The microbiome of the main deep-water scleractinian reef-framework engineers from the Southwestern Atlantic

Deep waters (>150 m) shelter half of the extant diversity of scleractinian corals, including framework reef-forming species. However, to date, the relationship between microorganisms and corals has focused mainly on their zooxanthellate shallow-water counterparts. Here, using 16S rRNA gene amplicon sequencing, we explore the microbiome of all major Atlantic deep-water scleractinian reef framework engineers (Desmophyllum pertusum, Solenosmilia variabilis, Madrepora oculata, and Enallopsammia rostrata), and correlated them with environmental characteristics. Colony fragments of each coral species used in the present study were sampled from three sedimentary basins off the Southeastern coast of Brazil, including two water masses (Antarctic Intermediate Water and South Atlantic Coastal Water). Although representing distant scleractinian evolutionarily lineages, some evolving apart for more than 300Ma, our results suggest a taxonomic homogeneity in their microbial profile. The species-specific microbial core, as well as the core common to all examined species, were identified. Such cores are composed of bacterial genera that have already been observed in other coral species, including those from zooxanthellate species. Such a pattern suggests an active selection of the microbial community by their hosts, a phenomenon that seems to be fundamental for holobiont fitness, especially in long-lived species, such as corals. Besides the microbial core, for all examined species, part of the determined microbiome was flexible and responded to environmental drivers. This flexibility is most probably related to the host's ability to adapt in ecological time scales. Taken together, these holobiont abilities may be crucial to its success in both ecological and geological timescales.