Active genetic elements present in the locus of enterocyte effacement in Escherichia coli O26 and their role in mobility

The locus of enterocyte effacement (LEE) is a large multigene chromosomal segment encoding gene products responsible for the generation of attaching and effacing lesions in many diarrheagenic Escherichia coli strains. A recently sequenced LEE harboring a pathogenicity island (PAI) from a Shiga toxin E. coli serotype 026 strain revealed a LEE PAI (designated LEE 026) almost identical to that obtained from a rabbit-specific enteropathogenic 015:H- strain. LEE 026 comprises 59,540 bp and is inserted at 94 min within the mature pheU tRNA locus. The LEE 026 PAI is flanked by two direct repeats of 137 and 136 bp (DR1 and DR2), as well as a gene encoding an integrase belonging to the P4 integrase family. We examined LEE 026 for horizontal gene transfer. By generating mini-LEE plasmids harboring only DR1 or DR2 with or without the integrase-like gene, we devised a simple assay to examine recombination processes between these sequences. Recombination was shown to be integrase dependent in a Delta recA E. coli K-12 strain background. Recombinant plasmids harboring a single direct repeat cloned either with or without the LEE 026 integrase gene were found to insert within the chromosomal pheU locus of E. coli K-12 strains with equal efficiency, suggesting that an endogenous P4-like integrase can substitute for this activity. An integrase with strong homology to the LEE 026 integrase was detected on the K-12 chromosome associated with the leuX tRNA locus at 97 min. Strains deleted for this integrase demonstrated a reduction in the insertion frequency of plasmids harboring only the DR into the pheU locus. These results provide strong evidence that LEE-harboring elements are indeed mobile and suggest that closely related integrases present on the chromosome of E. coli strains contribute to the dynamics of PAI mobility.

Titanium phosphate for Fuel Cell Proton Conduction Membranes

Environmental issues due to increases in emissions of air pollutants and greenhouse gases are driving the development of clean energy delivery technologies such as fuel cells. Low temperature Proton Exchange Membrane Fuel Cells (PEMFC) use hydrogen as a fuel and their only emission is water. While significant advances have been made in recent years, a major limitation of the current technology is the cost and materials limitations of the proton conduction membrane. The proton exchange membrane performs three critical functions in the PEMFC membrane electrode assembly (MEA): (i) conduction of protons with minimal resistance from the anode (where they are generated from hydrogen) to the cathode (where they combine with oxygen and electrons, from the external circuit or load), (ii) providing electrical insulation between the anode and cathode to prevent shorting, and (iii) providing a gas impermeable barrier to prevent mixing of the fuel (hydrogen) and oxidant. The PFSA (perfluorosulphonic acid) family of membranes is currently the best developed proton conduction membrane commercially available, but these materials are limited to operation below 100oC (typically 80oC, or lower) due to the thermochemical limitations of this polymer. For both mobile and stationary applications, fuel cell companies require more durable, cost effective membrane technologies capable of delivering enhanced performance at higher temperatures (typically 120oC, or higher. This is driving research into a wide range of novel organic and inorganic materials with the potential to be good proton conductors and form coherent membranes. There are several research efforts recently reported in the literature employing inorganic nanomaterials. These include functionalised silica phosphates [1,2], fullerene [3] titania phosphates [4], zirconium pyrophosphate [5]. This work addresses the functionalisation of titania particles with phosphoric acid. Proton conductivity measurements are given together with structural properties.

Variable effects of larval size on post-metamorphic performance in the field

Larval quality may be capable of explaining much of the variation in the recruitment and subsequent population dynamics of benthic marine invertebrates. Whilst the effects of larval nutritional condition on adult performance have received the most attention, recent work has shown that larval size may also be an important and ubiquitous source of variation in larval quality. We examined the effects of variation in larval size on the post-metamorphic survival and growth of Watersipora subtorquata in 2 very different habitats - experimental substrata and pier pilings. We found strong effects of larval size on colony performance, although these varied among experiments. For colonies on experimental substrata, larval size positively affected adult survival and, initially, growth. However, after 3 wk in the field, there was no relationship between larval size and colony size, possibly because colonies were completely surrounded by newly settled organisms. Larval size also positively affected post-metamorphic growth of colonies on pier pilings, but, surprisingly, colonies that came from larger larvae had lower survival than colonies from smaller larvae. Overall, variation in larval size will strongly affect the recruitment and subsequent performance of adults in this species, although this may vary among different habitats. This study highlights the importance of examining the effects of larval quality on adult performance in as realistic conditions as possible, because of the strong interaction between larval size effects and the environment.

Non-coding RNAs: the architects of eukaryotic complexity

Around 98% of all transcriptional output in humans is noncoding RNA. RNA-mediated gene regulation is widespread in higher eukaryotes and complex genetic phenomena like RNA interference, co-suppression, transgene silencing, imprinting, methylation, and possibly position-effect variegation and transvection, all involve intersecting pathways based on or connected to RNA signaling. I suggest that the central dogma is incomplete, and that intronic and other non-coding RNAs have evolved to comprise a second tier of gene expression in eukaryotes, which enables the integration and networking of complex suites of gene activity. Although proteins are the fundamental effectors of cellular function, the basis of eukaryotic complexity and phenotypic variation may lie primarily in a control architecture composed of a highly parallel system of trans-acting RNAs that relay state information required for the coordination and modulation of gene expression, via chromatin remodeling, RNA-DNA, RNA-RNA and RNA-protein interactions. This system has interesting and perhaps informative analogies with small world networks and dataflow computing.

Rare earth element fractionation in authigenic illite–smectite from Late Permian clastic rocks, Bowen Basin, Australia: implications for physico-chemical environments of fluids during illitization

REE analyses were performed on authigenic illitic clay. minerals from Late Permian mudrocks, sandstones and bentonites from the Bowen Basin (Australia). The mixed-layer illite-smectite exhibit REE patterns with an obvious fractionation of the HREE from the LREE and MREE, which is an apparent function of degree of illitization reaction. The highly illitic (R greater than or equal to 3) illite-smectite from the northern Bowen Basin show a depletion of LREE relative to the less illitic (R=0 and 1) clays. In contrast, an enrichment of HREE for the illite-rich clays relative to less. illitic clays is evident for the southern Bowen Basin samples. The North American Shale Composite-normalized (La/Lu)(sn) ratios show negative correlations with the illite content in illite-smectite and positive correlations with the delta(18)O values of the clays for both the northern and southern Bowen Basin samples. These correlations indicate that the increasing depletion of LREE in hydrothermal fluids is a function of increasing water/rock ratios in the northern Bowen Basin. Good negative correlations between (La/Lu)(sn) ratios and illite content in illite-smectite from the southern Bowen Basin suggest the involvement of fluids with higher alkalinity and higher pH in low water/ rock ratio conditions. Increasing HREE enrichment with delta(18)O decrease indicates the effect of increasing temperature at low water/rock ratios in the southern Bowen Basin. Results of the present study confirm the conclusions of some earlier studies suggesting that REE in illitic clay minerals are mobile and fractionated during illitization and that this fact should be considered in studies of sedimentary processes and in identifying provenance. Moreover, our results show that REE systematic of illitic clay minerals can be applied as an useful technique to gain information about physico-chemical conditions during thermal and fluid flow events in certain sedimentary basins. (C) 2003 Elsevier Science B.V. All rights reserved.

Modelling the fate of chromated copper arsenate in a sandy soil

A pulse of chromated copper arsenate (CCA, a timber preservative) was applied in irrigation water to an undisturbed field soil in a laboratory column. Concentrations of various elements in the leachate from the column were measured during the experiment. Also, the remnants within the soil were measured at the end of the experiment. The geochemical modelling package, PHREEQC-2, was used to simulate the experimental data. Processes included in the CCA transport modelling were advection, dispersion, non-specific adsorption (cation exchange) and specific adsorption by clay minerals and organic matter, as well as other possible chemical reactions such as precipitation/dissolution. The modelling effort highlighted the possible complexities in CCA transport and reaction experiments. For example, the uneven dosing of CCA as well as incomplete knowledge of the soil properties resulted in simulations that gave only partial, although reasonable, agreement with the experimental data. Both the experimental data and simulations show that As and Cu are strongly adsorbed and therefore, will mostly remain at the top of the soil profile, with a small proportion appearing in leachate. On the other hand, Cr is more mobile and thus it is present in the soil column leachate. Further simulations show that both the quantity of CCA added to the soil and the pH of the irrigation water will influence CCA transport. Simulations suggest that application of larger doses of CCA to the soil will result in higher leachate concentrations, especially for Cu and As. Irrigation water with a lower pH will dramatically increase leaching of Cu. These results indicate that acidic rainfall or significant accidental spillage of CCA will increase the risk of groundwater pollution.

Lipid droplets: a unified view of a dynamic organelle

Lipid droplets form the main lipid store in eukaryotic cells. Although all cells seem to be able to generate lipid droplets, their biogenesis, regulatory mechanisms and interactions with other organelles remain largely elusive. In this article, we outline some of the recent developments in lipid droplet cell biology. We show the mobile and dynamic nature of this organelle, and advocate the adoption of a unified nomenclature to consolidate terminology in this emerging field.

Measurement and state preparation via ion trap quantum computing

We investigate in detail the effects of a QND vibrational number measurement made on single ions in a recently proposed measurement scheme for the vibrational state of a register of ions in a linear rf trap [C. D'HELON and G. J. MILBURN, Phys Rev. A 54, 5141 (1996)]. The performance of a measurement shows some interesting patterns which are closely related to searching.

The generation of H-1-NMR-detectable mobile lipid in stimulated lymphocytes: Relationship ts cellular activation, the cell cycle, and phosphatidylcholine-specific phospholipase C

Mobile Lipids detected using H-1-NMR in stimulated lymphocytes were correlated with cell cycle phase, expression of the interleukin-2 receptor alpha and proliferation to assess the activation status of the lymphocytes. Mobile lipid levels, IL-2R alpha expression and proliferation increased after treatment with PMA and ionomycin. PMA or ionomycin stimulation alone induced increased IL-2R alpha expressiom but not proliferation, PMA- but not ionomycin-stimulation generated mobile lipid, Treatment with anti-CD3 antibody did not increase IL-2R alpha expression or proliferation but did generate increased amounts of mobile lipid, The cell cycle status of thymocytes treated with anti-CD3, PMA or ionomycin alone indicated an. accumulation of the cells in the G(1) phase of the cell cycle, The generation of mobile lipid was abrogated in anti-CD3 antibody-stimulated thymic lymphocytes but not in splenic lymphocytes, using a phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor which blocked cells in the G(1)/S phase of the cell cycle, This suggests that the H-1-NMR-detectable mobile Lipid may be generated in anti-CD3 antibody-stimulated thymic lymphocytes by the action of PC-PLC activity via the catabolism of PC, in the absence of classical signs of activation. (C) 1997 Academic Press.