Coral reef invertebrate microbiomes correlate with the presence of photosymbionts.

Coral reefs provide habitat for an array of marine invertebrates that host symbiotic microbiomes. Photosynthetic symbionts including Symbiodinium dinoflagellates and diatoms potentially influence the diversity of their host-associated microbiomes by releasing carbon-containing photosynthates and other organic compounds that fuel microbial metabolism. Here we used 16S ribosomal RNA (rRNA) gene amplicon pyrosequencing to characterise the microbiomes of 11 common Great Barrier Reef marine invertebrate species that host photosynthetic symbionts and five taxa in which they are absent. The presence of photosynthetic symbionts influenced the composition but not the species richness, evenness and phylogenetic diversity of invertebrate-associated microbiomes. Invertebrates without photosynthetic symbionts were dominated by Alphaproteobacteria, whereas those hosting photosynthetic symbionts were dominated by Gammaproteobacteria. Interestingly, many microbial species from photosymbiont-bearing invertebrates, including Oceanospirillales spp., Alteromonas spp., Pseudomonas spp., Halomonas spp., are implicated in the metabolism of dimethylsulfoniopropionate (DMSP). DMSP is produced in high concentrations by photosynthetic dinoflagellates and is involved in climate regulation by facilitating cloud formation. Microbiomes correlated with host taxa and replicate individuals from most sampled species grouped in distance-based redundancy analysis of retrieved 16S rRNA gene sequences. This study highlights the complex nature of invertebrate holobionts and confirms the importance of photosynthetic symbionts in structuring marine invertebrate bacterial communities.