Biology subjects

Sarlet, A.

Publications and source records attributed to Sarlet, A..

4 recordsLinked to original sources

bioRxiv2025

Wrinkles emerge from matrix complementarity in heterogenous biofilms

Biofilms are dynamic communities of microorganisms encased in a self-produced extracellular matrix. These resilient structures pose challenges across nearly all human activities, from healthcare to industry. The mechanical behaviour of a biofilm is shaped by the heterogenous composition of its matrix, both spatially and chemically. In turn, these mechanics influence the biofilms architecture at micro- and macroscopic scales, driving its complexity and adaptability. Morphologically, this is reflected in mechanical deformations of the biofilm known as wrinkles. In nature, biofilms often host different species of bacteria, allowing for a great diversity of matrix components. Here, we use a combination of two Escherichia coli strains as a model for a multispecies biofilm in which each bacterial strain produces one of two complementary matrix fibres: an amyloid protein (curli) or a polysaccharide (phosphoethanolamine-cellulose). Using fluorescence microscopy, we confirm that the two bacterial strains rapidly segregate into isogenic sectors, decreasing local heterogeneity. Furthermore, we show how wrinkles form, both in the homogenous central region of the biofilm, as well as at the boundary between sectors (i.e. where the two matrix producers co-localize). Finally, we show that increasing strain intermixing via the addition of bacteriophages results in thicker, taller wrinkles, irrespective of whether the two fibres are produced by two different strains or co-produced by the same bacteria.

biophysics↗

bioRxiv2025

Mechanical comparison of Escherichia coli biofilms with altered matrix composition: a study combining shear-rheology and microindentation

The mechanical properties of bacterial biofilms depend on the composition and micro-structure of their extracellular matrix (ECM), which constitutes a network of extracellular proteins and polysaccharide fibers. In particular, E. coli macrocolony biofilms were suggested to present tissue-like elasticity due to a dense fiber network consisting of amyloid curli and phosphoethanolamine-modified cellulose (pEtN-cellulose). To understand the contribution of these two main ECM components to the emergent mechanical properties of E. coli biofilms, we performed shear-rheology and microindentation experiments on biofilms grown from E. coli strains that produce different ECM. We measured that biofilms containing curli fibers are stiffer in compression than curli-deficient biofilms. We further quantitatively demonstrate the crucial contribution of pEtN-cellulose, and especially of the pEtN modification, to the stiffness and structural stability of biofilms when associated with curli fibers. To compare the differences observed between the two methods, we also investigated how the structure and mechanical properties of biofilms with different ECM compositions are affected by the sample preparation method used for shear-rheology. We found that biofilm homogenization, used prior to shear-rheology, destroys the macroscale structure of the biofilm while the microscopic ECM architecture may remain intact. The resulting changes in biofilm mechanical properties highlight the respective advantages and limitations of the two complementary mechanical characterization techniques in the context of biofilm research. As such, our work does not only describe the role of the ECM on the mechanical properties of E. coli biofilms. It also informs the biofilm community on considering sample preparation when interpreting mechanical data of biofilm-based materials.

biophysics↗

bioRxiv2024

Cell aspect ratio is a mechanical winning strategy in microbial competition

Bacterial competition shapes community architecture, yet a universally conserved determinant remains elusive. We show that cell aspect ratio -a simple morphological feature- confers a competitive advantage. Using growth-based range expansion experiments, we show that longer bacteria conquer the expanding front, even when initially in minority. Using an agent-based model of dividing bacteria, to isolate the effect of aspect ratio, we reveal that the takeover mechanism is collective alignment: groups of locally aligned bacteria form "nematic arms" bridging the central region of the colony to the expanding front. Once at the front, bacteria align parallel to it and block shorter bacteria from access to nutrients and space. We confirm this observation with single-cell experiments and further generalise our findings by introducing a generic continuum model of alignment-dominated competition, explaining both experimental and cell-based model observations. Moreover, we extend our predictions to spherical range expansions and confirm the competitive advantage, even though the effect is less pronounced than in surface-attached colonies. Our results uncover a simple, yet hitherto overlooked, mechanical mechanism determining the outcome of bacterial competition, which is potentially ubiquitous among various bacteria. Current advances in genetic engineering enable aspect ratio tuning as a mechanism with broad implications for biofilm control.

biophysics↗

bioRxiv2022

Influence of metal cations on the viscoelastic properties of Escherichia coli biofilms

Biofilms frequently cause complications in various areas of human life, e.g. in medicine and in the food industry. More recently, biofilms are discussed as new types of living materials with tuneable mechanical properties. In particular, Escherichia coli produces a matrix composed of amyloid-forming curli and phosphoethanolamine-modified cellulose fibres in response to suboptimal environmental conditions. It is currently unknown how the interaction between these fibres contributes to the overall mechanical properties of the formed biofilms and if extrinsic control parameters can be utilized to manipulate these properties. Using shear rheology, we show that biofilms formed by the E. coli K-12 strain AR3110 stiffen by a factor of two when exposed to the trivalent metal cations Al(III) and Fe(III) while no such response is observed for the bivalent cations Zn(II) and Ca(II). Strains producing only one matrix component did not show any stiffening response to either cation or even a small softening. No stiffening response was further observed when strains producing only one type of fibre were co-cultured or simply mixed after biofilm growth. These results suggest that the E. coli biofilm matrix is a uniquely structured composite material when both matrix fibres are produced from the same bacterium. While the exact interaction mechanism between curli, phosphoethanolamine-modified cellulose and trivalent metal cations is currently not known, our results highlight the potential of using extrinsic parameters to understand and control the interplay between biofilm structure and mechanical properties. This will ultimately aid the development of better strategies for controlling biofilm growth. Table of Contents Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/510089v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@12fdd08org.highwire.dtl.DTLVardef@1583efborg.highwire.dtl.DTLVardef@8ef241org.highwire.dtl.DTLVardef@c28dca_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗