Mapping of Bacterial Biofilm Local Mechanics by Magnetic Microparticle Actuation

Abstract

Most bacteria live in the form of adherent communities forming three-dimensional material anchored to artificial or biological surfaces, with profound impact on many human activities. Biofilms are recognized as complex systems but their physical properties have been mainly studied from a macroscopic perspective. To determine biofilm local mechanical properties, reveal their potential heterogeneity, and investigate their relation to molecular traits, we have developed a seemingly new microrheology approach based on magnetic particle infiltration in growing biofilms. Using magnetic tweezers, we achieved what was, to our knowledge, the first three-dimensional mapping of the viscoelastic parameters on biofilms formed by the bacterium Escherichia coli. We demonstrate that its mechanical profile may exhibit elastic compliance values spread over three orders of magnitude in a given biofilm. We also prove that heterogeneity strongly depends on external conditions such as growth shear stress. Using strains genetically engineered to produce well-characterized cell surface adhesins, we show that the mechanical profile of biofilm is exquisitely sensitive to the expression of different surface appendages such as F pilus or curli. These results provide a quantitative view of local mechanical properties within intact biofilms and open up an additional avenue for elucidating the emergence and fate of the different microenvironments within these living materials.

Biomechanical Analysis of Infectious Biofilms

“…Broadly similar spectra have been observed in a range of polymeric gels, including peptide fibrils [74], block copolymers [77] and intermediate filaments [56]. F pilus producing E. coli biofilms, but not curli producing ones, have also been compared to actin protein gels based on active microrheology experiments [37]. P. aeruginosa biofilms rapidly stiffen for frequencies exceeding 10 Hz [55], an effect not seen in the other systems mentioned.…”

“…For one particle, the motions of micron-scale particles undergoing passive Brownian motion are converted to G * (ω) or J * (ω) using thermodynamic relations [31,61,62], or they are actively driven via external forces and the moduli extracted directly [37,106]. These particles are either added, or are endogenous such as the cells themselves [76].…”

“…The non-linear response is also variable, with both shear thinning [55] and shear thickening [90] reported, although the empirical Cox-Merz rule relating linear oscillatory viscoelasticity to non-linear flow has been verified for P. aeruginosa matrix extracts [104] which, if found to be generally true, would aid the characterisation of biofilms in flow. An additional problem is the significant run-to-run variation, consistent with a broad, log-normal distribution [4], and the variation in stiffness, decreasing near the surface and increasing with age [37,54,76]. Such spatio-temporal variation can in principle be incorporated into suitably parameterised constitutive models, at the expense of an increased number of fit parameters and greater validation challenge.…”

Influence of Environmental Factors on Bacterial Biofilm Formation in the Food Industry: A Review

“…Physical properties of biofilms, such as cell density and strength of attachment, can be affected by fluid shear: static or low flow conditions may lead to isotropic structures, but higher unidirectional flow may produce filamentous cells or groupings of cells with evidence of directionality (Goller and Romeo, 2008). However, remodeling of E. coli biofilms was caused by a cell biological response to shear stress rather than by a direct physical effect on the material organization itself (Galy et al, 2012). It is generally considered that higher shear rates result in higher detachment forces leading to a decrease in the number of attached bacteria, while they make the biofilm denser and thinner (Katsikogianni and Missirlis, 2004).…”

Multicomponent model of deformation and detachment of a biofilm under fluid flow

“…Theoretical and experimental studies have shown that the viscoelastic biofilm gel-like matrix largely minimizes flow advection [56]. However, because of structural and local heterogeneities, biofilms contain zones behaving like a solid or a liquid rather than a viscoelastic gel [57]. Within fluidic areas, advection may have a significant role (e.g.…”