What is a small, circular piece of bacterial dna found to carry only a few genes?

Pili, or pilus is a small, circular piece of bacterial DNA found to carry only a few genes. It is a thin, rigid fiber made of protein found on the surface of many bacteria. The function of the pili is adhering to other bacterial cell (especially for mating) or to animal cells. Conjugation pili that allow for the transfer of DNA from one bacterial cell to another.