How Bacteria Use Type IV Pili Machinery on Surfaces

The bacterial type IV pilus (T4P) is a versatile molecular machine with a broad range of functions. Recent advances revealed that the molecular components and the biophysical properties of the machine are well conserved among phylogenetically distant bacterial species. However, its functions are diverse, and include adhesion, motility, and horizontal gene transfer. This review focusses on the role of T4P in surface motility and bacterial interactions. Different species have evolved distinct mechanisms for intracellular coordination of multiple pili and of pili with other motility machines, ranging from physical coordination to biochemical clocks. Coordinated behavior between multiple bacteria on a surface is achieved by active manipulation of surfaces and modulation of pilus–pilus interactions. An emerging picture is that the T4P actively senses and responds to environmental conditions.

TrendsThe proteins forming the type IV pilus (T4P) machine are conserved throughout two of the three domains of life. Single-molecule analyses revealed that the T4P fiber can withstand and generate force on the order of 100 piconewtons and adjust to high tension by elongation.Coordination of multiple type IV pili, and with other machines driving motility, has evolved differently across species. The mechanisms range from being consistent with purely mechanical coordination to molecular clocks that control the localization of the motors.Physicochemical surface properties govern T4P-driven twitching motility. Recent experiments reveal that bacteria actively modify the surface properties by secretion of extracellular polymers, most likely for controlling group behavior.