Force stabilizes a bond in bacterial adhesion

Biophysicists at the National University of Singapore have discovered how a special bacterial adhesion complex could be counterintuitively stabilized by mechanical stress at the single-molecule level.

A critical aspect of bacteria-host interactions is the physical contact between the bacteria and the host, as well as their responses to local mechanical stimuli. Bacterial adhesion complexes formed with hosts must be resistant to various mechanical stress conditions, associated with forces in a wide range, from nanonewtons in the urinary tract to piconewtons in capillaries. On the other hand, adherent bacteria need to retain the ability to spread, requiring sufficiently short lifetimes of adhesion complexes under stress-free conditions.

A long-standing hypothesis is that bacterial adhesion complexes may have evolved a unique mechanical property, conferring a counterintuitive force-dependent increase in lifetime, which is known as capture binding kinetics. To some extent, this is analogous to seat belts found in cars, which tighten when there is a sudden increase in tension.

Testing this important hypothesis has been hampered for years by the technological challenge of being able to quantify the force-dependent lifetime of a single bacterial adhesion complex over a force range of up to tens of piconewtons over extended periods.

A research team led by Professor Jie Yan from the Department of Physics at the National University of Singapore overcame the technological challenge and investigated the force-dependent lifetime of a family of bacterial adhesion complexes using ultra-stable magnetic tweezers. Strong capture bond kinetics are observed for all of these adhesion complexes, with a lifetime increase of several thousand folds when the applied forces increase from near zero to tens of piconewtons. A highly sensitive temperature dependence of the lifetimes is also revealed. This is shown by a drastic decrease in service life of more than 100 folds when the temperature increases from 23^eitherC at human body temperature of 37^eitherc.

Professor Yan said: “A unique force-dependent conformational change of adhesion complexes has been found to be the cleavage transition pathway of adhesion complexes. With this, the team derived a physical model that can quantitatively explain the observed binding strength dependent lifetimes of adhesion complexes, which is the first ever reported evidence of these binding kinetics in bacteria.”

The study is published in Journal of the American Chemical Society. In the future, the research team will extend their technology to examine the mechanical stability of a broader range of microbial adhesion complexes implicated in human disease and explore potential intermediate approaches to disrupt bacterial adhesions.