Dominance of Endozoicomonas bacteria throughout coral bleaching and mortality suggests structural inflexibility of the Pocillopora verrucosa microbiome

Abstract
The importance of Symbiodinium algal endosymbionts and a diverse suite of bacteria for coral holobiont health and functioning are widely acknowledged. Yet, we know surprisingly little about microbial community dynamics and the stability of host-microbe associations under adverse environmental conditions. To gain insight into the stability of coral host-microbe associations and holobiont structure, we assessed changes in the community structure of Symbiodinium and bacteria associated with the coral Pocillopora verrucosa under excess organic nutrient conditions. Pocillopora-associated microbial communities were monitored over 14 days in two independent experiments. We assessed the effect of excess dissolved organic nitrogen (DON) and excess dissolved organic carbon (DOC). Exposure to excess nutrients rapidly affected coral health, resulting in two distinct stress phenotypes: coral bleaching under excess DOC and severe tissue sloughing (>90% tissue loss resulting in host mortality) under excess DON. These phenotypes were accompanied by structural changes in the Symbiodinium community. In contrast, the associated bacterial community remained remarkably stable and was dominated by two Endozoicomonas phylotypes, comprising on average 90% of 16S rRNA gene sequences. This dominance of Endozoicomonas even under conditions of coral bleaching and mortality suggests the bacterial community of P. verrucosa may be rather inflexible and thereby unable to respond or acclimatize to rapid changes in the environment, contrary to what was previously observed in other corals. In this light, our results suggest that coral holobionts might occupy structural landscapes ranging from a highly flexible to a rather inflexible composition with consequences for their ability to respond to environmental change.

Citation
Pogoreutz C, Rädecker N, Cárdenas A, Gärdes A, Wild C, et al. (2018) Dominance of Endozoicomonas bacteria throughout coral bleaching and mortality suggests structural inflexibility of the Pocillopora verrucosa microbiome. Ecology and Evolution. Available: http://dx.doi.org/10.1002/ece3.3830.

Acknowledgements
We thank Dr. A. Al-Suwailem and Dr. Z. Batang for allocation of working space in the wet laboratory facilities at the Coastal and Marine Resources Core Lab (CMOR), P. Muller for technical support with coral maintenance, R. Al-Jadahli, H. Al-Jadahli, and B. Hession for support with diving operations, and C. G. B. Grupstra for technical assistance in the laboratory. We kindly thank K. A. Krogslund and C. Michell for support during sample analysis as well as the BioScience Core Lab (BCL) for sequencing assistance. The authors would also like to thank two anonymous reviewers for their constructive comments, which helped improving the manuscript. The contribution of C.P. was supported by GLOMAR—Bremen International Graduate School for Marine Sciences. N.R. acknowledges financial support by the DAAD Promos scholarship. C.P., N.R., C.R.V. acknowledge funding by the King Abdullah University of Science and Technology (KAUST). This work was also financially supported by the German Research Foundation (DFG) grant Wi 2677/9-1 to C.W.

Publisher
Wiley

Journal
Ecology and Evolution

DOI
10.1002/ece3.3830

Additional Links
http://onlinelibrary.wiley.com/doi/10.1002/ece3.3830/full

Relations
Is Supplemented By:
  • [Bioproject]
    Title: Pocillopora verrucosa metagenomePublication Date: 2017-07-16. bioproject: PRJNA394597 Handle: 10754/666482

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