Bacillus cereus and rhubarb regulate the intestinal microbiota of sea cucumber (Apostichopus japonicus Selenka): Species-species interaction, network, and stability

The homeostasis of intestinal microbiota plays a key role in host health. Probiotics and medicinal plant can affect the intestinal microbiota homeostasis but poorly understood. Dietary supplementation with Bacillus cereus BC-1 (BC group) and rhubarb (Rheum officinale Bail, RH group) had no significant impacts on the overall composition of intestinal bacterial community of sea cucumber in terms of α-diversity, richness, or evenness compared to Control group, although a significant reduction in Algibacter was observed in BC and RH groups, as well as Flavobacteriaceae in RH group. Based on species-species interaction, intestinal microbiota in Control, BC, and RH groups formed its own characteristic ecological network model, in which dominant microbes was the main component. In the network, some operational taxonomic units (OTUs) performed as connectors and module hubs and contributed to maintaining the stability of bacterial community. B. cereus BC-1 and rhubarb supplementation could promote the stability of bacterial community through strengthening the cooperative interactions between species, facilitating OTUs to form larger sub-modules, and increasing the number of module hubs. Collaboration between bacteria species could enhance bacterial metabolism and promote digestion of nutrients. B. cereus BC-1 supplementation could improve utilization of feed by increasing microbial fermentation of starch, sucrose and protein, and rhubarb improved microbial metabolism involved in carbohydrate and protein metabolism and reduced microbial lipid metabolism. Generally, our results suggested that though dietary supplementation with B. cereus BC-1 and rhubarb had no significant impacts on the composition of bacterial community, they promoted the homeostasis of intestinal microbiota by affecting interspecific interactions within bacterial community, and then improved the capacity of nutrient digestion of intestinal microbiota.