Diatoms with associated diazotrophic symbionts are important in open ocean ecosystems. There are two parts to this project. Part 1 focuses on whether other symbiotic partners (e.g. heterotrophic bacteria) are also present and contribute to the symbioses. This project aims at 1) understanding if other bacteria are also present 2) what their phylogenetic affiliation (16S rRNA) is, 3) their potential role. A second project focusses on the coordination of gene expression by host diatom (Hemiaulus) and its preferred endosymbiont (Richelia) under two experimental conditions: normal (control) and when the host is treated with a eukaryotic inhibitor (cycloheximide).