Characteristics and modeling of Escherichia coli growth in pouched food

Characteristics of the growth kinetics of Escherichia coli cells in pouched mashed potatoes under various conditions were studied with a mathematical model. Bacterial cells were inoculated in sterile mashed potatoes and then sealed in vinyl pouches, in which a very small amount of air was included. The growth curves of cells in the pouched mashed potatoes at constant temperature (12-34 degrees C) were sigmoidal with time on a semi-logarithmic plot and were successfully described with a new logistic model recently developed by us. The rate constant of growth showed a highly linear relationship to the temperature with the square-root model, and the lag period was longer at lower temperatures. The growth curve in glass tubes containing a large volume of air was similar to that in pouches, showing that the rate of growth was not affected by the volume of the surrounding air. The growth curves in pouched mashed potatoes were very similar to those in nutrient broth or on the surface of nutrient agar, which we previously reported. These results suggested that the growth kinetics of the bacterial cells under various conditions of rich nutrition might be almost identical, and can be described with a simple growth model like ours.     

Development of effective detection method for Coxiella burnetii in mayonnaise by real-time PCR and investigation of C. burnetii contamination in commercial mayonnaise in Tokyo

A PCR method for the effective detection of Coxiella burnetii in commercially available mayonnaise was developed. Sample preparations were isolated from 50 g portions of each mayonnaise product by four successive extraction steps in phosphate buffer with 2.0 M NaCl. These extracts were then centrifuged at 20,000 x g for 60 min. DNA was isolated from the solution containing the precipitate with a commercial kit, and amplified quantitatively using real-time PCR that targeted the com1 region of C. burnetii. The recoveries of C. burnetii from 2 kinds of commercial mayonnaise specimens, with a baseline control of 1 x 10(7) particles of the Nine Mile phase II strain, were 85.0 +/- 6.0% and 72.0 +/- 0.4%, respectively. The determination limit of this method was 500 C. burnetii particles per 50 g of mayonnaise. The DNA specimens isolated from 50 different commercial mayonnaise samples sold in Tokyo using this method were amplified using both nested PCR and real-time PCR. No contamination by C. burnetii was detected in any of the mayonnaise samples.     

Analysis of essential amino acid residues for catalytic activity of glutaminase from Micrococcus luteus K-3

Structural-based mutational analysis of salt-tolerant glutaminase from Micrococcus luteus K-3 (Micrococcus glutaminase) revealed that three amino acid residues, S64, K67, and E160, were essential to a catalytic reaction. The result suggested that Micrococcus glutaminase had a possible catalytic mechanism similar to class A beta-lactamase rather than glutaminase-asparaginase from Pseudomonas 7A.     

Nanoscale uniaxial pressure effect of a carbon nanotube bundle on tip-enhanced near-field Raman spectra

In situ measurement of tip-enhanced near-field Raman spectra of an isolated single-wall carbon nanotube (SWNT) bundle has been demonstrated by applying a uniaxial pressure up to approximately 2 GPa to the bundle via a metal-coated atomic force microscope tip. We investigated the pressure dependences of Raman frequencies and the intensity of the radial breathing mode bands, the D-band and the G-band, which were related to deformation of SWNTs caused by the tip pressure.     

High-throughput analysis of ligand-induced internalization of β2-adrenoceptors using the coiled-coil tag-probe method

Receptor internalization is a useful indicator of the activity of ligands. The N-terminus of the β(2)-adrenergic receptor expressed on the cell surface was labeled with fluorophores using a novel coiled-coil labeling system. Endocytosis of the receptors was automatically detected using a fluorescence image analyzer by evaluating (1) translocation of the receptor from cell-surface to intracellular regions and (2) acidification in endosomes. Both parameters increased upon agonist stimulation in a dose-dependent manner. The extent of endocytosis was significantly dependent on the agonist used, indicating the presence of a biased signaling for endocytosis. The receptor antagonists can also be screened by competitive inhibition of agonist-induced endocytosis. The image analysis approach has proven to be useful for high-throughput characterization and screening of GPCR ligands.     

Frictional Relaxation Time of 3He Normal Fluid Component in Aerogel Obtained by Fourth Sound Resonance

Recently, we revealed that the motion of the normal fluid component in the aerogel is well described by the frictional relaxation model (Higashitani et al. in Phys. Rev. B 71:134508, 2005). To clarify the origin of the friction between the quasiparitcles and the aerogel, we have performed the fourth sound resonance experiments at two different pressures. The fourth sound resonance experiment can derive both the static and the dynamic informations simultaneously, namely, the superfluid fraction and the energy loss. From the static part, we found that the superfluid fraction slightly changes with changing the pressure. We calculated the density of states in the impurity system by means of HSM and propose that the constituent of the normal fluid component is the quasiparticles at emerging levels in the energy gap, which we call the midgap states. From the dynamic part, we found that the energy loss depends on the pressure, in contrast to the superfluid fraction. The pressure dependence of the frictional relaxation time has been calculated, and we revealed that the response of the normal fluid component against the frictional force depends on the BCS coherence length.     

Review: current international research into cellulose nanofibres and nanocomposites

This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.     

Intracellular DNA damage induced by non-thermal, intense narrowband electric fields

Intracellular DNA damages caused by intense burst sinusoidal electric fields (IBSEFs) were investigated by means of an alkaline comet assay method. Non-thermal, 200 ?s-long IBSEF with various frequency values (300 kHz-100MHz) and strengths (up to 200 kV/m) was applied to Chinese hamster ovary (CHO) cells in a suspending medium between 1 mm gap parallel electrodes. The comet assay suggests that 100 kV/m IBSEF with frequencies exceeding 1 MHz or 100 MHz IBSEFs with field strengths exceeding 3 kV/m induces significant DNA damage. According to the numerical calculation of the electric field over a simplified cell model under an alternating electric field, the intracellular field strength increases with increasing alternating frequency. The minimum level of the field strength that induces the DNA damage is in the range of 10-30 kV/m. This intracellular strong field might trigger biological processes leading to the DNA damage.     

Calcium isotope separation by band chromatography using 18-crown-6-ether resin

To develop the ⁴⁸Ca enrichment process, a feasibility study on a band chromatography was made using 9 M HCl solution and crown ether resin synthesized in porous silica beads. Prior to the chromatographic experiments, distribution coefficients, Kd, of Ca²⁺ and Sr²⁺ were measured at different concentrations of these ionic species. The frontal boundary of the chromatography was made by a usual manner of the breakthrough mode of calcium feeding, and the rear boundary was made by introducing strontium as a following ion on the basis of the observed Kd values. It was confirmed that the heavy isotope ⁴⁸Ca was depleted in the rear boundary region, while ⁴⁸Ca was enriched in the front boundary region. The values of separation coefficient ε (= α – 1) in three chromatographic operations at different temperatures were observed as 2 × 10^?3 ~ 3 × 10^?3. The separation coefficients observed in the front boundary regions, where ⁴⁸Ca was enriched, agreed with those observed in the rear boundary regions, where ⁴⁰Ca was enriched.