The Response of Potentially Active Planktonic Actinobacteria to the Construction of Three Gorges Dam of the Yangtze River, China

The potentially active planktonic actinobacterial communities in the water columns behind and in front of the Three Gorges Dam (TGD) of the Yangzte River, China were investigated during two seasons (July and December 2009) with RNA-based 16S rRNA gene phylogentic analysis. A total of 417 actinobacterial 16S rRNA gene transcript clones were obtained and they could be classified into acI, acII, acIV, acSTL, Soil II+III [phylogenetic nomenclature for typical freshwater Actinobacteria made in Environ Microbiol 6(3): 242-253 and Appl Environ Microbiol 72(5): 3489-3497], some known suborders (e. g., Corynebacteriaceae, Micrococcineae, Micromonosporineae, Streptosporangineae), and unclassified Actinomycetales. Among these groups, RNA-based clone sequences affiliated with the acIV group were dominant, different from previously described freshwater ecosystems determined by using DNA techniques, suggesting that the planktonic actinobacterial community near the TGD may be unique. The seasonal (summer vs. winter) variation of the planktonic actinobacterial communities was more evident than the spatial (behind vs. in front of the dam) change. The effect of the TGD on actinobacterial community diversity and composition was more obvious in winter than in summer. Overall, the altered water dynamics due to the TGD construction are likely important reasons for the observed variations.