The arginine deiminase pathway in the wine lactic acid bacteria Lactobacillus hilgardii X1B: structural and functional study of the arcABC genes

The genes implicated in the catabolism of the amino acid arginine by Lactobacillus hilgardiiX1Bwere investigated to assess the potential for formation of ethyl carbamate precursors in wine. L. hilgardii X1B can use arginine via the arginine deiminase pathway. The complete nucleotide sequence of the arc genes involved in this pathway has been determined. They are clustered in an operon-like structure in the order arcABC. No evidence was found for the presence of a homologue of the arcD gene, coding for the arginine/ornithine antiporter. The arc genes have been expressed in Escherichia coli resulting in arginine deiminase (ArcA), ornithine carbamoyltransferase (ArcB) and carbamate kinase (ArcC) activities. The results indicate the need for caution in the selection of lactic acid bacteria for conducting malolactic fermentation in wine since arginine degradation could result in high amounts of ethyl carbamate.This work was supported by grant VIN00-016 from the Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) and Consejo de Investigaciones de la Universidad Nacional de Tucumán (CIUNT). M.E. Arena was a recipient of a Contrato UNT-Proyecto FOMEC 1214 from the Programa de Reforma de la Educación Superior. The nucleotide sequence of the arcABC gene cluster has been deposited in the EMBL/GenBank/DDBJ databases under accession number AJ421514.Peer reviewe

The Use of the Multi-channel Analysis of Surface Waves (MASW) Method as an Initial Estimator of Liquefaction Susceptibility in Greymouth, New Zealand

Combined analysis of the geomorphic evolution of Greymouth with Multi-channel Analysis of Surface Waves (MASW) provides new insight into the geotechnical implications of reclamation work. The MASW method utilises the frequency dependent velocity (dispersion) of planar Rayleigh waves created by a seismic source as a way of assessing the stiffness of the subsurface material. The surface wave is inverted to calculate a shear wave velocity (Park et al., 1999). Once corrected, these shear-wave (Vs) velocities can be used to obtain a factor of safety for liquefaction susceptibility based on a design earthquake. The primary study site was the township of Greymouth, on the West Coast of New Zealand’s South Island. Greymouth is built on geologically young (Holocene-age) deposits of beach and river sands and gravels, and estuarine and lagoonal silts (Dowrick et al., 2004). Greymouth is also in a tectonically active region, with the high seismic hazard imposed by the Alpine Fault and other nearby faults, along with the age and type of sediment, mean the probability of liquefaction occurring is high particularly for the low-lying areas around the estuary and coastline. Repeated mapping over 150 years shows that the geomorphology of the Greymouth Township has been heavily modified during that timeframe, with both anthropogenic and natural processes developing the land into its current form. Identification of changes in the landscape was based on historical maps for the area and interpreting them to be either anthropogenic or natural changes, such as reclamation work or removal of material through natural events. This study focuses on the effect that anthropogenic and natural geomorphic processes have on the stiffness of subsurface material and its liquefaction susceptibility for three different design earthquake events. Areas of natural ground and areas of reclaimed land, with differing ages, were investigated through the use of the MASW method, allowing an initial estimation of the relationship between landscape modification and liquefaction susceptibility. The susceptibility to liquefaction of these different materials is important to critical infrastructure, such as the St. John Ambulance Building and Greymouth Aerodrome, which must remain functional following an earthquake. Areas of early reclamation at the Greymouth Aerodrome site have factors of safety less than 1 and will liquefy in most plausible earthquake scenarios, although the majority of the runway has a high factor of safety and should resist liquefaction. The land west of the St. John’s building has slightly to moderately positive factors of safety. Other areas have factors of safety that reflect the different geology and reclamation history

TRF1 and TRF2 use different mechanisms to find telomeric DNA but share a novel mechanism to search for protein partners at telomeres

Human telomeres are maintained by the shelterin protein complex in which TRF1 and TRF2 bind directly to duplex telomeric DNA. How these proteins find telomeric sequences among a genome of billions of base pairs and how they find protein partners to form the shelterin complex remains uncertain. Using single-molecule fluorescence imaging of quantum dot-labeled TRF1 and TRF2, we study how these proteins locate TTAGGG repeats on DNA tightropes. By virtue of its basic domain TRF2 performs an extensive 1D search on nontelomeric DNA, whereas TRF1's 1D search is limited. Unlike the stable and static associations observed for other proteins at specific binding sites, TRF proteins possess reduced binding stability marked by transient binding (? 9-17 s) and slow 1D diffusion on specific telomeric regions. These slow diffusion constants yield activation energy barriers to sliding ? 2.8-3.6 ?(B)T greater than those for nontelomeric DNA. We propose that the TRF proteins use 1D sliding to find protein partners and assemble the shelterin complex, which in turn stabilizes the interaction with specific telomeric DNA. This 'tag-team proofreading' represents a more general mechanism to ensure a specific set of proteins interact with each other on long repetitive specific DNA sequences without requiring external energy sources

Geometric analysis of Arabidopsis root apex reveals a new aspect of the ethylene signal transduction pathway in development

8 pages, 4 figures.-- PMID: 16173465 [PubMed].-- Printed version published on Sep 14, 2005.Structurally, ethylene is the simplest phytohormone and regulates multiple aspects of plant growth and development. Its effects are mediated by a signal transduction cascade involving receptors, MAP kinases and transcription factors. Many morphological effects of ethylene in plant development, including root size, have been previously described. In this article a combined geometric and algebraic approach has been used to analyse the shape and the curvature in the root apex of Arabidopsis seedlings. The process requires the fitting of Bézier curves that reproduce the root apex shape, and the calculation of the corresponding curvatures. The application of the method has allowed us to identify significant differences in the root curvatures of ethylene insensitive mutants (ein2-1 and etr1-1) with respect to the wild-type Columbia.Peer reviewe

Apodized holographic beam combiners for dense wavelength multiplexing based on Gaussian-beam interference

The brightness of high-power diode-laser systems can be significantly increased by using dense wavelength-multiplexing technologies. Among these technologies, state-of-the-art volume holographic gratings (VHGs) are suitable wavelength-selective filters for scaling the power of frequency-stabilized high-power lasers. The frequency spacing is limited due to the sidelobes of the spectral filter characteristic. In this Letter, we present the simulation results of novel apodized VHGs produced by Gaussian-beam interference. Apodized VHGs offer increased sidelobe suppression of up to 22 dB with conventional grating dimensions and, moreover, will improve the spectral brightness of dense wavelength-multiplexing systems by a factor of approximately six

Electrical Engineering & Electromechanics. Vol. 1: Power Electronics and Energy-Efficient Electric Power Industry. Control and Monitoring Systems of Electric Energy Converters

Опубліковано роботи по новим досягненням в галузі електротехніки та електромеханіки, в сфері розробки і удосконалення електричних машин і апаратів, силової електроніки, питань теоретичної електротехніки та електрофізики, техніки сильних електричних і магнітних полів, кабельної техніки, електричного транспорту, електричних станцій, мереж і систем, безпеки електрообладнання

Frequency stabilisation of single emitters and the effect on the beam quality

We present the improvement of the lateral beam quality due to frequency stabilisation in a Dense Wavelength Division Multiplexing setup using Volume Bragg Gratings. The spectral width of each frequency stabilised channel amounts to less than 300 pm and an overall multiplexing efficiency of 86% has been measured. The near and far field intensity distributions consist of discrete modes and were observed with a post positioned beam analysis module. When operated with frequency stabilisation, the lateral beam quality factor M2 of the single emitters decreased by a factor of 1.4 on average compared to the free running source