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The term "fimbria" can refer to many different (structural) types of pilus. Indeed, many different types of pili have been used for adhesion, a case of convergent evolution. [3] The Gene Ontology system does not treat fimbriae as a distinct type of appendage, using the generic pilus (GO:0009289) type instead.
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]
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 flagellum in archaea is called the archaellum to note its difference from the bacterial flagellum. [7] [8] Eukaryotic flagella and cilia are identical in structure but have different lengths and functions. [9] Prokaryotic fimbriae and pili are smaller, and thinner appendages, with different functions. Cilia are attached to the surface of ...
They have other functions, including attachment to solid surfaces. Additionally, protein appendages can be present on the surface: fimbriae and pili can have different lengths and diameters and their functions include adhesion and twitching motility. [11] [12] [3]
Pili (sing. pilus) are cellular appendages, slightly larger than fimbriae, that can transfer genetic material between bacterial cells in a process called conjugation where they are called conjugation pili or sex pili (see bacterial genetics, below). [87] They can also generate movement where they are called type IV pili. [88]
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]
Fimbrial adhesion by the type I fimbriae in E. coli undergoes site specific inversion to regulate the expression of fimA, the major subunit of the pili, depending on the stage of infection. The invertible element has a promoter within it that depending on the orientation will turn on or off the transcription of fimA .