A polyphasic approach to assess the cyanobacterial diversity of summer samples from Czech reservoirs

We used a polyphasic approach combining data from microscopic assessment of fresh biomass and from clone libraries and DGGE fingerprints based on 16S rRNA gene sequences to investigate the cyanobacterial diversity of Czech reservoirs during the summer in 2001 and 2002. In total, 15 genera were identified using the microscopic analysis in 38 samples analysed. They were Aphanizomenon, Anabaena, Anabaenopsis, Aphanocapsa, Aphanothece, Pseudanabaena, Planktothrix, Planktolyngbya, Limnothrix, Woronichinia, Snowella, Romeria, Microcystis, Merismopedia, and Coelomoron. We recovered 113 DGGE band sequences from the same samples. In addition, 128 partial 16S rRNA sequences were obtained from two clone libraries of reservoirs Pilská and Orlík. The phylogenetic comparison with the currently available rRNA sequences in databases showed that our sequences belonged to 8 clusters: Woronichinia, Microcystis, Synechococcus, Snowella, Planktothrix, Anabaena/Aphanizomenon, Limnothrix and a plastid related to Chrysochromulina polylepis. The microscopic enumeration and the molecular results were generally congruent concerning the major populations determined in these samples (for 32 samples among 38). Anabaena/Aphanizomenon, Microcystis and Woronichinia were the major genera in the Czech reservoirs during summer, and were present in most of the samples. This study showed some discrepancies between the genera retrieved by the traditional method and the molecular analyses. Differences concerned the presence of minor populations belonging to Aphanothece, Romeria, Merismopedia, Synechococcus, Snowella and Pseudanabena. These differences could be explained by biases specific to each method (competitive amplification, difficulty to obtain sequences from DGGE bands, not precise microscopic observation of the small-sized genera).