Morphological and molecular analysis of bloom-forming Cyanobacteria in two eutrophic, shallow Mediterranean lakes

We investigated the diversity of Cyanobacteria by microscopic observation and sequencing of cyanobacterial-specific amplified 16S rRNA genes in the water column of two shallow, eutrophic lakes (Doirani and Kastoria, northern Greece) during summer blooms. Previous phytoplankton studies in these lakes have shown that prolonged cyanobacterial blooms can occur, which are dominated by known toxic species, as well as other less known, co-occurring species. A total of 118 clones were sequenced which were grouped in 23 Cyanobacteria and 11 chloroplast-like phylotypes. Phylogenetic analysis revealed that each library included several unique phylotypes, as well as members of all common bloom-forming Cyanobacteria. Most of the phylotypes belonged to the genera Microcystis, Anabaena, Aphanizomenon, Cylindrospermopsis-Raphidiopsis group, Limnothrix and Planktothrix, comprising most of the diversity previously recognized by morphological observations in cyanobacterial morphospecies in these lakes. In addition, novel phylotypes belonging to the Chroococcales were recognized in both lakes. The structure of the cyanobacterial communities of the lakes were very similar, as revealed by the diversity index H (2.06 and 2.01 for L. Doirani and Kastoria, respectively) and LIBSHUFF analysis (XY₁₂P-value = 0.122 and YX₁₂P-value = 0.536), due to occurrence of groups of common phylotypes. This study gives an example for successful cyanobacterial bloom analysis by the combination of morphological and phylogenetic methods useful for monitoring cyanobacteria and water quality in freshwaters.