Abstract
This study was conducted to evaluate the effects of Monascus purpureus M-32 fermented soybean meal (MFSM) on growth, immunity, intestinal morphology, intestinal microbiota, and intestinal metabolome of Pacific white shrimp (Litopenaeus vannamei). Four groups of diets were formulated, including control group (30% fish meal and 30% soybean meal [SBM] included in the basal diet) and three experimental groups which MFSM replaced 20% (MFSM20), 40% (MFSM40), and 60% (MFSM60) of SBM in control group, respectively. Results showed that the soluble proteins larger than 49 kDa in MFSM were almost completely degraded. Meanwhile, the crude protein, acid-soluble protein, and amino acid in MFSM were increased. The results of shrimp culture experiment showed that the replacement of SBM with MFSM decreased FCR (P < 0.001) and content of malondialdehyde (P = 0.007) in the experimental groups, and increased weight gain rate (P = 0.006), specific growth rate (P = 0.002), survival rate (P = 0.005), intestinal villus height (P < 0.001), myenteric thickness (P = 0.002), the activities of superoxide dismutase (P = 0.002), and lysozyme (P = 0.006) in experimental groups, as well as increased content of calcium (Ca(2+)) and phosphorus (PO43-) in blood and muscle, and enhanced resistance to Vibrio parahaemolyticus infection. The gut microbiota of MFSM groups was significantly different from that of the control group, and the abundance of Actinobacteria and Verrucomicrobia increased significantly in the MFSM60 group, whereas Proteobacteria and Firmicutes decreased. Compared with the control group, there were significant changes in the levels of several intestinal metabolites in the MFSM60 group, including leukotriene C5, prostaglandin A1, taurochenodeoxycholic acid, carnosine, and itaconic acid. The fermentation of SBM by the strain M. purpureus M-32 has the potential to enhance the nutritional quality of SBM, promote the growth of L. vannamei, boost immune response, improve intestinal morphology and microbiota composition, as well as influence intestinal metabolites.