Phytoplankton play a crucial role as a primary producer of organic carbon and main food source of the secondary producers in the marine ecosystem. It has been difficult to make a qualitative and quantitative analysis of its community structure by the traditional methods. We here developed a molecular method to estimate the phytoplankton community and its quantity by the combination of qPCR and NGS platform. The reliability of the method was tested using the water samples collected from the East/Japan Sea (EJS). Water samples were collected from six different latitudinal survey lines (Daejin (DJ), Ayajin (AY), Susan (SS), Jumunjin (JM), Mukho (MH), and Jukbyeon (JB)) with four different depths (0, 20, 50, and 100 m) between December 2016 and June 2017. Both qPCR and NGS analysis were based on the two universal primer sets (16S for total microbial community and 23S for phytoplankton community, respectively). The correlations between phytoplankton communities and other environmental components were analyzed by various statistical tools such as heatmap analysis and R package.
Results/Conclusions
qPCR assay method was established to estimate the quantity of phytoplankton and microorganisms in which 100 to 500 ml of seawater sample is appropriate volume for both qualitative and quantitative analyses. During the survey, copy numbers of total microorganism were highest on the surface water in April, whereas its numbers for phytoplankton were highest on the surface water in May. According to NGS results generated by Miseq (Illumina) platform, total 3,481 OTUs (22 phyla) and 14,053 OTUs (40 phlya) were identified by 23S and 16S universal primer sets, respectively. Total OTUs in phytoplankton species were exclusively presented by 23S universal primer set supporting the qPCR result. However, different from those by 16S universal primer set, only 22.6 % of total OTU showed more than 98 % or higher sequence identity to GenBank database, which suggests that their sequence data should be supplemented. The most abundant phytoplankton on the surface water changed according to the time from Ostreococcus tauri in January to cyanobacteria in June. The most abundant bacteria on the surface water also changed from Candidatus Pelagibacter in January to Synechococcus sp. in June. Phytoplankton communities on surface water were dissimilar with 100 m from April as the stratification occurs.