Characterization of bacterial community associated with phytoplankton bloom in a eutrophic lake in South Norway using 16S rRNA gene amplicon sequence analysis.

In this study, phytoplankton diversity was studied using traditional microscopic techniques and the bacterial communities associated with phytoplankton blooms were studied using High throughput Sequencing (HTS) data analysis of 16S rRNA gene amplicon (targeting the V1-V3 and V3-V4 hypervariable region). Samples were collected from Lake Akersvannet, a eutrophic lake in South Norway, during growth season from June to August 2013. The PCR amplification and sequencing was performed at Biomedicum Functional Genomics Unit (University of Helsinki, Finland) using Illumina MiSeq Sequencing platform (2×300 PE strategy) .Microscopic examination revealed that the phytoplankton community was mostly represented by Cyanobacteria and dinoflagellate Ceratium hirundinella. The NGS results revealed that Proteobacteria (Alpha, Beta, and Gamma), Bacteriodetes, Cyanobacteria, Actinobacteria and Verrucomicrobia represented the bacterial community with varying relative abundances throughout the sampling season. Species level identification of Cyanobacteria showed presence of a mixed population of Aphanizomenon flos-aquae, Microcystis aeruginosa and Woronichinia naegeliana. A significant proportion of the microbial community, was represented by low abundance bacterial groups, including many unclassified taxa which might be representing locally acclimatized freshwater bacterial groups. Comparison of cyanobacterial species composition from HTS and microscopy revealed significant discrepancies in the quantitative data of species abundance indicating a need for cross validation of results from these methods. This is the first study that uses HTS method for studying the bacterial community associated with a phytoplankton blooms in a Norwegian lake. The study demonstrates the importance of considering results from both traditional microscopic as well as HTS methods when studying bacterial communities associated with phytoplankton bloom.