Effects of polypeptidin feeding on growth and intestinal flora of Apostichopus japonicus

Apostichopus japonicus (A. japonicus) is known as one of the most popular varieties in aquaculture due to its rich nourishment and potential medicinal value. In recent years, with the abnormal change of marine environment and global climate, new challenges are arising continually in the culture process of A. japonicus. Intestinal flora plays an important role in host health and growth, and a lot of studies confirmed the close relationship between the composition change of intestinal flora and the growth of sea cucumbers. In this study, polypeptidin belonging to bacteriocins, was as an additive ingredient in sea cucumber feed. The growth of A. japonicus increased significantly after polypeptidin feeding, and the growth rate reached the highest with 1 % polypeptidin especially. Subsequently 16 S rRNA of gut microbiota from 1 % polypeptidin group was sequenced and analyzed for richness and diversity index, but the results showed that polypeptidin supplement did not markedly change the diversity and main composition of gut microbiota compared to the control. So the further analyze was performed by dependent t-test for paired samples, and found that the abundance of only a few of species at the class level changed significantly, including Alphaproteobacteria, Desulfotomaculia and Chlamydiae, but many species at the genus level changed significantly. Some important metabolic pathways were identified through function prediction, like TCA cycle, streptomycin biosynthesis and phenylalanine metabolism. At this basis, the analysis combined with the genuses and the metabolic pathways demonstrated that polypeptidin might regulate the richness of some bacteria, which could be involved in enzyme degradation, antibacterial substances secreting or underlying pathogenic tendency of gut microbiota ecosystem. These fine-tunings instead of main community structure change were probably more beneficial to the intestinal flora health, and finally contributed to the growth of A. japonicus. Thus, polypeptidin serves as a mild, non-stimulating feed supplement for A. japonicus, and has good prospects for application.