Importance of S-layer proteins in probiotic activity of Lactobacillus acidophilus M92

To investigate the functional role of surface layer proteins (S-layer) in probiotic strain Lactobacillus acidophilus M92, especially its influence on adhesiveness to mouse ileal epithelial cells.

Sodium dodecyl sulphate polyacrylamide gel electrophoresis of cell surface proteins revealed the presence of potential surface layer (S-layer) proteins, ca at 45 kDa in L. acidophilus M92. Southern blot with pBK1 plasmid, containing slpA gene, gave a positive signal, suggesting that L. acidophilus M92 has a slpA gene coding for the S-layer proteins. S-layer proteins of this strain are present during all phases of growth. The S-layer proteins appeared when cells treated with 5 mol l(-1) LiCl were allowed to grow again. Removal of the S-layer proteins reduced adhesion of L. acidophilus M92 to mouse ileal epithelial cells. Furthermore, the viability of cells without S-layer were reduced in simulated gastric juice at low pH range (2, 2.5, 3) and simulated pancreatic juice with bile salts (1.5 and 3 g l(-1)). S-layer proteins of L. acidophilus M92 were resistant to pepsin and pancreatin, in contrast, the treatment with proteinase K led to a significant proteolysis of the S-layer proteins.

These results demonstrated functional role of S-layer; it is responsible for adhesiveness of Lactobacillus acidophilus M92 to mouse ileal epithelial cells and has a protective role for this strain.

S-layer proteins have an important role in the establishment of probiotic strain Lactobacillus acidophilus M92 in the gastrointestinal tract.