Recombinant Bacillus subtilis expressing functional peptide and its effect on the growth, antioxidant capacity and intestine in Megalobrama amblycephala

P4 is a functional small peptide screened after enzymatic hydrolysis of cotton meal. Bacillus subtilis CM66 (OB) underwent recombination to yield Bacillus subtilis CM66-P4’ (RB), capable of secreting P4. This study aimed to assess the effects of RB on the growth, antioxidant capacity and intestine in blunt snout bream (Megalobrama amblycephala) through in vitro and in vivo experiments. Seven groups were formed: a control group (CG) with no additional bacteria, three groups with different concentrations of Bacillus subtilis CM66 (2 × 107, 2 × 108, 2 × 109 CFU/kg - referred to as LOG, MOG, HOG), and three groups with corresponding concentrations of Bacillus subtilis CM66-P4’ (2 × 107, 2 × 108, 2 × 109 CFU/kg - referred to as LRG, MRG, HRG). After 8 weeks of feeding, the results showed that OB and RB had no significant impact on growth performance. Compared with CG and MOG, the MRG group exhibited a significant increase in protease and total anti-oxidative capacity (T-AOC) in the intestine (P < 0.05). The mRNA expression of mucin-2 in MOG and MRG were significantly increased (P < 0.05). Compared with CG, muscle layer thickness (MLT) of MOG and MRG were significantly increased (P < 0.05), villus height (VH) and goblet cells numbers of MRG were increased (P < 0.05). Species richness and diversity of intestinal microbes were significantly increased in MOG and MRG (P < 0.05). P4 demonstrated a significant alleviation of the increase in sod expression in intestinal epithelial cells (IECs) treated with H2O2 and mitigated the decrease in cells activity (P < 0.05). In conclusion, P4 effectively mitigated the impact of H2O2 on IECs in blunt snout bream. Dietary supplementation of 2 × 108 CFU/kg RB (secreting P4) improved the intestinal microbes and intestinal barrier, resulting in enhanced antioxidant capacity.