was originally identified as "type IV fimbriae" by their appearance under the microscope. This classification survived as it happens to correspond to a clade. Type 1 fimbriae Another type are called type 1 fimbriae. They contain FimH adhesins at the "tips". The chaperone-usher pathway is responsible for moving many types of fimbriae out of the cell, including type 1 fimbriae and the P fimbriae. Curli "Gram-negative bacteria assemble functional amyloid surface fibers called curli." Curli are a type of fimbriae. Curli are composed of proteins called curlins. Some of the genes involved are CsgA, CsgB, CsgC, CsgD, CsgE, CsgF, and CsgG. Virulence Pili are responsible for virulence in the pathogenic strains of many bacteria, including E. coli, Vibrio cholerae, and many strains of Streptococcus. This is because the presence of pili greatly enhances bacteria's ability to bind to body tissues, which then increases replication rates and ability to interact with the host organism. If a species of bacteria has multiple strains but only some are pathogenic, it is likely that the pathogenic strains will have pili while the nonpathogenic strains don't. The development of attachment pili may then result in the development of further virulence traits. Fimbriae are one of the primary mechanisms of virulence for E. coli, Bordetella pertussis, Staphylococcus and Streptococcus bacteria. Their presence greatly enhances the bacteria's ability to attach to the host and cause disease. Nonpathogenic strains of V. cholerae first evolved pili, allowing them to bind to human tissues and form microcolonies. These pili then served as binding sites for the lysogenic bacteriophage that carries the disease-causing toxin. The gene for this toxin, once incorporated into the bacterium's genome, is expressed when the gene coding for the pilus is expressed (hence the name "toxin mediated pilus"). See also Bacterial nanowires Flagellum Sortase P fimbriae References External links Organelles Bacteria