Motility and adhesion through type IV pili in Gram-positive bacteria

Type IV pili are hair-like bacterial surface appendages that play a role in diverse processes such as cellular adhesion, colonization, twitching motility, biofilm formation, and horizontal gene transfer. These extracellular fibers are composed exclusively or primarily of many copies of one or more pilin proteins, tightly packed in a helix so that the highly hydrophobic amino-terminus of the pilin is buried in the pilus core. Type IV pili have been characterized extensively in Gram-negative bacteria, and recent advances in high-throughput genomic sequencing have revealed that they are also widespread in Gram-positive bacteria. Here, we review the current state of knowledge of type IV pilus systems in Gram-positive bacterial species and discuss them in the broader context of eubacterial type IV pili.