Significance
In the natural environment the majority of bacteria live within the confines of a structured social community called a biofilm. The stability of biofilms arises from the extracellular matrix, which consists of proteins, polysaccharides, and extracellular DNA. One of these proteins, BslA, forms a hydrophobic “raincoat” at the surface of the biofilm. We have uncovered the mechanism that enables this protein to function, revealing a structural metamorphosis from a form that is stable in water to a structure that prefers the interface where it self-assembles with nanometer precision to form a robust film. Our findings havewide-ranging implications,from the disruptionof harmful bacterial biofilms to the generation of nanoscale materials.