Persistence and genetic diversity among strains of phycoerythrinrich cyanobacteria from the picoplankton of Lake Constance

Twelve strains of phycoerythrin (PE)-rich unicellular cyanobacteriaof the Synechococcus type were isolated from the pelagial ofLake Constance in different phases during the growth periodof the year 1994. By analysing the restriction fragment lengthpolymorphism (RFLP) of the DNA three new genotypes were distinguished.The persistence of one strain during the course of the yearwas demonstrated. The data set was compared with the RFLP observedin PE-rich Synechococcus strains isolated in former years fromthe same sampling site. The plurality in the picoplanktic isolatesand the possibility of cultivation of strains is discussed withrespect to the oligotrophication of Lake Constance.