BopA Does Not Have a Major Role in the Adhesion of Bifidobacterium bifidum to Intestinal Epithelial Cells, Extracellular Matrix Proteins, and Mucus

Abstract

The ability of bifidobacteria to adhere to the intestine of the human host is considered to be important for efficient colonization and achieving probiotic effects. Bifidobacterium bifidum strains DSM20456 and MIMBb75 adhere well to the human intestinal cell lines Caco-2 and HT-29. The surface lipoprotein BopA was previously described to be involved in mediating adherence of B. bifidum to epithelial cells, but thioacylated, purified BopA inhibited the adhesion of B. bifidum to epithelial cells in competitive adhesion assays only at very high concentrations, indicating an unspecific effect. In this study, the role of BopA in the adhesion of B. bifidum was readdressed. The gene encoding BopA was cloned and expressed without its lipobox and hydrophobic signal peptide in Escherichia coli, and an antiserum against the recombinant BopA was produced. The antiserum was used to demonstrate the abundant localization of BopA on the cell surface of B. bifidum. However, blocking of B. bifidum BopA with specific antiserum did not reduce adhesion of bacteria to epithelial cell lines, arguing that BopA is not an adhesin. Also, adhesion of B. bifidum to human colonic mucin and fibronectin was found to be BopA independent. The recombinant BopA bound only moderately to human epithelial cells and colonic mucus, and it failed to bind to fibronectin. Thus, our results contrast the earlier findings on the major role of BopA in adhesion, indicating that the strong adhesion of B. bifidum to epithelial cell lines is BopA independent.

Bifidobacterium bifidum as an example of a specialized human gut commensal

“…However, recently the role of BopA in the adhesion of B. bifidum was reassessed and, in contrast to what was published earlier, the strong adhesion of B. bifidum to epithelial cell lines is mainly BopA-independent (Kainulainen et al, 2013). …”

Mucosal Prevalence and Interactions with the Epithelium Indicate Commensalism of Sutterella spp.

“…to Caco-2 and HT-29 cell lines (3, 8, and 21 days post-plating), mucus, and ECM proteins was studied as described previously (Kainulainen et al, 2013; Reunanen et al, 2015). Briefly, the Caco-2 and HT-29 cell lines were seeded on a 96-well tissue culture plate with 10,000 cells well -1 .…”

Akkermansia muciniphila Adheres to Enterocytes and Strengthens the Integrity of the Epithelial Cell Layer

“…Remarkably, A. muciniphila showed no binding to human colonic mucin, even though it lives in an intimate relationship with the intestinal mucosa and also utilizes it as a nutrient. We have shown previously, by using the same mucus binding assay, that the human intestinal isolates L. rhamnosus GG and Bifidobacterium bifidum DSM20456 and MIMBb75 bind strongly to human colonic mucus (15,18). However, L. rhamnosus and B. bifidum are nonmucolytic bacteria, whereas A. muciniphila is a mucin-degrading bacterium.…”

“…Live Akkermansia muciniphila cells were used to produce a polyclonal rabbit antiserum at the Laboratory Animal Centre of the University of Helsinki. Immunization was carried out as described previously (15). Briefly, overnight-grown cells were washed once with PBS and were resuspended in PBS to a final concentration of 10 9 ml Ϫ1 .…”

“…Human colonic mucus was isolated as described previously (15,16) from healthy parts of colons from colorectal cancer patients undergoing surgery. The use of human intestinal mucus in the adhesion studies was approved by the ethical committee of the Hospital District of Southwest Finland.…”