Mechanical stress compromises multicomponent efflux complexes in bacteria

Physical forces have long been recognized for their effects on the growth, morphology, locomotion, and survival of eukaryotic organisms. Recently, mechanical forces have been shown to regulate processes in bacteria, including cell division, motility, virulence, biofilm initiation, and cell shape, although it remains unclear how mechanical forces in the cell envelope lead to changes in molecular processes. In Gram-negative bacteria, multicomponent protein complexes that form rigid links across the cell envelope directly experience physical forces and mechanical stresses applied to the cell. Here we manipulate tensile and shear mechanical stress in the bacterial cell envelope and use single-molecule tracking to show that shear (but not tensile) stress within the cell envelope promotes disassembly of the tripartite efflux complex CusCBA, a system used by E. coli to resist copper and silver toxicity, thereby making bacteria more susceptible to metal toxicity. These findings provide the first demonstration that mechanical forces, such as those generated during colony overcrowding or bacterial motility through submicron pores, can inhibit the contact and function of multicomponent complexes in bacteria. As multicomponent, trans-envelope efflux complexes in bacteria are involved in many processes including antibiotic resistance, cell division, and translocation of outer membrane components, our findings suggest that the mechanical environment may regulate multiple processes required for bacterial growth and survival.