Self-Adaptation of Pseudomonas fluorescens Biofilms to Hydrodynamic Stress

Abstract

In some conditions, bacteria self-organize into biofilms, supracellular structures made of a self-produced embedding matrix, mainly composed of polysaccharides, DNA, proteins, and lipids. It is known that bacteria change their colony/matrix ratio in the presence of external stimuli such as hydrodynamic stress. However, little is still known about the molecular mechanisms driving this self-adaptation. In this work, we monitor structural features of Pseudomonas fluorescens biofilms grown with and without hydrodynamic stress. Our measurements show that the hydrodynamic stress concomitantly increases the cell density population and the matrix production. At short growth timescales, the matrix mediates a weak cell-cell attractive interaction due to the depletion forces originated by the polymer constituents. Using a population dynamics model, we conclude that hydrodynamic stress causes a faster diffusion of nutrients and a higher incorporation of planktonic bacteria to the already formed microcolonies. This results in the formation of more mechanically stable biofilms due to an increase of the number of crosslinks, as shown by computer simulations. The mechanical stability also relies on a change in the chemical compositions of the matrix, which becomes enriched in carbohydrates, known to display adhering properties. Overall, we demonstrate that bacteria are capable of self-adapting to hostile hydrodynamic stress by tailoring the biofilm chemical composition, thus affecting both the mesoscale structure of the matrix and its viscoelastic properties that ultimately regulate the bacteria-polymer interactions.

Mechanical Resilience of Biofilms toward Environmental Perturbations Mediated by Extracellular Matrix

“…Note that the cell-to-cell interaction we used is effective in the sense that it includes contributions from cell-VPS and VPS-VPS interactions; recent work has shown that these more complicated interactions can be modeled efficiently using an effective intercellular potential. [9,49] 27 cells in total are randomly distributed and relaxed in a simulation box of 10 × 10 × 10 µm 3 before performing the sheared flow simulation. As shown in Figure 3a, starting from a random organization (at 0 s −1 ), upon increasing the shear rate the simulated biofilm structure first becomes denser, and cells in the aggregate tend to align along the shear direction (at 60 s −1 ).…”

Experimental challenges in determining the rheological properties of bacterial biofilms

“…Therefore, as an increase in solid content not necessarily leads to an increase in mechanical strength, we hypothesize that only some biofilm components contribute to the network strength and elasticity. Recent work found that P. fluorescens exposed to hydrodynamic stresses formed mechanically stronger biofilms compared to those formed in static conditions, and this was attributed specifically to an increase in EPS content [65]. This increase in matrix components was hypothesized to lead to an increase in cross-linking density in the biofilm.…”

Mechanism Underlying the Role of LuxR Family Transcriptional Regulator abaR in Biofilm Formation by Acinetobacter baumannii

“…A recent study reported that genes that play a regulatory role in gluconeogenesis are significantly upregulated in biofilm cells compared with free cells [ 37 , p. 139]. It is reported that carbohydrates are the major composition of biofilms [ 38 ]. Carbon sources play a necessary role in the survival, growth, and infection of strains [ 39 , pp.…”