Cyanophage induced changes in cyanosphere of Nodularia spumigena

Filamentous cyanobacteria, Nodularia spumigena, are prevalent in brackish water ecosystems globally and play a crucial role in ecosystem productivity by releasing carbon sources and diazotrophically fixed nitrogen. In the Baltic Sea, N. spumigena forms extensive mid- to late-summer blooms, alleviating nutrient limitations and supporting heterotrophic microbial communities. These communities exhibit a range of interactions with N. spumigena, from loose associations to symbiotic relationships, potentially facilitating horizontal gene transfer.Cyanophages, viruses that infect cyanobacteria, significantly impact microbial food webs by lysing cyanobacteria, suppressing bloom formation, and increasing the vulnerability of cyanobacterial filaments to grazing. Viral lysis disrupts complex microbial interactions, promotes competition among heterotrophs for lysis-released organic compounds, and removes the protective benefits provided by cyanobacteria. The distinct composition of organic matter released by viral lysis, compared to that from uninfected cells or grazing, induces varied responses in the microbial community.The effects of cyanophages on cyanobacteria and their associated microbial communities depend on factors such as infection efficiency and multiplicity of infection (MOI). These factors influence the timing and magnitude of cyanophage impact, thereby altering the diversity and metabolism of the entire microbial community in a virus density-dependent manner.This project aims to understand the dynamic nature of microbial assemblages mediated by cyanobacteria succession and viral infections. Specifically, it assesses how heterotrophic bacteria associated with cyanobacteria respond to cyanobacterial lysis by virulent phages. We hypothesize that the effect on the microbial consortium is proportional to the abundance of cyanophages, with higher initial MOI leading to more significant changes and increased evenness due to relaxed competition for lysis-released resources. Additionally, we investigate the relationship between cyanophage density and genome diversification, expecting increased genetic variability under higher initial MOI due to stronger selection pressure.We used N. spumigena strain KAC68 and its lytic cyanophage vB_NodS-kac68v162, isolated from the Baltic Sea, as our model system. The study involved reconstructing genome-scale metabolic models (GEMs) for N. spumigena and its associated bacteria to explore potential metabolic interdependencies within the microbial consortium. We then analyzed changes in the cyanobacteria and its microbial community induced by cyanophage lysis.The results of this study are significant as they quantify the extent of ecologically relevant cyanobacteria loss to viral lysis under different viral pressures and demonstrate how this pressure propagates through the microbial community, ultimately restricting niche space. Understanding these interactions and their ecological implications can provide insights into the functioning and stability of aquatic ecosystems in the face of viral infections and cyanobacterial blooms.