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.
•The supramolecular structure of CMC was represented as a set of subspaces with different densities.•CMC is most expanded, has the largest Rg, persistence length, and size of heterogeneous regions at ...pKa.•Most CMC molecules reside in a few high density subspaces below pKa.•Above the pKa the CMC molecules are approximately uniformly distributed.•SAXS, SLS, DLS, microscopy and viscosimetry give coherent view of CMC structure from 1nm to 100μm scale.
Carboxymethyl cellulose (CMC) is one of the most widely used thickening agents in industry. The combination of small-angle X-ray scattering (SAXS), static and dynamic light scattering, as well as viscosity measurements and microscopy at different pH values was utilized to explore the physicochemical properties of CMC on a scale ranging from individual macromolecules to supramolecular assemblies. The supramolecular structure of CMC was represented as a set of characteristic sample subspaces based on SAXS data utilizing the string-of-beads model. The results indicate that at pH 7.0 individual CMC molecules are approximately uniformly distributed in a supramolecular structure owing to strong intra- and intermolecular repulsive interactions. The structure of CMC is most expanded at the value of pKa, where it has the largest radius of gyration, persistence length, and size of heterogeneous regions. Below pKa the majority of the CMC sample volume belongs to the low density subspaces. Most of CMC molecules, however, reside in a few high density subspaces. Dynamically, supramolecular structure of CMC is composed of fast diffusive relaxation processes embedded in a background of non-diffusive slow relaxation process at high pH and mostly slow relaxation processes at low pH. The rheological properties of CMC at different pH values were directly related to the CMC supramolecular structure in the aqueous environment.
The polysaccharide levan is a homopolymer of fructose and appears in nature as an important structural component of some bacterial biofilms. This paper reports the structural and dynamic properties ...of aqueous solutions of levan of various origin obtained from dynamic rheological, small-angle X-ray scattering, static and dynamic light scattering, as well as density and sound velocity measurements, determination of polymer branching after per-O-methylation, and microscopy. Besides samples of commercially available levan from Zymomonas mobilis and Erwinia herbicola, we also isolated, purified, and studied a levan sample from the biofilm of Bacillus subtilis. The results of dynamic rheological and light scattering measurements revealed very interesting viscoelastic properties of levan solutions even at very low polymer concentrations. The findings were complemented by small-angle X-ray scattering data that revealed some important differences in the structure of the aqueous levan solutions at the molecular level. Besides presenting detailed dynamic and structural results on the polysaccharide systems of various levans, one of the essential goals of this work was to point out the level of structural information that may be obtained for such polymer systems by combining basic physicochemical, rheological, and various light scattering techniques.
Polysaccharide levan is a homopolymer of fructose and is an important component of plants, yeast, fungi and some bacterial biofilms. In this paper we report on the structural properties of aqueous ...solutions of bacterial levan utilizing smallangle X-ray scattering and light microscopy. In addition to commercially available levan isolated from Zymomonas mobilis and Erwinia herbicola, we also studied levan isolated and purified from the biofilm of Bacillus subtilis. The smallangle X-ray scattering data were analyzed by the string-of-beads model that revealed qualitative differences in the structure of levan molecules. Levan can be represented as a semi-flexible chain that interacts intra- and inter-molecularly and therefore forms various suprastructures on larger size scales. Increasing the concentration of levan makes the levan structure more compact, which was observed on the nano as well as on the micro scale. The structures with most homogeneously distributed polymer local density were found in B. subtilis levan solutions.
Structural changes of carboxymethyl cellulose (CMC) during biodeterioration with Bacillus subtilis subsp. subtilis NCIB 3610 were studied with small-angle X-ray scattering (SAXS), size exclusion ...chromatography, and viscosity measurements. Cleavage of CMC polymers changed flow characteristics from those of non-Newtonian pseudoplastic fluid to those of Newtonian fluid. The viscosity decreased from 10 to 1.4 mPas and the concentration of reducing sugar increased by 18-fold. Upon biodeterioration the average radius of gyration decreased from 147 to 123 Å; cleaved polymer chains remained in close contact in unstirred medium as reflected by a relatively large apparent radius of gyration. However, such degraded CMC aggregates were easily dispersed with shear stress. The results suggest that biodeterioration mainly affects CMC structural features that are larger than 5 nm. Furthermore, the results also suggest that CMC metabolism and biodeterioration may be decoupled; B. subtilis subsp. subtilis NCIB 3610 produces cellulases that effectively cleave CMC but cannot efficiently utilize hydrolyzed products. There were no structural or rheological changes observed in the absence of B. subtilis subsp. subtilis NCIB 3610 growth.
► CMC degradation with Bacillus subtilis subsp. subtilis NCIB 3610 was studied with SAXS, SEC and viscosity measurements. ► Biodeterioration mainly affects CMC structural features that are larger than 5 nm ► Biodeterioration changed flow characteristics from non-Newtonian pseudoplastic to Newtonian fluid. ► The average radius of gyration decreased from 147 to 123 Å.
The effects of local geology on ground-motion amplification and building damage were studied in the Upper Soča valley (western Slovenia), which was struck by an earthquake (
M
LV=5.6) on 12 April ...1998 with an epicentre in the Krn mountains. Nakamura's method of microtremor analysis and one-dimensional modelling based on geophysical data (seismic refraction method, seismic velocity measurements in boreholes and DC electrical sounding) were applied in this study. Both methods showed significantly higher amplification in the frequency range of building vulnerability (2–10 Hz) in the Mala vas area of Bovec than in the central part of the town. This finding is consistent with the distribution of the earthquake damage in the area. In Koritnica, large differences in amplification were observed between the eastern rim of the village, built on carbonate bedrock and its central part lying on glacial deposits. In Čezsoča, where the thickness of fluvial deposits is about 20 m, amplifications between 2 and 3 in the frequency range of 2–10 Hz were obtained. In Plužna, which is located on flysch rocks covered with a thin layer of soil, the amplification in the same frequency range was low. In Sp. Drežniške Ravne, one of the most damaged villages during this earthquake, the amplification function has two distinctive peaks at 2 and 10.5 Hz. In Drežnica, however, where only slight damage was reported, the amplification level in the frequency range 2–10 Hz is low. The findings of this study indicate that large differences in damage to the buildings in the Upper Soča valley could be attributed to variations in the thickness and physical properties of Quaternary deposits, which appear to be rather heterogeneous.
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