Unexpected diversity of Endozoicomonas in deep-sea corals

Ca Kellogg,Za Pratte

doi:10.3354/meps13844

Abstract

The deep ocean hosts a large diversity of azooxanthellate cold-water corals whose associated microbiomes remain to be described. While the bacterial genus Endozoicomonas has been widely identified as a dominant associate of tropical and temperate corals, it has rarely been detected in deep-sea corals. Determining microbial baselines for these cold-water corals is a critical first step to understanding the ecosystem services their microbiomes contribute, while providing a benchmark against which to measure responses to environmental change or anthropogenic effects. Samples of Acanthogorgia aspera, A. spissa, Desmophyllum dianthus, and D. pertusum (Lophelia pertusa) were collected from western Atlantic sites off the US east coast and from the northeastern Gulf of Mexico. Microbiomes were characterized by 16S rRNA gene amplicon surveys. Although D. dianthus and D. pertusum have recently been combined into a single genus due to their genetic similarity, their microbiomes were significantly different. The Acanthogorgia spp. were collected from submarine canyons in different regions, but their microbiomes were extremely similar and dominated by Endozoicomonas. This is the first report of coral microbiomes dominated by Endozoicomonas occurring below 1000 m, at temperatures near 4°C. D. pertusum from 2 Atlantic sites were also dominated by distinct Endozoicomonas, unlike D. pertusum from other sites described in previous studies, including the Gulf of Mexico, the Mediterranean Sea and a Norwegian fjord.

Highlights

There are more species of corals in the deep ocean than there are in shallow waters (Roberts & Hirshfield 2004, Roberts et al 2009)
Deep-sea octocoral microbiomes show variation in their most abundant taxa: Paragorgia arborea is dominated by Tenericutes (Weiler et al 2018), Anthothela grandiflora is dominated by a combination of Gammaproteobacteria and Spirochaetes (Lawler et al 2016), Primnoa resedaeformis and Paramuricea placomus are both dominated by Proteobacteria, but vary in whether Alpha- or Gammaproteobacteria are more abundant (Kellogg et al 2016, Goldsmith et al 2018)
We found both Acanthogorgia spp., as well as D. pertusum, to be dominated by Gammaproteobacteria, but D. dianthus had a variable mixture of Alpha- and Gammaproteobacteria (Fig. S3)

Summary

Introduction

There are more species of corals in the deep ocean than there are in shallow waters (Roberts & Hirshfield 2004, Roberts et al 2009) This incredible diversity of cold-water corals, including both calcifying scleractinians and soft octocorals, serves a fundamental role in creating 3-dimensional structure in the deep sea (Roberts et al 2006). This structure provides the foundation for biodiversity hot spots that support a large variety of invertebrates as well as economically important fish species (Buhl-Mortensen & Mortensen 2004, 2005, Stone 2006, Cordes et al 2008). Baseline descriptions of the bacterial communities of a number of deep-sea octocorals have been published (Gray et al 2011, Kellogg et al 2016, Lawler et al 2016, Goldsmith et al 2018, Weiler et al 2018)

Objectives

Methods

Results

Discussion

Conclusion