Sea star microbiome and potential role in sea star wasting disease

During the summer of 2013, Pisaster ochraceus experienced a mass die-off event due to a poorly understood syndrome called sea star wasting disease (SSWD). Symptoms prior to death included lesions, limb detachment, and tissue degradation. Since then, SSWD has spread to much of the North American Pacific Coast and has been found in over twenty species of sea stars. The focus of our research was to explore the role of sea star associated bacteria in SSWD. We collected several hundred bacterial isolates from the epidermal surfaces of healthy and diseased sea stars that can degrade collagen, the major component of sea star epidermis. We assigned tentative identifications via 16S rRNA gene sequencing and comparison with extant databases. We then explored the community interactions among these isolates with an antagonism assay involving co-culture in Petri plates. Finally, we collected endosymbionts from beneath the epidermal surface by growing out bacteria from surface-sterilized tissues, and assigned tentative identification as above. While our research does not identify a causal agent of SSWD, it provides a foundation for understanding the microbiome of sea star epidermal tissues. We hypothesize that bacteria within the sea star microbiome include both protective and opportunistically pathogenic species.