FIGURE 1.

Variability of surface proteome and of adhesion among strains of Propionibacterium freudenreichii. (A) Guanidine-extracted surface layer associated proteins are variable. Seven strains of P. freudenreichii were cultured in milk ultrafiltrate and subjected to guanidine-extraction followed by SDS–PAGE (10%) gel electrophoretic analysis of the extracts. Gels were either Coomassie-Blue-stained (A) or transferred to a PVDF membrane. Surface proteins previously identified by mass spectrometry as InlA, LspA, SlpE, SlpA and SlpB in strain CB129 are indicated by 1, 2, 3, 4, and 5, respectively. (B) Western Blotting detection of surface layer protein SlpB. PVDF membranes were treated using rabbit antibodies raised against P. freudenreichii surface layer protein SlpB. (C) Adhesion to cultured human colon epithelial cells is variable. HT-29 cells were cultured to confluence in DMEM prior to co-incubation. Each well (1 × 10⁶ HT-29 cells) was added with 1 × 10⁸ colony-forming unit (CFU) of P. freudenreichii. Co-incubation was 60 min at 37°C in DMEM. After thorough washing with PBS, adhered bacteria were enumerated by CFU plate counting in trypsinized cells. Numbers of the strains used are indicated. Asterisks represent statistically significant differences between strains and were indicated as follows: ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.001. Adhesion is presented as a percent of the reference CB129 P. freudenreichii strain. Original gels and western blots, uncropped, are provided in Supplementary Figure S1.