Microbiology Procedure

Index >> Bacterial Structure >> Structure of Fimbriae / Pili

Bacterial Structure
Part 1
Structure of Fimbriae or Pili
Functions of Fimbriae or Pili
Parts of Flagella
Bacterial Movement
Spirochaetal Movement
Gliding Movement
Nucleoid (Nucleus)
Plasmids
Classes of Plasmids
Gene Pickup and Sex Factors
R Plasmids
Plasmids Conferring Pathogenecity to mammals
Col Plasmids
Degradative Plasmids
Mercury Resistance Plasmids
Tumor Inducing Plasmid in Agrobacterium Tumifaciens
Cryptic Plasmids
Staphylococcal Plasmids

Structure of Fimbriae / Pili

	Structure of Fimbriae / Pili - Fimbriae and pili are like flagella in that they are cytoplasmic diffusions through the cell wall. They originate from the cytoplasm /and penetrate through the peptidoglycan layers of the cell wall. They, however, differ from flagella in no showing the characteristic sinuous wayes of,-~ 2.5 nm wavelength. The fimbriae of E. coli are nearly 100% protein. The protein of fimbriae has been called fimbrilin. It has a molecular weight or about 16,000, as compared to about 40,000 for the flagellar protein flagellin.
It consists of at least 163 amino acid, which occur mostly in the L form, with a large amount of hydrocarbon side chains. The fimbriae of E. coli have a rod-shaped, rigid, helical structure similar to that of bacterial flagella. The sex pili of E. coli (both F and I pili) are helically built tubules with a hollow core (25-31A) and a cylinder of repeating units. With reference to the presence or absence of fimbriae, at least three types of cells occur in a single colony of E. coli.Fim+ - fimbriated cells which are genotypically and phenotypically fimbriate.
Fim(+ )-phenotypically in the nonfimbriate phase but genotypically fimbriate. Fim- - mutant strains which remain nonfimbriate under any condition, i. e. which are genotypically as well as phenotypically nonfimbriate. Conjugation of the Fim- strain with Fim+ or Fim(+ ) can make the former fimbriate. Sex pili are filamentous structures which are determined by sell factors (plasmids) such as F, Col I and R factor. These sex factors control the synthesis of the sex pili, their specific properties, their antigenic features and their capacity to adsorb bacteriophage. The pili have a greater c1iameter (65-135A) and length (up to 20 /Lm) than fimbriae, and are usually less numerous (1-10).
The sex pilus appear to have an axial hole 25-30A in diameter. Electron micrographs reveal the presence of terminal knobs 150-800A in diameter. Two types of sex pili can be distinguished in E. coli F pili and I pili. F pili are determined by F or F-like R factors and the I pili by Col I or I-like R factors. The F pili have receptor sites at which are adsorbed RNA phages such as f2 and MS2 and DNA phages such as fl and M13. The I pili adsorb the DNA phages If1 and If2, which do not adsorb to the, F pili.

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