Salmonella lipopolysaccharide‐containing supported lipid bilayers as platforms to study bacteriophage interactions
Authors: Hudson P. Pace, Alyssa Borges, Charles Arnaud, Tove Karlsson, Nina K. Bröker, Stefanie Barbirz, Marta Bally
Journal: FEBS Lett
Abstract:
Lipopolysaccharides (LPS) are a key component in the defensive barrier of the outer membrane (OM) of Gram-negative bacteria; they are a major drug target and bacteriophage access point. Biomimetic platforms presenting LPS are therefore important to study OM biophysics of pathogens and initial bacteriophage infection steps. Herein, we present robust protocols for the preparation of LPS-containing supported lipid bilayers (SLBs) incorporating either Salmonella LPS or OM vesicles (OMVs). We characterized SLBs using quartz crystal microbalance with dissipation (QCM-D) and fluorescence microscopy. We probed their interactions with O-antigen specific Salmonella phages and their tailspike receptor binding proteins. Altogether, this work provides a roadmap to create versatile LPS-based platforms that facilitate studies of interactions between phages and Gram-negative bacterial membranes.
Rechargeable aluminum batteries (RABs) are promising post-lithium energy storage systems due to the high abundance and volumetric capacity of aluminum, yet stable positive electrodes development remains a bottleneck. Cross-linked poly(3-vinyl-N-methylphenothiazine) (X-PVMPT) as a p-type redox polymer shows reversible two-electron redox chemistry at relatively high potentials and excellent cycling stability in RABs when paired with chloroaluminate-based ionic liquid electrolytes. Here, we present the investigation of volume expansion and morphological evolution of X-PVMPT composite electrodes during cycling using electrochemical (ec-) atomic force microscopy (AFM) and cyclic voltammetry. ec-AFM data reveals the dynamics of reversible expansion during anion insertion and (ir)reversible changes associated with prolonged cycling. In situ linescan profiling and 2D nanomechanical imaging allows visualization of pronounced and reversible volume change during cycling, associated with the insertion of AlCl4− / Al2Cl7− anions. Complementary electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurements validate these observations at the macroscopic scale, confirming that volume expansion and electrochemical stiffening are homogeneous, bulk phenomena of the X-PVMPT framework. We determined a reversible swelling amplitude of 1.1 ± 0.1 µm during anion insertion for a 9.6 µm thick film, correlated with a 4-fold increase in stiffness. While initial cycles involve large-scale structural changes, the network rapidly reaches a mechanically stabilized state after the initial cycle, where the polymer matrix undergoes irreversible reorganization. After the steady-state phase (from cycle 120 onwards), the swelling amplitude drops by 60-75% to 0.3 – 0.4 µm with sustained faradaic performance, highlighting the ability of the cross-linked matrix to establish ion-conduction pathways during prolonged cycling.
The ability of bacterial pathogens to colonise indwelling medical devices, particularly urinary catheters, and to establish drug-resistant biofilms accounts for approximately 60 % of all nosocomial infections, underscoring the urgent need for effective strategies to mitigate biofilm development on catheter surfaces. In this study, we developed a multilayer nano-composite coating for urinary catheters, assembled via sequential deposition of bioadhesive catechol-functionalised chitosan (catCS), hyaluronic acid (HA), and antimicrobial aminated lignin nanoparticles (N-LigNPs). Sono-enzymatically phenolated, aminated, and formulated lignin nanoparticles (NPs) served as both structural and functional components within the coatings, whose assembly was monitored in real time using a quartz crystal microbalance with dissipation. Atomic force microscopy was employed to characterise the coating topography, complemented by surface zeta potential measurements and lubricity analysis. Cross-linking of N-LigNPs with catCS, catalysed by the oxidative enzyme laccase, increased the mechanical integrity of the coating beyond that afforded by electrostatic interactions alone. This translated into durable antimicrobial and antibiofilm performance of the functionalised catheters over 7 days in a hydrodynamic model simulating a catheterised human bladder, reducing S. aureus and Escherichia coli biofilm formation by more than 60 %, while exhibiting no cytotoxic effects on mammalian cells. Moreover, the clinical, histological, and microbiological data obtained from in vivo studies in a rabbit model demonstrated that the coating was biocompatible and effectively prevented catheter-associated urinary tract infections during a 10-day indwelling period.
Biofouling in electrochemically driven water treatment processes, like electrodialysis (ED), is of critical concern due to its effect on ion fluxes and energy consumption. Biofilm formation begins with microbial adhesion to surfaces mediated by extracellular polymeric substances (EPS). In ED, ions are removed from water by external electric field through charged ion exchange membranes (IEMs). While this process is well established, the influence of the ED specific conditions on EPS adsorption remains poorly understood. Brackish water biofilms were grown on cation and anion exchange membranes (CEM & AEM) in an ED cell, with and without electric fields. Biofilm viability and EPS were analyzed by confocal laser scanning microscopy (CLSM), while EPS adhesion properties were characterized using Electrochemical Quartz Crystal Microbalance with Dissipation (E-QCMD), applying chronoamperometry (CA) and cyclic voltammetry (CV). Zeta potential analysis showed all EPS samples were negatively charged, with charge density influenced by membrane type and electric field. Positively charged AEMs accumulated more highly negative EPS, whereas less negative fractions preferentially attached to negatively charged CEMs. Applied electric fields results in EPS fractions with reduced negative zeta potentials on both membranes due to electrostatic repulsion on CEMs and selective attraction of less negative EPS to AEMs under shear. CA E-QCMD results indicated stronger electrostatic responses for AEM derived EPS, while CEM derived EPS interactions were mainly hydrophobic. CV analyses revealed that EPS from both membranes formed more compact and stable layers after exposure to negative potentials, regardless of field conditions during formation, highlighting the dominance of hydrophobic interactions. Biofouling caused greater ion flux decline on AEMs, correlating with higher EPS and biomass accumulation. These findings improve understanding of biofouling mechanisms in electrically driven membrane systems, supporting improved ion transport, membrane performance, and energy efficiency.
