(A) Details of construction of the recombinant plasmid pPG-E-α-β2-ε-β1. (B) The constitutive expression of screening marker enhanced green fluorescent protein (EGFP) observed by ultra-high-resolution microscopy. (C) The constitutive expression of the fusion protein identified by western blotting using mouse anti-α, β2, ε, and β1 toxoid monoclonal antibody, respectively. (D) Segregational stability results of the recombinant lactobacillus with serial subcultures targeting the genes of interest. Lane 1: positive recombinant plasmid pPG-E-α-β2-ε-β1 control; lanes 2–11: the identification results of every five generations of subcultures pPG-E-α-β2-ε-β1/L. casei targeting the fusion gene α-β2-ε-β1 for 50 generations. (E) Segregational stability results of the recombinant lactobacillus targeting the screening marker EGFP. The tolerance of the recombinant lactobacillus to hypertonic environment (F), simulated intestinal fluid environment (G), 0.5% bile salt (H), and simulated gastric environment (I).