It’s sweet to move on – bacteriophage infection and processing of glycan-based biofilms

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In many ecosystems, microorganisms organize themselves in biofilms, complex mixtures of biopolymers like proteins, DNA or polysaccharides, the extracellular, polymeric substance (EPS). The EPS offers advantageous conditions for the embedded cells and shields them against external influences, e.g. antibiotics. Also the access of bacterial viruses (bacteriophages) to their bacterial hosts is restricted by the biofilm that also has impact on their infection rate. However, so far only a few studies describe interactions of bacteriophages with biofilms, although phage-mediated gene transfer is intimately linked to the evolution of biofilm-forming bacterial communities.In the biofilm, the EPS forms a tight network that slows down particle diffusion – also that of bacteriophages. Especially the polysaccharide component is responsible for a biofilm’s viscoelastic stability and network character. Goal of our project is to analyze bacteriophage infection in glycan-dominated biofilms. Many bacteriophages, as part of their tails, contain glycosidases, enzymes that cleave the EPS polysaccharides (depolymerases) and thus actively reduce biofilm stability. So far, no systematic studies exist on the impact of these depolymerases on the dynamics of bacteriophage infection inside biofilms.Plant pathogens of the genus Erwinia, e.g. the causative agent of fire blight in apple trees, E. amylovora, form viscous glycan-based biofilms that we will use in our studies to analyze the infection behavior of Erwinia phages. Fluorescence correlation spectroscopy (FCS) is a well-suited method to follow diffusion of phage particles in biofilms with high spatiotemporal resolution. We will use FCS to study phage mobility and infection rates of Erwinia phages in biofilms and include this data into theoretical models of population dynamics, especially in the presence of depolymerases that dissipate the biofilm. Depolymerases most likely also act synergistically in mixtures of different phages present in a biofilm. For this it is highly important to completely and reliably identify glycan-biofilm depolymerases in viral genomes. Due to their modular architecture this necessitates new algorithm for depolymerase annotation which we will develop in this project. We will use them to screen metagenomes for new viral depolymerases, to gain a deeper understanding of phage-host relationships in biofilms. Moreover, the discovery of new biofilm depolymerases is highly desirable for biotechnology as antimicrobial agents active against biofilm-forming pathogens.