Single particle tracking reveals spatial and dynamic organization of theEscherichiacolibiofilm matrix

Abstract

Biofilms are communities of surface-adherent bacteria surrounded by secreted polymers known as the extracellular polymeric substance (EPS). Biofilms are harmful in many industries, and thus it is of great interest to understand their mechanical properties and structure to determine ways to destabilize them. By performing single particle tracking with beads of varying surface functionalization it was found that charge interactions play a key role in mediating mobility within biofilms. With a combination of single particle tracking and microrheological concepts, it was found that Escherichia coli biofilms display height dependent charge density that evolves over time. Statistical analyses of bead trajectories and confocal microscopy showed inter-connecting micron scale channels that penetrate throughout the biofilm, which may be important for nutrient transfer through the system. This methodology provides significant insight into a particular biofilm system and can be applied to many others to provide comparisons of biofilm structure. The elucidation of structure provides evidence for the permeability of biofilms to microscale objects, and the ability of a biofilm to mature and change properties over time.

The particle in the spider's web: transport through biological hydrogels

“…The mesh sizes of mucus, biofilm EPS, and ECM vary and are on the order of 10-1000nm. 19,20,23,24,42–46 Note that measurements of mesh size may be incorrect if the particles used to probe the mesh size interact with the gel; 47 we discuss adhesive interactions in detail in Section 4. The nuclear pore is filled with intrinsically disordered proteins called nucleoporins that form a mesh with a mesh size ∼2.5-5 nm in size that excludes proteins and protein complexes larger than 30-100 kDa, unless they are chaperoned by a nuclear transport receptor (NTR).…”

“…For example, some biofilms contain channels that allow efficient passage of large particles to cells deep in the biofilm. 46,50 In mucus, nanoparticles often show a broad diffusivity distribution in particle tracking experiments, suggesting that some nanoparticles are trapped while others diffuse nearly freely. 32,45,51 One important question is whether the regions that allow free diffusion are connected enough to allow efficient penetration through macroscopic mucus layers, or whether these regions are simply large water-filled pores surrounded by impassable polymeric barriers.…”

“…46,91,92 SPT is more difficult for smaller solutes because of the difficulty inherent in resolving individual molecules with fluorescence microscopy; this technique is rarely if ever used to study diffusion of proteins or smaller molecules in gels.…”

Quantifying Biofilm Formation of <i>Sinorhizobium meliloti</i> Bacterial Strains in Microfluidic Platforms by Measuring the Diffusion Coefficient of Polystyrene Beads

“…Potential reasons why D changes include: 1) EPS production that increases the environment's viscosity, 2) electrostatic interactions between the beads and the EPS matrix [7], 3) the irregular structure of the EPS matrix [26], 4) interactions between bacteria and beads, especially when the bacteria are at a high concentration, as is the case in cell clusters, 5) high density of stationary cells that effectively trap the beads, 6) motion of cells (e.g. swarming) that forces the microspheres' motion, or a combination of the above.…”

“…In one such study, SPT was used to obtain the diffusion coefficients of differently charged beads showing in this way that surface functionalization of the particles affects their mobility in 1-day old B. multivorans and P. aeruginosa biofilms and in cystic fibrosis sputum [6]. In another study, SPT was used to find the beads' mean-square displacement in E. coli biofilms at their 2 nd and 4 th day of growth so as to determine how the motion of the beads is affected by their size and charge [7].…”