Polyphasic Characterisation and Taxonomic Revision of Planktonic Cyanobacteria Anabaena spp. (Nostocaceae)

Morphological diversity of planctonic Anabaena populations (Nostocaceae, cyanobacteria) was studied in fishponds and reservoirs of the Czech Republic in 2004-2009. Clonal strains of various morphospecies were isolated and maintained under constant culture conditions. The plasticity of morphological features used for single morphospecies identification was studied in eight selected strains under varied experimental conditions (temperature, light intensity, nitrogen, phosphorus). Phosphorus concentration was the main driving factor of morphological variability. Morphologies of the Anabaena strains studied were compared with the field morphologies of 61 Anabaena populations observed in the Czech Republic. The range of morphological variability of single strains in laboratory spanned the total variability of the populations of relevant morphospecies or morphospecies complex observed in the field. Delimitations and proper descriptions of single Anabaena morphospecies were discussed in the light of partial 16S rRNA gene sequences of the studied strains. A new generic entity Sphaerospermum was defined for morphospecies with spherical akinetes adjacent to heterocytes that also displayed 16S rRNA gene sequence markedly different from other planktonic Anabaena morphospecies (approx. 92% sequence similarity). The type species of this genus is S. reniforme and the genus also comprises species S. aphanizomenoides and S. kisselevianum.