Structure and Dynamics of a Model Polymer Mixture Mimicking a Levan-Based Bacterial Biofilm of Bacillus subtilis

Abstract

In this paper, we report on the structure and dynamics of biologically important model polymer mixtures that mimic the extracellular polymeric matrix in native biofilm of Bacillus subtilis. This biofilm is rich in nonionic polysaccharide levan, but also contains other biopolymers such as DNA and proteins in small concentrations. Aiming to identify the contribution of each component to the formation of the biofilm, our investigations encompassed dynamic rheology, small-angle X-ray scattering, dynamic light scattering, microscopy, densitometry, and sound velocity measurements. As it turned out, this very powerful combination of techniques is able to provide solid results on the dynamical and structural aspects of the microbiologically and chemically complex biofilm formations. Macroscopic rheological measurements revealed that the addition of DNA to levan solution increased the viscosity, pseudoplasticity, and elasticity of the system. The addition of protein contributed similarly, but also increased the rigidity of the system. This confirms that the presence of minor biofilm components is essential for biofilm formation. DNA and proteins appear to confine levan molecules within their supramolecular structure and, in this way, restrict the role of levan to merely a filling agent. These findings were complemented by small-angle X-ray scattering data, which provided insight into the structure on a molecular scale. One of the essential goals of this work was to compare the structural properties of the native biofilm and synthetic biofilm mixture.

Raffinose Induces Biofilm Formation by Streptococcus mutans in Low Concentrations of Sucrose by Increasing Production of Extracellular DNA and Fructan

“…Then, we focused on the role of fructan in the biofilm features. Levan, which is a type of fructan, was reported to enhance the viscosity of DNA solutions and was necessary for biofilm formation by Bacillus subtilis (24). Here, we showed that fructan from S. mutans facilitated cell aggregation when it interacted with eDNA.…”

“…Therefore, these results indicated that fructan was involved in the biofilm morphology without impacting the biofilm volume. Recently, the addition of levan (a type of fructan) to a DNA solution was reported to increase the viscosity of the solution (24). Ftf from S. mutans synthesizes inulin, which is a different type of fructan.…”

Supramolecular structure of methyl cellulose and lambda- and kappa-carrageenan in water: SAXS study using the string-of-beads model

“…Due to their chemical and structural variability they exhibit different structural and dynamic phenomena that continue to present a great research challenge, even for modern techniques. In our studies we focused on structural and dynamic investigations utilizing various scattering techniques, i.e., small-angle X-ray scattering (SAXS), static light scattering (SLS) and dynamic light scattering (DLS) Benigar et al, 2015;Benigar et al, 2016;Cerar, Jamnik, & Tomsic, 2015;Dogsa, Štrancar, Laggner, & Stopar, 2008;Dogsa et al, 2014;Orehek et al, 2013). The advantage of these techniques is that they are, in general, nondestructive and can directly probe the polymers in aqueous solutions.…”

“…The fact is that in such systems the longer-lived polymer entanglement regions are not simply homogeneous scattering moieties, but are more-or-less structured at the molecular or even nanoscale. Such a nanostructure introduces an additional level in the hierarchical structure of such polymer systems and causes an additional contribution to the scattering signal (Benigar et al, 2016), which obviously represents some problem for the classic interpretation approach to the SAXS data of polymer solutions, utilizing Eq. (S2) given in Supporting Information, Appendix A.…”

“…Nonetheless, in the present study we successfully extend the range of the appropriate SAXS data analysis for the studied polysaccharide systems by also taking into account the contribution of the form factor of the polymer chain or its segments. We achieve this by applying the string-of-beads model (Benigar et al, 2015;Benigar et al, 2016;Dogsa et al, 2008;Dogsa et al, 2014;Orehek et al, 2013), which is briefly described later in the text and provides some additional information about the polymer structure in comparison to the classic approach. Furthermore, it also enables a straightforward visualization of the modeled molecular configurations and even of the anticipated modeled supramolecular structure of the system.…”