THE SURFACE-STRUCTURE OF LEPTOTRICHIA-BUCCALIS

Leptotrichia buccalis shows a mosaic of surface structure on its outer membrane consisting of curved ridges 35 nm high and 22 nm apart, and erect on that surface. Fimbriae (common pill) are not present and nor is an S layer. The flap-like ridges consist of strings of macromolecul es radiating from the cell surface. This ridge structure is not solubl e in any of the usual chaotropes and can only be released when the out er membrane has been damaged or dispersed by extracting envelope prepa rations with 0.5% SDS at room temperature. The ridge is then found to be attached firmly to the peptidoglycan sacculus, which may be the poi nt of origin of the structure. When so prepared the macromolecules for ming the ridge can be removed from the sacculus by treatment with 6 M guanidine HCl, and SDS-PAGE analysis of the extract reveals a 210-kDa polypeptide as a major component and a 15-kDa minor component. The lat ter is probably a peptidoglycan-associated protein and much of it rema ins with the sacculus. Each string forming the ridge is of a volume co nsistent with being made of three elongated 210-kDa molecules, which a re united in series by strong hydrophobic association and laterally wi th neighboring strings by slightly weaker forces. We confirm that L. b uccalis causes haemagglutination and the bacteria are known to attach to various tissue cells. Human group A red blood corpuscles remove bot h of the proteins from solution, which supports the hypothesis that th e ridges are adhesin structures. It is likely but not proven that the 210-kDa molecule is the adhesin.