| Summary: | <i>Skeletonema dohrnii</i> is a common red tide microalgae occurring in the coastal waters and throughout the world. The associated heterotrophic or autotrophic bacteria play vital roles in regulating algal growth, production, and physiology. In this study, we investigated the detailed bacterial community structure associated with the growth of <i>S. dohrnii</i>’s using high-throughput sequencing-based on 16S rDNA. Our results demonstrated that Bacteroidetes (48.04%) and Proteobacteria (40.66%) in all samples accounted for the majority of bacterial populations. There was a significant linear regression relationship between the abundance of bacterial phyla and culture time. Notable shifts in bacterial community composition were observed during algal growth: Flavobacteriales accounted for the vast majority of sequences at the order level. Furthermore, the relative abundance of Rhodobacterales was gradually reduced during the whole growth process of <i>S. dohrnii</i> (0–12 days). However, beyond that, the relative abundance of <i>Marinobacter</i> was slowly increasing. It is noteworthy that five fluorophores (Peaks T<sub>1</sub>, T<sub>2</sub>, I, M, and A) were detected during the growth stage of <i>S. dohrnii</i>. The characteristic indexes (fluorescence index, humification index, and biological index) of chromophoric dissolved organic matter (CDOM) also varied with the culture time. In addition, the taxa of bacteria had certain effects on CDOM and they were inextricably linked to each other.
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