Abstract
The sea urchin Strongylocentrotus purpuratus (order Camarodonta, family Strongylocentrotidae) can be found dominating low intertidal pool biomass on the southern coast of Oregon, USA. In this case study, three adult sea urchins were collected from their shared intertidal pool, and the bacteriome of their pharynx, gut tissue, and gut digesta, including their tide pool water and algae, was determined using targeted high-throughput sequencing (HTS) of the 16S rRNA genes and bioinformatics tools. Overall, the gut tissue demonstrated Arcobacter and Sulfurimonas (Epsilonproteobacteria) to be abundant, whereas the gut digesta was dominated by Psychromonas (Gammaproteobacteria), Propionigenium (Fusobacteria), and Flavobacteriales (Bacteroidetes). Alpha and beta diversity analyses indicated low species richness and distinct microbial communities comprising the gut tissue and digesta, while the pharynx tissue had higher richness, more closely resembling the water microbiota. Predicted functional profiles showed Kyoto Encyclopedia of Genes and Genomes (KEGG) Level-2 categories of energy metabolism, membrane transport, cell motility, and signal transduction in the gut tissue, and the gut digesta represented amino acid, carbohydrate, vitamin and cofactor metabolisms, and replication and repair. Co-occurrence network analysis showed the potential relationships and key taxa, such as the highly abundant Arcobacter and Propionigenium, influencing population patterns and taxonomic organization between the gut tissue and digesta. These results demonstrate a trend of microbial community integration, allocation, predicted metabolic roles, and taxonomic co-occurrence patterns in the S. purpuratus gut ecosystem.
Highlights
IntroductionThe purple sea urchin Strongylocentrotus purpuratus (order Camarodonta, family Strongylocentrotidae) inhabits the rocky tide pools along the North-East Pacific from Alaska to Baja Mexico
The purple sea urchin Strongylocentrotus purpuratus inhabits the rocky tide pools along the North-East Pacific from Alaska to Baja Mexico
The role of gut bacteria in host health and digestion have been of interest beginning with the work of Lasker and Giese [9], who isolated gut bacteria from the gut digesta of S. purpuratus, showing the potential for these bacteria to digest polysaccharides from algal sources
Summary
The purple sea urchin Strongylocentrotus purpuratus (order Camarodonta, family Strongylocentrotidae) inhabits the rocky tide pools along the North-East Pacific from Alaska to Baja Mexico. The low intertidal tide pools on the southern Oregon coast are dominated by S. purpuratus and are interspersed with mosaics of tufted algae and invertebrate assemblages representing multiple phyla [7] The microhabitats of these tide pools are influenced by the feeding activity of the inhabiting sea urchins [7]. The pharynx tissue contains specialized mucus cells that contribute to the formation of a mucous envelope of ingested feed [10], forming individual pellets of gut digesta [11] This gut digesta pellet formation has been considered an evolved digestive strategy of this organism, likely as a result of water flow dynamics in the gut lumen environment [12]. The importance of gut bacteria in sea urchin host health was further supported in S. droebachiensis, in which microbial suppression through antibiotics showed a reduced capacity for host incorporation of essential amino acids [14]
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