Abstract
Marine invertebrates associate with diverse microorganisms. Microorganisms even inhabit coelomic fluid (CF), namely, the fluid filling the main body cavity of echinoderms. The CF microbiota potentially impacts host health and disease. Here, we analysed the CF microbiota in two common coastal starfish species, Patiria pectinifera and Asterias amurensis. Although microbial community structures were highly variable among individual starfish, those of P. pectinifera were compositionally similar to those in the surrounding seawater. By contrast, many A. amurensis individuals harboured unique microbes in the CF, which was dominated by the unclassified Thiotrichales or previously unknown Helicobacter-related taxon. In some individuals, the Helicobacter-related taxon was the most abundant genus-level taxon, accounting for up to 97.3% of reads obtained from the CF microbial community. Fluorescence in situ hybridization using a Helicobacter-related-taxon-specific probe suggested that probe-reactive cells in A. amurensis were spiral-shaped, morphologically similar to known Helicobacter species. Electron microscopy revealed that the spiral cells had a prosthecate-like polar appendage that has never been reported in Helicobacter species. Although culture of Helicobacter-related taxon was unsuccessful, this is the first report of the dominance of a Helicobacter-related taxon in invertebrates and non-digestive organs, reshaping our knowledge of the phylogeography of Helicobacter-related taxa.
Highlights
Marine animals live with a diverse array of microorganisms
We found that the Coelomic fluid (CF) of echinoderms could be a reservoir for unique microorganisms including potentially pathogenic and/or symbiotic bacteria
Many factors potentially influence the composition of starfish CF microbiota, including genetic background, diet, age, stress and environmental factors
Summary
Marine animals live with a diverse array of microorganisms. Like the human microbiome, fish gut bacteria have been intensively studied and suggested to play various significant roles in nutrition, immunity, and defence[1,2,3]. Understood in many phyla of marine invertebrates, the natural diversity of host-associated microbiota has little been studied in Echinodermata members such as starfish, sea urchins, and sea cucumbers[10, 11]. The coelomocytes phagocytose cell debris and the microorganisms, e.g. microorganisms that invade into the body after injury and autotomy[15] Despite this immune system activity, the CF of sea cucumber was reported to harbour unique microbial communities including Sulfurospirillum- and Sulfuricurvum-related taxa within the class Epsilonproteobacteria[16]. These starfish are top predators in some marine ecosystems, they are under attack by viruses and bacteria[17]. We addressed the questions of whether the CF bacterial composition of A. amurensis and P. pectinifera differs from that of the surrounding seawater, and whether the composition shows a geographical pattern
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