Reparative potentials of commensal-derived cellular components in juvenile Lateolabrax maculatus fed high soybean meal diet: Insight into growth performance, immunity, antioxidant capacity and liver health

An eight-week feeding trial was designed to estimate the effects of commensal Bacillus siamensis LF4-derived whole cell wall (CW), cell wall protein (CWP), lipoteichoic acid (LTA) and peptidoglycan (PGN) supplementation in a high soybean meal (SM) diet on the growth, immunity and liver health of spotted seabass (Lateolabrax maculatus). Fish continuously fed low SM (containing 16 % SM) and high SM (containing 40 % SM) diets were served as positive (LSM) and negative (HSM) control, respectively. After feeding high SM diet for 28 days, fish were fortified with B. siamensis LF4-derived CW, CWP, LTA or PGN until 56 days. The results showed that CW, LTA, and PGN application significantly increased FBW, WGR, and SGR (P<0.05), but not affect CF, VSI, HSI, IFR, ILI, and ISI (P > 0.05) in spotted seabass (L. maculatus) fed with high SM diet. Distal intestinal protease activity reduction caused by dietary high SM inclusion was significantly repaired when spotted seabass (L. maculatus) fortified with LTA and PGN (P<0.05). CW, LTA and PGN administration effectively increased serum immunity by enhancing ACP activity and C3, C4, IgM contents and reduced IL-1 beta content in serum of spotted seabass (L. maculatus) fed high SM diet (P<0.05). Significantly decreased serum MDA content in groups CW, LTA and PGN and significantly increased liver GSH content in group CWP were observed as compared to those in group HSM (P<0.05). Dietary CW, LTA and PGN supplementation, rather than CWP, repaired SM-induced liver injury by improving liver morphology and significantly reducing GOT and GPT activities (P<0.05). In summary, CW, LTA and PGN derived from B. siamensis LF4 effectively repaired SM-induced growth, feed utilization, immunity suppression and liver injury in spotted seabass (L. maculatus).