The type IVc pilus: just a Tad different

Bacteria utilize type IV pili (T4P) to interact with their environment, where they facilitate processes including motility, adherence, and DNA uptake. T4P require multisubunit, membrane-spanning nanomachines for assembly. The tight adherence (Tad) pili are an Archaea-derived T4P subgroup whose machinery exhibits significant mechanistic and architectural differences from bacterial type IVa and IVb pili. Most Tad biosynthetic genes are encoded in a single locus that is widespread in bacteria due to facile acquisition via horizontal gene transfer. These loci experience extensive structural rearrangements, including the acquisition of novel regulatory or biosynthetic genes, which fine-tune their function. This has permitted their integration into many different bacterial lifestyles, including the Caulobacter crescentus cell cycle, Myxococcus xanthus predation, and numerous plant and mammalian pathogens and symbionts. •Type IVc (Tad) pili were acquired from Archaea and use a distinct molecular machine.•The core components of the Tad machinery are conserved across bacteria.•Lineage-specific accessory proteins fine-tune the function of the Tad pilus.•Tad loci undergo extensive and frequent interspecies structural rearrangements.•Tad pili are used for many important physiological functions in bacteria.