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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.
The centurion of its first centuria, the Primus Pilus, commanded the first cohort and was also the most senior centurion in the legion. Legio – A legion was composed of nine cohorts and one first cohort. The legion's overall commander was the legatus legionis, assisted by the praefectus castrorum and other senior officers.
Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. [1] This takes place through a pilus.
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 pilus is composed of VirB2 and VirB5, with VirB2 being the major component. [1] In A. tumefaciens, the pilus is 8-12 nm in diameter, and less than one μm in length. F pili, another commonly examined type of pilus, are much longer with a length of 2-20 μm. [2]
The virulence operon includes many genes that encode for proteins that are part of a Type IV secretion system that exports from the bacterium proteins and DNA (delineated by specific recognition motifs called border sequences and excised as a single strand from the virulence plasmid) into the plant cell through a structure called a pilus.
The typical structure of a bacterial adhesin is that of a fimbria or pilus. [3] The bacterial adhesin consists primarily of an intramembranous structural protein which provides a scaffold upon which several extracellular adhesins may be attached. [ 3 ]
The commander of the first cohort's first century was known as the primus pilus or primipilus, [4] a legion's most senior centurion. The primus pilus was eligible for promotion to praefectus castrorum or camp prefect, the third most senior officer in a legion, responsible for the day-to-day administration of a legion.