Analysis of the microbiome of corals from deep-sea features in the Great Australian Bight

Tissue samples of octocorals and antipatharian soft corals were collected from geological features, including sea mounts and mineral seeps, in the Great Australian Bight at depths between 1000-3000 m, the first specimens to be studied from such depths. The microbiome of these corals was surveyed with the hypothesis that the geochemical conditions at the site from which specimens were collected would influence microbiome composition. DNA was extracted and next generation sequencing of the v1-v3 region of the 16S rRNA gene was used to generate operational taxonomic units (OTUs) at 97% similarity. A distinct coral microbiome, with clear compositional differences from adjacent sediment, was found in all samples. Most of the bacteria associated with these coral samples belonged to the Alpha-, Gamma- and Delta-proteobacteria. Instead of being influenced by site geochemistry, microbiome composition was most influenced by coral host phylogeny. The predicted functions of the microbiome also did not vary between different deep-sea sites. The consistent composition of the microbiome in these organisms, despite the geochemical differences in their environments, and the similarity to other soft corals, but not reef building corals, suggests that these coral associated bacteria play an important, if not fully understood, role in the host coral physiology.