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A pilus (Latin for 'hair'; pl.: pili) is a hair-like cell-surface appendage found on many bacteria and archaea. [1] The terms pilus and fimbria (Latin for 'fringe'; plural: fimbriae ) can be used interchangeably, although some researchers reserve the term pilus for the appendage required for bacterial conjugation .
P fimbriae are large, linear structures projecting from the surface of the bacterial cell. With lengths of 1-2um, the pili can be larger than the diameter of the bacteria itself. [4] The main body of the fimbriae is composed of approx. 1000 copies of the major fimbrial subunit protein PapA, forming a helical rod. [5]
Though the bacteria possess pili, they are not used for traditional movement or motility, and the bacterium is still considered to be non-motile. [ 18 ] The cell wall of H. influenzae bacterium contains various proteins, referred to as autotransporters, for adherence and colony formation.
The F-pili are extremely resistant to mechanical and thermochemical stress, which guarantees successful conjugation in a variety of environments. [10] Several proteins coded for in the tra or trb locus seem to open a channel between the bacteria and it is thought that the traD enzyme, located at the base of the pilus, initiates membrane fusion.
Pili are similar in structure to fimbriae but are much longer and present on the bacterial cell in low numbers. Pili are involved in the process of bacterial conjugation where they are called conjugation pili or "sex pili". Type IV pili (non-sex pili) also aid bacteria in gripping surfaces.
The Saf pilin N-terminal extension protein domain helps the pili to form, via a complex mechanism named the chaperone/usher pathway. It is found in all c-u pilins. [8] This protein domain is very important for such bacteria, as without pili formation, they could not infect the host. Saf is a Salmonella operon containing a c-u pilus system. [8]
The pili are a pivotal virulence factor for N. gonorrhoeae; without them, the bacterium is unable to promote colonization. [44] For motility, individual bacteria use their pili in a manner that resembles a grappling hook: first, they are extended from the cell surface and attach to a substrate. Subsequent pilus retraction drags the cell forward.
The pili function on initial bacterial adhesion, invasion and biofilm formation, has been mainly studied for Gram-negative bacteria. There are some works on the synthesis of pilicides, chemical agents synthesized to target the chaperone–subunit interaction and the chaperone interaction with a protein involved in the biogenesis of the pili in ...