Coral metabolite gradients affect microbial community structures and act as a disease cue

Michael A Ochsenkühn,Philippe Schmitt-Kopplin,Mourad Harir,Shady A Amin

doi:10.1038/s42003-018-0189-1

Abstract

Corals are threatened worldwide due to prevalence of disease and bleaching. Recent studies suggest the ability of corals to resist disease is dependent on maintaining healthy microbiomes that span coral tissues and surfaces, the holobiont. Although our understanding of the role endosymbiotic microbes play in coral health has advanced, the role surface-associated microbes and their chemical signatures play in coral health is limited. Using minimally invasive water sampling, we show that the corals Acropora and Platygyra harbor unique bacteria and metabolites at their surface, distinctly different from surrounding seawater. The surface metabolites released by the holobiont create concentration gradients at 0–5 cm away from the coral surface. These molecules are identified as chemo-attractants, antibacterials, and infochemicals, suggesting they may structure coral surface-associated microbes. Further, we detect surface-associated metabolites characteristic of healthy or white syndrome disease infected corals, a finding which may aid in describing effects of diseases.

Highlights

Corals are threatened worldwide due to prevalence of disease and bleaching
Coral surface samples (0 cm) were collected with a soft silicon nozzle attached to a syringe, coral vicinity samples (5 cm) were collected with a 5-cm capped cylinder connected to a syringe with inlets at 5 cm above the coral surface and seawater samples (50 cm) were collected with a regular syringe placed ~50 cm away from the coral colony (Fig. 1)
We reasoned that the dominance of Pelagibacterales would interfere with any interesting patterns of other bacterial abundance at the sampled distances; we examined the composition of the 10 most abundant bacterial operational taxonomic units (OTUs) after removing Pelagibacterales reads

Summary

Introduction

Corals are threatened worldwide due to prevalence of disease and bleaching. Recent studies suggest the ability of corals to resist disease is dependent on maintaining healthy microbiomes that span coral tissues and surfaces, the holobiont. Coral mucus generally consists of a gel-like matrix of glycoproteins (e.g., mucins), polysaccharides, and lipids[4], which is constantly regenerated by the animal host[5] This layer serves numerous functions including sediment cleansing, protection against UV damage and desiccation, growing substrate for bacteria and protection from pathogens and other stressors[4,5,6]. The dinoflagellate symbiont produces essential sugars that are used in coral mucus production and regeneration; this symbiont is expelled during bleaching events at high temperatures[4,19] These observations suggest that environmental stress often leads to the disruption of this mucus layer and/or its resident microbiome, which could be detrimental to the coral host. White band disease, a type of white syndrome diseases, though widely investigated to have rapid disease progression[23] and high infection rates in corals under stress[24,25], has an unclear cause of infection

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Results

Conclusion