Spatiotemporal mapping of oxygen in model porous media biofilms using 19 F magnetic resonance oximetry
Simkins, Jeffrey William
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Biofilms, microbial aggregates anchored to a surface using a sticky matrix of metabolic products called extracellular polymeric substances (EPS), are the dominant form of bacterial life and are widespread in nature, from glaciers to hot springs. The transition from the planktonic state to a biofilm is associated with striking changes to microbial phenotype which confer unique, biofilm-specific properties to resident cells that have important implications for medicine, industry, and environmental study. Many of these properties are caused in large part by oxygen transport limitation, which arises due to restriction of fluid flow in cell aggregates and consumption of oxygen for respiration. The balance of reactive and diffusive processes establishes strong spatial gradients in oxygen concentration which lead to profound spatial heterogeneity in bacterial species composition, growth yield, antimicrobial susceptibility, and reaction kinetics, among other traits. However, despite the importance of oxygen gradients in a host of highly-relevant biofilm phenomena, quantification of oxygen profiles in biofilms is difficult, both in the field and the lab, with the gold standard of measurement, the microelectrode, having significant limitations. 19 F Nuclear Magnetic Resonance (NMR) oximetry, a magnetic resonance-based technique for oxygen quantification that has been used to characterize oxygen usage in blood tissues and tumors, exploits the linear dependence of spin-lattice relaxation rate R 1 on local oxygen partial pressure for fluorine nuclei in perfluorocarbon (PFC) phases. In the current work, we apply 19 F NMR oximetry to a model packed bed biofilm system to generate novel insights into microbial oxygen usage and to introduce a complimentary oximetry tool for biofilm experimenters. We develop methodology for the introduction and fixation of a fluorinated oxygen sensor to facilitate long-term oxygen monitoring. We use 19 F oxygen distribution measurements in compliment to traditional NMR methods to correlate fluid flow with growth rate, generate spatial maps of oxygen utilization rate, identify differences in oxygen utilization behavior between different species, characterize infection persistence during antibiotic therapy, mathematically model macroscale oxygen sink development, and quantify local mass transfer phenomena.