Microbial community composition and metabolic potential during a succession of algal blooms from sp. to sp.

Elucidating the interactions between algal and microbial communities is essential for understanding the dynamic mechanisms regulating algal blooms in the marine environment. Shifts in bacterial communities when a single species dominates algal blooms have been extensively investigated. However, bacterioplankton community dynamics during bloom succession when one algal species shift to another is still poorly understood. In this study, we used metagenomic analysis to investigate the bacterial community composition and function during algal bloom succession from sp. to sp. The results revealed that bacterial community structure and function shifted with bloom succession. The dominant group in the bloom was , while and dominated the bloom. The most noticeable feature during the successions was the change from to in the bacterial communities. The Shannon diversity indices were significantly higher in the transitional phase of the two blooms. Metabolic reconstruction of the metagenome-assembled genomes (MAGs) showed that dominant bacteria exhibited some environmental adaptability in both blooms, capable of metabolizing the main organic compounds, and possibly providing inorganic sulfur to the host algae. Moreover, we identified specific metabolic capabilities of cofactor biosynthesis (e.g., B vitamins) in MAGs in the two algal blooms. In the bloom, family members might participate in synthesizing vitamin B and B to the host, whereas in the bloom, was the potential contributor for synthesizing vitamin B to the host. In addition, signal communication (quorum sensing and indole-3-acetic acid molecules) might have also participated in the bacterial response to bloom succession. Bloom-associated microorganisms showed a noticeable response in composition and function to algal succession. The changes in bacterial community structure and function might be an internal driving factor for the bloom succession.