Analysis of potential host-colonization factors in Bifidobacterium bifidum S17

Abstract

B. bifidum S17, isolated form feces of a breast-fed infant, was identified as a strain with high adhesion to intestinal epithelial cells (IECs) and anti-inflammatory capacity. In this study, possible structures mediating adhesion to IECs and extracellular matrix proteins are investigated. Bioinformatic analysis allowed the identification of genes encoding exopolysaccharide (EPS) biosynthesis, pili and single adhesion structures, as well as a cell envelope protease. The presence of a compact and patchy EPS layer for B. bifidum S17 and a thick and fuzzy EPS layer for B. longum E18 were shown by TEM and SEM. Furthermore, gene expression analysis showed that most of the identified genes are higher expressed when bacteria in exponential growth phase. In line with this result, B. bifidum S17 shows higher adhesion to Caco-2 cells in exponential growth phase. Adhesion assay with recombinant bifidobacteria expressing putative single adhesins showed that at least five single adhesins indeed play a role in adhesion. However, adhesion of B. longum E18 was not increased upon expression of the respective adhesins possibly as a result of the thick EPS layer preventing interaction with the receptors. Additionally, B. bifidum S17 adheres strongly to fibronectin but adhesion is significantly reduced when the subtilisin-like cell envelope protease was overexpressed suggesting a role in fibronectin binding and degradation.