Chlamydomonas reinhardtii phycosphere culture collection

Microscopic algae release organic compounds to the region immediately surrounding their cells, known as phycosphere, constituting a niche for colonization by heterotrophic bacteria. These bacteria uptake algal photoassimilates and in turn provide beneficial functions to their host, in a process that resembles the establishment of microbial communities associated with the roots and rhizospheres of land plants. Here, we characterize the microbiota of the model alga Chlamydomonas reinhardtii and reveal extensive taxonomic and functional overlap with the root microbiota of land plants. Reconstitution experiments using synthetic communities derived from C. reinhardtii and Arabidopsis thaliana show that phycosphere and root bacteria assemble into taxonomically equivalent communities on either host. We show that provision of diffusible metabolites is not sufficient for phycosphere community establishment, which additionally requires physical proximity to their host. Our data suggests that the microbiota of photosynthetic organisms, from green algae to flowering plants, assembles according to core ecological principles.