A polymeric defense coat – characterization of a unique exopolysaccharide from Vibrio cholerae biofilm

Bacterial exopolysaccharides (EPS) are crucial for the mechanics and survival of biofilms, surface-attached aggregates of bacterial cells surrounded by EPS. Here, we focus on a unique biopolymer, Vibrio polysaccharide (VPS), produced by Vibrio cholerae - the causal agent of pandemic cholera. We focus on its rheological behavior and structures in aqueous solutions across varying concentrations. By recording the amplitude/frequency sweeps in linear rheology and large-amplitude oscillatory shear (LAOS) responses, we quantify the concentration-dependent viscoelastic properties of VPS. Our results reveal a transition from dilute to semi-dilute regimes, with the viscosity increasing sharply beyond a critical concentration.  LAOS measurements further demonstrate nonlinear strain-stiffening and thickening, consistent with the formation transient network. We complemented the rheological measurement with characterization of single chain dynamics by small angle X-ray scattering (SAXS), molecular weight measurement with SEC-MALS, and molecular dynamics simulations. This work provides mechanistic insight into VPS solution behavior and establishes VPS as a model system linking polysaccharide characteristics to macroscopic rheological properties of bacterial biofilm.