Lipoprotein Lpp regulates the mechanical properties of the E. coli cell envelope.

The mechanical properties of the cell envelope in Gram-negative bacteria are controlled by the peptidoglycan, the outer membrane, and the proteins interacting with both layers. In Escherichia coli, the lipoprotein Lpp provides the only covalent crosslink between the outer membrane and the peptidoglycan. Here, we use single-cell atomic force microscopy and genetically engineered strains to study the contribution of Lpp to cell envelope mechanics. We show that Lpp contributes to cell envelope stiffness in two ways: by covalently connecting the outer membrane to the peptidoglycan, and by controlling the width of the periplasmic space. Furthermore, mutations affecting Lpp function substantially increase bacterial susceptibility to the antibiotic vancomycin, indicating that Lpp-dependent effects can affect antibacterial drug efficacy.