18S SSU rRNA amplicon sequencing of oomycete and diatom symbionts of marine macroalgae

Oomycetes are receiving increased attention as pathogens of seaweeds. Seaweeds are a diverse group of macroalgae that are extremely important for marine ecosystem productivity and have enormous potential in carbon capture and industrial applications around biofuels, food security or pharmacology. However, very little is known about the natural distribution of key marine oomycete species and their physiological affinities to particular host seaweed species. In this study, we provide the first overview of the diversity and composition of eukaryotic microbial symbiont communities in brown, red and green seaweeds collected from natural populations in the subarctic, subantarctic and tropical parts of the Atlantic Ocean. We show unexpectedly high phylogenetic diversity in oomycete communities and that key pathogens (e.g., Eurychasma dicksonii) have cosmopolitan distributions and affect all three groups of seaweeds. These results signify a pressing need for more detailed studies of host-pathogen interactions in natural and aquacultured seaweed populations.