Differences between Flagella and Pili

S.N Flagella S.N Pili
1. These are helical structures but are not straight. 1. These are non-helical structures but are straight.
2. These are long whip like filamentous structures. 2. These are short hair like, filamentous, and tubular microfibers.
3. Comparatively thicker than pili. 3. Comparatively thinner than flagella.
4. Diameter of flagella is 10-30 nm. 4. Diameter of pili is 3-10 nm.
5. Occur in different forms in the cell like lateral, peritrichous and polar. 5. Occur throughout the entire surface of the cell.
6. Presence noticed in both gram positive and gram negative bacteria. 6. Presence noticed in only gram negative bacteria.
7. Flagellin protein is their main content. 7. Pilin protein is their main content.
8. These structures arise from cell wall. 8. These structures arise from cytoplasmic membrane.
9. These are bacterial, archaeal and eukaryotic type. 9. These are conjugative and type IV in types.
10. Provide motility to the cell and sometimes act as sensory organ. 10. Provide attachment or adherence to the other cell for conjugation process.
11. Generally show undulating and sinusoidal motion. 11. Generally show twitching motility mostly by type IV pili.
12. Number is less as compared to pili. 12. Number is more compared to flagella.
13. Origin is interior. 13. Origin is external.
14. About 5-20 µm in length. 14. About 0.3-1.0 µm in length.
15. Genes present in nucleoid region controls their formation. 15. Gene present in plasmids controls their formation.
16. These are more rigid than pili. 16. Comparatively less rigid than flagella.
17. No role in genetic exchange between the organisms. 17. Sex pili through conjugation tube transfer the genetic materials.
18. Do not function as receptors to any viruses. 18. Function as receptors to some viruses.
19. A complex motor system is present for propulsion at the base. 19. This motor system is not present in pili.
20. E. coli, Salmonella, Campylobacter, Helicobacter, Enterococcus, Listeria, etc. bear flagella. 20. E. coli, N. gonorrhea, Pseudomonas, Salmonella, Shigella, etc. bear pili.

Differences between Fimbriae and Pili

Image source: microbiologynotes

References: 

i) https://microbenotes.com/flagella-and-pili-fimbriae/

ii) https://pediaa.com/difference-between-flagella-and-pili/

iii) https://www.easybiologyclass.com/difference-between-pili-and-flagella-of-bacteria-a-comparison-table/

Differences between Flagella and Pili

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