The self-binding of bacterial cells, or autoaggregation, is, together with surface colonization, one of the first steps in the formation of a mature biofilm. In this work, the autoaggregation of B. ...subtilis in dilute bacterial suspensions was studied. The dynamics of cell lysis, eDNA release, and bacterial autoaggregate assembly were determined and related to the spatial autocorrelation of bacterial cells in dilute planktonic bacterial suspensions. The non-random distribution of cells was associated with an eDNA network, which stabilized the initial bacterial cell-cell aggregates. Upon the addition of DNase I, the aggregates were dispersed. The release of eDNA during cell lysis allows for the entrapment of bacterial drifters at a radius several times the size of the dying bacteria. The size of bacterial aggregates increased from 2 to about 100 μm in diameter in dilute bacterial suspensions. The results suggest that B. subtilis cells form previously unnoticed continuum of autoaggregate structures during planktonic growth.
Bacteriophage M13 major coat protein is extensively used as a biophysical, biochemical, and molecular biology reference system for studying membrane proteins. The protein has several elements that ...control its position and orientation in a lipid bilayer. The N-terminus is dominated by the presence of negatively charged amino acid residues (Glu2, Asp4, and Asp5), which will always try to extend into the aqueous phase and therefore act as a hydrophilic anchor. The amphipathic and the hydrophobic transmembrane part contain the most important hydrophobic anchoring elements. In addition there are specific aromatic and charged amino acid residues in these domains (Phe 11, Tyr21, Tyr24, Trp26, Phe42, Phe45, Lys40, Lys43, and Lys44) that fine-tune the association of the protein to the lipid bilayer. The interfacial Tyr residues are important recognition elements for precise protein positioning, a function that cannot be performed optimally by residues with an aliphatic character. The Trp26 anchor is not very strong: depending on the context, the tryptophan residue may move in or out of the membrane. On the other hand, Lys residues and Phe residues at the C-terminus of the protein act in a unique concerted action to strongly anchor the protein in the lipid bilayer.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
How the viscoelastic properties of the extracellular matrix affect the various biological functions conferred by biofilms is an important question in microbiology. In this study, the viscoelastic ...response of Escherichia coli biofilms to the genetically altered expression of extracellular matrix components was studied. Biofilms of the wild type E. coli MG1655 and its mutant strains producing different amounts of extracellular matrix components (curli, colanic acid, and poly-β-1,6-N-acetyl-d-glucosamine) were used to examine the viscoelastic behavior of biofilms grown at the solid-atmosphere interface. The results suggest that the presence of curli proteins dominates biofilm mechanical behavior. The rheological data indicate that the cohesive energy of the biofilm was the highest in the wild type strain. The results demonstrate the importance of extracellular matrix composition for biofilm mechanical properties. We propose that by genetically altering the expression of extracellular matrix polymers, bacteria are able to modulate the mechanical properties of their local environment in accordance with bulk environmental conditions.
•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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Display omitted
Surfactin uniquely influences lipid bilayer structure by initially inducing membrane invaginations before solubilization. In this study, we exposed DOPC giant vesicles to various ...surfactin concentrations at different temperatures and observed surfactin-induced membrane invaginations by using differential interference contrast and confocal laser fluorescence microscopy. These invaginations were stable at room temperature but not at higher temperatures. Surfactin molecules induce membrane nanodomains with negative spontaneous curvature and membrane invaginations despite their intrinsic conical shape and intrinsic positive curvature. Considering the experimentally observed capacity of surfactin to fluidize lipid acyl chains and induce partial dehydration of lipid headgroups, we propose that the resulting surfactin-lipid complexes exhibit a net negative spontaneous curvature. We further conducted 3D numerical Monte Carlo (MC) simulations to investigate the behaviour of vesicles containing negative curvature nanodomains within their membrane at varying temperatures. MC simulations demonstrated strong agreement with experimental results, revealing that invaginations are preferentially formed at low temperatures, while being less pronounced at elevated temperatures. Our findings go beyond the expectations of the Israelachvili molecular shape and packing concepts analysis. These concepts do not take into account the influence of specific interactions between neighboring molecules on the inherent shapes of molecules and their arrangement within curved membrane nanodomains. Our work contributes to a more comprehensive understanding of the complex factors governing vesicle morphology and membrane organization and provides insight into the role of detergent-lipid interactions in modulating vesicle morphology.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
It is known that giant vesicles undergo dynamic morphological changes when exposed to a detergent. The solubilization process may take multiple pathways. In this work, we identify lipid vesicle shape ...dynamics before the solubilization of 1,2-dioleoyl-sn-glycero-3-phosphocholine giant vesicles with Triton X-100 (TR) detergent. The violent lipid vesicle dynamics was observed with laser confocal scanning microscopy and was qualitatively explained via a numerical simulation. A three-dimensional Monte Carlo scheme was constructed that emulated the nonequilibrium conditions at the beginning stages of solubilization, accounting for a gradual addition of TR detergent molecules into the lipid bilayers. We suggest that the main driving factor for morphology change in lipid vesicles is the associative tendency of the TR molecules, which induces spontaneous curvature of the detergent inclusions, an intrinsic consequence of their molecular shape. The majority of the observed lipid vesicle shapes in the experiments were found to correspond very well to the numerically calculated shapes in the phase space of possible solutions. The results give an insight into the early stages of lipid vesicle solubilization by amphiphilic molecules, which is nonequilibrium in nature and very difficult to study.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, we combine selective laser melting (SLM) and spark plasma sintering (SPS) to fabricate new materials with high virucidal potential. Various bioactive disc-shaped ceramics, metal alloys, ...and composites were fabricated and tested against bacteriophage Phi6—a model system for RNA-enveloped viruses. We prepared silver-doped titanium dioxide (TiO
2
+ 2.5‒10% Ag), copper-doped titanium dioxide (TiO
2
+ 2.5‒10% Cu), Cu2NiSiCr, and Cu15Ni8Sn composite materials (metal lattices filled with ceramics). The virucidal tests of the ceramic and metal powders were performed in buffered suspensions, while the surfaces of the discs were tested by swabbing. The results show that the virus titer on the TiO
2
+ 10% Ag ceramic and CuNi2SiCr metal discs decreased by 4 logs after 15 min of exposure to the surfaces compared to the control ceramic and steel discs. We show that SLM 3D printed pre-alloyed CuNi2SiCr filled with bioactive TiO
2
+ 10% Ag nanopowders and sintered by the SPS process combines the simplicity of printing with the strength and virucidal properties of Ag and Cu materials. The proposed new virucidal materials were also used for the fabrication of prototype elevator buttons.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Pigments such as melanin, scytonemin and carotenoids protect microbial cells against the harmful effects of ultraviolet (UV) radiation. The role in UV protection has never been assigned to the ...prodigiosin pigment. In this work, we demonstrate that prodigiosin provides a significant level of protection against UV stress in
Vibrio
sp. DSM 14379. In the absence of pigment production,
Vibrio
sp. was significantly more susceptible to UV stress, and there was no difference in UV survival between the wild-type strain and non-pigmented mutant. The pigment’s protective role was more important at higher doses of UV irradiation and correlated with pigment concentration in the cell. Pigmented cells survived high UV exposure (324 J/m
2
) around 1,000-fold more successfully compared to the non-pigmented mutant cells. Resistance to UV stress was conferred to the non-pigmented mutant by addition of exogenous pigment extract to the growth medium. A level of UV protection equivalent to that exhibited by the wild-type strain was attained by the non-pigmented mutant once the prodigiosin concentration had reached comparable levels to those found in the wild-type strain. In co-culture experiments, prodigiosin acted as a UV screen, protecting both the wild-type and non-pigmented mutants. Our results suggest a new ecophysiological role for prodigiosin.
Full text
Available for:
BFBNIB, EMUNI, NMLJ, NUK, PNG, SAZU, SBMB, SBNM, UL, UM, UPUK
We studied the viscoelastic properties of homogeneous and inhomogeneous levan-DNA mixtures using optical tweezers and a rotational rheometer. Levan and DNA are important components of the ...extracellular matrix of bacterial biofilms. Their viscoelastic properties influence the mechanical as well as molecular-transport properties of biofilm. Both macro- and microrheology measurements in homogeneous levan-DNA mixtures revealed pseudoplastic behavior. When the concentration of DNA reached a critical value, levan started to aggregate, forming clusters of a few microns in size. Microrheology using optical tweezers enabled us to measure local viscoelastic properties within the clusters as well as in the DNA phase surrounding the levan aggregates. In phase-separated levan-DNA mixtures, the results of macro- and microrheology differed significantly. The local viscosity and elasticity of levan increased, whereas the local viscosity of DNA decreased. On the other hand, the results of bulk viscosity measurements suggest that levan clusters do not interact strongly with DNA. Upon treatment with DNase, levan aggregates dispersed. These results demonstrate the advantages of microrheological measurements compared to bulk viscoelastic measurements when the materials under investigation are complex and inhomogeneous, as is often the case in biological samples.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
