Metagenomic analysis of stressed coral holobionts

TLDR

The coral holobiont comprises diverse metazoans, protists, and microbes, and disruptions in these associations are linked to disease, yet the transition from mutualism to pathogenesis remains poorly understood. This study aimed to assess how increased temperature, elevated nutrients, dissolved organic carbon, and reduced pH alter the structure and function of Porites compressa’s microbial community. Researchers collected and pyrosequenced metagenomic samples from stressed corals to analyze microbial community changes. Stressors elevated genes for virulence, stress resistance, sulfur and nitrogen metabolism, motility, chemotaxis, lipid utilization, and secondary metabolism, while shifting the microbiota from healthy-associated taxa (Cyanobacteria, Proteobacteria, Symbiodinium) to disease-associated taxa (Bacteroidetes, Fusobacteria, Fungi) and showing that low-abundance Vibrio spp.

Abstract

The coral holobiont is the community of metazoans, protists and microbes associated with scleractinian corals. Disruptions in these associations have been correlated with coral disease, but little is known about the series of events involved in the shift from mutualism to pathogenesis. To evaluate structural and functional changes in coral microbial communities, Porites compressa was exposed to four stressors: increased temperature, elevated nutrients, dissolved organic carbon loading and reduced pH. Microbial metagenomic samples were collected and pyrosequenced. Functional gene analysis demonstrated that stressors increased the abundance of microbial genes involved in virulence, stress resistance, sulfur and nitrogen metabolism, motility and chemotaxis, fatty acid and lipid utilization, and secondary metabolism. Relative changes in taxonomy also demonstrated that coral-associated microbiota (Archaea, Bacteria, protists) shifted from a healthy-associated coral community (e.g. Cyanobacteria, Proteobacteria and the zooxanthellae Symbiodinium) to a community (e.g. Bacteriodetes, Fusobacteria and Fungi) of microbes often found on diseased corals. Additionally, low-abundance Vibrio spp. were found to significantly alter microbiome metabolism, suggesting that the contribution of a just a few members of a community can profoundly shift the health status of the coral holobiont.