Linking Matrix Composition with Spatially Resolved Mechanical Properties in Polymicrobial Biofilms

OVERVIEW: Biofilms are soft multicomponent biological materials composed of microbial communities attached to surfaces and encased in a hydrated matrix of extracellular polymeric substances (EPS) thought to provide mechanical stability. Despite the crucial relevance of biofilms to diverse industrial, medical, and environmental applications, little is known about how local biofilm mechanical properties are mediated by biomolecular EPS composition, community diversity, and biofilm physical structure. To address this knowledge gap, the PIs propose to adapt emerging spatially resolved microrheological and imaging approaches to probe the relationship between microscale biofilm viscoelastic and cohesive/ adhesive mechanical properties, EPS and community composition, and physical structure. The project team will investigate structure/ composition-mechanical property relationships in biofilms of increasing complexity, from axenic to dual species and finally complex environmentally relevant mixed culture biofilms. The project team will also examine how environmental cues modify EPS composition and structure-property relationships. Efforts will be organized around three specific objectives: 1) Study local structure- composition-viscoelastic property relationships in biofilms; 2) Study biofilm-substratum adhesion properties at ultrahigh strain rates; and 3) Understand cohesive failure of polymicrobial biofilms subjected to large local deformations. Experimental results will be used to test if the constitutive relationship varies depending on biofilm composition, and will be integrated into a continuum model that couples fluid- structure interactions to spatial variability in biofilm structure and composition in order to predict deformation and detachment. INTELLECTUAL MERIT: This proposal advances understanding of critical yet poorly understood interrelationships between molecular composition (EPS), physical structure, and mechanical properties in polymicrobial biofilms exposed to disparate environmental cues. The majority of the work to-date on biofilm mechanical properties has employed macrorheological tools that neglect the inherent local heterogeneity in biofilms, and has focused primarily on pure culture biofilms (e.g. P. aeruginosa alone) that are not representative of, and likely differ greatly in EPS composition and mechanical properties from, polymicrobial biofilms that are found in medical, environmental and industrial settings. Project results will specifically elucidate, for the first time, how microscale variations in EPS constituents (e.g. polysaccharides, proteins, eDNA) mediate local heterogeneity in shear moduli and viscosity, adhesion strength, and cohesive fracture energy in dual and mixed culture biofilms, and how this relationship is modified by environmental cues and microbial populations present. This improved understanding of spatially resolved structure/ composition- mechanical property relationships will provide the basis for rational management and control of biofilms. BROADER IMPACTS: Detrimental biofilms cause billions of dollars per year of damage via biofouling or corrosion of ship hulls, heat exchangers, water treatment and distribution infrastructure, membranes, and in the food, oil, and beverage industries, and account for 65% of nosocomial infections, affecting 17 million people and causing at least 550,000 deaths annually in the US. Conversely, beneficial biofilms are increasingly harnessed to clean water and remediate groundwater and soil. Project results will directly inform strategies to manage bio