Description
Bacteria motility is a key factor in understanding bacteria activity and the interaction with their surroundings. Confinement within porous matrices, concentration, and flow are some of the most critical parameters affecting bacteria motility [1]. Dense bacterial colonies can give rise to specific multicellular aggregates such as biofilms. These structures limit movements but provide greater protection against harmful agents, resulting in the most common form that can be found in infection scenarios [2]. We recently investigated the motility of B. subtilis, a model microorganism non-pathogenic and simple to manage, under different degrees of confinement induced by PEGDA porous hydrogels [3]. The bacterial motility, along with the pore morphology, was characterized by Laser Scanning Confocal Microscopy (Fig. 1) and particle tracking. The dynamical behavior of the bacteria at short times was estimated through mean squared displacements (MSDs) revealing that the run-and-tumble dynamics of unconfined B. subtilis progressively turns into sub-diffusive motion with increasing confinement. Analyzing single-trajectories, we showed that the average dynamical behavior is the result of complex displacements, in which active, diffusive and sub-diffusive segments coexist. These findings were interpreted using a recently proposed hopping and trapping model. Moreover, we found that the introduction of negative charges in the polymer network of the hydrogel, through the addition of acrylic acid, determines globally a reduction of the available pore volume for the bacteria displacement. All the results collected so far, obtained in a 2D section of the hydrogels, are not however sufficient to fully understand biofilm formation on complex surfaces of 3D porous materials. We therefore recently extended these studies to investigate motility in 3D under similar confinement conditions, and in comparison with the bulk phase. These studies are the starting point for a comprehensive characterization of confined bacterial motility in 3D, that will later consider more complex interactions (gel functionalization) as well as variations of the size and shape of the pore architecture. Furthermore, another aspect we are planning to determine is the dependence of the bacterial activity on the presence of flow in all the proposed cases. For this purpose, various flow regimes will be applied and explored using appropriate microfluidic devices. This can represent an innovative research field, as bacterial biofilm formation has so far been mainly studied under static conditions, with limited attention to the specific hydrodynamic regime imposed.
[1] E. Secchi et al., Nat. Commun. 11 (2020) 2851
[2] T. Trunk et al., AIMS Microbiol. 4 (2018) 140-164
[3] G. Bassu et al., Coll. Surf. B 236 (2024) 113797