Temporal variability of free-living microbial culturability and community composition after an Akashiwo sanguinea bloom in Shenzhen, China

Dinoflagellate blooms currently caused serious environmental problems in different areas of the world. Recent studies revealed close relationship between dinoflagellate blooms and microbial community dynamics, while less attention has been paid on the bacterial culturability change associated with the bloom. Here, we investigated the temporal variation of microbial community composition and culturability during the decline stage of an Akashiwo sanguinea bloom occurred in Shenzhen, China. The daily microbial community phylogenetic structures in water samples collected during a four-day period after the bloom peak were assessed through 16S rRNA gene amplicons sequencing on the MiSeq (Illumina) platform. The environmental parameters, Chlorophyll a concentrations, and total viable and culturable bacterial densities were also measured. Our results showed that Gamma-proteobacteria comprising mostly of Pseudoalteromonadaceae and Vibrionaceae was the predominant microbial class in the post-bloom samples, except for the second day. During that day, the represented groups switched to Alpha-proteobacteria (Rhizobiales) and Beta-proteobacteria (Comamonadaceae), with the microbial culturability decreased. Total viable bacterial densities reached the maximum value on the third day, with Gamma-proteobacteria regained the dominance till the fourth day. The dramatic microbial community succession and culturability variation observed in this study indicated the complication of algae-bacteria interactions during dinoflagellate bloom.