Variability of S-layer proteins in Lactobacillus helveticus strains

The presence of S-layer proteins in the cell envelope of Lactobacillus helveticus may be technologically important. S-layer proteins are the adhesion site for cell envelope proteinase, which forms the proteolytic pathway in bacteria. Eleven strains of L. helveticus were examined for the presence of S-layer proteins and slpH genes. S-layer proteins from six strains were identified and sequenced. Multiple alignments of the deduced amino acid sequences demonstrated a strong sequence conservation of all Slp studied. Transmission Electron Microscopy analysis of the cells revealed the typical cell wall architecture of the S-layer. This is the first report on characterisation of glycosylated S-layer proteins from different strains of L. helveticus. The amino acid composition, the secondary structure, and the physical properties of these proteins were found to be quite similar to those of S-layer proteins from other lactobacilli. However, PCR analysis revealed that five of the examined strains of L. helveticus did not have slpH genes. This finding suggests that S-layer protein genes cannot be considered as housekeeping genes and cannot be used as molecular markers for L. helveticus.