The coral core microbiome identifies rare bacterial taxa as ubiquitous endosymbionts

TLDR

Corals, despite their simplicity, host highly diverse and abundant microbial communities. The study aims to differentiate core symbiotic bacteria from the diverse coral microbiome to characterize their functional contributions. The authors characterize the coral core microbiome, revealing phylogenetic and functional divisions among micro‑scale niche habitats within the host. The study identifies seven universally present bacterial phylotypes, two of which co‑localize with endosymbiotic algae and host cells, suggesting these symbioses support dinoflagellate endosymbiosis across diverse environments.

Abstract

Abstract Despite being one of the simplest metazoans, corals harbor some of the most highly diverse and abundant microbial communities. Differentiating core, symbiotic bacteria from this diverse host-associated consortium is essential for characterizing the functional contributions of bacteria but has not been possible yet. Here we characterize the coral core microbiome and demonstrate clear phylogenetic and functional divisions between the micro-scale, niche habitats within the coral host. In doing so, we discover seven distinct bacterial phylotypes that are universal to the core microbiome of coral species, separated by thousands of kilometres of oceans. The two most abundant phylotypes are co-localized specifically with the corals’ endosymbiotic algae and symbiont-containing host cells. These bacterial symbioses likely facilitate the success of the dinoflagellate endosymbiosis with corals in diverse environmental regimes.