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A hallmark of microbial biofilms is the self-production of an extracellular molecular matrix that encases the resident cells. The matrix provides protection from the environment, while spatial heterogeneity of gene expression influences the structural morphology and colony spreading dynamics. Bacillus subtilis is a model bacterial system used to uncover the regulatory pathways and key building blocks required for biofilm growth and development. In this work, we report on the emergence of a highly active population of bacteria during the early stages of biofilm formation, facilitated by the extraction of fluid from the underlying agar substrate. We trace the origin of this fluid extraction to the production of poly-γ-glutamic acid (PGA). The flagella-dependent activity develops behind a moving front of fluid that propagates from the boundary of the biofilm towards the interior. The extent of fluid proliferation is controlled by the presence of extracellular polysaccharides (EPS). We also find that PGA production is positively correlated with higher temperatures, resulting in high-temperature mature biofilm morphologies that are distinct from the rugose colony biofilm architecture typically associated with B. subtilis. Although previous reports have suggested that PGA production does not play a major role in biofilm morphology in the undomesticated isolate NCIB 3610, our results suggest that this strain produces distinct biofilm matrices in response to environmental conditions.

The composite materials based on hydroxyapatite (HA), sodium alginate (Alg)–magnetite (Fe3O4) were synthesized by the “wet chemistry method” under the influence of microwave irradiation and ultrasound. The biomagnetic samples were investigated by XRD, RFA, SEM, TEM and colorimetric assay methods. The cytotoxicity was assessed on fibroblasts cultures. It was found that the synthesis of Fe3O4 particles in the presence of Alg macromolecules leads to magnetite nanoparticles’ average size decreasing (up to 8 nm). The presence of samples with applied magnetite content (1% of HA) in a nutrient medium did not influence on cells viability. It was shown that the hydrogels were more conducive to cells survival and provide a greater degree of cell proliferation in comparison with beads. It was concluded that Fe3O4-loaded hydroxyapatite–alginate composites are characterized by good adhesive ability of the fibroblast cells and its bioactivity.

The purpose of this study was to determine whether increased expression of SUR2A, a regulatory subunit of sarcolemmal ATP-sensitive K+ (KATP) channels, improves adaptation to physical stress and regulates cardiac electrophysiology in physical stress. All experiments have been done on transgenic mice in which SUR2A expression was controlled by cytomegalovirus immediate-early (CMV) promoter (SUR2A) and their littermate wild-type controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR. Electrocardiogram (ECG) was monitored with telemetry. The physical adaptation to stress was elucidated using treadmill. We have found that SUR2A mice express 8.34 ± 0.20 times more myocardial SUR2A mRNA than WT (n = 8–18). The tolerated workload on exercise stress test was more than twofold higher in SUR2A than in WT (n = 5–7; P = 0.01). The pattern of Q-T interval from the beginning of the exercise test until drop point was as follows in the wild type: (1) increase in Q-T interval, (2) decrease in Q-T interval, (3) steady stage with a further decrease in Q-T interval, and (4) a sharp increase in Q-T interval. The pattern of Q-T interval was different in transgenic mice and the following stages have been observed: (1) increase in Q-T interval, (2) decrease in Q-T interval, and (3) prolonged steady-state stage with a slight decrease in Q-T interval. In SUR2A mice, no stage 4 (a sharp increase in Q-T interval) was observed. Based on the obtained results, we conclude that an increase in the expression of SUR2A improves adaptation to physical stress and physical endurance by increasing the number of sarcolemmal KATP channels and, by virtue of their channel activity, improving Ca2+ homeostasis in the heart.

Ageing is characterized by decline in physical endurance which has been suggested to be partly due to diminished functional and adaptive reserve capacity of the heart. Ageing is associated with decrease in numbers of sarcolemmal ATP-sensitive K(+) (K(ATP)) channels, but whether this has anything to do with ageing-induced decline in physical endurance is yet to be determined. We have previously shown that the numbers of sarcolemmal K(ATP) channels are controlled by the level of expression of SUR2A, a K(ATP) channel regulatory subunit. Here, we have found that ageing decreases the level of SUR2A mRNA in the heart without affecting expression of pore-forming K(ATP) channel subunits, Kir6.1 and Kir6.2. This effect of ageing was associated with decrease in levels of fully-assembled sarcolemmal K(ATP) channels. At the same time, ageing was associated with decreased physical endurance. In order to determine whether increased expression of SUR2A would counteract ageing-induced decrease in physical endurance, we have taken advantage of mice which SUR2A levels are regulated by more efficient CMV promoter. These mice had increased resistance of cardiomyocytes to metabolic stress/hypoxia and increased physical endurance when compared to the wild type. In transgenic mice, ageing did not affect the level of SUR2A mRNA in the heart and the level of fully-assembled sarcolemmal K(ATP) channels. The effect of increased SUR2A to resistance of cardiomyocytes to hypoxia and physical endurance was retained in old mice. The magnitude of these effects was such that they were significantly increased even when compared to those in wild type young mice. We conclude that (1) the level of SUR2A expression in the heart is important factor in regulating physical endurance, (2) ageing-induced decrease in cardiac SUR2A is, at least in part, responsible for ageing-induced decline in physical fitness and (3) up-regulation of SUR2A could be a viable strategy to counteract ageing-induced decline in physical endurance.

One mechanism of increase in the heating temperature of the analytical zone of the graphite tube furnace of the atomic-absorption spectrometer as a result of wear is discussed. The influence of the furnace profile on its heating temperature is shown, and the calculated heating temperature of the standard tube is compared to the temperature in the special case where the cross-section area of the analytical zone of the furnace is reduced by half. Experimental proofs of a given temperature excess, as well as of a relation between the change in the tube profile and the decrease in its mass, are given. The dependence of temperature on the furnace mass and the number of measurements has been investigated. The necessity of taking into account the increase in the heating temperature of the furnace in the wear process has been considered.

We have attempted to use heat treatment followed by ultrasonic treatment to separate the apatite from the non-apatite components of bone mineral in samples from different animals. The Mg content and the Ca/P ratio in the temperature range 560°C–720°C in the samples before and after ultrasonic treatment were determined by electron-probe x-ray microanalysis. Furthermore, we used atomic absorption spectrometry to measure the Mg content in powdered bone samples only after annealing and in distilled water, which was the “sonication” medium. We obtained evidence for thermally activated transition of Mg from a structurally bound state to a labile state at 680°C–720°C. At the same temperature, the Ca-deficient apatite is transformed to stoichiometric apatite. The data presented are evidence that crystals of Ca-deficient bioapatite are surrounded by Ca-enriched surface layers. As a result of thermal transformations at 680°C-720°C, all the Mg in the biomineral is found in the non-apatite environment surrounding the crystals and is removed by ultrasonic treatment, while the surface-localized Ca penetrates into the apatite lattice, restoring its stoichiometry.

Using x-ray diffraction, electrothermal atomization atomic absorption spectroscopy, and scanning electron microscopy with an x-ray microanalysis, we have studied the phase decomposition of biogenic and synthetic Mg-containing apatite at 900°C with formation of β-tricalcium-magnesium phosphate (β-TCMP). Employing simplified model representations, we obtained a relation that couples the initial Mg concentration with the degree of transformation of apatite into β-TCMP. It is shown that for the β-TCMP contents measured in bioapatite samples and on replacement of calcium by magnesium to about 8% in this phase the calculated range of Mg concentrations coincides with that available in literature sources (0.2–0.6 wt. %). A comparative investigation of the products of decomposition of biogenic and synthetic apatite by the methods of analysis of the composition and structure has established that the formation of β-TCMP is limited by both the insufficient concentration of magnesium and the small sizes of the crystals. The results of the investigations carried out together with the experimental data known from the literature are indicative of the nonuniform distribution of magnesium in the bulk of crystals of biogenic and synthetic apatite, with its predominant localization at the surface sites of the lattice.

A kinetic phenomenological model of the processes of atomization for atomic-absorptional spectrometry with electrothermal atomization that is based on solution of a one-dimensional equation of diffusion with two independent sources is suggested. The model takes into account the processes occurring both on the surface of a graphite furnace and inside its wall. The proposed model is used for describing the electrothermal atomization of copper and zinc.

Release of neurotransmitter occurs when synaptic vesicles fuse with the plasma membrane. This neuronal exocytosis is triggered by calcium and requires three SNARE (soluble-N-ethylmaleimide-sensitive factor attachment protein receptors) proteins: synaptobrevin (also known as VAMP) on the synaptic vesicle, and syntaxin and SNAP-25 on the plasma membrane1,2,3,4. Neuronal SNARE proteins form a parallel four-helix bundle that is thought to drive the fusion of opposing membranes5,6. As formation of this SNARE complex in solution does not require calcium, it is not clear what function calcium has in triggering SNARE-mediated membrane fusion. We now demonstrate that whereas syntaxin and SNAP-25 in target membranes are freely available for SNARE complex formation, availability of synaptobrevin on synaptic vesicles is very limited. Calcium at micromolar concentrations triggers SNARE complex formation and fusion between synaptic vesicles and reconstituted target membranes. Although calcium does promote interaction of SNARE proteins between opposing membranes, it does not act by releasing synaptobrevin from synaptic vesicle restriction. Rather, our data suggest a mechanism in which calcium-triggered membrane apposition enables syntaxin and SNAP-25 to engage synaptobrevin, leading to membrane fusion.

High-frequency point-contact spectroscopy as well as conventional low-frequency PC spectroscopy has been used for determining the spectral functions of the electron-phonon interaction (EPI) for three disilicides TiSi2, TaSi2, and VSi2. The temperature dependences of resistivity have been calculated from obtained EPI functions. Comparison of calculated dependences with known experimental data allowed correction of the electron-phonon interaction constants for the studied disilicides.

A kinetic model is proposed for describing the shape of an atomic absorption signal in the case of first-order kinetics. The formation energy of free copper ions (87 x 7 kJ/mol) and other kinetic parameters of an atomic absorption signal of copper at 2273–3073 K were determined from the experimental data.

Enthalpies of solution in water, ΔHsolo, and of sublimation, ΔHsublo, were determined experimentally for a number of crystalline N-methyl adenines: m6Ade, m26,6Ade, m9Ade, m26,9Ade, and m36,6,9Ade. Derived standard enthalpies of hydration ΔHhydro, were corrected for the calculated cavity terms ΔHcavo to yield enthalpies of interaction ΔHinto of the solutes with their hydration shells. The increments of ΔHinto per unit area of the water-accessible molecular surface SB, δΔHinto (CH3)/δSB (CH3), for the particular methyl groups: is considered to be the net effect of the gain in the energy resulting from van der Waals' interactions and of the loss in the energy due to polar interactions upon methyl substitution. It proved to vary somewhat numerically in agreement with the theoretically predicted hydration schemes of adenine. Comparison of ΔHinto/SB value for adenine with those previously determined for uracil and thymine indicates that the aminopurine moiety is less hydrated than the diketopyrimidine ring.

FOR an understanding at the molecular level of the stability and interactions of nucleic acids, including the mechanisms of mutational events, the thermodynamic characteristics of base-pair formation must be determined1. The most fundamental expression of these characteristics relates to the interaction in vacuo. We describe here the measurement of binding enthalpy of a single base pair from various combinations of bases in vacuo. We used pyrimidine bases methylated at the 1 position and purine bases methylated at the 9 position. As expected2,3, the results obtained differ appreciably from those of earlier experiments4 on solutions, involving indirect methods of observing base pairing.