Nutrient availability influencesE. colibiofilm properties and the structure of purified curli amyloid fibers

ABSTRACT Bacterial biofilms are highly adaptable and resilient to challenges. Nutrient availability can induce changes in biofilm growth, biomass, morphology, architecture and mechanical properties. Bacterial extracellular matrix plays a major role in achieving biofilm stability under different environmental conditions. Curli amyloid fibers are determining for the architecture and stiffness of E. coli biofilms, but how this major matrix component adapts to different environmental cues remains unclear. Here, we investigated for the first time the effect of nutrient availability on both i) biofilm materials properties and ii) the structure and properties of curli amyloid fibers extracted from the biofilms. For this, we cultured E. coli W3110, which main matrix component is curli fibers. We quantified the size, mass and water content of the resulting biofilms and estimated their mechanical properties by microindentation. The curli amyloid fibers were then purified from the biofilms and their molecular structure and properties were studied by spectroscopic techniques. Our results show that the availability of nutrients in the substrate influences the yield of curli fibers, their structural composition and chemical stability, and suggest that these molecular features contribute to the stiffness of the biofilms. Biofilms grown on substrates with high nutrient concentration are softer, contain less curli fibers, and these fibers exhibit low β-sheet content and chemical stability. Our multiscale study sheds new light on the relationship between the molecular structure of bacterial matrix and the macroscopic properties of biofilms. This knowledge will benefit the development of both anti-biofilm strategies and biofilm-based materials. Graphical abstract