Metagenome-assembled genomes (MAGs) of octocoral symbionts. Metagenomics-resolved genomics provides novel insights into chitin turnover, metabolic specialization, and niche partitioning in the octocoral microbiome.

Octocorals live in association with a distinct microbiome, frequently dominated by so-far uncultured Endozoicomonadaceae and other Gammaproteobacteria phylotypes. However, the role of these associates is still poorly understood. This study aimed to retrieve metagenome-assembled genomes (MAGs) from these elusive symbionts to shed light on their functional features and putative mechanisms of interactions with their host. Using the integrated binning module of the MetaWRAP pipeline, 66 high- and medium quality MAGs were obtained from 17 shotgun-sequenced microbial metagenome samples of three octocoral species (healthy and necrotic Eunicella gazella tissue, healthy Eunicella verrucosa and Leptogorgia sarmentosa) and surrounding seawater. The 66 MAGs encompassed 30 bacterial and archaeal species. MAGs retrieved from healthy octocorals were affiliated with yet uncultured Gammaproteobacteria of the families Endozoicomonadaceae (11 MAGs), Candidatus Thioglobaceae (6 MAGs) and DT-91 (Pseudomonadales, 2 MAGs,), followed by several Alphaproteobacteria taxa (5 MAGs), Mollicutes (Mycoplasmodiales, 3 MAGs) and Chlamydiae (1 MAG).