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Bacterial appendages

They are filamentous structures that stand out on the cell surface, among which we can highlight the flagella, the hairs or pili and the fimbriae. There are bacteria that do not have an appendix.


The flagella are very long and thin filamentous appendages, which allow the bacteria to move. Formed by a protein called flagellin, they have a simpler structure than that of eukaryotes.

Depending on where the flagella are located, the following bacteria are distinguished:

  • Monotric: they only have one scourge. (A)
  • Lophometric: they have several flagella, but very close. (B)
  • Amphiphitic: they have a single flagellum at each opposite end. (C)
  • Peritric: they have several flagella distributed throughout the bacterial surface. (D)

By Mike Jones [GFDL or CC BY 3.0], via Wikimedia Commons

Bacterial flagella are much simpler than those of eukaryotic cellsIn them two parts are distinguished: the basal area and the stem.

Pili (hairs) and fimbriae

They are short, hollow tubes, made up of proteins that appear on the outer surface of some Gram negative bacteria.

The fimbriae are short and very numerous, and they serve so that the cell can attach itself to the substrate.

The pili are long and only one or two appear per bacterium. In the conjugation process, they intervene in the exchange of genetic material with other bacteria.

Prokaryote cell.svg
By This vector image is completely made by Ali Zifan - Own work; used information from Biology 10e Textbook (chapter 4, Pg: 63) by: Peter Raven, Kenneth Mason, Jonathan Losos, Susan Singer · McGraw-Hill Education., CC BY-SA 4.0, Link