The type IV pili play a role in an unusual type of motility known as twitching motility, where a pilus attaches to a solid surface and then contracts, pulling the bacterium forward in a jerky motion.īacterial motility is typically provided by structures known as flagella. The conjugative pili participate in the process known as conjugation, which allows for the transfer of a small piece of DNA from a donor cell to a recipient cell. It really boils down to the fact that a few specific pili participate in functions beyond attachment.
Pili are typically longer than fimbriae, with only 1-2 present on each cell, but that hardly seems enough to set the two structures apart. So, why would some researchers bother differentiating between fimbriae and pili? Pili can be used for attachment as well, to both surfaces and host cells, such as the Neisseria gonorrhea cells that use their pili to grab onto sperm cells, for passage to the next human host. Pili are very similar to fimbriae (some textbooks use the terms interchangeably) in that they are thin filamentous appendages that extend from the cell and are made of pilin proteins.
