New binding assay and preparative trial of cell-surface lectin from Lactobacillus acidophilus group lactic acid bacteria.

To select Lactobacillus acidophilus group bacteria as a probiotic yogurt starter, we designed a new screening method that measures the binding activity of surface layer protein to rat colonic mucin, which contains sugar chains similar to those in human colonic mucin. The B1 subgroup (Lactobacillus gasseri), which is the dominant strain in the human intestinal tract, showed the highest binding activity to rat colonic mucin among all the subgroups of L. acidophilus. The binding activity of the surface layer protein was also shown to be significantly reduced after periodate oxidation of the rat colonic mucin. This new screening method is useful for rapid selection of L. acidophilus strains that have high adhesion to the human intestinal tract. Lectin-like proteins that were bound to rat colonic mucin were isolated from the surface layer proteins with a rat colonic mucin-coated membrane and were analyzed by SDS-PAGE. A few main bands together with several minor bands were observed on the electrophoretograms obtained from the strains tested. It is possible that those lectin-like proteins contribute to adhesion of the bacterial cell to human colonic mucosa by binding specifically to carbohydrate portions.