CLUSTERING OF FIBRONECTIN ADHESINS TOWARD TREPONEMA-DENTICOLA TIPS UPON CONTACT WITH IMMOBILIZED FIBRONECTIN

Treponema denticola has been shown to bind to immobilized fibronectin (Fn) by its tips. Yet labeling of cells in suspension with an Fn-gold conjugate to localize the Fn adhesins shows that they are distributed in patches along the entire cell length. Subsequent experiments have s hown that the number and proportion of tip-oriented cells increase wit h time, suggesting that Fn contact stimulates T. denticola to rearrang e adhesins toward its tips. To test this hypothesis, T. denticola cell s were allowed to migrate in a 2% methylcellulose column toward nitroc ellulose filters coated with Fn, laminin, bovine serum albumin, or pho sphate-buffered saline. Cells close to and distant from the filters we re collected, labeled with Fn-gold probes, and examined by transmissio n electron microscopy. The number of gold particles on each of 20 cell s was counted, dividing each cell into thirds along its length: the en d third with the most label (end 1), the middle third, and the end wit h the least label (end 2). The mean number (+/- standard deviation) of gold probes per third was calculated. Fn-gold probes clustered toward one end of T. denticola cells when in contact with Fn-coated nitrocel lulose, with > 55% of probes in end 1. In contrast, no clustering towa rd T. denticola ends occurred with laminin-, bovine serum albumin, or phosphate-buffered saline-coated filters or in the absence of a filter . Blocking access of the T. denticola cells to the Fn-coated nitrocell ulose filter by placing an uncoated filter between them prevented clus tering of Pn-gold. Removal of T. denticola cells from direct contact w ith the Fn-coated filter did not promote redistribution of clustered p robes. These data suggest that T. denticola is stimulated to cluster F n adhesins irreversibly toward its tips when it migrates into contact with immobilized Fn. This might be significant for establishing multip le adhesive interactions with host cells and ligands.