Bacterial community composition in gut content and ambient sediment of two tropical wild sea cucumbers (Holothuria atra and H. leucospilota)

Sea cucumbers play an important role in sediment bioturbation in coral reef and rocky intertidal ecosystems, and bacteria were a commonly-reported component of holothuroid diets. Bacterial community composition in the foregut and hindgut of two common tropical sea cucumbers ( Holothuria atra and H. leucospilota ) and the ambient surface sediment were investigated using high throughput sequencing based on 16S rRNA gene analysis. A total of 5 584 operational taxonomic units (OTUs) were obtained from 25 samples based on a 97% threshold, and more than half of the OTUs ( n =3 694, 66.2%) were shared by the gut contents of two species of sea cucumbers and surrounding sediments. Bacterial richness and diversity in sediment samples were significantly higher than those in the gut content samples ( P