BacFilm · Structure and Regulation of Bacterial Biofilm-Promoting Exopolysaccharide Secretion Systems

Bacteria are commonly defined as unicellular organisms; however, they constantly exchange substances and information with their confrères and the environment, and can efficiently shelter themselves and achieve homeostasis by building multicellular collaborative macrocolonies called biofilms. Members of these sessile communities can undergo significant functional differentiation and are typically embedded in complex extracellular matrix that secures both mechanical protection and a medium for intercellular exchange. Importantly, the switch between sessile and motile life-styles in pathogenic bacteria can correlate directly with the development of chronic vs. acute infections, whereas extracted bacterial matrix components can find a variety of beneficial biotechnological applications. Exopolysaccharides (EPS) are a major biofilm matrix component and are typically produced by trans-envelope secretion nanomachines, many of which are controlled at multiple levels by the intracellular second messenger c-di-GMP. Here, we will consolidate our expertise in biofilm formation, cyclic dinucleotide signaling, bacterial secretion and integrative structural biology to decipher EPS secretion system assembly and function in several medically and industrially relevant species. We will use complementary recombinant and in situ structural biology approaches together with established genetic and imaging techniques to decipher the molecular events controlling EPS biogenesis from transcription initiation, interdependent protein folding and cooperative subunit interactions; through secretion system assembly, formation of supramolecular secretory nanoarrays and EPS modifications; to harnessing the biosynthetic processes for the engineering of novel anti-infectives or beneficial EPS superproducers. Over the last years we have spearheaded these studies by unprecedented mechanistic insights into several secretion systems and have demonstrated the feasibility of such an ambitious project.