Seasonal Succession, Host Associations and Biochemical Roles of Aquatic Viruses in a Eutrophic Lake Plagued by Cyanobacterial Blooms

Abstract

Abstract Background. Viruses are important biogeochemical mediators and ecological drivers in freshwater ecosystems. Although the environmental implications of viruses in ecosystems have been preliminarily explored, the dynamics of viruses and host associations over the seasons and blooming periods in eutrophic freshwater ecosystems remain elusive. Results. Here, we recovered 41,997 unique viral clusters at approximately species level from planktonic microbiomes of Lake Taihu, a large and eutrophic lake that suffered from yearly Microcystis-dominated harmful algal blooms (HABs) in China. The viral clusters showed distinct seasonal succession driven by environmental factors (mainly nutrients and temperature) and microbial communities (mainly Cyanobacteria and Planctomycetes). Host prediction highlighted the roles of the viruses in affecting the bacteria-driven nitrogen and phosphate cycling through infection. Further statistical analyses revealed that the HAB-induced environmental and microbial variations affected viral strategies including lifestyles, host range, and virus-encoded auxiliary metabolic genes (vAMGs) distributions. Viruses infecting Proteobacteria and Actinobacteria showed enhanced lysogenic lifestyle and condensed host ranges during HAB peak in summer, while viruses infecting Bacteroidota selected the opposite strategy. Notably, vAMGs were most abundant before HAB outbreak in spring, compensating for host bacterial metabolism including carbohydrates metabolism, photosynthesis, and phosphate regulation. Conclusion. This study elucidated relationship between viral community and bloom-associated environment, suggested the dynamic viral strategies and prominent biochemical roles in the eutrophic freshwater ecosystems.