bluuebunny/crossref_metadata_2025 huggingface dataset:
Multistage Turbine Erosion
Authors: Menguturk M. , Gunes D. , Erten M. , Sverdrup E. F.
Published: November 2009

This paper presents a computer package developed to calculate the blade erosion rates in multistage turbines that use particle-laden hot expansion gases. This package is an extension of the single-stage erosion code presented in some of our earlier papers. The present package calculates gas flow and particle trajectories in each stage. The calculated particle outlet conditions of a given stage are processed statistically to generate the particle inlet conditions to the next stage enabling trajectory and erosion calculations to be advanced beyond a single turbine stage. The package allows erosion predictions to be obtained either based on the semi-empirical erosion formula presented earlier or by using an improved model which relies upon direct interpolation of available experimental data. This computer package has been applied to a four-stage electric utility gas turbine. It has been found that, in addition to the first-stage rotor blades, as indicated by our earlier studies, the second-stage rotor and the second and third-stage stator blades may also be exposed to critical erosion damage.
Effect of Area Ratio on the Performance of a 5.5:1 Pressure Ratio Centrifugal Impeller
Authors: Schumann L. F. , Clark D. A. , Wood J. R.
Published: November 2009

A centrifugal impeller which was initially designed for a pressure ratio of approximately 5.5 and a mass flow rate of 0.959 kg/s was tested with a vaneless diffuser for a range of design point impeller area ratios from 2.322 to 2.945. The impeller area ratio was changed by successively cutting back the impeller exit axial width from an initial value of 7.57 mm to a final value of 5.97 mm. In all, four separate area ratios were tested. For each area ratio a series of impeller exit axial clearances was also tested. Test results are based on impeller exit surveys of total pressure, total temperature, and flow angle at a radius 1.115 times the impeller exit radius. Results of the tests at design speed, peak efficiency, and an exit tip clearance of 8 percent of exit blade height show that the impeller equivalent pressure recovery coefficient peaked at a design point area ratio of approximately 2.748 while the impeller aerodynamic efficiency peaked at a lower value of area ratio of approximately 2.55. The variation of impeller efficiency with clearance showed expected trends with a loss of approximately 0.4 points in impeller efficiency for each percent increase in exit axial tip clearance for all impellers tested. The data also indicated that the impeller would probably separate at design area ratios greater than 2.748. An analysis was performed with a quasi-three-dimensional inviscid computer code which confirmed that a minimum velocity ratio was attained near this area ratio thus indicating separation. These data can be used to verify impeller flow models which attempt to account for very high diffusion and possible separation.
The Development of the Profile Boundary Layer in a Turbine Environment
Authors: Hourmouziadis J. , Buckl F. , Bergmann P.
Published: November 2009

Cascade testing tries to simulate the actual flow conditions encountered in a turbine. However, it is possible to reproduce neither the free-stream turbulence structure of the turbomachinery, nor the periodic wake effects of upstream blade rows. The usual understanding is that the latter in particular results in a significantly different behavior of the boundary layer in the engine. Experimental results from cascades and turbine rigs are presented. Grid-generated free-stream turbulence structure is compared to that in the turbine. Measurements of the profile pressure distribution, flush-mounted hot films, and flow visualization were used for the interpretation of the test results. Some observations of the boundary layer development in the cascade, on the guide vanes, and on rotor blades with typically skewed boundary layers are shown indicating essentially similar behavior in all cases.
Shock-Induced Flow Oscillations in Steam Turbine Diffusers
Authors: Maier R. , Wachter J.
Published: November 2009

In exhaust diffusers of steam turbines pressure oscillations may occur at certain operating conditions, due to shock–boundary layer interactions. These self-excited flow oscillations are caused by the high-speed clearance flow between blade tip and outer contour, leading to an excitation of the running blades. The paper describes the behavior of this unsteady flow phenomenon in the diffuser, identified with steady state and unsteady measurements at the wall, along with probe measurements behind the runner blading. A deeper physical understanding was gained by simulation of this flow pattern on the base of the water analogy.
Procedures for Determining Surface Heat Flux Using Thin Film Gages on a Coated Metal Model in a Transient Test Facility
Authors: Doorly J. E.
Published: November 2009

The paper describes how thin film surface heat flux gages may be used to measure surface heat transfer rate to enamel-coated metal turbine blades. Flexible methods, which are also computationally efficient, for obtaining the heat transfer rate are described. Experimental results, using the new coated metal turbine blades and processing techniques, in a stationary transient cascade facility are given, and are shown to agree well with results using the existing method for gages on single-layer substrate blades. The application of the gages for measuring highly unsteady heat transfer is also discussed.
Numerical Computation of Nonisentropic Potential Equations for Transonic Cascade Flows
Authors: Xu J. Z. , Du J. Y. , Ni W. Y.
Published: November 2009

Based on the analysis of the momentum equations and the nonisentropic flow, an “isentropic density,” which is computed according to the isentropic relation and is dependent on the temperature only, is separated from the density. The entropy increase across the shock may be directly calculated from the momentum equations in the divergence form. Iterating with the classical potential equation may solve the nonisentropic transonic flowfield conveniently. It is seen from the calculations of transonic cascade flow on the surface of revolution that the shock in the nonisentropic calculation is weaker and is located farther upstream compared to the classical potential solution, and is in agreement with the experimental results. In the calculations, the effect of entropy increase on both the Kutta condition and the outlet boundary conditions has been taken into consideration.
Influence of Upstream Flow Conditions on the Heat Transfer to Nozzle Guide Vanes
Authors: Krishnamoorthy V. , Pai B. R. , Sukhatme S. P.
Published: November 2009

The influence of a combustor located just upstream of a nozzle guide vane cascade on the heat flux distribution to the nozzle guide vane was experimentally investigated. The surface temperature distribution around the convectively cooled vane of the cascade was obtained by locating the cascade, firstly in a low-turbulence uniform hot gas stream, secondly in a high-turbulence, uniform hot gas stream, and thirdly in a high-turbulence, nonuniform hot gas stream present just downstream of the combustor exit. The results indicate that the increased blade surface temperatures observed for the cascade placed just downstream of the combustor can be accounted for by the prevailing turbulence level measured at cascade inlet in cold-flow conditions and the average gas temperature at the cascade inlet.
Turbulence Measurements and Secondary Flows in a Turbine Rotor Cascade
Authors: Gregory-Smith D. G. , Walsh J. A. , Graves C. P. , Fulton K. P.
Published: November 2009

This paper presents results for turbulence measurements that have been made using hot-wire anemometry in the endwall region of a high turning rotor blade cascade. It is shown that the levels of turbulence are very high in the regions of the flowfield containing the passage vortex and its associated loss core. A comparison with the total pressure loss measurements illustrates the mechanisms of loss generation within the cascade. The growth of turbulent kinetic energy was much less than the growth of loss indicating significant viscous dissipation.
Aerodynamic and Heat Transfer Measurements on a Transonic Nozzle Guide Vane
Authors: Wedlake E. T. , Brooks A. J. , Harasgama S. P.
Published: November 2009

Experimental determination of heat transfer rates to gas turbine blading plays an important part in the improvement of both the validation of existing design methods and the development of improved design codes. This paper describes a series of tests on an annular cascade of nozzle guide vanes designed for a high-work-capacity single-stage transonic turbine. The tests were carried out in the Isentropic Light Piston Cascade at the Royal Aerospace Establishment, Pyestock, and a brief description of this new test facility is included. Measurements of local heat transfer rates and aerodynamic data around the blade surface and on the end walls are described.
Numerical Simulation of Inviscid Transonic Flow Through Nozzles With Fluctuating Back Pressure
Authors: Bo¨lcs A. , Fransson T. H. , Platzer M. F.
Published: November 2009

The study presents a numerical method, based on the flux vector splitting approach, to the problem of unsteady one-dimensional and two-dimensional inviscid transonic flows, with emphasis on the numerical determination of the shock position, through nozzles with time-varying back pressure. The model is first validated by comparison with exact (one dimension) and numerical (two dimensions) steady-state solutions. It is thereafter applied to the problem of time-fluctuating back pressure in quasi-one-dimensional and two-dimensional nozzles. The one-dimensional results are validated by comparison with a small perturbation analytical unsteady solution, whereafter a few sample cases are presented with the objective of understanding fundamental aspects of unsteady transonic flows. It is concluded that both the amplitude and frequency of the imposed fluctuating exit pressure are important parameters for the location of the unsteady shock. It is also shown that the average unsteady shock position is not necessarily identical with the steady-state position, and that the unsteady shock may, under certain circumstances, propagate upstream into the subsonic flow domain. The pressure jump over the shock, as well as the unsteady post-shock pressure, is different for identical shock positions during the cycle of fluctuation, which implies that an unsteady shock movement, imposed by oscillating back pressure, may introduce a significant unsteady lift and moment. This may be of importance for flutter predictions. It is also noted that, although the sonic velocity is obtained in the throat of steady-state, quasi-one-dimensional flow, this is not necessarily true for the unsteady solution. During part of the period with fluctuating back pressure, the flow velocity may be subsonic at the throat and still reach a supersonic value later in the nozzle. This phenomenon depends on the frequency and amplitude of the imposed fluctuation, as well as on the nozzle geometry.
Monitoring the Dissemination of the Broad-Host-Range Plasmid pB10 in Sediment Microcosms by Quantitative PCR
Authors: Bonot Sébastien , Merlin Christophe
Published: November 2009

Studying the transfer of specific mobile genetic elements in complex environmental matrices remains difficult because suitable molecular tools are not yet available to back up classical culture-dependent approaches. In this report, we show that quantitative PCR could be used to monitor the dissemination of the broad-host-range plasmid pB10 in sediment microcosms. This approach lies in the differential measurement of the host and plasmid DNAs used to inoculate the microcosms, using a particular design of quantitative PCR primers/probes where we took advantage of the mosaic aspect of the bacterial genomes to achieve a highly specific quantitative PCR detection system.
Ecological Genetic Divergence of the Fungal PathogenDidymella rabieion Sympatric Wild and DomesticatedCicerspp. (Chickpea)
Authors: Frenkel Omer , Peever Tobin L. , Chilvers Martin I. , Özkilinc Hilal , Can Canan , Abbo Shahal , Shtienberg Dani , Sherman Amir
Published: November 2009

For millennia, chickpea (Cicer arietinum) has been grown in the Levant sympatrically with wildCicerspecies. Chickpea is traditionally spring-sown, while its wild relatives germinate in the autumn and develop in the winter. It has been hypothesized that the human-directed shift of domesticated chickpea to summer production was an attempt to escape the devastating Ascochyta disease caused byDidymella rabiei. We estimated genetic divergence betweenD. rabieiisolates sampled from wildCicer judaicumand domesticatedC. arietinumand the potential role of temperature adaptation in this divergence. Neutral genetic markers showed strong differentiation between pathogen samples from the two hosts. Isolates from domesticated chickpea demonstrated increased adaptation to higher temperatures when grownin vitrocompared with isolates from the wild host. The distribution of temperature responses among progeny from crosses of isolates fromC. judaicumwith isolates fromC. arietinumwas continuous, suggesting polygenic control of this trait.In vivoinoculations of host plants indicated that pathogenic fitness of the native isolates was higher than that of their hybrid progeny. The results indicate that there is a potential for adaptation to higher temperatures; however, the chances for formation of hybrids which are capable of parasitizing both hosts over a broad temperature range are low. We hypothesize that this pathogenic fitness cost is due to breakdown of coadapted gene complexes controlling pathogenic fitness on each host and may be responsible for maintenance of genetic differentiation between the pathogen demes.
Water- and Air-Distributed Conidia Differ in Sterol Content and Cytoplasmic Microviscosity
Authors: Van Leeuwen M. R. , Van Doorn T. M. , Golovina E. A. , Stark J. , Dijksterhuis J.
Published: November 2009

Airborne and waterborne fungal spores were compared with respect to cytoplasmic viscosity and the presence of ergosterol. These parameters differed markedly between the two spore types and correlated with spore survival. This suggests that the mode of spore dispersal has a bearing on cellular composition, which is relevant for the eradication of industrially relevant fungal propagules.
Tetralin-Induced and ThnR-Regulated Aldehyde Dehydrogenase and β-Oxidation Genes in
Sphingomonas macrogolitabida
Strain TFA
Authors: López-Sánchez Aroa , Floriano Belén , Andújar Eloisa , Hernáez Maria José , Santero Eduardo
Published: November 2009

A new cluster of genes has been found downstream of the previously identified
thnA2
gene. The gene products are similar to nonacylating aldehyde dehydrogenases (ThnG) and to proteins representing a complete β-oxidation pathway (ThnH to ThnP). ThnG has a nonacylating NAD-dependent pimelic semialdehyde dehydrogenase activity that renders pimelic acid a seven-carbon dicarboxylic acid. For further metabolism via β-oxidation, pimelic acid could be acylated by a constitutive acyl coenzyme A (acyl-CoA) ligase found in
Sphingomonas macrogolitabida
strain TFA or by ThnH, which would transfer CoA from a previously acylated molecule. The first round of β-oxidation is expected to render glutaryl-CoA and acetyl-CoA. Glutaryl-CoA dehydrogenase (ThnN) would catalyze the oxidation and decarboxylation of glutaryl-CoA and yield crotonyl-CoA, which enters the central metabolism via acetyl-CoA. Mutagenesis studies have shown that these genes are not essential for growth on tetralin or fatty acids, although a
thnG
disruption mutant showed threefold less pimelic semialdehyde dehydrogenase activity. Transcriptional analysis indicated that these genes are induced by tetralin, subjected to catabolite repression, and regulated by the same regulatory factors previously identified to regulate other
thn
structural genes. In the present study, transcription initiation upstream of
thnH
and
thnM
has been detected by primer extension analysis, and putative promoters were identified by sequence analysis. In addition, binding of the activator ThnR to its putative binding sites at the P
H
and P
M
promoter regions has been characterized. These results provide a complete characterization of the biodegradation pathway of tetralin to central metabolites and describe the transcriptional organization of the
thn
operons in
S. macrogolitabida
strain TFA.
Requirement of theLactobacillus caseiMaeKR Two-Component System forl-Malic Acid Utilization via a Malic Enzyme Pathway
Authors: Landete José María , García-Haro Luisa , Blasco Amalia , Manzanares Paloma , Berbegal Carmen , Monedero Vicente , Zúñiga Manuel
Published: November 2009

Lactobacillus caseican metabolizel-malic acid via malolactic enzyme (malolactic fermentation [MLF]) or malic enzyme (ME). Whereas utilization ofl-malic acid via MLF does not support growth, the ME pathway enablesL. caseito grow onl-malic acid. In this work, we have identified in the genomes ofL. caseistrains BL23 and ATCC 334 a cluster consisting of two diverging operons,maePEandmaeKR, encoding a putative malate transporter (maeP), an ME (maeE), and a two-component (TC) system belonging to the citrate family (maeKandmaeR). Homologous clusters were identified inEnterococcus faecalis,Streptococcus agalactiae,Streptococcus pyogenes, andStreptococcus uberis. Our results show that ME is essential forl-malic acid utilization inL. casei. Furthermore, deletion of either the gene encoding the histidine kinase or the response regulator of the TC system resulted in the loss of the ability to grow onl-malic acid, thus indicating that the cognate TC system regulates and is essential for the expression of ME. Transcriptional analyses showed that expression ofmaeEis induced in the presence ofl-malic acid and repressed by glucose, whereas TC system expression was induced byl-malic acid and was not repressed by glucose. DNase I footprinting analysis showed that MaeR binds specifically to a set of direct repeats [5′-TTATT(A/T)AA-3′] in themaepromoter region. The location of the repeats strongly suggests that MaeR activates the expression of the diverging operonsmaePEandmaeKRwhere the first one is also subjected to carbon catabolite repression.
Metabolic Engineering of Fungal Strains for Conversion of
d
-Galacturonate to
meso
-Galactarate
Authors: Mojzita Dominik , Wiebe Marilyn , Hilditch Satu , Boer Harry , Penttilä Merja , Richard Peter
Published: November 2009

d
-Galacturonic acid can be obtained by hydrolyzing pectin, which is an abundant and low value raw material. By means of metabolic engineering, we constructed fungal strains for the conversion of
d
-galacturonate to
meso
-galactarate (mucate). Galactarate has applications in food, cosmetics, and pharmaceuticals and as a platform chemical. In fungi
d
-galacturonate is catabolized through a reductive pathway with a
d
-galacturonate reductase as the first enzyme. Deleting the corresponding gene in the fungi
Hypocrea jecorina
and
Aspergillus niger
resulted in strains unable to grow on
d
-galacturonate. The genes of the pathway for
d
-galacturonate catabolism were upregulated in the presence of
d
-galacturonate in
A. niger
, even when the gene for
d
-galacturonate reductase was deleted, indicating that
d
-galacturonate itself is an inducer for the pathway. A bacterial gene coding for a
d
-galacturonate dehydrogenase catalyzing the NAD-dependent oxidation of
d
-galacturonate to galactarate was introduced to both strains with disrupted
d
-galacturonate catabolism. Both strains converted
d
-galacturonate to galactarate. The resulting
H. jecorina
strain produced galactarate at high yield. The
A. niger
strain regained the ability to grow on
d
-galacturonate when the
d
-galacturonate dehydrogenase was introduced, suggesting that it has a pathway for galactarate catabolism.
A Genomic Island Defines Subspecies-Specific Virulence Features of the Host-Adapted Pathogen
Campylobacter fetus
subsp.
venerealis
Authors: Gorkiewicz Gregor , Kienesberger Sabine , Schober Caroline , Scheicher Sylvia R. , Gülly Christian , Zechner Rudolf , Zechner Ellen L.
Published: November 2009

The pathogen
Campylobacter fetus
comprises two subspecies,
C. fetus
subsp.
fetus
and
C. fetus
subsp.
venerealis
. Although these taxa are highly related on the genome level, they are adapted to distinct hosts and tissues.
C. fetus
subsp.
fetus
infects a diversity of hosts, including humans, and colonizes the gastrointestinal tract. In contrast,
C. fetus
subsp.
venerealis
is largely restricted to the bovine genital tract, causing epidemic abortion in these animals. In light of their close genetic relatedness, the specific niche preferences make the
C. fetus
subspecies an ideal model system to investigate the molecular basis of host adaptation. In this study, a subtractive-hybridization approach was applied to the genomes of the subspecies to identify different genes potentially underlying this specificity. The comparison revealed a genomic island uniquely present in
C. fetus
subsp.
venerealis
that harbors several genes indicative of horizontal transfer and that encodes the core components necessary for bacterial type IV secretion. Macromolecular transporters of this type deliver effector molecules to host cells, thereby contributing to virulence in various pathogens. Mutational inactivation of the putative secretion system confirmed its involvement in the pathogenicity of
C. fetus
subsp.
venerealis
.
CytochromedBut Not CytochromeoRescues the Toluidine Blue Growth Sensitivity ofarcMutants ofEscherichia coli
Authors: Alvarez Adrian F. , Malpica Roxana , Contreras Martha , Escamilla Edgardo , Georgellis Dimitris
Published: November 2009

The Arc (anoxic redox control) two-component signal transduction system, consisting of the ArcB sensor kinase and the ArcA response regulator, allows adaptive responses ofEscherichia colito changes of O2availability. ThearcAgene was previously known as thedyegene because null mutants were growth sensitive to the photosensitizer redox dyes toluidine blue and methylene blue, a phenotype whose molecular basis still remains elusive. In this study we report that the toluidine blue O (TBO) effect on thearcmutants is light independent and observed only during aerobic growth conditions. Moreover, 16 suppressor mutants with restored growth were generated and analyzed. Thirteen of those possessed insertion elements upstream of thecydABoperon, rendering its expression ArcA independent. Also, it was found that, in contrast to cythocromed, cythocromeowas not able to confer toluidine blue resistance toarcmutants, thereby representing an intriguing difference between the two terminal oxidases. Finally, a mechanism for TBO sensitivity and resistance is discussed.
Polar Localization of the CckA Histidine Kinase and Cell Cycle Periodicity of the Essential Master Regulator CtrA in
Caulobacter crescentus
Authors: Angelastro Peter S. , Sliusarenko Oleksii , Jacobs-Wagner Christine
Published: November 2009

The phosphorylated form of the response regulator CtrA represses DNA replication initiation and regulates the transcription of about 100 cell cycle-regulated genes in
Caulobacter crescentus
. CtrA activity fluctuates during the cell cycle, and its periodicity is a key element of the engine that drives cell cycle progression. The histidine kinase CckA controls the phosphorylation not only of CtrA but also of CpdR, whose unphosphorylated form promotes CtrA proteolysis. Thus, CckA has a central role in establishing the cell cycle periodicity of CtrA activity by controlling both its phosphorylation and stability. Evidence suggests that the polar localization of CckA during the cell cycle plays a role in CckA function. However, the exact pattern of CckA localization remains controversial. Here, we describe a thorough, quantitative analysis of the spatiotemporal distribution of a functional and chromosomally produced CckA-monomeric green fluorescent protein fusion that affects current models of cell cycle regulation. We also identify two
cis
-acting regions in CckA that are important for its proper localization and function. The disruption of a PAS-like motif in the sensor domain affects the stability of CckA accumulation at the poles. This is accompanied by a partial loss in CckA function. Shortening an extended linker between β-sheets within the CckA catalysis-assisting ATP-binding domain has a more severe effect on CckA polar localization and function. This mutant strain exhibits a dramatic cell-to-cell variability in CpdR levels and CtrA cell cycle periodicity, suggesting that the cell cycle-coordinated polar localization of CckA may be important for the robustness of signal transduction and cell cycle progression.
The Aromatic Ring of Phenylalanine 334 Is Essential for Oligomerization ofVibrio vulnificusHemolysin
Authors: Kashimoto Takashige , Ueno Shunji , Koga Takeshi , Fukudome Shinji , Ehara Hayato , Komai Mayumi , Sugiyama Hiroyuki , Susa Nobuyuki
Published: November 2009

Vibrio vulnificushemolysin (VVH) is thought to be a member of the cholesterol-dependent cytolysin (CDC) family of pore-forming toxins. To date, the structure-function relationships of CDCs produced by Gram-negative bacteria remain largely unknown. We show here that the aromatic ring of phenylalanine residue conserved inVibrionaceaehemolysins is essential for oligomerization of VVH. We generated the VVH mutants; substituted Phe 334 for Ile (F334I), Ala (F334A), Tyr (F334Y), or Trp (F334W); and tested their binding and oligomerizing activity on Chinese hamster ovary cells. Binding in all mutants fell by approximately 50% compared with that in the wild type. Oligomerizing activities were completely eliminated in F334I and F334A mutants, whereas this ability was partially retained in F334Y and F334W mutants. These findings indicate that both hydrophobicity and an aromatic ring residue at the 334th position were needed for full binding activity and that the oligomerizing activity of this toxin was dependent on the existence of an aromatic ring residue at the 334th position. Our findings might help further understanding of the structure-and-function relationships inVibrionaceaehemolysins.
Genomic and Biological Analysis of Phage Xfas53 and Related Prophages of
Xylella fastidiosa
Authors: Summer Elizabeth J. , Enderle Christopher J. , Ahern Stephen J. , Gill Jason J. , Torres Cruz P. , Appel David N. , Black Mark C. , Young Ry , Gonzalez Carlos F.
Published: November 2009

We report the plaque propagation and genomic analysis of Xfas53, a temperate phage of
Xylella fastidiosa
. Xfas53 was isolated from supernatants of
X. fastidiosa
strain 53 and forms plaques on the sequenced strain Temecula. Xfas53 forms short-tailed virions, morphologically similar to podophage P22. The 36.7-kb genome is predicted to encode 45 proteins. The Xfas53 terminase and structural genes are related at a protein and gene order level to P22. The left arm of the Xfas53 genome has over 90% nucleotide identity to multiple prophage elements of the sequenced
X. fastidiosa
strains. This arm encodes proteins involved in DNA metabolism, integration, and lysogenic control. In contrast to Xfas53, each of these prophages encodes head and DNA packaging proteins related to the siphophage lambda and tail morphogenesis proteins related to those of myophage P2. Therefore, it appears that Xfas53 was formed by recombination between a widespread family of
X. fastidiosa
P2-related prophage elements and a podophage distantly related to phage P22. The lysis cassette of Xfas53 is predicted to encode a pinholin, a signal anchor and release (SAR) endolysin, and Rz and Rz1 equivalents. The holin gene encodes a pinholin and appears to be subject to an unprecedented degree of negative regulation at both the level of expression, with rho-independent transcriptional termination and RNA structure-dependent translational repression, and the level of holin function, with two upstream translational starts predicted to encode antiholin products. A notable feature of Xfas53 and related prophages is the presence of 220- to 390-nucleotide degenerate tandem direct repeats encoding putative DNA binding proteins. Additionally, each phage encodes at least two BroN domain-containing proteins possibly involved in lysogenic control. Xfas53 exhibits unusually slow adsorption kinetics, possibly an adaptation to the confined niche of its slow-growing host.
FolX and FolM Are Essential for Tetrahydromonapterin Synthesis in
Escherichia coli
and
Pseudomonas aeruginosa
Authors: Pribat Anne , Blaby Ian K. , Lara-Núñez Aurora , Gregory Jesse F. , de Crécy-Lagard Valérie , Hanson Andrew D.
Published: November 2009

Tetrahydromonapterin is a major pterin in
Escherichia coli
and is hypothesized to be the cofactor for phenylalanine hydroxylase (PhhA) in
Pseudomonas aeruginosa
, but neither its biosynthetic origin nor its cofactor role has been clearly demonstrated. A comparative genomics analysis implicated the enigmatic
folX
and
folM
genes in tetrahydromonapterin synthesis via their phyletic distribution and chromosomal clustering patterns.
folX
encodes dihydroneopterin triphosphate epimerase, which interconverts dihydroneopterin triphosphate and dihydromonapterin triphosphate.
folM
encodes an unusual short-chain dehydrogenase/reductase known to have dihydrofolate and dihydrobiopterin reductase activity. The roles of FolX and FolM were tested experimentally first in
E. coli
, which lacks PhhA and in which the expression of
P. aeruginosa
PhhA plus the recycling enzyme pterin 4a-carbinolamine dehydratase, PhhB, rescues tyrosine auxotrophy. This rescue was abrogated by deleting
folX
or
folM
and restored by expressing the deleted gene from a plasmid. The
folX
deletion selectively eliminated tetrahydromonapterin production, which far exceeded folate production. Purified FolM showed high, NADPH-dependent dihydromonapterin reductase activity. These results were substantiated in
P. aeruginosa
by deleting
tyrA
(making PhhA the sole source of tyrosine) and
folX
. The Δ
tyrA
strain was, as expected, prototrophic for tyrosine, whereas the Δ
tyrA
Δ
folX
strain was auxotrophic. As in
E. coli
, the
folX
deletant lacked tetrahydromonapterin. Collectively, these data establish that tetrahydromonapterin formation requires both FolX and FolM, that tetrahydromonapterin is the physiological cofactor for PhhA, and that tetrahydromonapterin can outrank folate as an end product of pterin biosynthesis.
Promoter and Riboswitch Control of the Mg
2+
Transporter MgtA from
Salmonella enterica
Authors: Cromie Michael J. , Groisman Eduardo A.
Published: November 2009

The MgtA protein from
Salmonella enterica
serovar Typhimurium mediates Mg
2+
uptake from the periplasm into the cytoplasm. Here we report that the PhoP/PhoQ two-component regulatory system, which responds to periplasmic Mg
2+
, governs
mgtA
transcription initiation at all investigated Mg
2+
concentrations and that the Mg
2+
-sensing 5′ leader region of the
mgtA
gene controls transcription elongation into the
mgtA
coding region when
Salmonella
is grown in media with <50 μM Mg
2+
. Overexpression of the Mg
2+
transporter CorA, which is believed to increase cytoplasmic Mg
2+
levels, decreased
mgtA
transcription in a manner dependent on a functional
mgtA
5′ leader.
P1 Plasmid Segregation: Accurate Redistribution by Dynamic Plasmid Pairing and Separation
Authors: Sengupta Manjistha , Nielsen Henrik Jorck , Youngren Brenda , Austin Stuart
Published: November 2009

Low-copy-number plasmids, such as P1 and F, encode a type Ia partition system (P1paror Fsop) for active segregation of copies to daughter cells. Typical descriptions show a single central plasmid focus dividing and the products moving to the cell quarter regions, ensuring segregation. However, using improved optical and analytical tools and large cell populations, we show that P1 plasmid foci are very broadly distributed. Moreover, under most growth conditions, more than two foci are frequently present. Each focus contains either one or two plasmid copies. Replication and focus splitting occur at almost any position in the cell. The products then move rapidly apart for approximately 40% of the cell length. They then tend to maintain their relative positions. The segregating foci often pass close to or come to rest close to other foci in the cell. Foci frequently appear to fuse during these encounters. Such events occur several times in each cell and cell generation on average. We argue that foci pair with their neighbors and then actively separate again. The net result is an approximately even distribution of foci along the long cell axis on average. We show mathematically thattrans-pairing and active separation could greatly increase the accuracy of segregation and would produce the distributions of foci that we observe. Plasmid pairing and separation may constitute a novel fine-tuning mechanism that takes the basic pattern created when plasmids separate after replication and converts it to a roughly even pattern that greatly improves the fidelity of plasmid segregation.
THE QUASITRIANGULAR STRUCTURES FOR ω-SMASH COPRODUCT HOPF ALGEBRAS
Authors: JIAO ZHENGMING
Published: November 2009

In this paper, the quasitriangular structures of ω-smash coproduct Hopf algebras Bω ⋈ H as constructed by Caenepeel, Ion, Militaru and Zhu were studied. Necessary and sufficient conditions for ω-smash coproduct Hopf algebras to be quasitriangular Hopf algebras are given in terms of properties of their components. As applications of our results, some special cases are discussed. Especially, The quasitriangular structures for D(H)* and H4ω ⋈ kℤ2 are constructed.
Thiol-metabolizing proteins and endothelial redox state: differential modulation of eNOS and biopterin pathways
Authors: Sugiyama Toru , Michel Thomas
Published: November 2009

The intracellular redox state is stringently maintained by thiol-based antioxidants to establish a balance for the physiological and pathophysiological roles of reactive oxygen species. The relative contributions of the thioredoxin (Trx) and glutathione/glutaredoxin systems to intracellular redox balance are incompletely understood, as are the consequences of altered thiol metabolism on endothelial nitric oxide (NO) synthase (eNOS) and NO-dependent pathways in the endothelium. We designed duplex small interfering RNA (siRNA) constructs to specifically “knock down” the expression of three key thiol-metabolizing enzymes in cultured aortic endothelial cells. Transfection of siRNA constructs targeting glutathione reductase (GR), cytosolic Trx reductase (TrxR1), or mitochondrial Trx reductase (TrxR2) significantly decreased the intracellular reduced glutathione-to-oxidized glutathione ratio. siRNA-mediated knockdown of either GR, TrxR1, or TrxR2 markedly suppressed VEGF-induced NO production (measured by an electrochemical NO sensor) and also blocked eNOS enzyme activity (using the [3H]arginine/[3H]citrulline assay). Pretreatment of endothelial cells with N, N′-bis(2-chloroethyl)- N-nitrosourea, an inhibitor of GR and TrxR, significantly decreased VEGF-induced NO production. siRNA-mediated TrxR2 knockdown led to a marked increase in hydrogen peroxide (H2O2) production in endothelial cells. In contrast, knockdown of GR or TrxR1 only slightly increased H2O2 production. Supplementation of endothelial cells with tetrahydrobiopterin prevented the increase in H2O2 generation seen with siRNA-mediated knockdown of GR. These studies show that the differential regulation of thiol-metabolizing proteins leads to critical changes in oxidative and nitrosative stress pathways. Greater understanding of the differential regulation of thiol-metabolizing proteins may lead to the development of new pharmacological targets for diseases associated with oxidative stress in the vascular wall.
Effects of mental stress on autonomic cardiac modulation during weightlessness
Authors: Aubert André E. , Verheyden Bart , d′Ydewalle Constantin , Beckers Frank , Van den Bergh Omer
Published: November 2009

Sustained weightlessness affects all body functions, among these also cardiac autonomic control mechanisms. How this may influence neural response to central stimulation by a mental arithmetic task remains an open question. The hypothesis was tested that microgravity alters cardiovascular neural response to standardized cognitive load stimuli. Beat-to-beat heart rate, brachial blood pressure, and respiratory frequency were collected in five astronauts, taking part in three different short-duration (10 to 11 days) space missions to the International Space Station. Data recording was performed in supine position 1 mo before launch; at days 5 or 8 in space; and on days 1, 4, and 25 after landing. Heart rate variability (HRV) parameters were obtained in the frequency domain. Measurements were performed in the control condition for 10 min and during a 5-min mental arithmetic stress task, consisting of deducting 17 from a four-digit number, read by a colleague, and orally announcing the result. Our results show that over all sessions (pre-, in-, and postflight), mental stress induced an average increase in mean heart rate (Δ7 ± 1 beats/min; P = 0.03) and mean arterial pressure (Δ7 ± 1 mmHg; P = 0.006). A sympathetic excitation during mental stress was shown from HRV parameters: increase of low frequency expressed in normalized units (Δ8.3 ± 1.4; P = 0.004) and low frequency/high frequency (Δ1.6 ± 0.3; P = 0.001) and decrease of high frequency expressed in normalized units (Δ8.9 ± 1.4; P = 0.004). The total power was not influenced by mental stress. No effect of spaceflight was found on baseline heart rate, mean arterial pressure, and HRV parameters. No differences in response to mental stress were found between pre-, in-, and postflight. Our findings confirm that a mental arithmetic task in astronauts elicits sympathovagal shifts toward enhanced sympathetic modulation and reduced vagal modulation. However, these responses are not changed in space during microgravity or after spaceflight.
Role of cholesterol in the biophysical dysfunction of surfactant in ventilator-induced lung injury
Authors: Vockeroth Dan , Gunasekara Lasantha , Amrein Matthias , Possmayer Fred , Lewis James F. , Veldhuizen Ruud A. W.
Published: November 2009

Mechanical ventilation may lead to an impairment of the endogenous surfactant system, which is one of the mechanisms by which this intervention contributes to the progression of acute lung injury. The most extensively studied mechanism of surfactant dysfunction is serum protein inhibition. However, recent studies indicate that hydrophobic components of surfactant may also contribute. It was hypothesized that elevated levels of cholesterol significantly contribute to surfactant dysfunction in ventilation-induced lung injury. Sprague-Dawley rats ( n = 30) were randomized to either high-tidal volume or low-tidal volume ventilation and monitored for 2 h. Subsequently, the lungs were lavaged, surfactant was isolated, and the biophysical properties of this isolated surfactant were analyzed on a captive bubble surfactometer with and without the removal of cholesterol using methyl-β-cyclodextrin. The results showed lower oxygenation values in the high-tidal volume group during the last 30 min of ventilation compared with the low-tidal volume group. Surfactant obtained from the high-tidal volume animals had a significant impairment in function compared with material from the low-tidal volume group. Removal of cholesterol from the high-tidal volume group improved the ability of the surfactant to reduce the surface tension to low values. Subsequent reconstitution of high-cholesterol values led to an impairment in surface activity. It is concluded that increased levels of cholesterol associated with endogenous surfactant represent a major contributor to the inhibition of surfactant function in ventilation-induced lung injury.
Altered lung surfactant system in a Rab38-deficient rat model of Hermansky-Pudlak syndrome
Authors: Osanai Kazuhiro , Higuchi Junko , Oikawa Rieko , Kobayashi Makoto , Tsuchihara Katsuma , Iguchi Masaharu , Huang Jyongsu , Voelker Dennis R. , Toga Hirohisa
Published: November 2009

Several Long-Evans rat substrains carrying the phenotype of oculocutaneous albinism and bleeding diathesis are a rat model of Hermansky-Pudlak syndrome (HPS). The mutation responsible for the phenotype ( Ruby) was identified as a point mutation in the initiation codon of Rab38 small GTPase that regulates intracellular vesicle transport. As patients with HPS often develop life-limiting interstitial pneumonia accompanied by abnormal morphology of alveolar type II cells, we investigated lung surfactant system in Long-Evans Cinnamon rats, one strain of the Ruby rats. The lungs showed conspicuous morphology of type II cells containing markedly enlarged lamellar bodies. Surfactant phosphatidylcholine and surfactant protein B were increased in lung tissues and lamellar bodies but not in alveolar lumen. Expression levels of mRNA for surfactant proteins A, B, C, and D were not altered. Isolated type II cells showed aberrant secretory pattern of newly synthesized [3H]phosphatidylcholine, i.e., decreased basal secretion and remarkably amplified agonist-induced secretion. [3H]phosphatidylcholine synthesis and uptake by type II cells were not altered. Thus Rab38-deficient type II cells appear to carry abnormality in lung surfactant secretion but not in synthesis or uptake. These results suggest that aberrant lung surfactant secretion may be involved in the pathogenesis of interstitial pneumonia in HPS.
Lunatic Fringe-mediated Notch signaling is required for lung alveogenesis
Authors: Xu Keli , Nieuwenhuis Erica , Cohen Brenda L. , Wang Wei , Canty Angelo J. , Danska Jayne S. , Coultas Leigh , Rossant Janet , Wu Megan Y. J. , Piscione Tino D. , Nagy Andras , Gossler Achim , Hicks Geoff G. , Hui Chi-Chung , Henkelman R. Mark , Yu Lisa X. , Sled John G. , Gridley Thomas , Egan Sean E.
Published: November 2009

Distal lung development occurs through coordinated induction of myofibroblasts, epithelial cells, and capillaries. Lunatic Fringe ( Lfng) is a β1–3N-acetylglucosamine transferase that modifies Notch receptors to facilitate their activation by Delta-like (Dll1/4) ligands. Lfng is expressed in the distal lung during saccular development, and deletion of this gene impairs myofibroblast differentiation and alveogenesis in this context. A similar defect was observed in Notch2β-geo/+Notch3β-geo/β-geocompound mutant mice but not in Notch2β-geo/+or Notch3β-geo/β-geosingle mutants. Finally, to directly test for the role of Notch signaling in myofibroblast differentiation in vivo, we used ROSA26-rtTA/+; tetO-CRE/+; RBPJκflox/floxinducible mutant mice to show that disruption of canonical Notch signaling during late embryonic development prevents induction of smooth muscle actin in mesenchymal cells of the distal lung. In sum, these results demonstrate that Lfng functions to enhance Notch signaling in myofibroblast precursor cells and thereby to coordinate differentiation and mobilization of myofibroblasts required for alveolar septation.
The APOE ε4 Allele Is Associated with Incident Mild Cognitive Impairment among Community-Dwelling Older Persons
Authors: Boyle Patricia A. , Buchman Aron S. , Wilson Robert S. , Kelly Jeremiah F. , Bennett David A.
Published: November 2009

Background: The apolipoprotein E (APOE) ε4 allele is a well-known risk factor for the development of Alzheimer’s disease, but little is known about the association of the ε4 allele with incident mild cognitive impairment (MCI). Objective: Test the hypothesis that the ε4 allele is associated with an increased risk of developing MCI. Methods: More than 600 older Catholic clergy members from the Religious Orders Study without any cognitive impairment at baseline underwent APOE genotyping and detailed annual clinical evaluations for up to 16 years of follow-up (mean: 10.17 years; range: 2–16 years) to document incident MCI and rates of decline in global cognition and 5 cognitive domains (i.e. episodic memory, semantic memory, working memory, perceptual speed and visuospatial abilities). Results: During up to 16 years of annual follow-up, 339 of 607 persons (56%) developed MCI. In a proportional hazards model adjusted for age, sex and education, the presence of the APOE ε4 allele was associated with a 1.4-fold increased risk of incident MCI (hazard ratio: 1.36; 95% CI: 1.04, 1.78). Further, this association persisted in analyses that required MCI to persist for at least one year (hazard ratio: 1.50; 95% CI: 1.05, 2.14). Finally, the ε4 allele was associated with an increased rate of decline in global cognition and 4 out of 5 cognitive systems (i.e. episodic memory, semantic memory, working memory and perceptual speed). Conclusion: The presence of the APOE ε4 allele is associated with an increased risk of MCI and a more rapid rate of cognitive decline in old age.
2. Strengthening Technical Aid by Social Research
Authors: Dodd Stuart C.
Published: November 2009

Proposals to measure technical aid achievements in part by polling the knowledge and satisfactions of the relevant peoples and their leaders. A world-wide, continuous system is visualized.
5. The "Political Behavior" Approach
Authors: Kirkpatrick Evron M.
Published: November 2009

Excerpts from an address on "Political Science and the Secondary Schools," in which the author, disagreeing with a PROD editorial, says that political behavior is a certain approach to political science and proceeds to describe its nature and limits.
10. Disarmament and the Fallibility of Inspection
Authors: Singer J. David
Published: November 2009

Inspection may not be psychologically foolprooof, even if technically so. Social scientists have almost ignored applied research on the possibilities of disarmament, because of several improbable theories. They should address themselves to a number of questions aimed at bringing about disarmament under imperfect conditions.
11. Political and Apolitical Personality
Authors: Hennessy Bernard
Published: November 2009

Personality-and-culture study is contrasted with intracultural personality studies. A preliminary project comparing politicians and apolitical citizens in Arizona is described as a key type of intracultural study.
The Intelligence Function: Built-in Errors
Authors: Lasswell Harold D.
Published: November 2009

The function of intelligence deserves more comparative study than it has received. The component factors affecting an intelligence system are noted: culture, class, interest, personality, crisis. Attention is directed to two important sources of distorted intelligence, with special reference given to the foreign environment of a nation-state or of other large-scale organizations. Intelligence tends to over-report a few spots and to under-report the others, a result of power and respect rivalries. Intelligence also tends to exhibit errors prepared by the successes obtained during inter-crisis periods, and by the desire to avoid minority positions. A number of proposals are made for redressing the balance.
Testing Deutsch's Indices of Community
Authors: Rohn Peter H.
Published: November 2009

Deutsch's indices of international community are put to empirical use on six pairs of countries and prove too crude. But the methodological difficulties provoke further research and theory along the same lines.
Make Political Theory More What?
Authors: Roelofs H. Mark
Published: November 2009

A political theorist expresses his anxiety over PROD's " operationalism," and operationalism as presently practiced in Political Science. Snyder's work is characteristic of much current research, in that it uses techniques incompatible with the context in which they are applied, and unconsciously makes ideological recommendations .
The Khrushchev Visit: The Role of Social Research
Authors: Dichter Ernest
Published: November 2009

The President of the Institute for Motivational Research, Inc., warns of the psychological dangers inherent in Khracshchev's imminent visit to America. He asks why social science has not been used to facilitate the preparation of the public for this event, giving examples of what might have been done beforehand. He makes four suggestions for improved last-minute planning.