Gram-negative bacteria possess a complex cell envelope that consists of a plasma membrane, a peptidoglycan cell wall and an outer membrane. The envelope is a selective chemical barrier that defines cell shape and allows the cell to sustain large mechanical loads such as turgor pressure. It is widely believed that the covalently cross-linked cell wall underpins the mechanical properties of the envelope. Here we show that the stiffness and strength of Escherichia coli cells are largely due to the outer membrane. Compromising the outer membrane, either chemically or genetically, greatly increased deformation of the cell envelope in response to stretching, bending and indentation forces, and induced increased levels of cell lysis upon mechanical perturbation and during L-form proliferation. Both lipopolysaccharides and proteins contributed to the stiffness of the outer membrane. These findings overturn the prevailing dogma that the cell wall is the dominant mechanical element within Gram-negative bacteria, instead demonstrating that the outer membrane can be stiffer than the cell wall, and that mechanical loads are often balanced between these structures.

Chronic inflammation is associated with a variety of pathological conditions in epithelial tissues, including cancer, metaplasia and aberrant wound healing. In relation to this, a significant body of evidence suggests that aberration of epithelial stem and progenitor cell function is a contributing factor in inflammation related disease, although the underlying cellular and molecular mechanisms remain to be fully elucidated. In this study, we have delineated the effect of chronic inflammation on epithelial stem/progenitor cells using the corneal epithelium as a model tissue. Using a combination of mouse genetics, pharmacological approaches and in vitro assays, we demonstrate that chronic inflammation elicits aberrant mechanotransduction in the regenerating corneal epithelium. As a consequence, a YAP-TAZ/β-catenin cascade is triggered, resulting in the induction of epidermal differentiation on the ocular surface. Collectively, this study demonstrates that chronic inflammation and mechanotransduction are linked and act to elicit pathological responses in regenerating epithelia.

Nanoscale characterization of living samples has become essential for modern biology. Atomic force microscopy (AFM) creates topological images of fragile biological structures from biomolecules to living cells in aqueous environments. However, correlating nanoscale structure to biological function of specific proteins can be challenging. To this end we have built and characterized a correlated single molecule localization microscope (SMLM)/AFM that allows localizing specific, labeled proteins within high-resolution AFM images in a biologically relevant context. Using direct stochastic optical reconstruction microscopy (dSTORM)/AFM, we directly correlate and quantify the density of localizations with the 3D topography using both imaging modalities along (F-)actin cytoskeletal filaments. In addition, using photo activated light microscopy (PALM)/AFM, we provide correlative images of bacterial cells in aqueous conditions. Moreover, we report the first correlated AFM/PALM imaging of live mammalian cells. The complementary information provided by the two techniques opens a new dimension for structural and functional nanoscale biology.

We report the coencapsulation of glutathione reductase and disulfide-linked polymer-oligopeptide conjugates into capsosomes, polymer carrier capsules containing liposomal subcompartments. The architecture of the capsosomes enables a temperature-triggered conversion of oxidized glutathione to its reduced sulfhydryl form by the encapsulated glutathione reductase. The reduced glutathione subsequently induces the release of the encapsulated oligopeptides from the capsosomes by reducing the disulfide linkages of the conjugates. This study highlights the potential of capsosomes to continuously generate a potent antioxidant while simultaneously releasing small molecule therapeutics.