Quantitative Analysis of Amyloid-Integrated Biofilms Formed by Uropathogenic Escherichia coli at the Air-Liquid Interface

Abstract

Bacterial biofilms are complex multicellular assemblies, characterized by a heterogeneous extracellular polymeric matrix, that have emerged as hallmarks of persistent infectious diseases. New approaches and quantitative data are needed to elucidate the composition and architecture of biofilms, and such data need to be correlated with mechanical and physicochemical properties that relate to function. We performed a panel of interfacial rheological measurements during biofilm formation at the air-liquid interface by the Escherichia coli strain UTI89, which is noted for its importance in studies of urinary tract infection and for its assembly of functional amyloid fibers termed curli. Brewster-angle microscopy and measurements of the surface elasticity (G(s)') and stress-strain response provided sensitive and quantitative parameters that revealed distinct stages during bacterial colonization, aggregation, and eventual formation of a pellicle at the air-liquid interface. Pellicles that formed under conditions that upregulate curli production exhibited an increase in strength and viscoelastic properties as well as a greater ability to recover from stress-strain perturbation. The results suggest that curli, as hydrophobic extracellular amyloid fibers, enhance the strength, viscoelasticity, and resistance to strain of E. coli biofilms formed at the air-liquid interface.

Films of bacteria at interfaces: three stages of behaviour

“…There are a few notable recent studies in this field; for example, at air-aqueous interfaces, the structure and properties of interfacial biofilms or pellicles of B. subtilis [26,27] have been studied to investigate the role of amyloid fibers in providing structural integrity to the films. The time evolution and mechanics of FBI formed by E. coli have been also studied, revealing rich interface rheology dependent on microbial secretions [28][29][30][31][32] with implications in infec-tion [29,32]. FBI at oil-water interfaces have been studied [30,[33][34][35][36][37][38], motivated by their relevance to petroleum technologies, including oil recovery from oil sands [33][34][35][36][37][38].…”

Cellulose as an Architectural Element in Spatially Structured Escherichia coli Biofilms

“…It should be noted that a recent report attributed ethanol-induced or dimethyl sulfoxide-induced increased cohesion and elasticity of pellicle biofilms of the uropathogenic E. coli UTI89 to increased curli expression (44,45). Unfortunately, cellulose was not considered in those studies, and our observations of the distinct biofilm properties conferred by curli and cellulose, as well as the coregulation of both components by CsgD and c-di-GMP, suggest that cellulose biosynthesis may well be stimulated in parallel to curli expression under these conditions.…”

Molecular Determinants of Mechanical Properties of V. cholerae Biofilms at the Air-Liquid Interface

“…Interfacial rheology has been used extensively to study complex fluid interfaces formed by surfactants, particles, polymers, biomolecules, and other materials (16)(17)(18)(19) and has emerged as a powerful tool to measure the evolution of the mechanical properties of bacterial biofilms, including changes in the viscoelasticity of the film, in real time. We recently examined the specific contributions of functional amyloid fibers termed curli to biofilm formation in uropathogenic Escherichia coli and discovered that increased curli production increased the mechanical strength and elasticity of the pellicle and enhanced the ability to recover from physical perturbation (20,21). These results correlated molecular composition with macroscopic mechanical properties and function and revealed the importance of curli in the development and maintenance of the film elasticity.…”