Phages and biofilms are ubiquitous in natural environments, and their interaction has contributed to accelerate the evolution of phages and their bacterial hosts in these particular niches. Biofilms have represented a protective mode of microbial life against harsh environments for millions of years, and it appears that biofilms are also a beneficial trait in pathogenesis, as the majority of chronic infections are caused by cells organized into biofilms. A characteristic property of the mature biofilm is that it has antibiotic resistance. Moreover, biofilm bacteria become inaccessible to immune cell attacks. Most bacterial species have the ability to colonize inorganic or biological surfaces and embed themselves in a gel formed by polysaccharides, DNA and proteins they excrete, the extracellular polymeric substance (EPS). EPS regulates the selective transport of molecules and is a diffusion barrier for bacteriophages.We chose Salmonella P22 podovirus as a model to analyze hydrodynamic behavior of bacteriophages inside biofilms, using a polysaccharide matrix produced by Pantoea stewartii as model for a glycan-based biofilm. To this end, the hindrance factor of the phage as well as beads of different sizes were determined using single particle tracking (SPT) and fluorescence correlation spectrometry (FCS). We describe bacteriophage diffusion in relation to physicochemical properties of the stewartan matrix like polysaccharide concentration, the solvent pH and the tracer properties [1]. In addition, we show that the degradation of stewartan by glycan-depolymerizing enzymes is an important regulatory mechanism that can rapidly modulate particle dynamics within the matrix. In the following, we will link bacteriophage diffusion properties to host infection dynamics to understand how bacteriophages address their associated pathogens depending on the hydrodynamic properties of viscous biofilms.

[1] Dunsing V, Irmscher T, Barbirz S, Chiantia S. Purely Polysaccharide-Based Biofilm Matrix Provides Size-Selective Diffusion Barriers for Nanoparticles and Bacteriophages. Biomacromolecules. 2019;20(10):3842-54.