First description of the Haliclystus auricula (Cnidaria: Staurozoa) jellyfish bacterial microbiome.

The bacterial microbiomes of cnidarians are currently being studied from different angles, which includes studies of the influence of bacteria on the nutrition, life cycles regulation and health. Additionally, symbiotic bacteria in cnidarians are considered as a potential source of new biologically active substances. At present, there is data available on microbiomes of all cnidarian classes - Anthozoa, Scyphozoa, Hydrozoa and Cubozoa except for the Staurozoa, a poorly studied group of the marine stalked jellyfish. Using a metagenomic approach, we have firstly described the bacterial microbiome of the staurozoan Haliclystus auricula from the Barents Sea.We showed qualitative composition of the bacterial community, associated with H. auricula, and revealed at least 18 core bacterial genera. The Colwellia sp. and Marinomonas sp. were dominant, whereas the relative abundance of other bacteria was lower. Most of the core bacteria were psychrophilic or psychrotolerant, and some of them were previously shown to be capable of complex polysaccharide degradation and antimicrobial compounds production. A comparison of the H. auricula bacterial microbiome with those of other cnidarian species revealed common features at high taxonomic levels, but significant differences at the genus level. However, the most abundantly represented genera of bacteria were found in all studied species, but their relative abundance in H. auricula was unique. Apparently, the composition of the bacterial community in H. auricula is heavily influenced by Barents Sea which may explain its differences from other, warmer-water cnidarians.