Introducing the starlet sea anemone Nematostella vectensis as a model for investigating microbial mediation of health and disease in hexacorals

Abstract

All animals in their natural state harbor complex communities of microbes including those that are beneficial (symbionts), neutral, or harmful (pathogens). The dynamic interactions between animals and their microbiota often dictate the balance between health and disease. Environmental perturbations may disrupt this delicate balance and allow proliferation of pathogens. A global example of this is the case of reef-building corals (class Anthozoa, subclass Hexacorallia) where rising seawater temperatures and coastal eutrophication have been correlated to increased prevalence of microbial diseases and coral bleaching. Despite such correlations, factors that govern whether animal-associated microbes support health or cause disease are largely unknown. Here I employ an emerging Cnidarian model, the starlet sea anemone Nematostella vectensis, to investigate whether hexacorals maintain communities of beneficial microbes. I hypothesize that loss of this beneficial community by environmental perturbations will negatively impact the physiology of the host. As a first step to testing my hypothesis I have characterized the microbial communities associated with apparently healthy N. vectensis under natural and laboratory conditions using 16S rRNA gene clone libraries, terminal restriction fragment length polymorphism analysis (T- RFLP), fluorescent in situ hybridization (FISH) and cultivation-based analysis. N. vectensis microbiomes revealed the presence of a novel lineage of epsilon-Proteobacteria associated with animals collected from salt marshes in Sippewissett (Massachusetts), Clinton (Connecticut) and Mahone Bay (Nova Scotia).

(cont.) In addition, ribotypes of Pseudomonas pseudoalcaligenes, Endozoicimonas elysicola and Spirochaetes were found associated with multiple environments. Most of the microbial populations in the N. vectensis microbiome were closely related to microbial associates of other hexacorallians. Observation of shared ribotypes among different sampling locations suggests a specific association with N. vectensis, consistent with a hypothesized role as symbionts. We also observed significant microbial community shifts in reduced-flora N. vectensis raised under sterile laboratory conditions and the persistence of a naturally occurring P. pseudoalcaligenes ribotype in the microbiome under different antibiotic perturbations, supporting the hypothesis that this population maintains association with N. vectensis across changing environmental conditions. Finally FISH analysis using eubacteria and ribotype-specific probes revealed that microbes form cell aggregates in tight association with animal mesentery tissues, suggesting that host-microbe interactions may be tissue-specific.