Conjugation is one of the method of gene transfer among bacteria. Obviously once we are taking about transfer of gene (genetic information) at least two bacterias there. One is called donor which donate gene and other is recipient which receive genes.
This process of conjugation is compared to sexual relation in higher organisms. But there is a big difference in it. Female bacterium after receiving genetic information turns into male cell.
As we have understood there are two bacteria taking part in conjugation. Donor is called as male and receiver is called as female. The maleness or donor status of a cell is determined by the presence of a plasmid which code for specialized fimbria (sex pilus) which project from the surface of the cell.
These pilus help in conjugation to hold female (receiver) while conjugation take place.
When the other similar plasmids were also discovered, the term ‘transfer factor’ came to be used for all such plasmids which conferred on their host cells the ability to act as donors in conjugation.