Multiscale X-ray study of Bacillus subtilis biofilms reveals interlinked structural hierarchy and elemental heterogeneity

Abstract

Biofilms are surface-associated soft microbial communities, which may be either detrimental or beneficial to their hosting environment. They develop from single cells into mature colonies, that are composed of cells and sometimes (in Firmicutes phylum) spores, held together by an extracellular matrix (ECM) of secreted biomolecular components. Biofilm development is a dynamic process, during which cells organize into subgroups, creating functionally distinct regions in space. Specific examples of functional-spatial division in Bacillus subtilis biofilms include matrix and spore formation as well as water channels that form beneath wrinkles. An interesting question arising is whether the division of labor in biofilms is also reflected in the molecular-level order across whole biofilms. Using combined X-ray diffraction (XRD)/X-ray fluorescence (XRF), we studied the molecular order in intact biofilms across multiple length scales. We discovered that biofilms display a distinct spatio-temporal XRD signature that depends on highly ordered structures in spores and on cross beta sheet structures in matrix components. Spore signal is found especially enhanced with water molecules and metal-ions signals along macroscopic wrinkles, known to act as water channels. Demonstrating in situ the link between molecular structures, metal ions distribution and division of labor across whole biofilms in time and space, this study provides new pivotal insight to the understanding biofilm development.

Molecular architecture of the TasA biofilm scaffold in Bacillus subtilis

“…In contrast, a recent study proposed that TasA fibres consist of a linear arrangement of globular subunits that does not involve structural rearrangements in the transition of TasA monomers to fibres, suggesting that fibres formed by recombinant TasA are not amyloid [27]. Moreover, a recent X-ray diffraction study showed that TasA fibrils only possess a weak cross-β-sheet pattern [11]. Given a lack of direct structural data, it is not possible to relate these previous observations to the underlying molecular arrangement of TasA.…”

“…The soil bacterium Bacillus subtilis is one of the best-studied model organisms for investigating biofilm formation [6][7][8][9][10][11][12]. The B. subtilis biofilm ECM is rich in exopolysaccharide and protein components, the major proteinaceous component being a 26 kDa fibre-forming protein called TasA [13,14].…”

Gradients of Orientation, Composition, and Hydration of Proteins for Efficient Light Collection by the Cornea of the Horseshoe Crab

“…The occurrence of these peaks is indicative of cross‐beta structures in proteins. [ 16,17 ] Cross‐beta protein organization is common in arthropod cuticles, however it is often difficult to discriminate the protein reflections from those of chitin as they typically coincide and since chitin‐poor or protein‐rich layers are usually thin with respect to the probed volume. [ 18,19 ] In L. polyphemus an especially thick epicuticle (the part of the cuticle that is devoid of chitin) allows direct insight into the dominant protein structure in the cuticle.…”

Gradients of orientation, composition and hydration of proteins for efficient light collection by the cornea of the horseshoe crab

“…2A, violet curve). The occurrence of these peaks is indicative of cross-beta structures in proteins ( 16 , 17 ). Cross-beta protein organization is common in arthropod cuticles ( 18 , 19 ), however it is often difficult to discriminate the protein reflections from those of chitin as they typically coincide and since chitin-poor or protein-rich layers are usually thin with respect to the probed volume.…”