  Biopolymers are vital structures for many living organisms; for a variety of
bacteria, adhesion polymers play a crucial role for the initiation of
colonization. Some bacteria express, on their surface, attachment organelles
(pili) that comprise subunits formed into stiff helix-like structures that
possess unique biomechanical properties. These helix-like structures possess a
high degree of flexibility that gives the biopolymers a unique extendibility.
This has been considered beneficial for piliated bacteria adhering to host
surfaces in the presence of a fluid flow. We show in this work that helix-like
pili have the ability to act as efficient dampers of force that can, for a
limited time, lower the load on the force-mediating adhesin-receptor bond on
the tip of an individual pilus. The model presented is applied to bacteria
adhering with a single pilus of either of the two most common types expressed
by uropathogenic Escherichia coli, P or type 1 pili, subjected to realistic
flows. The results indicate that for moderate flows (~25 mm/s) the force
experienced by the adhesin-receptor interaction at the tip of the pilus can be
reduced by a factor of ~6 and ~4, respectively. The uncoiling ability provides
a bacterium with a "go with the flow" possibility that acts as a damping. It is
surmised that this can be an important factor for the initial part of the
adhesion process, in particular in turbulent flows, and thereby be of use for
bacteria in their striving to survive a natural defense such as fluid rinsing
actions.
