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Live commensal Bacillus siamensis LF4 showed reparative potentials against high SM-induced negative effects, but whether its paraprobiotic (heat-killed B. siamensis , HKBS) and postbiotic (cell-free supernatant, CFS) forms had reparative functions and potential mechanisms are not yet known. In this study, the reparative functions of HKBS and CFS were investigated by establishing an injured model of spotted seabass (Lateolabrax maculatus) treated with dietary high soybean meal (SM). The results showed that HKBS and CFS effectively mitigated growth suppression, immune deficiency, and liver injury induced by dietary high SM. Simultaneously, HKBS and CFS application positively shaped intestinal microbiota by increased the abundance of beneficial bacteria (Fusobacteria, Firmicutes, Bacteroidota, and Cetobacterium) and decreased harmful bacteria (Proteobacteria and Plesiomonasare). Additionally, HKBS and CFS improved SM-induced intestinal injury by restoring intestinal morphology, upregulating the expression of tight junction proteins, anti-inflammatory cytokines, antimicrobial peptides, downregulating the expression of pro-inflammatory cytokines and apoptotic proteins. Furthermore, HKBS and CFS intervention significantly activated TLR2, TLR5 and MyD88 signaling, and eventually inhibited p38 and NF-κB pathways. In conclusion, paraprobiotic (HKBS) and postbiotic (CFS) from B. siamensis LF4 can improve growth, immunity, repair liver and intestinal injury, and shape intestinal microbiota in L. maculatus fed high soybean meal diet, and TLRs/p38 MAPK/NF-κB signal pathways might be involved in those processes. These results will serve as a base for future application of paraprobiotics and postbiotics to prevent and repair SM-induced adverse effects in fish aquaculture. • Paraprobiotic and postbiotic from B. siamensis LF4 improved growth, immunity and liver health. • Paraprobiotic and postbiotic improved the intestinal barrier function and microbiota via modulating TLRs/MAPKs/NF-κB pathways. • Paraprobiotic and postbiotic showed better reparative potentials. [ABSTRACT FROM AUTHOR]

β-conglycinin and glycinin, two major heat-stable anti-nutritional factors in soybean meal (SM), have been suggested as the key inducers of intestinal inflammation in aquatic animals. In the present study, a spotted seabass intestinal epithelial cells (IECs) were used to compare the inflammation-inducing effects of β-conglycinin and glycinin. The results showed that IECs co-cultured with 1.0 mg/mL β-conglycinin for 12 h or 1.5 mg/mL glycinin for 24 h significantly decreased the cell viability (P < 0.05), and overstimulated inflammation and apoptosis response by significantly down-regulating anti-inflammatory genes (IL-2, IL-4, IL-10 and TGF-β1) expressions and significantly up-regulated pro-inflammatory genes (IL-1β, IL-8 and TNF-α) and apoptosis genes (caspase 3, caspase 8 and caspase 9) expressions (P < 0.05). Subsequently, a β-conglycinin based inflammation IECs model was established and used for demonstrating whether commensal probiotic B. siamensis LF4 can ameliorate the adverse effects of β-conglycinin. The results showed β-conglycinin-induced cell viability damage was completely repaired by treated with 109 cells/mL heat-killed B. siamensis LF4 for ≥12 h. At the same time, IECs co-cultured with 109 cells/mL heat-killed B. siamensis LF4 for 24 h significantly ameliorated β-conglycinin-induced inflammation and apoptosis by up-regulating anti-inflammatory genes (IL-2, IL-4, IL-10 and TGF-β1) expressions and down-regulated pro-inflammatory genes (IL-1β, IL-8 and TNF-α) and apoptosis genes (caspase 3, caspase 8 and caspase 9) expressions (P < 0.05). In summary, both β-conglycinin and glycinin can lead to inflammation and apoptosis in spotted seabass IECs, and β-conglycinin is more effective; commensal B. siamensis LF4 can efficiently ameliorate β-conglycinin induced inflammation and apoptosis in IECs. • β-conglycinin and glycinin can lead to inflammation and apoptosis in spotted seabass IECs. • β-conglycinin is more effective than glycinin in inducing inflammation and apoptosis. • B. siamensis LF4 can ameliorate β-conglycinin induced inflammation and apoptosis. [ABSTRACT FROM AUTHOR]