# Distinct patterns of microbial association across deep-sea corals from the Western Pacific Magellan Seamounts

## TL;DR

This study explores the unique microbial communities associated with deep-sea corals in the Western Pacific, revealing distinct patterns linked to specific coral families and ecological roles.

## Contribution

The paper reports the first characterization of microbiomes for three deep-sea coral families and identifies novel microbial associations, such as ammonia-oxidizing archaea in Schizopathidae.

## Key findings

- Schizopathid corals are dominated by Nitrosopumilus archaea, which may aid in ammonia-driven carbon fixation.
- Cladopathid corals host bacteria capable of utilizing nitric oxide, possibly for oxygen generation or defense.
- Most coral samples are dominated by single microbial species, suggesting strong host-microbe selection.

## Abstract

Ahermatypic corals are common inhabitants in the Magellan Seamounts of the Western Pacific Ocean, yet their microbiomes are largely unexplored. In the present study, we used 16S rRNA gene amplicon sequencing targeting the V4 variable region to characterize the microbiomes of 30 deep-sea coral samples from 9 coral families collected from this area, including members of the families Schizopathidae, Victorgorgiidae, and Chrysogorgiidae, whose microbiomes had not been previously described. Our analyses revealed distinct patterns of microbial association between the coral families, with most coral samples being dominated by single amplicon sequence variants belonging to 11 prokaryotic genera. Ammonia-oxidizing archaea of the genus Nitrosopumilus were abundant exclusively in schizopathid corals, with relative 16S rRNA gene read abundances ranging from 29.4% to 99.8%. In contrast, Nitrosopumilus was either absent or constituted no more than 5.3% of the reads in the remaining coral families. This may be attributed to the catabolism of the protein-rich zooplankton preferred by schizopathid corals, which could, in turn, facilitate ammonia-driven carbon fixation within the holobiont. Three cladopathid corals hosted abundant sequences of two distantly related bacteria capable of utilizing nitric oxide, which could be used by the symbionts either to generate oxygen for aerobic metabolisms or be reduced as a defense against the host’s antibacterial activity. The distinct patterns of microbial association between coral taxa indicate that the microbiomes have differential roles in the adaptation of the hosts to specific ecological niches in the deep-sea environments.

Microbiomes play crucial roles in host development, physiology, and health, especially in the deep-sea environments. In this study, we collected 30 deep-sea corals from the Western Pacific Magellan Seamounts at depths ranging from 805 to 5,572 m. These samples spanned nine coral families, including three whose microbiomes have not been previously described. Our analyses revealed distinct patterns of microbial association between coral taxa. A majority of the deep-sea corals were dominated by single microbial species, indicating strong selection for certain microbial symbionts and thus functions, such as chemolithoautotrophy, the production of oxygen or secondary metabolites. Furthermore, we observed an overwhelming dominance of sequences from the ammonia-oxidizing archaeal genus Nitrosopumilus exclusively in black corals from the family Schizopathidae, a phenomenon not previously reported. This may be attributed to the catabolism of the protein-rich zooplankton preferred by the schizopathid corals, which could, in turn, facilitate ammonia-driven carbon fixation within the coral holobiont.