described as two distinct phases in bacteria: piliated and non-piliated. However, the term

“fimbriae” was introduced in 1975, by Ottow [6]. They are filamentous surface structures of

many different Gram-negative bacteria. In 1968, the pili were detected and described by

Yanagawa et al. [8] on the surface of a Corynebacterium renale Gram-positive bacteria

by using electron microscopy. These structures were employed by the bacteria for

several functions such as attachment, biofilm formation, motility, and DNA transport

through bacteria membranes. Bacterial pili are characterized by their uniform diameter,

straightness, and fragility. Also, they can be removed by mechanical agitation in a high-

speed mixer [7]. On the basis of their biosynthetic pathways, different pilus classes are

characterized and described based on the assembly pathways in Gram-negative bacteria

(Figure 11.1) [9]. The pili have been employed in many functions and used for attachment

in host cells, a biofilm, or for the formation of an extracellular matrix. Along with that, it

can function as nanowires or as a support structure for the secretion of proteins and

nucleic acids.

11.2.1 Chaperone-Usher (CU) Pili

The Chaperone-Usher (CU) pili are ubiquitous appendages mainly found in Gram-

negative bacteria [10]. The CU pili are typically 1–2 µm in length fibers composed with

the pilin subunits arranged in a helical fashion, consisting of pilus subunits (pilins). The

CU pili play a crucial role in the infection and virulence, often constituting an important

factor in attachment and adhesion to host tissues. The genes involved in the assembly of

pili belong to the chaperone/usher biosynthesis clustered into operons. These operons

encoded can be classified into three different proteins: a major structural pili subunit,

FIGURE 11.1

Schematic of different pili and biosynthesis pathways in Gram-negative. Reprinted with permission [ 9].

Copyright © 2008 European Molecular Biology Organization, With permission from Wiley and Sons. The article

is available under the Creative Commons CC-BY-NC-ND license.

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