Freshwater cyanobacteria perform a substantial part of the primary productivity of various aquatic systems worldwide. However, these cyanobacteria can form blooms which can be toxic. Phages (viruses of bacteria) can play a significant role in the top-down control of cyanobacteria. We study the web of interactions between cyanobacteria and their phages. In this project, we aim to answer questions such as: What are the molecular mechanisms that confer resistance to the different predators and what is their role in this ecosystem? How does selection by phages affect the evolution of the cyanobacteria genomes? Does this selection take any part in shaping the size/structure of the cyanobacteria?