In conjugation, what structure serves as a bridge between two bacterial cells?

Pilus

Explanation:

Conjugation can be described as one of the processes by which a bacteria transfers it's DNA into another bacteria. In this method of DNA transfer, the donor bacterium cell forms a pilus and joins with the recipient bacterial cell. This allows the DNA from the donor cell to get transferred into the recipient cell. Mostly, the DNA is a plasmid which is transferred. The pilus is formed by the F factor of the donor DNA.