Our research is focusing on phage (phage=virus that infect bacteria) ecology in different aquatic environments, ranging from the open ocean and surface microlayer in the the Baltic Sea and the Arctic, deep subsurface environments and freshwater systems. We investigate the phage community and their interactions with their microbial hosts using sequencing of isolated phage-bacteria model systems, metagenomic sequencing and transcriptomics. Through our research we expand our knowledge regarding previously unknown phages regarding their genetic diversity, evolution, metabolic potential and interactions with their hosts. Through long-term sampling of the viral community in the Baltic Sea we are able to investigate the temporal dynamics of both isolated phages as well as the major, uncultured part of the viral community. In addition, metagenomic and isolation of viruses in the surface microlayer compared to underlying waters provide interesting dynamics of the movement of viruses on a micro scale. Also, spatial and phenological variations within costal viral communities is investigated along the Swedish east coast, using both isolation and metagenomic investigations. Both metagenomic and isolate based investigations provides important information on the metabolic potential of phages in the different investigated environments: a potential that is expressed while the phages replicate within their hosts with cascading effects on biogeochemical cycles. This is further investigated within our ongoing transcriptomic experiments, where we determine the effects of viral infection on their hosts. Overall, our research provides important and novel understanding of phage-host interactions in aquatic environments.