Abstract

Bacteriophage viruses have the striking appearance of microscopic spaceships. One of the most abundant entities in our planet, they crowd fluid environments in anticipation of a random encounter with bacteria, and use a remarkable nanometre-size machinery for infection: fibres that recognise and attach to specific receptors on their victim’s surface and a hollow tube through which their genetic material is ejected inside the host cell cytoplasm for replication. Flagellotropic phages first attach to the flagella of bacteria and find a way to reach the cell body for infection since they lack the ability to move independently. The means by which they move up the flagellum has intrigued the scientific community for over 30 years. In 1973 Berg and Anderson proposed the nut-and-bolt mechanism and 26 years later, Berg’s group provided supporting evidence for it. Just like a nut being rotated will move along a bolt, under this scenario the phage wraps itself around a flagellum possessing helical grooves (due to the helical rows of flagellin molecules) and exploits the rotation of the flagellum in order to passively travel along it. In this work, we provide a first-principle theoretical model for this nut-and-bolt mechanism and show that it is able to predict experiment observations.