part of has role has disposition bacterial adhesion disposition macromolecule pilus http://purl.obolibrary.org/obo/go.owl A proteinaceous hair-like appendage on the surface of bacteria ranging from 2-8 nm in diameter. In GO, pilus is a subclass of 'cell projection'. It was necessary to also assert it as a subclass of 'macromolecule' in order to add axioms ensuring that pilus is also an inferred subclass of 'adhesion factor' and 'virulence factor'. pili fimbria fimbrium It should be noted that 'pilus' is sometimes used for any hair-like appendage on bacteria or archaea. But some researchers reserve the term 'pilus' for the appendage of bacteria. GO seems to be following the latter usage. -SB (axiom editor) Shane Babcock fimbriae cell projection virulence factor disposition bacterium antigen role