Inter-domain microbial diversity within the coral holobiontSiderastrea sidereafrom two depth habitats

Abstract

Corals host diverse microbial communities that are involved in acclimatization, pathogen defense, and nutrient cycling. Surveys of coral-associated microbes have been particularly directed towardSymbiodiniumand bacteria. However, a holistic understanding of the total microbiome has been hindered by a lack of analyses bridging taxonomically disparate groups. Using high-throughput amplicon sequencing, we simultaneously characterized theSymbiodinium, bacterial, and fungal communities associated with the Caribbean coralSiderastrea sidereacollected from two depths (17 and 27 m) on Conch reef in the Florida Keys.S. sidereahosted an exceptionally diverseSymbiodiniumcommunity, structured differently between sampled depth habitats. While dominated at 27 m by aSymbiodiniumbelonging to clade C, at 17 mS. sidereaprimarily hosted a mixture of clade B types. Most fungal operational taxonomic units were distantly related to available reference sequences, indicating the presence of a high degree of fungal novelty within theS. sidereaholobiont and a lack of knowledge on the diversity of fungi on coral reefs. Network analysis showed that co-occurrence patterns in theS. sidereaholobiont were prevalent among bacteria, however, also detected between fungi and bacteria. Overall, our data show a drastic shift in the associatedSymbiodiniumcommunity between depths on Conch Reef, which might indicate that alteration in this community is an important mechanism facilitating local physiological adaptation of theS. sidereaholobiont. In contrast, bacterial and fungal communities were not structured differently between depth habitats.