The overarching aim of my research is to explain how CO2 availability affects mixed microbial communities: productivity of phototrophs, their trophic and environmental interactions, and impacts on the community diversity and evolution. I use cyanobacteria as a model system because they are principal oxygenic photosynthetic organisms, which evolved into CO2-rich environment, gave rise to all other photosynthetic organisms and oxidised Earth’s surface in geological time.