PS 52-192 - Microbial dysbiosis precedes the onset of sea star wasting disease in Pycnopodia helianthoides

Background/Question/Methods

Sea star wasting (SSW) disease, a massive and ongoing epidemic, has affected more than 20 species of asteroids, leading to rapid death and decimation of sea star populations with cascading ecological consequences. The cause of the disease is yet unknown, however, a complex interaction of abiotic and biotic factors has been implicated. Here, we compare the microbiomes of the sunflower sea star, Pycnopodia helianthoides, before (Naïve) and during (Exposed and Wasting) the 2016 outbreak in Southeast Alaska to identify changes and interactions in the microbial communities associated with sea star health and exposure. Through microbial community analysis, we sought to answer the following questions: (1) How does the diversity of microbial taxa differ between and within Naïve, Exposed, and Wasting asteroids? (2) What microbial taxa are differentially abundant across these groups and may play a role in disease progression? (3) Is SSW characterized by certain microbial interactions (co-occurrence)?

Results/Conclusions

We found a marked increase in the bacterial taxa diversity (alpha and beta diversity) preceding signs of SSW and differentiation in microbial composition. We observed a loss of resident aerobic taxa (Spirochaetaceae, Flammeovirgaceae, and order Rickettsiales) accompanied by proliferation of putatively pathogenic and facultative anaerobic taxa (Vibrionaceae and Moritellaceae) in both Exposed and Wasting animals–along with the appearance of obligate anaerobe taxa (Fusobacteriaceae, and order Clostridiales) predominantly in Wasting animals. Furthermore, analysis of bacterial co-occurrence networks between site/animal health groups revealed an increase in the number of correlations between putatively pathogenic taxa associated with anaerobic processes, that also exhibited negative correlations with aerobic taxa normally present in healthy stars. Prediction of metabolic pathways identified significant gain of metabolic functions in Exposed compared to Naive stars, followed by depletion of metabolic functions as animals show physical signs of disease. Altogether, these findings support a model where perturbations in the sea star’s microenvironment lead to proliferation of copiotrophic and anaerobic taxa prior to the onset of SSW signs. These early community shifts lead to oxygen depletion and further changes in microbiome composition including the loss of normally beneficial microbial taxa prior to the onset of signs of disease.