Binding of Human Plasminogen toBifidobacterium

Abstract

Bifidobacteria constitute up to 3% of the total microbiota and represent one of the most important health-promoting bacterial groups of the human intestinal microflora. The presence ofBifidobacteriumin the human gastrointestinal tract has been directly related to several health-promoting activities; however, to date, no information about the specific mechanisms of interaction with the host is available. In order to provide some insight into the molecular mechanisms involved in the interaction with the host, we investigated whetherBifidobacteriumwas able to capture human plasminogen on the cell surface. By using flow cytometry, we demonstrated a dose-dependent human plasminogen-binding activity for four strains belonging to three bifidobacterial species:Bifidobacterium lactis,B. bifidum, andB. longum. The binding of human plasminogen toBifidobacteriumwas dependent on lysine residues of surface protein receptors. By using a proteomic approach, we identified five putative plasminogen-binding proteins in the cell wall fraction of the model strainB. lactisBI07. The data suggest that plasminogen binding toB. lactisis due to the concerted action of a number of proteins located on the bacterial cell surface, some of which are highly conserved cytoplasmic proteins which have other essential cellular functions. Our findings represent a step forward in understanding the mechanisms involved in theBifidobacterium-host interaction.