Purely Polysaccharide-Based Biofilm Matrix ProvidesSize-Selective Diffusion Barriers for Nanoparticles and Bacteriophages

Biofilms are complex mixtures of proteins, DNA and polysaccharides surrounding bacterial communities as protective barriers that can be biochemically modified during the bacterial life cycle. However, their compositional heterogeneity impedes a precise analysis of the contributions of individual matrix components to the biofilm structural organization. To investigate the structural properties of glycan-based biofilms, we analyzed the diffusion dynamics of nanometer-sized objects in matrices of the megadalton-sized anionic polysaccharide stewartan, the major biofilm component of the plant pathogen Pantoea stewartii. Fluorescence correlation spectroscopy and single particle tracking of nano-beads and bacteriophages indicated notable sub-diffusive dynamics dependent on probe size and stewartan concentration, in contrast to free diffusion of small molecules. Stewartan enzymatic depolymerization by bacteriophage tailspike proteins rapidly restored unhindered diffusion. We thus hypothesize that the glycan polym...