The antigen recognized by the α-La scFv is the S-layer protein A. A) Western blot using α-La scFv as primary antibody and α-SV5-Alkaline Phosphatase as secondary for detection. An obvious ~45KDa band appeared in the lane containing L. acidophilus (La) lysate and not the lane containing L. johnsonii (Lj) lysate was extracted and identified using MS/MS. B) Protein alignment of S-layer proteins from closely related Lactobacillus species (La = Lactobacillus acidophilus, Lh = Lactobacillus helveticus, Lo = Lactobacillus oris). The two La peptide sequences recovered after MS/MS analysis are indicated with solid triangles or circles above the sequence.