Experimental challenges in determining the rheological properties of bacterial biofilms

Abstract

Bacterial biofilms are communities living in a matrix consisting of self-produced, hydrated extracellular polymeric substances. Most microorganisms adopt the biofilm lifestyle since it protects by conferring resistance to antibiotics and physico-chemical stress factors. Consequently, mechanical removal is often necessary but rendered difficult by the biofilm’s complex, viscoelastic response, and adhesive properties. Overall, the mechanical behaviour of biofilms also plays a role in the spreading, dispersal and subsequent colonization of new surfaces. Therefore, the characterization of the mechanical properties of biofilms plays a crucial role in controlling and combating biofilms in industrial and medical environments. We performed in situ shear rheological measurements of Bacillus subtilis biofilms grown between the plates of a rotational rheometer under well-controlled conditions relevant to many biofilm habitats. We investigated how the mechanical history preceding rheological measurements influenced biofilm mechanics and compared these results to the techniques commonly used in the literature. We also compare our results to measurements using interfacial rheology on bacterial pellicles formed at the air–water interface. This work aims to help understand how different growth and measurement conditions contribute to the large variability of mechanical properties reported in the literature and provide a new tool for the rigorous characterization of matrix components and biofilms.

Air–liquid intestinal cell culture allows in situ rheological characterization of intestinal mucus

“…It is reasonable to suspect the removal of the mucus from the cells and transport onto the plastic dish could permanently alter mucus properties, as has been found to occur in biofilms, which exhibit reduced viscoelasticity when gently scraped onto a rheometer. 47 Furthermore, the process of pipetting the mucus layer off the culture surface could leave behind the most adherent and solid-like mucus. 48 Finally, we also characterized the extracted mucus properties using dynamic light scattering microrheology.…”

Microstructural and Rheological Transitions in Bacterial Biofilms

“…This approach had been shown to cause differences in the magnitude of elastic and viscous modulus, however, the difference was much lower in agar‐grown biofilms compared to submerged biofilms. [ 8 , 65 ] In both approaches, the evolution of elastic and viscous behavior as a function of strain remained unchanged. The top plate was lowered to a gap height of 1 mm and the normal force was set to 0.1 N. A solvent trap was used to prevent sample dehydration during measurement.…”

Editorial: theme issue on complex rheology in biological systems

“…For this theme issue, we gratefully received contributions from across the physics and life sciences with interests in biorheology ranging in length scale from the rheological properties of intracellular biomolecular networks [ 1 , 10 ] to the scale of the direct extracellular environment [ 3 , 7 , 10 , 12 , 13 , 16 ], tissues [ 3 – 5 ] and even entire organs that actively exert forces onto non-Newtonian fluids [ 6 ]. The mechanical properties at the cellular level are discussed in relationship to cancer [ 2 ], as well as in relationship to the transport of red blood cells in disordered porous environments, be it in vascular networks or in microfluidic devices.…”

“…The mechanical properties at the cellular level are discussed in relationship to cancer [ 2 ], as well as in relationship to the transport of red blood cells in disordered porous environments, be it in vascular networks or in microfluidic devices. The interaction of a cell with its environment, and in particular the consequence of these interactions to cell mobility, is discussed in the context of (i) blood flow in vascular networks [ 5 ], (ii) male infertility [ 7 ], (iii) the stability of biofilms [ 12 , 13 ] and (iv) new opportunities of using liquid crystals to impose controlled constraints to cell motion [ 16 ].…”