Changes in bacterial community structure associated with phytoplankton succession in outdoor experimental ponds

Changes in bacterial community structure were followed in two outdoor experimental ponds. To compare the changes in bacterial community, Microcystis was inoculated into one of the ponds but not to the other one. In both ponds, Chlorophyceae algae from the genera Cosmarium and Scenedesmus were dominant in the first and last months of the study. During the middle period of the study, cyanobacteria were dominant. Microcystis and Aphanizomenon dominated in one pond, and Planktothrix dominated in the other. To investigate bacterial phylogenetic abundance and these compositions, we used catalyzed reporter deposition fluorescence in situ hybridization (CARDFISH) and denaturing gradient gel electrophoresis (DGGE). A significant relationship was observed between the number of α-proteobacterial operational taxonomic units (OTUs) and the abundance of Chlorophyceae algae (p ＜ 0.001), although no significant relationship was identified between the abundances of the two groups. The sequencing analysis of DGGE bands detected microcystin-degrading bacteria belonging to the α-proteobacteria as one of the dominant bacterial phylogenetic groups when Microcystis was the dominant phytoplankton. To our knowledge, this is the first report demonstrating changes in the abundance and composition of bacterial groups during the wax and wane of dominant phytoplankton taxa, using two different molecular methods.