Stable morphospecies within the 16S rRNA monophyletic genus Microcystis (Kützing) Kützing

The main morphological features (size of cells, way of multiplication, shape of colonies) were analyzed in natural populations, semi-cultures derived from natural populations and in cultivated strains of Microcystis morphospecies. Samples were taken from selected eutrophic and hypertrophic water-bodies in the Czech Republic and from the Italian reservoir Bubano Basin. Investigated strains are maintained in the cyanobacterial collections of the Hydrobiological Institute AS CR, ?eské Bud?jovice (Czech Republic ) and the CNR-Institute for Ecosystem Study, Firenze (Italy). Cell diameter was investigated in detail, to determine its statisically significant decisive ranges (ANOVA statistical software). Cell size isa the sole criterion to differentiate between some of the "botanical species" (M. ichthyoblabe and M. flos-aquae, for example). It was confirmed that three of the investigated morphospecies (M. aeruginosa, M. viridis and M. wesenbergii) kept well their cell sizes when measured either as natural populations or as cultivated strains. According to our results, M. flos-aquae and M. ichthyoblabe populations did not differ. Large and small cells had the same origin, since small cells derived from large ones during a fast reproduction phase after transition of the population to better physical and nutritional conditions. The aim of this paper was to confirm existence of some stable characters of morphotypes inside a phylogenetically monophyletic genus based on the 16S rRNA gene sequences, and thus to encourage future genetic investigation that should provide more information on internal diversity of this important genus.