In lakes, oceans, rivers etc., microscopic organisms take up and recycle nutrients, forming the base of the aquatic food web. These organisms contribute to 50% of the oxygen produced on the planet and to sustaining all levels of life in the aquatic ecosystem. We have a basic understanding of the nature and mechanisms of the transfer of nutrients within the food web, but we don't know exactly who is doing what or which processes they are involved in or perform. My research focus on the interactions between phytoplankton and bacteria at a community level, thus including all organisms smaller than 90 micrometer (in one study), or smaller than 3 micrometer (in another study). By using molecular methods, i.e. by extracting DNA and RNA from water samples, and sequence these molecules, I can find out which organisms are present in a sample, and I can study which enzymes are expressed at a certain timepoint. Together with measurements made from the environment at the time of sampling, the molecular methods allow us to interpret which environmental conditions or changes cause community shifts, and what these shift entail with regards to function, with a special focus on the transfer of nutrients.