Zooming in on dynamics of marine microbial communities in the phycosphere of Akashiwo sanguinea (Dinophyta) blooms

Abstract Background: Characterising ecological relationships between viruses, bacteria, and phytoplankton in the ocean are critical to understanding the ecosystem, yet these relationships are infrequently investigated together. To understand the dynamics of microbial communities and environmental factors in harmful algal blooms (HABs), we examined the environmental factors and microbial communities during Akashiwo sanguinea HABs in the Jangmok coastal waters of South Korea by metagenomics. Results: Specific bacterial communities showed synergistic and antagonistic relationships with A. sanguinea bloom. Endoparasitic dinoflagellate Amoebophrya sp. 1 controlled the bloom dynamics, as an increase in their abundance was correlated with HAB decline. In the nucleocytoplasmic large DNA viruses, abundance of Pandoraviridae increased following an increase in HAB. Operational taxonomic units and environmental factors associated with A. sanguinea were also visualized by network analysis: A. sanguinea-Amoebophrya sp. 1 (r=0.81, Time-lag: 2 day) and A. sanguinea-Pandoravirus dulcis (0.64, 0 day) relationships showed close association. A. sanguinea-dissolved organic carbon and -dissolved inorganic phosphorus relationships were also very closely correlated (each 0 day time-lag, respectively). Conclusions: Microbial communities and the environment dynamically and complexly changed in A. sanguinea bloom, and a rapid turnover of microorganisms could respond to ecological interactions. A. sanguinea bloom dramatically changes the environments through their exudation of dissolved carbohydrates by autotrophic processes, followed by changes in microbial communities involving host-specific viruses, bacteria, and parasitoids. Thus, microbial communities in HAB ecology are composed of various organisms and they interact in a complex way. Therefore, to interpret their ecosystem, the complex reactions among various microorganisms should be studied rather than studying a simple 1:1 reaction, such as a prey-predator interaction.