High adhesiveness of encapsulated Neisseria meningitidis to epithelial cells is associated with the formation of bundles of pili

Abstract

Pili are indispensable in adhesion of encapsulated Neisseria meningitidis (MC) to eukaryotic cells. Intrastrain variability with respect to the degree of adhesion is the result of pilin antigenic variation. We have localized the region responsible for this variability to the 20-amino-acid hypervariable domain of pilin. The replacement of an aspartic acid, located in the hypervariable region of a low-adhesive variant by a lysine restored high adhesiveness. To assess whether hyperadhesiveness conferred by some pilin variants was related to the generation of a new pilus-associated ligand, high- and low-adhesive variants were purified. In a first step, low- and high-adhesive pilins were fused to maltose binding protein (MBP). These hybrid proteins bound epithelial cells with the same affinity. Truncated MBP pilin fusions identified a cell-binding domain within the 77 residues of the N-terminal end of mature pilin. This region of the protein is common to low- and high-adhesive derivatives used in this work, thus eliminating the possibility that high adhesiveness conferred by some pilin variants was because of the generation of a new pilus-associated ligand. Electron-microscopic examination showed that low-adhesive derivatives expressed long and distinct pili and adhered as single cells. In contrast, pili of derivatives expressing high-adhesive pilins, either wild type or mutagenized from the low-adhesive variant, formed large bundles which bound bacteria and caused them to grow as colonies on infected monolayers. These data demonstrate that aggregative pili promote high adhesiveness of encapsulated MC.

Characterization of the fimA gene encoding bundle-forming fimbriae of the plant pathogen Xanthomonas campestris pv. vesicatoria

“…vesicatoria in creation of bacterial microcolonies on the leaf surface and in thus increasing epiphytic survival and stress tolerance of Xanthomonas under field conditions. Type IV fimbriae of certain human pathogens have been associated with cell aggregation and ability to form adherent colonies on the surface of the target epithelial cells, a phenomenon called localized adherence (17,25,42). The autoagglutination caused by a member of type IV family fimbriae, the toxin-coregulated pilus of Vibrio cholera, has been correlated with serum resistance and colonization ability (8).…”

“…Type IV fimbriae are virulence factors of several human and animal pathogens and mediate bacterial adhesion to host epithelial cells (45). They also are involved in bacterial motility, the so-called twitching and social gliding motilities (45,52), as well as in cell aggregation of human pathogens (8,12,17,25,42). As a step to analyze the role of fimbriae in X. campestris infections, we describe here the characterization of the fimA gene encoding bundle-forming fimbriae and cell aggregation of X. campestris pv.…”

Type IV Pilin Proteins: Versatile Molecular Modules

“…The propensity of T4P to aggregate laterally into bundles of fibers promotes microcolony formation, an important virulence trait for pathogens such as Neisseria, V. cholerae, S. Typhi, and enteropathogenic E. coli (227,255,258,266,290), and it increases the retraction forces generated by piliated cells (47). In Neisseria, pilus-mediated aggregation was linked to the noncore minor pi- lin, PilX, which was proposed to inhibit retraction of adjacent, antiparallel pili through interaction of D-region protrusions of PilX molecules on opposing fibers (175,176).…”

3D structure/function analysis of PilX reveals how minor pilins can modulate the virulence properties of type IV pili

“…We reported that a pilX mutant, despite having quantitatively and qualitatively unaltered fibers, displays a selective loss of Tfp-linked phenotypes. Although motile and naturally competent, this mutant is unable to form bacterial aggregates and to adhere to human cells (17) because interbacterial interactions are essential for Tfp-facilitated adhesion (5,6). Interestingly, because aggregation is restored in a pilX/T double mutant, it seemed that PilX participates in the formation of aggregates by somehow counterbalancing PilTmediated Tfp retraction.…”

“…These organelles mediate bacterial adhesion to surfaces as diverse as stainless steel (4) and host cells (1), a property that is tightly linked to their ability to promote the formation of adhesive 3D microcolonies by mediating interbacterial interactions (5,6). Tfp are therefore one of the most widespread virulence factors in bacteria and play a key role in infection in several human pathogens, including our working model Neisseria meningitidis.…”