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

• Published in: Ecology and evolution Vol. 8; no. 4; pp. 2240 - 2252
• Main Authors: Pogoreutz, Claudia, Rädecker, Nils, Cárdenas, Anny, Gärdes, Astrid, Wild, Christian, Voolstra, Christian R.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.02.2018; Wiley Open Access; John Wiley and Sons Inc; Wiley
• Subjects: Acclimatization; Algae; Bacteria; Chlorophyll; Communities; Community structure; Coral bleaching; Coral reefs; Corals; Dissolved organic carbon; Dissolved organic nitrogen; Dominance; Dynamic stability; Endosymbionts; Endozoicomonas; Environmental changes; Environmental conditions; Environmental Sciences; Experiments; Gene sequencing; host–microbe interaction; Laboratories; Life Sciences; Metabolism; metaorganism; Microbial activity; microbiome; Microbiomes; Microorganisms; Mortality; Nutrients; Organic nitrogen; Original Research; Phenotypes; Pocillopora verrucosa; pollution; rRNA 16S; Stability analysis; Symbiodinium; symbiosis; Red Sea; host–microbe interaction; pollution; microbiome; coral reefs; symbiosis; metaorganism
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3830

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. 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 conditions of excess organic carbon (DOC) and nitrogen (DON) over a set of independent 14‐day experiments. Exposure to excess nutrients rapidly affected coral health, resulting in two distinct stress phenotypes: coral bleaching under excess DOC and coral mortality (>90% tissue loss) under excess DON. In contrast to the algal endoysmbionts, the associated bacterial community remained remarkably stable and was dominated by two Endozoicomonas phylotypes, suggesting that the bacterial microbiome of P. verrucosa may be unable to respond or acclimatize to rapid changes in the environment, contrary to what was previously observed in many other corals.