Nutritional evaluation of Pleurotus eryngii stem wastes and soybean meal fermented by probiotics alone or in combination with proteolytic and cellulolytic enzymes in Larimichthys crocea

BFPS and EBFPS improved growth performance, feed utilization, and serum immunity. • EBFPS showed better potential in improving intestinal morphology and microbial homeostasis than BFPS. • EBFPS activated TLRs signaling and inhibited intestinal inflammation, while conversely in BFPS. A 56-day feeding trial was carried out to compare the effects of king oyster mushroom ( Pleurotus eryngii ) and soybean meal (SM) fermented by microorganisms ( Saccharomyces cerevisiae Sa, Bacillus pumilus SE5, and Lactobacillus lactis 17, BFPS) alone or in combination with enzymes (cellulase and protease, EBFPS) on growth performance, serum biochemistry, and intestinal health in large yellow croaker ( Larimichthys crocea ). Large yellow croaker was randomly assigned to three groups (control, BFPS, and EBFPS) with four replicates (160 fish per replicate) per group. Results showed that BFPS and EBFPS improved growth performance and feed utilization, but did not affect organ-somatic indices. Dietary BFPS and EBFPS decreased serum aspartate transaminase and alanine transferase activities, implying superior liver health of croakers. Moreover, there were significant enhancements of serum alkaline phosphatase and acid phosphatase activities in BFPS and EBFPS groups, as well as immunoglobulin M content in EBFPS group. In terms of inflammatory cytokines, serum IL-1β and TGF-β1 contents were reduced in croakers fed with BFPS-contained diet, while croakers fed with EBFPS-contained diet showed reduction of serum IL-1β content, but not TGF-β1. Dietary BFPS decreased MT, VH, VW, and expressions of occlidin and jam , while enhanced MT, VH, VW, and zo-1 mRNA level were observed in fish fed with EBFPS-contained diet. Dietary BFPS resulted in significant up-regulation of pro-inflammatory il-1β and il-6 mRNA levels, as well as significant down-regulation of il-4/13a , il-4/13b , il-10 and tgf-β1 , tlr1 and tlr2b mRNA levels. Inconsistently, dietary EBFPS up-regulated il-4/13a , il-10 , tlr1 , tlr2a , and tlr2b mRNA levels. EBFPS, rather than BFPS, increased α-diversity of intestinal microbiota, and β-diversity revealed that the cluster of the EBFPS group was notably separated from the control and BFPS groups' cluster. Furthermore, the enhancement of beneficial Firmicutes and the reduction of pathogenic Proteobacteria and Brevinema were observed in croakers fed with EBFPS-contained diet. BFPS increased Proteobacteria and reduced Brevinema . Overall, EBFPS, as a functional protein source, could efficiently improve growth, immunity, and intestinal health of large yellow croaker ( L. crocea ) compared to BFPS.