bluuebunny/crossref_metadata_2025 huggingface dataset:
FlrA, a σ
54
-Dependent Transcriptional Activator in
Vibrio fischeri,
Is Required for Motility and Symbiotic Light-Organ Colonization
Authors: Millikan Deborah S. , Ruby Edward G.
Published: May 2003

Flagellum-mediated motility of
Vibrio fischeri
is an essential factor in the bacterium's ability to colonize its host, the Hawaiian squid
Euprymna scolopes
. To begin characterizing the nature of the flagellar regulon, we have cloned a gene, designated
flrA
, from
V. fischeri
that encodes a putative σ
54
-dependent transcriptional activator. Genetic arrangement of the
flrA
locus in
V. fischeri
is similar to motility master-regulator operons of
Vibrio cholerae
and
Vibrio parahaemolyticus
. In addition, examination of regulatory regions of a number of flagellar operons in
V. fischeri
revealed apparent σ
54
recognition motifs, suggesting that the flagellar regulatory hierarchy is controlled by a similar mechanism to that described in
V. cholerae
. However, in contrast to its closest known relatives,
flrA
mutant strains of
V. fischeri
ES114 were completely abolished in swimming capability. Although
flrA
provided in
trans
restored motility to the
flrA
mutant, the complemented strain was unable to reach wild-type levels of symbiotic colonization in juvenile squid, suggesting a possible role for the proper expression of FlrA in regulating symbiotic colonization factors in addition to those required for motility. Comparative RNA arbitrarily primed PCR analysis of the
flrA
mutant and its wild-type parent revealed several differentially expressed transcripts. These results define a regulon that includes both flagellar structural genes and other genes apparently not involved in flagellum elaboration or function. Thus, the transcriptional activator FlrA plays an essential role in regulating motility, and apparently in modulating other symbiotic functions, in
V. fischeri
.
Posttranscriptional Control of Quorum-Sensing-Dependent Virulence Genes by DksA in
Pseudomonas aeruginosa
Authors: Jude Florence , Köhler Thilo , Branny Pavel , Perron Karl , Mayer Matthias P. , Comte Rachel , van Delden Christian
Published: May 2003

Pseudomonas aeruginosa
controls the secretion of extracellular virulence factors, including rhamnolipids and LasB elastase, by the
las
and
rhl
quorum-sensing systems. Here, we mutated the
dksA
gene of
P. aeruginosa
by insertion of an Ω-Hg cassette. The mutant displayed growth rates similar to that of the wild type in rich medium but was impaired in growth in defined minimal medium. Production of rhamnolipids and LasB elastase by the
dksA
mutant was only 4 and 10%, respectively, of wild-type levels. These defects could be partially complemented by introduction of the plasmid-encoded
dksA
genes from
P. aeruginosa
or
Escherichia coli
. In the
dksA
mutant, the expression of
rhlI
was increased early during exponential growth, but expression of other quorum-sensing regulator genes—
lasR
,
lasI
, and
rhlR
—was not affected. Although the transcription of the
lasB
and
rhlAB
genes was comparable between the
dksA
mutant and the wild-type strain in peptone tryptic soy broth medium, we observed reduced translation of both genes in the
dksA
mutant. Similarly, we found that full translation of
lasB
and
rhlAB
genes in
E. coli
also requires the
dksA
gene. DksA is therefore a novel regulator involved in the posttranscriptional control of extracellular virulence factor production in
P. aeruginosa
.
Flagellar Phase Variation inSalmonella entericaIs Mediated by a Posttranscriptional Control Mechanism
Authors: Bonifield Heather R. , Hughes Kelly T.
Published: May 2003

Salmonella entericahas two antigenically distinct flagellin genes,fliCandfljB, that are alternatively expressed. ThefljAgene is cotranscribed withfljBand encodes a protein that has been characterized as a transcriptional repressor of the unlinkedfliCgene when FljB is expressed. In this study we report genetic evidence that FljA prevents the production of FliC protein through an interaction with the 5′-untranslated region of thefliCmRNA transcript. Studies with operon and gene fusions, Western analyses, and T2RNase protection assays were performed for strains with thefljBApromoter locked in either the on or the off orientation. β-Galactosidase assays offliCtranscriptional and translational fusions to thelacoperon demonstrated that while FljA inhibitsfliCtranscription fivefold in thefljBAONorientation, it has a 200-fold effect on bothfliCtranscription and translation, indicating that the FljA inhibitor might act at both the transcriptional and translational level. T2RNase protection assays also demonstrated a fivefold decrease infliCtranscript levels for cells locked in thefljBAONorientation compared to those in thefljBAOFForientation, and an eightfold decrease in FliC protein levels was observed by Western analysis. This reduction in FliC protein levels is greater than the decrease observed for the transcript. These results are consistent with a new model whereby FljA inhibits FliC expression by an attenuation or translational control mechanism.
Characterization of the Second LysR-Type Regulator in the Biphenyl-Catabolic Gene Cluster of
Pseudomonas pseudoalcaligenes
KF707
Authors: Watanabe Takahito , Fujihara Hidehiko , Furukawa Kensuke
Published: May 2003

Pseudomonas pseudoalcaligenes
KF707 possesses a biphenyl-catabolic (
bph
) gene cluster consisting of
bphR1A1A2-
(
orf3
)
-bphA3A4BCX0X1X2X3D
. The
bphR1
(formerly
orf0
) gene product, which belongs to the GntR family, is a positive regulator for itself and
bphX0X1X2X3D
. Further analysis in this study revealed that a second regulator belonging to the LysR family (designated
bphR2
) is involved in the regulation of the
bph
genes in KF707. The
bphR2
gene was not located near the
bph
gene cluster, and its product (BphR2) exhibited a high level of similarity to NahR (the naphthalene- and salicylate-catabolic regulator belonging to the LysR family) in plasmid NAH7 of
Pseudomonas putida
. A strain containing a disrupted
bphR2
gene failed to grow on biphenyl as a sole source of carbon, and the BphD (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid hydrolase) activity was significantly reduced compared to that of wild-type strain KF707. Furthermore, the same strain exhibited extremely low transcription of
bphR1
,
bphA1
,
bphC
,
bphX0
, and
bphD
. However, when the
bphR2
gene was provided in
trans
to the
bphR2
-disrupted strain, the transcription level of these genes was restored. These results indicate that
bphR2
regulates the
bph
genes positively as a second regulator together with BphR1.
Suppression of Temperature-Sensitive Chromosome Replication of anEscherichia coli dnaX(Ts) Mutant by Reduction of Initiation Efficiency
Authors: Blinkova Alexandra , Hermandson Mary Jo , Walker James R.
Published: May 2003

Temperature sensitivity of DNA polymerization and growth of adnaX(Ts) mutant is suppressible at 39 to 40°C by mutations in the initiator gene,dnaA. These suppressor mutations concomitantly cause initiation inhibition at 20°C and have been designated Cs,Sx to indicate both phenotypic characteristics of cold-sensitive initiation and suppression ofdnaX(Ts).OnednaA(Cs,Sx) mutant, A213D, has reduced affinity for ATP, and two mutants, R432L and T435K, have eliminated detectable DnaA box binding in vitro. Two models have explaineddnaA(Cs,Sx) suppression ofdnaX, which codes for both the τ and γ subunits of DNA polymerase III. The initiation deficiency model assumes that reducing initiation efficiency allows survival of thednaX(Ts) mutant at the somewhat intermediate temperature of 39 to 40°C by reducing chromosome content per cell, thus allowing partially active DNA polymerase III to complete replication of enough chromosomes for the organism to survive. The stabilization model is based on the idea that DnaA interacts, directly or indirectly, with polymerization factors during replication. We present five lines of evidence consistent with the initiation deficiency model. First, adnaA(Cs,Sx) mutation reduced initiation frequency and chromosome content (measured by flow cytometry) and origin/terminus ratios (measured by real-time PCR) in both wild-type anddnaX(Ts) strains growing at 39 and 34°C. These effects were shown to result specifically from the Cs,Sx mutations, because thednaX(Ts) mutant is not defective in initiation. Second, reduction of the number of origins and chromosome content per cell was common to all three known suppressor mutations. Third, growing thednaA(Cs,Sx)dnaX(Ts) strain on glycerol-containing medium reduced its chromosome content to one per cell and eliminated suppression at 39°C, as would be expected if the combination of poor carbon source, the Cs,Sx mutation, the Ts mutation, and the 39°C incubation reduced replication to the point that growth (and, therefore, suppression) was not possible. However, suppression was possible on glycerol medium at 38°C. Fourth, thednaX(Ts) mutation can be suppressed also by introduction oforiCmutations, which reduced initiation efficiency and chromosome number per cell, and the degree of suppression was proportional to the level of initiation defect. Fifth, introducing adnaA(Cos) allele, which causes overinitiation, into thednaX(Ts) mutant exacerbated its temperature sensitivity.
Escherichia coli
O157:H7 Shiga Toxin-Encoding Bacteriophages: Integrations, Excisions, Truncations, and Evolutionary Implications
Authors: Shaikh Nurmohammad , Tarr Phillip I.
Published: May 2003

As it descended from
Escherichia coli
O55:H7, Shiga toxin (Stx)-producing
E. coli
(STEC) O157:H7 is believed to have acquired, in sequence, a bacteriophage encoding Stx2 and another encoding Stx1. Between these events, sorbitol-fermenting
E. coli
O157:H
−
presumably diverged from this clade. We employed PCR and sequence analyses to investigate sites of bacteriophage integration into the chromosome, using evolutionarily informative STEC to trace the sequence of acquisition of elements encoding Stx. Contrary to expectations from the two currently sequenced strains, truncated bacteriophages occupy
yehV
in almost all
E. coli
O157:H7 strains that lack

stx
1

(

stx
1

-negative strains). Two truncated variants were determined to contain either GTT or TGACTGTT sequence, in lieu of 20,214 or 18,895 bp, respectively, of the bacteriophage central region. A single-nucleotide polymorphism in the latter variant suggests that recombination in that element extended beyond the inserted octamer. An

stx
2

bacteriophage usually occupies
wrbA
in

stx
1

+
/

stx
2

+
E. coli
O157:H7, but
wrbA
is unexpectedly unoccupied in most

stx
1

-negative/

stx
2

+
E. coli
O157:H7 strains, the presumed progenitors of

stx
1

+
/

stx
2

+
E. coli
O157:H7. Trimethoprim-sulfamethoxazole promotes the excision of all, and ciprofloxacin and fosfomycin significantly promote the excision of a subset of complete and truncated
stx
bacteriophages from the
E. coli
O157:H7 strains tested; bile salts usually attenuate excision. These data demonstrate the unexpected diversity of the chromosomal architecture of
E. coli
O157:H7 (with novel truncated bacteriophages and multiple

stx
2

bacteriophage insertion sites), suggest that

stx
1

acquisition might be a multistep process, and compel the consideration of multiple exogenous factors, including antibiotics and bile, when chromosome stability is examined.
Molecular Characterization of Inulosucrase fromLeuconostoc citreum: a Fructosyltransferase within a Glucosyltransferase
Authors: Olivares-Illana Vanesa , López-Munguía Agustín , Olvera Clarita
Published: May 2003

The gene coding for inulosucrase inLeuconostoc citreumCW28,islA, was cloned, sequenced, and expressed inEscherichia coli. The recombinant enzyme catalyzed inulin synthesis from sucrose like the wild-type enzyme. Inulosucrase presents an unusual structure: its N-terminal region is similar to the variable region of glucosyltransferases, its catalytic domain is similar to fructosyltransferases from various microorganisms, and its C-terminal domain presents similarity to the glucan binding domain from alternansucrase, a glucosyltransferase fromLeuconostoc mesenteroidesNRRL B-1355. From sequence comparison, it was found that this fructosyltransferase is a natural chimeric enzyme resulting from the substitution of the catalytic domain of alternansucrase by a fructosyltransferase. Two different forms of theislAgene truncated in the C-terminal glucan binding domain were successfully expressed inE. coliand retained their ability to synthesize inulin but lost thermal stability. This is the first report of an inulosucrase bearing structural features of both glucosyltransferases and fructosyltransferases.
Role of the
Enterococcus faecalis
GelE Protease in Determination of Cellular Chain Length, Supernatant Pheromone Levels, and Degradation of Fibrin and Misfolded Surface Proteins
Authors: Waters Christopher M. , Antiporta Michelle H. , Murray Barbara E. , Dunny Gary M.
Published: May 2003

Gelatinase (GelE), a secreted Zn-metalloprotease of
Enterococcus faecalis
, has been implicated as a virulence factor by both epidemiological data and animal model studies. Expression of
gelE
is induced at a high cell density by the
fsr
quorum-sensing system. In the present study, GelE was shown to be responsible for the instability of a number of Asc10 (aggregation substance) mutant proteins, implying that GelE functions to clear the bacterial cell surface of misfolded proteins. Disruption of GelE production led to increased cell chain length of
E. faecalis
, from a typical diplococcus morphology to chains of 5 to 10 cells. This function of GelE was also exhibited when the protein was expressed in
Streptococcus pyogenes
. GelE-expressing
E. faecalis
strains were more autolytic, suggesting that GelE affects chain length through activation of an autolysin. GelE was also essential for degradation of polymerized fibrin. GelE expression reduced the titer of cCF10, the peptide pheromone that induces conjugation of pCF10, and pCF10 had increased conjugation into non-GelE-expressing strains. These new functions attributed to GelE suggest that it acts to increase the dissemination of
E. faecalis
in high-density environments.
Variation between Pathogenic Serovars within
Salmonella
Pathogenicity Islands
Authors: Amavisit P. , Lightfoot D. , Browning G. F. , Markham P. F.
Published: May 2003

Although four of the five
Salmonella
pathogenicity islands (SPIs) have been characterized in detail for
Salmonella enterica
serovar Typhimurium, and the fifth has been characterized for
Salmonella enterica
serovar Dublin, there have been limited studies to examine them in detail in a range of pathogenic serovars of
S. enterica
. The aim of this study was to examine these regions, shown to be crucial in virulence, in pathogenic serovars to identify any major deletions or insertions that may explain variation in virulence and provide further understanding of the elements involved in the evolution of these regions. Multiple strains of each of the 13 serovars were compared by Southern blot hybridization using a series of probes that together encompassed the full length of all five SPIs. With the exception of serovar Typhimurium, all strains of the same serovar were identical in all five SPIs. Those serovars that differed from serovar Typhimurium in SPI-1 to SPI-4 and from serovar Dublin in SPI-5 were examined in more detail in the variant regions by PCR, and restriction endonuclease digestion and/or DNA sequencing. While most variation in hybridization patterns was attributable to loss or gain of single restriction endonuclease cleavage sites, three regions, in SPI-1, SPI-3, and SPI-5, had differences due to major insertions or deletions. In SPI-1 the
avrA
gene was replaced by a 200-base fragment in three serovars, as reported previously. In SPI-5, two serovars had acquired an insertion with similarity to the
pagJ
and
pagK
genes between
pipC
and
pipD.
In SPI-3 the genes
sugR
and
rhuM
were deleted in most serovars and in some were replaced by sequences that were very similar to either the
Escherichia coli
fimbrial operon, flanked by two distinct insertion sequence elements, or to the
E. coli
retron phage ΦR73. The distribution of these differences suggests that there have been a number of relatively recent horizontal transfers of genes into
S. enterica
and that in some cases the same event has occurred in multiple lineages of
S. enterica.
Thus, it seems that insertion sequences and retron phages are likely to be involved in continuing evolution of the pathogenicity islands of pathogenic
Salmonella
serovars.
Electron Microscopic Analysis of Membrane Assemblies Formed by the Bacterial Chemotaxis Receptor Tsr
Authors: Weis Robert M. , Hirai Teruhisa , Chalah Anas , Kessel Martin , Peters Peter J. , Subramaniam Sriram
Published: May 2003

The serine receptor (Tsr) from
Escherichia coli
is representative of a large family of transmembrane receptor proteins that mediate bacterial chemotaxis by influencing cell motility through signal transduction pathways. Tsr and other chemotaxis receptors form patches in the inner membrane that are often localized at the poles of the bacteria. In an effort to understand the structural constraints that dictate the packing of receptors in the plane of the membrane, we have used electron microscopy to examine ordered assemblies of Tsr in membrane extracts isolated from cells engineered to overproduce the receptor. Three types of assemblies were observed: ring-like “micelles” with a radial arrangement of receptor subunits, two-dimensional crystalline arrays with approximate hexagonal symmetry, and “zippers,” which are receptor bilayers that result from the antiparallel interdigitation of cytoplasmic domains. The registration among Tsr molecules in the micelle and zipper assemblies was sufficient for identification of the receptor domains and for determination of their contributions to the total receptor length. The overall result of this analysis is compatible with an atomic model of the receptor dimer that was constructed primarily from the X-ray crystal structures of the periplasmic and cytoplasmic domains. Significantly, the micelle and zipper structures were also observed in fixed, cryosectioned cells expressing the Tsr receptor at high abundance, suggesting that the modes of Tsr assembly found in vitro are relevant to the situation in the cell.
Antisense RNA Downregulation of Coenzyme A Transferase Combined with Alcohol-Aldehyde Dehydrogenase Overexpression Leads to Predominantly Alcohologenic
Clostridium acetobutylicum
Fermentations
Authors: Tummala Seshu B. , Junne Stefan G. , Papoutsakis Eleftherios T.
Published: May 2003

Plasmid pAADB1 for the overexpression of the alcohol-aldehyde dehydrogenase (
aad
) gene and downregulation of the coenzyme A transferase (CoAT) using antisense RNA (asRNA) against
ctfB
(the second CoAT gene on the polycistronic
aad-ctfA-ctfB
message) was used in order to increase the butanol/acetone ratio of
Clostridium acetobutylicum
ATCC 824 fermentations. Acetone and butanol levels were drastically reduced in 824(pCTFB1AS) (expresses only an asRNA against
ctfB
) compared to 824(pSOS95del) (plasmid control). Compared to strain 824(pCTFB1AS), 824(pAADB1) fermentations exhibited two profound differences. First, butanol levels were ca. 2.8-fold higher in 824(pAADB1) and restored back to plasmid control levels, thus supporting the hypothesis that asRNA downregulation of
ctfB
leads to degradation of the whole
aad-ctfA-ctfB
transcript. Second, ethanol titers in 824(pAADB1) were ca. 23-fold higher and the highest (ca. 200 mM) ever reported in
C. acetobutylicum
. Western blot analysis confirmed that CoAT was downregulated in 824(pAADB1) at nearly the same levels as in strain 824(pCTFB1AS). Butyrate depletion in 824(pAADB1) fermentations suggested that butyryl-CoA was limiting butanol production in 824(pAADB1). This was confirmed by exogenously adding butyric acid to 824(pAADB1) fermentations to increase the butanol/ethanol ratio. DNA microarray analysis showed that
aad
overexpression profoundly affects the large-scale transcriptional program of the cells. Several classes of genes were differentially expressed [strain 824(pAADB1) versus strain 824(pCTFB1AS)], including genes of the stress response, sporulation, and chemotaxis. The expression patterns of the CoAT genes (
ctfA
and
ctfB
) and
aad
were consistent with the overexpression of
aad
and asRNA downregulation of
ctfB
.
Oxidative Stress in
Synechococcus
sp
.
Strain PCC 7942: Various Mechanisms for H
2
O
2
Detoxification with Different Physiological Roles
Authors: Perelman Alexander , Uzan Avraham , Hacohen Dalia , Schwarz Rakefet
Published: May 2003

This study focuses on the mechanisms for hydrogen peroxide detoxification in
Synechococcus
sp. strain PCC 7942. To gain better understanding of the role of different routes of hydrogen peroxide detoxification, we inactivated
tplA
(thioredoxin-peroxidase-like), which we recently identified. In addition, we inactivated the gene encoding catalase-peroxidase and examined the ability to detoxify H
2
O
2
and to survive oxidative stress in both of the single mutants and in the double mutant. Surprisingly, we observed that the double mutant survived H
2
O
2
concentrations that the single catalase-peroxidase mutant could not tolerate. This phenotype correlated with an increased ability of the double mutant to detoxify externally added H
2
O
2
compared to the catalase-peroxidase mutant. Therefore, our studies suggested the existence of a hydrogen peroxide detoxification activity in addition to catalase-peroxidase and thioredoxin-peroxidase. The rate of detoxification of externally added H
2
O
2
was similar in the wild-type and the TplA mutant cells, suggesting that, under these conditions, catalase-peroxidase activity was essential for this process and TplA was dispensable. However, during excessive radiation, conditions under which the cell might experience oxidative stress, TplA appears to be essential for growth, and cells lacking it cannot compete with the wild-type strain. Overall, these studies suggested different physiological roles for various cellular hydrogen peroxide detoxification mechanisms in
Synechococcus
sp. strain PCC 7942.
Trigger Factor-Mediated Prolyl Isomerization Influences Maturation of the
Streptococcus pyogenes
Cysteine Protease
Authors: Lyon William R. , Caparon Michael G.
Published: May 2003

Trigger factor, a ribosome-associated chaperone and peptidyl-prolyl
cis
-
trans
isomerase (PPIase), is essential for the secretion and maturation of the cysteine protease of the pathogenic gram-positive bacterium
Streptococcus pyogenes
. In the absence of trigger factor, the nascent protease polypeptide is not targeted to the secretory pathway. Some partial-function mutations restore targeting. However, the secreted protease does not efficiently mature into an enzymatically active form, suggesting that trigger factor has an additional role in protease biogenesis. Here, we show that, while not required for targeting, the PPIase activity of trigger factor is essential for maturation of the protease following its secretion from the bacterial cell. Site-specific mutations introduced into
ropA
, the gene which encodes trigger factor in
S. pyogenes
, produced mutant proteins deficient in PPIase activity. When these mutant alleles were used to replace the wild-type gene on the streptococcal chromosome, analysis of protease biogenesis revealed that, although the protease was secreted normally, it did not efficiently mature to an active form. Furthermore, mutation of a single proline residue in the protease prodomain suppressed the requirement for PPIase activity, suggesting that this residue is the target of trigger factor. These data support a model in which trigger factor-mediated prolyl isomerization influences the conformation of the prodomain, which in turn directs the protease into one of several alternative folding pathways.
Involvement of Cyclic AMP (cAMP) and cAMP Receptor Protein in Anaerobic Respiration of
Shewanella oneidensis
Authors: Saffarini Daad A. , Schultz Ryan , Beliaev Alex
Published: May 2003

Shewanella oneidensis
is a metal reducer that can use several terminal electron acceptors for anaerobic respiration, including fumarate, nitrate, dimethyl sulfoxide (DMSO), trimethylamine
N
-oxide (TMAO), nitrite, and insoluble iron and manganese oxides. Two
S. oneidensis
mutants, SR-558 and SR-559, with Tn
5
insertions in
crp
, were isolated and analyzed. Both mutants were deficient in Fe(III) and Mn(IV) reduction. They were also deficient in anaerobic growth with, and reduction of, nitrate, fumarate, and DMSO. Although nitrite reductase activity was not affected by the
crp
mutation, the mutants failed to grow with nitrite as a terminal electron acceptor. This growth deficiency may be due to the observed loss of cytochromes
c
in the mutants. In contrast, TMAO reduction and growth were not affected by loss of cyclic AMP (cAMP) receptor protein (CRP). Fumarate and Fe(III) reductase activities were induced in rich medium by the addition of cAMP to aerobically growing wild-type
S. oneidensis
. These results indicate that CRP and cAMP play a role in the regulation of anaerobic respiration, in addition to their known roles in catabolite repression and carbon source utilization in other bacteria.
Altered Substrate Selection of the Melibiose Transporter (MelY) of
Enterobacter cloacae
Involving Point Mutations in Leu-88, Leu-91, and Ala-182 That Confer Enhanced Maltose Transport
Authors: Shinnick Steven G. , Perez Stephanie A. , Varela Manuel F.
Published: May 2003

We isolated mutants of
Escherichia coli
HS4006 containing the melibiose-H
+
symporter (MelY) from
Enterobacter cloacae
that had enhanced fermentation on 1% maltose MacConkey plates. DNA sequencing revealed three site classes of mutations: L-88-P, L-91-P, and A-182-P. The mutants L-88-P and L-91-P had 3.6- and 5.1-fold greater maltose uptake than the wild type and enhanced apparent affinities for maltose. Energy-coupled transport was defective for melibiose accumulation, but detectable maltose accumulation for the mutants indicated that active transport is dependent upon the substrate transported through the carrier. We conclude that the residues Leu-88, Leu-91 (transmembrane segment 3 [TMS-3]), and Ala-182 (TMS-6) of MelY mediate sugar selection. These data represent the first MelY mutations that confer changes in sugar selection.
Xenorhabdus nematophila
Requires an Intact
iscRSUA-hscBA-fdx
Operon To Colonize
Steinernema carpocapsae
Nematodes
Authors: Martens Eric C. , Gawronski-Salerno Joseph , Vokal Danielle L. , Pellitteri Molly C. , Menard Megan L. , Goodrich-Blair Heidi
Published: May 2003

An insertion between
iscA
and
hscB
of the
Xenorhabdus nematophila iscRSUA-hscBA-fdx
locus, predicted to encode Fe-S assembly machinery, prevented colonization of
Steinernema carpocapsae
nematodes. The insertion disrupted cotranscription of
iscA
and
hscB
, but did not reduce
hscB
A expression, suggesting that
X. nematophila
requires coordinated expression of the
isc-hsc-fdx
locus for colonization.
Regulatory strategies to reduce tobacco addiction in youth
Authors: Henningfield J E , Moolchan E T , Zeller M
Published: May 2003

Preventing tobacco addiction and achieving cessation in established users are the cornerstones of efforts to reduce tobacco use and disease. It has been increasingly recognised that reducing tobacco toxin exposure has theoretical potential to reduce disease in continuing tobacco users. This has been controversial because such approaches also carry the potential to undermine prevention and cessation. As complicated as harm reduction issues are for adults, they are still more complicated for youth. Harm reduction is not a singular approach, but rather a concept that encompasses an extremely diverse array of potential approaches. These carry equally diverse potential risks and benefits. The regulatory framework (for example, whether or not the Food and Drug Administration regulates the approach) is also predicted to be a major factor in determining the consequences of harm reduction approaches. This paper examines the various issues and potential approaches concerning the application of harm reduction to youth. We conclude that although some carry great risk, others may actually support broader tobacco control efforts to prevent tobacco use and foster cessation in youth and adults.
Youth tobacco prevention mass media campaigns: past, present, and future directions
Authors: Farrelly M C , Niederdeppe J , Yarsevich J
Published: May 2003

This paper focuses on countermarketing efforts aimed at curbing youth smoking. We review the literature on the effectiveness of tobacco countermarketing campaigns, characterise current state and national campaign approaches, present findings from qualitative approaches and laboratory experiments that explore a variety of messages (for example, health consequences, industry manipulation), and discuss newer, non-traditional approaches to countermarketing. In conclusion, we outline research needed to fill gaps in our existing knowledge and discuss future directions in tobacco countermarketing aimed at youth.
The potential of the internet as a medium to encourage and discourage youth tobacco use
Authors: Ribisl K M
Published: May 2003

The internet is fast becoming a new battleground between tobacco control advocates and pro-tobacco forces, and this new media will certainly have a greater impact on tobacco use behaviour in the future. This paper reviews how the internet can encourage youth smoking by providing youth access to tobacco products and offering content that glamorises smoking lifestyle and culture, particularly in hundreds of websites and chat rooms. These sites feature pictures of celebrity smokers, provide information about smoking in movies, and provide smoking advice to teen smokers. In contrast, youth smoking is discouraged on online grassroots advocacy and countermarketing websites. Although these strategies show promise, more research is needed to evaluate their impact. Recommendations are made for future research to study pro-smoking internet content and ways to counteract it, as well as to monitor the online activities of the tobacco companies. Finally, some of the challenges in addressing tobacco related internet content are discussed.
Teen penalties for tobacco possession, use, and purchase: evidence and issues: Figure 1
Authors: Wakefield M , Giovino G
Published: May 2003

A handful of empirical studies have related changes in youth smoking to popular laws that penalise tobacco possession, use, and purchase (PUP). In this paper, we review the literature and outline reasons why PUP laws may be unlikely to reduce youth smoking significantly at the population level. In theoretical terms, we argue that PUP laws lack important features required for punishment to be effective in changing behaviour. In practical terms, PUP transgressions seem difficult to detect. Conceptually, there is potential for PUP laws to undermine conventional avenues of discipline, such as the parent–child relationship and the school environment. Strategically, PUP laws may divert policy attention from effective tobacco control strategies, relieve the tobacco industry of responsibility for its marketing practices, and reinforce the tobacco industry’s espoused position that smoking is for adults only. To assist further debate and discussion, we identify research issues requiring attention.
Smoking on the rise among young adults: implications for research and policy
Authors: Lantz P M
Published: May 2003

This paper investigates hypotheses regarding the cause of the recent apparent increase in young adult smoking, compares trends in smoking among young adults with trends in the use of other substances, and considers the implications for youth tobacco control research and policy. Time series analyses of national data suggest that the recent observed increase in smoking among young adults is primarily an artefact of the almost simultaneous increase in smoking among high school students. In addition, however, it also appears that there have been real changes in smoking patterns among young adults. While many questions remain regarding recent trends in tobacco and other drug use among adolescents and young adults, what is known leads to a clarion call for increased intervention and policy action for the prevention and control of tobacco use among young adults in the USA.
Thermal behaviour of nitric acid dihydrate in 1:2 HNO3/H2O solutions
Authors: Lebrun N , Mahe F , Foulon M , Gors C , Petit J C
Published: May 2003

The liquid-solid phase transitions of 1:2 HNO3/H2O solutions were investigated in bulk samples. Two forms of nitric acid dihydrate (NAD) (denoted further NAD(I) and NAD(II)) can precipitate. After cooling down to 200 K, NAD(I) crystallizes and melts congruently at 238 K. On cooling down to 173 K, NAD(I) first crystallizes and a polymorphic form NAD(II) appears on heating at about 210 K, which is governed by a nucleation process at temperatures below 200 K. NAD(II) then transforms into nitric acid trihydrate at 235 K via a peritectic reaction. The existence of the two forms is confirmed by Raman studies. Our infrared experiments on bulk samples are in good agreement with those reported in the literature leading to the conclusion that the NAD(I) studied here is also observed in polar-stratospheric-cloud (PSC) particles. In stratospheric conditions, NAD(II) probably cannot freeze in the PSC particles.

PACS Nos.: 64.70, 64.60, 61.10, 05.70
Segregation, transport, and interaction of climate proxies in polycrystalline ice
Authors: Rempel A W , Wettlaufer J S
Published: May 2003

The most detailed records of the Earth's climate during the past few hundred millennia are derived from ice cores retrieved from Greenland and Antarctica. The analyses of these records assume that the distributions of the trace constituents that are used as proxies for past climate have not significantly altered since deposition at the surface, and yet careful studies, at high spatial resolution, have identified core segments where appreciable post-depositional changes have occurred. To improve the reliability and resolution of paleoclimate interpretations, we have examined the mechanisms underlying the transport and interaction of climate proxies in polycrystalline ice, many of which are soluble impurities that are found principally in premelted liquid that lines the boundaries between ice grains. We find that the rate of post-depositional alteration depends critically on where the trace constituents reside; whether in the premelted liquid, in which case they exert a controlling influence on the total volume fraction of liquid that is present, or in the grains themselves. In the former case, the premelted liquid reservoir contains the principle conduits through which many of the impurities are transported and interact, and in the latter case, the temporal evolution of impurity concentration is both slower and more complex. We provide quantitative models that describe these processes and highlight the importance of impurity segregation for our understanding of past climates.

PACS Nos.: 66.30Jt, 91.60Ed, 92.40Sn, 92.40Vq, 92.70-j
Compressive strength of iceberg ice
Authors: Jones S J , Gagnon R E , Derradji A , Bugden A
Published: May 2003

The uniaxial compressive strength of iceberg ice was determined over a wide range of strain rates from 108 to 10+1 s1 at 10°C. It was found that for strain rates less than 104 s1, strength increased in a power-law manner with strain rate. Above 104 s1, the strength was essentially constant at 4 MPa, dropping slightly between 103 and 101 s1, before rising again to a value of about 10 MPa at 10+1 s1. Thin sections of the ice revealed a small grain size of about 3.5 mm and elongated air bubbles with a ratio of length to width of about 10. In the practical strain-rate range of interest, the maximum failure stress observed was 4.8 MPa.

PACS No.: 62.20
Point defects and electrical properties of ice
Authors: Whitworth R W
Published: May 2003

This paper is a brief summary of a review lecture in which the essential features of the standard theory of electrical properties of ice were described and attention was drawn to current problems concerning the nature of protonic point defects on which the theory is based.

PACS Nos.: 61.72Ji, 66.10Ed, 66.30Dn, 77.22
Strain and temperature dependence of crack populations in columnar-grain ice
Authors: Gold L W
Published: May 2003

It has been shown that the development of grain-boundary and transgranular crack populations in transverse isotropic columnar-grain ice by a uniaxial compressive stress is a random process. The lognormal distribution function was found to be a good descriptor of the strain dependence of the crack density and of the crack length. It is shown, in the present paper, that the populations are induced in the first 102 strain and within the time range for the anelastic strain. These time and strain limits, and the strain-rate, stress, temperature, and grain-size dependence of the characteristics of the crack populations, indicate a two-stage process involving the development of precursors and the formation of cracks. The increasing probability for the formation of grain-boundary cracks with increasing strain rate is consistent with a time-dependent growth of voids and an increase in the associated stress intensity factors. The increasing probability for the formation of transgranular cracks with decreasing stain rate is consistent with an increasing density of dislocations and grain distortion due to shear.

PACS Nos.: 62.20MK, 62.40-x
The magnetic properties of oxygen-hole aluminum centres in crystalline SiO2. VI: A stable AlO4/Li centre
Authors: Walsby C J , Lees N S , Claridge R FC , Weil J A
Published: May 2003

A new study, by electron paramagnetic resonance (EPR) spectroscopy at cryogenic temperatures, of aluminum oxygenic-hole centres in a α-quartz single crystal is reported. The well-known centre [AlO4]0 has been reinvestigated with somewhat improved techniques and computer analysis, confirming previous results in the literature. A previously unreported AlLi centre has now been well characterized by EPR. From the fitted parameter matrices g, A(27Al), P(27Al), A(7Li), and P(7Li) we have determined not only that the hole resides on a "long-bonded" oxygen anion, as in [AlO4]0, but have also established the position of the near-by interstitial lithium ion. One model for this centre is that it consists of a lithium atom Li0 linked to the diamagnetic centre [AlO4], yielding hole-bearing species [AlO4/Li] via internal charge transfer.

PACS Nos.: 7630Da, 7630Mi
Ice nucleation by kerosene soot under upper tropospheric conditions
Authors: Suzanne J , Ferry D , Popovitcheva O , Shonija N K
Published: May 2003

Quasi-elastic neutron scattering (QENS) and neutron diffraction (ND) experiments were conducted to characterize the dynamics and structure of water/ice confined in a well-defined kerosene-soot pores network at 40, 60, and 100% relative humidity and at temperatures from 283 to 204 K. The QENS spectra indicate that about 35% of the adsorbed water is in an amorphous solid-like state at T = 283 K and that an appreciable amount of liquid water exists in the soot supermicropores down to the lowest temperature investigated, i.e., 204 K. The depression in freezing temperature is related to the pore dimensions. At T [Formula: see text] 260 K ND shows a mixture of amorphous ice, probably located in the soot mesopores coexisting with ice Ih at the surface of the soot primary particles. The results are discussed within the context of aircraft-generated soot aerosols in the upper troposphere as candidates for heterogeneous ice nucleation responsible for contrails and cirrus formation.

PACS Nos.: 82.33Tb, 92.60Mt, 81.05Rm, 61.12-q
Measured temperature and pressure dependence of compressional (Vp) and shear (Vs) wave speeds in compacted, polycrystalline ice Ih
Authors: Helgerud M B , Waite W F , Kirby S H , Nur A
Published: May 2003

We report on laboratory measurements of compressional- and shear-wave speeds in a compacted, polycrystalline ice-Ih sample. The sample was made from triply distilled water that had been frozen into single crystal ice, ground into small grains, and sieved to extract the 180250 µm diameter fraction. Porosity was eliminated from the sample by compacting the granular ice between a hydraulically driven piston and a fixed end plug, both containing shear-wave transducers. Based on simultaneous compressional- and shear-wave-speed measurements, we calculated Poisson's ratio and compressional-wave, bulk, and shear moduli from 20 to 5°C and 22 to 33 MPa.

PACS Nos.: 91.60Lj
Iceice friction measurements, and water lubrication and adhesion-shear mechanisms
Authors: Maeno N , Arakawa M , Yasutome A , Mizukami N , Kanazawa S
Published: May 2003

The results of systematic measurements of iceice friction coefficients are summarized and the applicability of the two physical mechanisms of ice friction, namely, the water lubrication and the adhesion-shear deformation of ice, are discussed.

PACS Nos.: 68.35Np, 81.20Ev, 81.40Pq, 83.80Nb
Structural studies of gas hydrates
Authors: Klapproth A , Goreshnik E , Staykova D , Klein H , Kuhs W F
Published: May 2003

An overview of recent structural work focusing on the gas hydrates of methane and carbon dioxide is given. Both the crystal structure and the microstructure are considered. We report on the pressure-dependent molecular structure of methane clathrate hydrate using laboratory-made hydrogenous and deuterated samples investigated by neutron and hard-X-ray synchrotron diffraction experiments. The isothermal compressibilities are determined for hydrogenated and deuterated CH4 hydrate, and isotopic differences between both compounds are established for the first time. The cage filling of carbon dioxide and methane hydrate is determined and compared with predictions from statistical thermodynamic theory. In the case of small cages in methane hydrate, experimental results and predictions do not agree. Field-emission scanning electron microscopy reveals the meso- to macro-porous nature of gas hydrates formed with an excess of free gas. Furthermore, in situ measurements of the formation kinetics of porous hydrates are reported in which differences between methane and carbon dioxide are established quantitatively and the transient existence of a type II carbon dioxide structure is found.

PACS Nos.: 82.75-z, 61.10Nz, 61.12Ld, 68.37Hk
High-pressure Raman and Brillouin studies of single crystalline gas hydrates
Authors: Shimizu H
Published: May 2003

Methane hydrate (MH) and argon hydrate (AH) single crystals were synthesized in a diamond anvil cell to investigate their intrinsic high-pressure properties by visual observation and in situ Raman and Brillouin-scattering measurements. Single crystalline MH shows clearly two phase transitions at P =0.9 and 1.9 GPa in its crystalline shape and state under a microscope, and in the change in its Raman spectra of CH stretching vibrations of guest CH4 molecules. The first determination of the elastic properties in MH sI phase has revealed that MH is about 10% softer than the most common ice Ih, which is accounted for by MH's void-rich and open structures. For a single-crystal AH, we have observed two phase transitions from AH-I (sII) to AH-II at about P =0.65 GPa and from AH-II to AH-III at P =1.02 GPa. The breakdown of the cage structure in AH-III was confirmed by the disappearance of the OH stretching mode of host H2O lattices. The possibility of Ar double occupancy in the large cages of sII and higher pressure phases is investigated by the low-frequency Raman peak observed around 120 ~ 140 cm1 in view of recent MD calculations.

PACS Nos.: 62.30+d, 62.50+p, 62.65+k, 64.70-p, 78.30-j, 78.35+c
A sapphire cell for high-pressure, low-temperature neutron-scattering experiments on gas hydrates
Authors: Rondinone A J , Jones C Y , Marshall S L , Chakoumakos B C , Rawn C J , Lara-Curzio E
Published: May 2003

A single-crystal sapphire cell for performing neutron-scattering experiments on gas hydrates synthesized in situ was designed and fabricated to operate at pressures up to 350 bar (1 bar = 105 Pa) and temperatures between 10 and 300 K. The single-crystal cell is cut off-axis from the c-axis of sapphire to avoid Bragg diffraction in the scattering plane for the DebyeScherrer geometry. The cell is pressurized from a boosted pumping station via a small-diameter stainless-steel pipe. The cell is cylindrical with no external supports. The design of the cell allows the unobstructed detection of neutrons scattered from the sample. This requirement necessitated a departure from the predominant style of sapphire cells reported in the literature. Several iterations of design modifications and finite-element modeling were performed prior to building the prototype. The cell was tested hydrostatically at room temperature. Preliminary inelastic neutron scattering data are reported to verify the performance of the cell.

PACS No.: 61.12ex
The microstructural location of impurities in ice
Authors: Baker I , Cullen D , Iliescu D
Published: May 2003

The microstructural locations of impurities in natural ice have been of interest for over a century, but only in recent years have efforts been made to determine their location. Here, we outline the few measurements that have been performed. The focus is on a technique that we developed, which has also been subsequently used by others, that involves the controlled sublimation of uncoated ice in a low-vacuum scanning electron microscope. This process leaves behind concentrated impurities, in both the grain boundaries and the grain interiors, which are then identified using energy dispersive X-ray microanalysis. An overview of observations on meteoric ice from both Greenland and Antarctica; on accretion ice from Vostok Station, Antarctica; and on temperate pond and river ice is presented.

PACS No.: 61.72-y
Inelastic neutron scattering and molecular dynamics studies on low-frequency modes of clathrate hydrates
Authors: Itoh H , Chazallon B , Schober H , Kawamura K , Kuhs W F
Published: May 2003

Low-frequency modes of gas hydrates with Xe, Ar, O2, and N2 atoms/molecules have been studied by inelastic neutron-scattering and molecular dynamics simulations. Type I and type II clathrate hydrates show some small but significant differences of the low-frequency host contribution to the density of states. Both differ markedly from that of ice Ih and depend only weakly on the guest. The vibrational modes associated with Xe atoms were observed at 2.2, 2.9, and 4.0 meV (T = 100 K). They are in good agreement with predictions from molecular dynamics simulations. In the case of N2 hydrate we found a well-defined peak at about 2 meV, which shows a remarkable shift to higher frequency with increasing temperature. This peak and a broad peak that is overlapped with the host lattice modes (6.5 and 10.5 meV) are assigned to the vibration of N2 molecules in the large and small cages, respectively. The calculated vibrational spectra of N2 molecules in doubly occupied large cages show a significant distinct spectral distribution. The anharmonic shift of the guest atoms in large cages is significantly less pronounced in Xe hydrates suggesting that guest-host interactions can vary considerably from one system to another.

PACS Nos.: 82.75-z, 78.70N, 71.15Pd, 63
Coexistence of structure I and II hydrates formed from a mixture of methane and ethane gases
Authors: Takeya S , Kamata Y , Uchida T , Nagao J , Ebinuma T , Narita H , Hori A , Hondoh T
Published: May 2003

X-ray diffraction measurements were conducted to determine the hydrate structures formed from a mixture of CH4 and C2H6 gases at 263 K. With increasing initial fractions of C2H6 in the gas, the crystal structures of the hydrate were structure I, structure I + structure II, structure II, structure I + structure II, and structure I. In situ observations of the growth processes of the mixed gas hydrates under constant gas concentration suggest that the coexistence of structure I and structure II hydrate were caused by occurrences of metastable hydrate structure.

PACS No.: 82.75Fq