Co-occurrence patterns between Chlorophyta and nucleocytoplasmic large DNA virus in coastal ecosystem, South Korea.

Nucleocytoplasmic large DNA viruses (NCLDVs) are known to infect phytoplankton and play a significant role in regulating their population dynamics. In this study, we aimed to investigate the co-occurrence patterns between phytoplankton and NCLDVs in the southern coastal ecosystem of South Korea. We collected seawater every month from March 2018 to December 2020 and analyzed the samples using Cytochrome c Oxidase subunit I metabarcoding and metagenomic analyses. Chlorophyta (36.08%) was the most abundant eukaryotic taxon, with Bathycoccaceae (58.25%) and Mamiellaceae (41.51%) being the most dominant families within Chlorophyta. Bathycoccaceae was dominant in winter, whereas Mamiellaceae was dominant in summer. In the NCLDV community, Phycodnaviridae (75.12%) was found to be the major family. The co-occurrence pattern of Phycodnaviridae showed a high correlation with Bathycoccaceae and Mamiellaceae, which is explained by the "boom-and-bust" concept. In particular, we predicted co-occurrence patterns between Bathycoccus prasinos and Prasnovirus, with known infectious relationships, and confirmed co-occurrence patterns between B. prasinos and Coccolithovirus and Micromonas pusilla and Prymnesiovirus, with unknown infectious relationships. These co-occurrence patterns between Chlorophyta and Phycodnaviridae provide valuable insights into the control of pico-sized primary production and the microbial loop of the coastal ecosystem.