Cell Surface-associated Proteins of Gastrointestinal Strains of Lactobacilli

Abstract

Twenty-eight strains of gastrointestinal lactobacilli, comprising isolates classified as Lactobacillus reuteri , L. acidophilus , L. delbrueckii , L. fermentum , L. gasseri and L. salivarius , were examined for the presence of cell-surface polypeptides. Whole cells were radioactively labelled with 125 I using lactoperoxidase or chloramine T as catalyst, proteins were extracted with sodium dodecyl sulphate (SDS) and separated by SDS-polyacrylamide gel electrophoresis. All lactobacilli tested had between 5 and 20 proteins that were accessible to the labelling agents on the surface of whole cells. Strains of L. reuteri had similar surface polypeptide profiles and were characterised by the presence of a high molecular mass band of approximately 185 kDa. Strains of L. acidophilus could be grouped on the basis of their surface protein patterns. In one group (five strains) the surface protein profile was dominated by a surface array protein of molecular mass 45 kDa. In the other groups approximately 15 polypeptides were identified as being surface exposed and these ranged in molecular mass from c . 15 to 100 kDa. Strains of L. fermentum had either a characteristic surface protein profile (with bands at 135 kDa) or were poorly surface labelled. Fowl or rodent strains of different species possessed high molecular mass surface proteins (> 130 kDa). There was no correlation however between the presence of a specific polypeptide and the ability of a strain to adhere to stratified, squamous epithelial surfaces either in vitro or in vivo . Surface protein profiles may provide an aid to classification of lactobacillus strains of some species. Keywords: Gastrointestinal lactobacilli; Surface proteins; Lactobacillus proteins; Cell-surface labelling.