Spatiotemporal changes of cyanobacterial and bacterial communities during an algal bloom in a subtropical water source reservoir ecosystem of China

<title>Abstract</title> Massive nitrogen and phosphorus input into aquatic ecosystems makes algal bloom as one of the most concerning problems in China. Algal blooms not only threaten the health and stability of aquatic ecosystems, but also influence the microbial community within. However, less is known regarding how algal bloom affects the spatiotemporal variation of aquatic microbial community, including cyanobacteria and other bacteria. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community diversity and composition spatiotemporally vary along main algal bloom phases in upstream rivers of a eutrophicated water source reservoir. For both cyanobacteria and bacteria, their diversities demonstrated temporal significance amongst different phases in each river, indicating the apparent impact of algal bloom. Dominant cyanobacterial taxa included Chloroplast, Cyanobacteriales, and Synechococcales, and dominant bacterial taxa comprised Acinetobacter, CL500-29,<italic> hgc</italic>I clade, Limnohabitans, Flavobacterium, Rhodoluna, Porphyrobacter, Rhodobacter, Pseudomonas, and Rhizobiales, whose relative abundance varied along the algal bloom, rendering distinct community composition for each river. Non-metric multidimensional scaling analysis additionally indicated significant differences amongst different phases, and the linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) helped to identify the significant biomarkers (OTUs) in each river at different phases. Canonical correlation analysis (CCA) or redundancy analysis (RDA) revealed distinct correlation patterns of cyanobacterial and bacterial communities with the environmental parameters, which implies their distinct ecological functions. In general, these results demonstrated the significant influence of algal bloom on microbial communities in a eutrophicated water source reservoir basin. These observations also arouse universal demands for strategies conserving the aquatic microbial equilibrium and alleviating algal blooms in reservoirs.