Biology subjects

Ghrayeb, M.

Publications and source records attributed to Ghrayeb, M..

4 recordsLinked to original sources

bioRxiv2026

A bacterial extracellular matrix protein forms a supramolecular metallogel

The microbial extracellular matrix (ECM) is a complex network of self-secreted biopolymers uniting the cells in biofilms, providing them with structural integrity, and contributing to their elevated resistance to antibiotic treatments. Recently, there is a growing realization that a regulated, bidirectional cross-talk of bacteria and ECM confers biofilms with tissue-like traits, however, the mechanisms of spatio-temporal self-organisation of ECM and its regulation are still poorly understood. In the model organism for biofilm formation Bacillus subtilis, TasA is the major protein component of the extracellular matrix. We recently showed that TasA, isolated in the form of stable and structured globules, assembles into elongated and ordered fibers via a donor-strand complementation mechanism. In this study, we discovered that in the presence of zinc metal ions, TasA is able to form hydrogels with > 97% water content. Electron- and atomic force-microscopies as well as small angle X-ray scattering measurements show that cross-linking with zinc ions induces a transition in TasA morphology from one-dimensional fibers to two-dimensional sheets. Electron paramagnetic resonance measurements then show that such a significant morphological shift is associated with molecular changes in the coordination environment of zinc ions, which lead to structural changes at the protein level. When assembling into macroscopic networks, TasA-Zn metallogels exhibit viscoelastic properties and a fast recovery following an excessive strain. These metallogels represent a novel class of bacterially-derived ECMs that form easily at room temperature without covalent crosslinking, and may be used as a natural matrix-mimics in biofilm models for infection studies.

biochemistry↗

bioRxiv2025

Bi-directional relationship between the biofilm of Porphyromonas gingivalis and the amyloid-beta peptide.

Periodontitis and Porphyromonas gingivalis infections are significant risk factors for the onset of Alzheimers disease (AD). Despite P. gingivalis relying on biofilm for its survival and virulence, the impact of the extracellular matrix on ADs neuropathological hallmarks was never examined. In this study, we report a bidirectional relationship between the amyloid beta (A{beta}) peptide, which plays a central role in AD, and the biofilm of P. gingivalis. Using multiple fluorescent markers for biofilm components, we observed that A{beta}1-40 inhibited biofilm formation while A{beta}1-42 increased extracellular matrix production. Also, using thioflavin T staining and atomic force microscopy, we observed co-aggregation between the biofilm and monomeric A{beta}1-40, resulting in a quicker aggregation and significant changes in aggregate structures. Our findings propose mechanistic explanations for the role of P. gingivalis as a risk factor for AD and offer potential mechanisms for the microbial involvement in AD etiology. ImportanceWhile the etiology of Alzheimers disease has been studied extensively for the past 50 years, its exact causes remain unknown. Our current understanding is that the accumulation of multiple genetic and environmental risk factors would lead to the onset of the disease. Porphyromonas gingivalis is a bacterium that produces biofilm and elicits periodontitis, a chronic infection of the gums that constitutes a risk factor for Alzheimers disease. While studies have looked at the effects of P. gingivalis in triggering Alzheimers symptoms in animal models, none have explored the impact of the biofilm, which is ubiquitous to this bacterium. Our study seeks to bridge that gap by demonstrating a bi-directional relationship between the biofilm of P. gingivalis and amyloid beta, one of the brain lesions involved in Alzheimers. By understanding risk factors involved in Alzheimers and their impact, we hope to provide valuable knowledge on prevention and treatment.

microbiology↗

bioRxiv2022

Molecular architecture of the TasA biofilm scaffold in Bacillus subtilis

Many bacteria in nature exist in multicellular communities termed biofilms. Cells within biofilms are embedded in a primarily self-secreted extracellular polymeric matrix that provides rigidity to the biofilm and protects cells from chemical and mechanical stresses. In the Gram-positive model biofilm-forming bacterium Bacillus subtilis, TasA is the major protein component of the biofilm matrix, where it has been reported to form functional amyloid fibres contributing to biofilm structure and stability. The structure of TasA fibres, however, and how fibres scaffold the biofilm at the molecular level, is not known. Here, we present electron cryomicroscopy structures of TasA fibres, which show that rather than forming amyloid fibrils, TasA monomers assemble into filaments through donor strand complementation, with each subunit donating a {beta}-strand to complete the fold of the next subunit along the filament. Combining electron cryotomography, atomic force microscopy, and mutational studies, we show how TasA filaments congregate in three dimensions to form abundant fibre bundles that are essential for B. subtilis biofilm formation. This study explains the previously observed biochemical properties of TasA and shows, for the first time, how a bacterial extracellular globular protein can assemble from monomers into {beta}-sheet-rich fibres, and how such fibres assemble into bundles in biofilms. We establish a hierarchical, atomic-level assembly mechanism of biofilm scaffolding that provides a structural framework for understanding bacterial biofilm formation.

microbiology↗

bioRxiv2021

Spores and extracellular matrix components impart molecular order in Bacillus subtilis biofilms.

Biofilms are multicellular microbial communities that encase themselves in an extracellular matrix (ECM) of secreted biopolymers and attach to surfaces and interfaces. Bacterial biofilms are detrimental in hospital and industrial settings, but they can be beneficial in agricultural contexts. An essential property of biofilms that grants them with increased survival relative to planktonic cells is phenotypic heterogeneity; the division of the biofilm population into functionally distinct subgroups of cells. Phenotypic heterogeneity in biofilms can be traced to the cellular level, however, the molecular structures and elemental distribution across whole biofilms as well as possible linkages between them remain unexplored. Mapping X-ray diffraction (XRD) across intact biofilms in time and space, we revealed the dominant structural features in Bacillus subtilis biofilms, stemming from matrix components, spores and water. By simultaneously following the X-ray fluorescence (XRF) signal of biofilms and isolated matrix components, we discovered that the ECM preferentially binds calcium ions over other metal ions, specifically, zinc, manganese and iron. These ions, remaining free to flow below macroscopic wrinkles that act as water channels, eventually accumulate and lead to sporulation. The possible link between ECM properties, regulation of metal ion distribution and sporulation across whole intact biofilms unravels the importance of molecular-level heterogeneity in shaping biofilm physiology and development. Significance StatementBiofilms are multicellular soft microbial communities that are able to colonize synthetic surfaces as well as living organisms. To survive sudden environmental changes and efficiently share their common resources, cells in a biofilm divide into subgroups with distinct functions, leading to phenotypic heterogeneity. Here, by studying intact biofilms by synchrotron X-ray diffraction and fluorescence, we revealed correlations between biofilm macroscopic architectural heterogeneity and the spatio-temporal distribution of extracellular matrix, spores, water and metal ions. Our findings demonstrate that biofilm heterogeneity is not only affected by local genetic expression and cellular differentiation, but also by passive effects resulting from the physicochemical properties of the molecules secreted by the cells, leading to differential distribution of nutrients that propagates through macroscopic length scales.

microbiology↗