Meeting Abstract
Heart urchins (Echinoidea: Spatangoida) of the genus Brisaster are often abundant in deep water soft-sediment marine communities. They are deposit feeders and important bioturbators, but little is known of how these mud-dwellers process and digest food. Recently, a novel organ, the intestinal caecum, has been found in several spatangoid genera, but its physiological role is presently unknown. In B. townsendi (Agassiz, 1898), a heart urchin common in southern California, this organ is distinct from the rest of the gut in that it contains no sediment, but instead is filled with a dense microbial mass. We used next-generation sequencing to compare microbial communities in the stomach, intestine, intestinal caecum, and rectum of B. townsendi with the goal of understanding the caecum’s role in the echinoid’s biology. We collected B. townsendi from ~300 m depth off Long Beach, CA, and sampled the contents of each of the four gut regions from two specimens; in addition, the contents of the caecum were analyzed from an additional eight specimens. We extracted genomic DNA and amplified 16S rRNA genes using Illumina MiSeq. The results show that the caecum harbors a diverse community of anaerobic bacteria with large contributions from sulfate-reducing bacteria of Desulfobacterales averaging approximately 15.97% of the microbial community, as well as Spirochaetales (9.17%) and Bacteroidales (34.64%); this community is distinct from that of the rest of the gut. Using the relative abundance of microbial taxa within the different gut regions as well as additional data, a model for the role of the intestinal caecum in the digestive process of B. townsendi is presented.
