What is the function of conjugation pilus?

Hint: -A pilus (plural: pili) is a long, thin, and filamentous hair like appendages on the surface of many bacteria.
-Due to its role in conjugation, it is also called as, 'conjugation pilus' or 'sex pilus'.

Complete answer:
Conjugation occurs between two adjacent cells due to contact between the cells by ‘mating bridge’. It is another type of ‘horizontal gene transfer' in bacteria. In the surface of the bacteria, there are a number of pili, that help in pairing of two cells during conjugation. It also has other important functions in the cell.
Function of conjugation pilus
-Conjugation pilus is present in the ${F}^{+}$ cell, which has the capacity to act as a donor cell in conjugation. In cases, it can act as a recipient cell as well.
-In the F- cells, the absence of pili indicates the absence of F factor. Thus it can't act as a donor cell.
Pili of donor cells attract the recipient cell and form the 'mating bridge' between them.
-The 'mating bridge' forms a controlled pore through which transfer of genetic material takes place.
-Pili attaches the bacteria to the host cell and then degenerates, allowing close contact between the bacterial cell wall and the host cells.
-Pili are composed of the pilin protein, that function as an antigen and initiate the adaptive immune response.
-Type IV pili enables the bacteria with motility to move over the surface of the host cell.

Notes:
-Conjugation is a type of genetic recombination, that allows the transfer of genetic material between two adjacent cells.
-As the pili, there are also other appendages found on the cell surface of bacteria. They are-flagella, fimbriae and spinae.
-The fimbriae is composed of pilin protein, but is shorter than the pilus.
Flagella is composed of flagellin, while the spinae is made up of spinin.