerant strain B O 9203 was demonstrated by restriction fragment length polymorphism of psbA genes under light stress conditions. Apparently, strain BO 9203, isolated from an algal bloom in the spring, can core better with high light intensities than strain BO 8808, isolated in the autumn. (C) 19 98 Federation of European Microbiological Societies. Published by Else vier Science B.V.