Revealing the Hidden Complexity of Bacterial Biofilms

(A) Optical image of a wrinkle at the edge of the biofilm (reproduced from ref. 14). (B) SEM image of a biofilm showing resemblance to a hydrogel structure with cells embedded in the dense meshwork of ECM. (C) Images of a biofilm grown on a permeable membrane that went through the cycle of de- and re-hydration (see ref. 21 for experimental details). (D) A cross-section of a biofilm wrinkle that contains a water-filled channel (reproduced from ref. 14). (E) IR measurements of surface temperature of a biofilm where lower temperature is indicative of cooling down due to water evaporation. When the dish with the biofilm is covered (Left panel), there is very little evaporation. When the lid is open (Right panel), evaporation is active and highest at the ridges of the biofilm; see ref. 14. (F) Characteristic X-ray diffraction patterns of whole dry and hydrated biofilms. Peak deconvolution (dashed lines) shows that the contribution from free water at 26 nm signal in biofilm wrinkles disappears in dry biofilms, yet retaining the bound water signal at 19 nm (Left panel). Distribution of the intensity of the respective peaks in a macroscopic area of the whole living biofilm (Right panel) indicates a gradual drying out of the part of the sample (red dry, green hydrated) and higher water signal in the wrinkles (reproduced from ref. 17). Courtesy of Liraz Chai, Vasily Zaburdaev, Roberto Kolter

September 25, 2024

New research reveals insights into the development of bacterial biofilms, highlighting how these communities adapt to environmental stress through complex interactions between physical and biological processes occurring in the surrounding environment. The research could have broad implications for fields such as medicine, environmental science, and industry.

Led by professor Liraz Chai from the Institute of Chemistry and The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, and in collaboration with professor Vasily Zaburdaev from Friedrich-Alexander-Universität Erlangen-Nürnberg and Max-Planck-Zentrum für Physik und Medizin, and professor Roberto Kotler from Harvard Medical School, this research describes how physical and chemical processes occurring in the extracellular space of bacterial communities work together to shape biofilm morphology and physiology, thereby also allowing them to survive in challenging environments.

Bacterial biofilms, often seen as slimy layers on various surfaces, for example, catheters, teeth and even plant roots, have long been studied for their complex behavior and resistance to external threats like antibiotics. However, this new perspective paper takes a unique approach by combining molecular biology with biophysics to highlight the importance of extracellular rather then intracellular processes in determining biofilm organization into complex structures that resemble human tissues. By using Bacillus subtilis, a beneficial bacterium, as a model, the researchers were able to look closely at the interactions between extracellular molecules and between molecules and cells within these communities on both small and large scales.

In their assay the researchers explain that we need to broaden the discussion from the extracellular matrix to the extracellular space. The extracellular matrix is just one component within a complex environment, immersed in water, dissolved nutrients, signaling molecules, waste products, and metal ions. In this milieu, various physical processes directly influence biofilm physiology as molecules and bacteria interact and affect one another.

The study highlights the role of proteins, polysaccharides, water channels, and metal ions in shaping the biofilm’s morphology. These components help create the macroscopic wrinkles and water-filled channels that allow biofilms to thrive. In addition to understanding macroscopic structures in biofilms , the research also delves into how processes at the molecular scale allows biofilms adapt to environmental stressors such as dehydration. The findings suggest that the cross talk between cells in biofilms and molecular processes in the extracellular space enable complex biological processes, such as differentiation, to adjust their physiology to survive in changing environments.

This work serves as a reminder of how closely intertwined biological and physical processes are in shaping the microscopic world. Opening up new possibilities for understanding complex space-time hierarchical organization in biofilms from the nanometer scale of individual proteins to whole biofilms at the scale of centimeters, it offers an exciting step forward in biofilm research, with potential applications in combating biofilm-related infections, improving industrial processes, and protecting ecosystems.

Source: The Hebrew University of Jerusalem

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