The Role of Polar Pili in the Adherence of Pseudomonas Aeruginosa to Injured Canine Tracheal Cells: A Semiquantitative Morphologic Study

Pseudomonas aeruginosa adheres to respiratory epithelial cells in a highly specific fashion. In order to study the role of P. aeruginosa polar pili in the adherence process we conducted a quantitative morphological electron microscopic examination of P. aeruginosa adherence to SO2 injured canine tracheal cells in vitro. A pilin lacking background strain of P. aeruginosa PAK (BLP2) was constructed using a gene replacement and it in turn was engineered to express either the pilin gene of P. aeruginosa PAO, PAK , or no pilin gene . After 30 minutes incubation of these bacterial strains with injured canine tracheal rings the P. aeruginosa strains expressing pili adhered quantitatively more to the injured tracheal cells than did the pili lacking strains. PAO bearing strains adhered in greater numbers than PAK bearing strains. Healthy tracheal cells did not have any bacteria bound to their surfaces. The bacteria bound to the cilia and lateral edge of the exfoliating tracheal cells. Invasion of tracheal cells by piliated P. aeruginosa bacteria and penetration into the submucosa was also demonstrated. These data confirm the role of pili as important adhesins to injured tracheal cells. The difference in the adherence characteristics of pilin types PAK versus PAO may relate to the differences in the primary structure of these two pilin molecules

Solid solutions of CdxHg₁₋xTe:V:Mn, CdxHg₁₋xTe:Ti:Mn (x = 0.9 – 0.95): growth and properties

Single crystals of CdxHg₁₋xTe:V:Mn, CdxHg₁₋xTe:V: Mn (x = 0.9–0.95) with different concentrations of vanadium, titanium and manganese have been obtained via the modified Bridgman method and their optical, photoelectrical and galvano-magnetic properties have been studied. According to the performed investigations, the grown crystals proved to be satisfactorily homogeneous and highly sensitive within technically important spectral range of 1–1.5 mm. Energy position of vanadium and titanium level in the material under investigation determined from R(T) dependence is of about 0.73–0.82 eV; 0.65–0.72 eV, respectively

Bacterial Surface Appendages Strongly Impact Nanomechanical and Electrokinetic Properties of Escherichia coli Cells Subjected to Osmotic Stress

The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO3, cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700–900 kPa and ∼100–300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions

Automated Force Volume Image Processing for Biological Samples

Atomic force microscopy (AFM) has now become a powerful technique for investigating on a molecular level, surface forces, nanomechanical properties of deformable particles, biomolecular interactions, kinetics, and dynamic processes. This paper specifically focuses on the analysis of AFM force curves collected on biological systems, in particular, bacteria. The goal is to provide fully automated tools to achieve theoretical interpretation of force curves on the basis of adequate, available physical models. In this respect, we propose two algorithms, one for the processing of approach force curves and another for the quantitative analysis of retraction force curves. In the former, electrostatic interactions prior to contact between AFM probe and bacterium are accounted for and mechanical interactions operating after contact are described in terms of Hertz-Hooke formalism. Retraction force curves are analyzed on the basis of the Freely Jointed Chain model. For both algorithms, the quantitative reconstruction of force curves is based on the robust detection of critical points (jumps, changes of slope or changes of curvature) which mark the transitions between the various relevant interactions taking place between the AFM tip and the studied sample during approach and retraction. Once the key regions of separation distance and indentation are detected, the physical parameters describing the relevant interactions operating in these regions are extracted making use of regression procedure for fitting experiments to theory. The flexibility, accuracy and strength of the algorithms are illustrated with the processing of two force-volume images, which collect a large set of approach and retraction curves measured on a single biological surface. For each force-volume image, several maps are generated, representing the spatial distribution of the searched physical parameters as estimated for each pixel of the force-volume image

Studies on the mechanism of absorption of vitamin B12 by normal and neoplastic tissues.

Cyanocobalamin bound to normal human gastric juice (NHGJ) or to guinea pig stomach extract (GPSE) is taken up by guinea pig ileum to a greater extent than unbound cyanocobalamin. Almost all of the cyanocobalamin taken up in the presence of GPSE is removable by washing the intestinal tissue with ethylenediaminetetraacetate (EDTA), whereas the same washing procedure removes only one third of the cyanocobalamin taken up in the presence of NHGJ. The cyanocobalamin which is removed by washing with EDTA may be the same as that which is actively absorbed by guinea pig intestine

Growing Cd₁₋x₋yMnyHgxTe single crystals and their optoelectronic properties

Single crystals of Cd₁₋x₋yMnyHgxTe:V (х = 0.05; у = 0.03-0.07, NV = 1∙10¹⁹ cm⁻³) have been grown and their electrical and optical properties have been studied. The transmission spectra of the samples with the composition x = 0.05; y = 0.07 were characterized by the minimum in the 3.5-5.5 μm spectral range. In order to understand the nature of it the energy diagram of vanadium levels has been considered. The band gap of the studied solid solutions with different manganese content has been found from the absorption coefficient spectra and compared with those calculated