Pilus
A thin, hairlike protein appendage extending from a bacterial cell. Pili enable functions such as attachment, movement, and DNA transfer.
Type IV pilus: A retractile bacterial surface appendage involved in attachment, movement, and DNA uptake. Its extension and retraction can pull cells across surfaces or bring them into contact.
Bacterial adhesion: The attachment of bacteria to surfaces, tissues, or other cells. Pili can bind host cells and abiotic surfaces, helping bacteria establish contact.
Bacterial cell envelope: The layers surrounding a bacterial cell, including its membrane and, in many species, a cell wall. Pili emerge through the envelope, whose architecture shapes their assembly and passage.
Flagellum: A rotating bacterial propeller that drives swimming through liquid or across surfaces. Flagella provide propulsion by rotation, unlike pili that attach, retract, or mediate DNA transfer.
Conjugative pilus: A filament produced by some bacteria that helps establish contact for DNA transfer between cells. It helps connect donor and recipient cells during bacterial conjugation.
Biofilm: A community of microorganisms embedded in a self-produced matrix on a surface. Pili can promote the initial attachment and cell arrangement needed for biofilm formation.
Gram-negative bacteria: Bacteria with a thin peptidoglycan wall between inner and outer membranes. Many well-studied pili cross this two-membrane envelope during assembly.
Curli: Amyloid fibers produced by some bacteria that support adhesion and biofilm formation. Curli are extracellular protein fibers, but they are not pili and assemble by a different route.
Twitching motility: Surface-associated movement powered by repeated extension and retraction of bacterial appendages. Type IV pili generate this movement by attaching to surfaces and pulling cells forward.
Uropathogenic Escherichia coli: A group of E. coli strains that cause urinary tract infections. Fimbrial adhesins help these bacteria attach to cells in the urinary tract.