Evaluation of regulatory capacity of three lactic acid bacteria on the growth performance, non-specific immunity, and intestinal microbiota of the sea cucumber Apostichopus japonicus

Lactic acid bacteria (LAB) have been extensively used as probiotics in aquaculture. However, probiotic effects of different inter-generic strains of LAB on sea cucumber Apostichopus japonicus are still poorly understood. Here, sea cucumber were fed with five diets for 63 days, including a basal diet (the control, C group), a florfenicol diet (15 mg/kg; the positive control, FL group) and three LAB diets, i.e., the basal diets supplemented with Lactobacillus plantarum W2 (LP group), Enterococcus faecium LYB (EF group) and Pediococcus acidilactici Nj (PA group) at the dose of 1 × 1010 CFU/kg diet, respectively. A stimulation test with inactivated Vibrio splendidus was then performed and characterized immune responses of sea cucumber over 168 h. The results showed that all three LAB significantly enhanced the growth performance of sea cucumber, with the LP diet showed the best growth-promoting effect. The LP and PA diets significantly increased coelomocyte phagocytic, respiratory burst, superoxide dismutase, alkaline phosphatase, acid phosphatase, catalase, and lysozyme activities. The LP and EF diets significantly up-regulated the intestinal immune genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) expression levels, while PA diet did not significantly up-regulate the Aj-p50 gene expression level. Meanwhile, all three LAB significantly enhanced intestinal immune response. Florfenicol diet significantly decreased phagocytic and alkaline phosphatase activities, down-regulated the Aj-lys gene expression, and suppressed intestinal immune response. L. plantarum W2 significantly increased the diversity of the intestinal microbiota in sea cucumber, and the P. acidilactici Nj significantly improved both the diversity and richness. A higher relative abundance of Actinobacteriota, norank_f_Rhodobacteraceae, and Sedimentitalea was observed in the LP, EF, and PA groups, respectively, while a lower relative abundance of Firmicutes was showed in the FL group. All three LAB improved the stability of the intestinal microbial networks and up-regulated the functional pathways of intestinal microbiota associated with amino acid metabolism. However, florfenicol reduced microbial network stability and significantly inhibited the intestinal microbiota functions. In conclusion, L. plantarum W2, E. faecium LYB, and P. acidilactici Nj can be effectively used as probiotics in sea cucumber aquaculture. Among them, L. plantarum W2 exhibited the best effect on sea cucumber when the growth performance, non-specific immunity, and intestinal microbial structure and functions were considered collectively.