bluuebunny/crossref_metadata_2025 huggingface dataset:
The R1 Conjugative Plasmid Increases
Escherichia coli
Biofilm Formation through an Envelope Stress Response
Authors: Yang Xiaole , Ma Qun , Wood Thomas K.
Published: March 2008

Differential gene expression in biofilm cells suggests that adding the derepressed conjugative plasmid R1
drd
19 increases biofilm formation by affecting genes related to envelope stress (
rseA
and
cpxAR
), biofilm formation (
bssR
and
cstA
), energy production (
glpDFK
), acid resistance (
gadABCEX
and
hdeABD
), and cell motility (
csgBEFG, yehCD, yadC
, and
yfcV
); genes encoding outer membrane proteins (
ompACF
), phage shock proteins (
pspABCDE
), and cold shock proteins (
cspACDEG
); and phage-related genes. To investigate the link between the identified genes and biofilm formation upon the addition of R1
drd
19, 40 isogenic mutants were classified according to their different biofilm formation phenotypes. Cells with class I mutations (those in
rseA, bssR, cpxA
, and
ompA
) exhibited no difference from the wild-type strain in biofilm formation and no increase in biofilm formation upon the addition of R1
drd
19. Cells with class II mutations (those in
gatC, yagI, ompC, cspA, pspD, pspB, ymgB, gadC, pspC, ymgA, slp, cpxP, cpxR, cstA, rseC, ompF
, and
yqjD
) displayed increased biofilm formation compared to the wild-type strain but decreased biofilm formation upon the addition of R1
drd
19. Class III mutants showed increased biofilm formation compared to the wild-type strain and increased biofilm formation upon the addition of R1
drd
19. Cells with class IV mutations displayed increased biofilm formation compared to the wild-type strain but little difference upon the addition of R1
drd
19, and class V mutants exhibited no difference from the wild-type strain but increased biofilm formation upon the addition of R1
drd
19. Therefore, proteins encoded by the genes corresponding to the class I mutant phenotype are involved in R1
drd
19-promoted biofilm formation, primarily through their impact on cell motility. We hypothesize that the pili formed upon the addition of the conjugative plasmid disrupt the membrane (induce
ompA
) and activate the two-component system CpxAR as well as the other envelope stress response system, RseA-σ
E
, both of which, along with BssR, play a key role in bacterial biofilm formation.
Impact of Vacuum Cooling onEscherichia coliO157:H7 Infiltration into Lettuce Tissue
Authors: Li Haiping , Tajkarimi Mehrdad , Osburn Bennie I.
Published: March 2008

Vacuum cooling is a common practice in the California leafy green industry. This study addressed the impact of vacuum cooling on the infiltration ofEscherichia coliO157:H7 into lettuce as part of the risk assessment responding to theE. coliO157:H7 outbreaks associated with leafy green produce from California. Vacuum cooling significantly increased the infiltration ofE. coliO157:H7 into the lettuce tissue (2.65E+06 CFU/g) compared to the nonvacuumed condition (1.98E+05 CFU/g). A stringent surface sterilization and quadruple washing could not eliminate the internalized bacteria from lettuce. It appeared that vacuuming forcibly changed the structure of lettuce tissue such as the stomata, suggesting a possible mechanism ofE. coliO157:H7 internalization. Vacuuming also caused a lower reduction rate ofE. coliO157:H7 in stored lettuce leaves than that for the nonvacuumed condition.
Randomly Amplified Polymorphic DNA PCR as a Tool for Assessment of Marine Viral Richness
Authors: Winget Danielle M. , Wommack K. Eric
Published: March 2008

Recent discoveries have uncovered considerable genetic diversity among aquatic viruses and raised questions about the variability of this diversity within and between environments. Studies of the temporal and spatial dynamics of aquatic viral assemblages have been hindered by the lack of a common genetic marker among viruses for rapid diversity assessments. Randomly amplified polymorphic DNA (RAPD) PCR bypasses this obstacle by sampling at the genetic level without requiring viral isolation or previous sequence knowledge. In this study, the utility of RAPD-PCR for assessing DNA viral richness within Chesapeake Bay water samples was evaluated. RAPD-PCR using single 10-mer oligonucleotide primers successfully produced amplicons from a variety of viral samples, and banding patterns were highly reproducible, indicating that each band likely represents a single amplicon originating from viral template DNA. In agreement with observations from other community profiling techniques, resulting RAPD-PCR banding patterns revealed more temporal than spatial variability in Chesapeake Bay virioplankton assemblages. High-quality hybridization probes and sequence information were also easily generated from single RAPD-PCR products or whole reactions. Thus, the RAPD-PCR technique appears to be practical and efficient for routine use in high-resolution viral diversity studies by providing assemblage comparisons through fingerprinting, probing, or sequence information.
Isolation and Identification of Rhizoxin Analogs from
Pseudomonas fluorescens
Pf-5 by Using a Genomic Mining Strategy
Authors: Loper Joyce E. , Henkels Marcella D. , Shaffer Brenda T. , Valeriote Frederick A. , Gross Harald
Published: March 2008

The products synthesized from a hybrid polyketide synthase/nonribosomal peptide synthetase gene cluster in the genome of
Pseudomonas fluorescens
Pf-5 were identified using a genomics-guided strategy involving insertional mutagenesis and subsequent metabolite profiling. Five analogs of rhizoxin, a 16-member macrolide with antifungal, phytotoxic, and antitumor activities, were produced by Pf-5, but not by a mutant with an insertion in the gene cluster. The five rhizoxin analogs, one of which had not been described previously, were differentially toxic to two agriculturally important plant pathogens,
Botrytis cinerea
and
Phytophthora ramorum
. The rhizoxin analogs also caused swelling of rice roots, a symptom characteristic of rhizoxin itself, but were less toxic to pea and cucumber roots. Of the rhizoxin analogs produced by Pf-5, the predominant compound, WF-1360 F, and the newly described compound 22
Z
-WF-1360 F were most toxic against the two plant pathogens and three plant species. These rhizoxin analogs were tested against a panel of human cancer lines, and they exhibited potent but nonselective cytotoxicity. This study highlights the value of the genomic sequence of the soil bacterium
P. fluorescens
Pf-5 in providing leads for the discovery of novel metabolites with significant biological properties.
Identification of Differentially Regulated
Francisella tularensis
Genes by Use of a Newly Developed Tn
5
-Based Transposon Delivery System
Authors: Buchan Blake W. , McLendon Molly K. , Jones Bradley D.
Published: March 2008

Francisella tularensis
is the etiologic agent of an intracellular systemic infection of the lymphatic system in humans called tularemia. The organism has become the subject of considerable research interest due to its classification as a category A select agent by the CDC. To aid genetic analysis of this pathogen, we have constructed a temperature-sensitive Tn
5
-based transposon delivery system that is capable of generating chromosomal reporter fusions with
lacZ
or
luxCDABE
, enabling us to monitor gene expression. Transposition is catalyzed by the hyperactive Tn
5
transposase, whose expression is driven by the
Francisella groES
promoter. When high-temperature selection (42°C) is applied to a bacterial culture carrying the transposon delivery plasmid, ∼0.1% of the population is recovered with Tn
5
insertions in the chromosome. Nucleotide sequence analysis of a sample of mutants revealed that the insertions occur randomly throughout the chromosome. The kanamycin-selectable marker of the transposon is also flanked by FLP recombination target sequences that allow deletion of the antibiotic resistance gene when desired. This system has been used to generate transposon mutant libraries for the
F. tularensis
live vaccine strain as well as two different virulent
F. tularensis
strains. Chromosomal reporters delivered with the transposon were used to identify genes upregulated by growth in Chamberlain's defined medium. Genes in the
fsl
operon, reported to be involved in iron acquisition, as well as genes in the
igl
gene cluster were among those identified by the screen. Further experiments implicate the ferric uptake regulator (Fur) protein in the negative regulation of
fsl
but not
igl
reporters, which occurs in an iron-dependent manner. Our results indicate that we have created a valuable new transposon that can be used to identify and characterize virulence genes in
F. tularensis
strains.
MADS-Box Transcription Factor Mig1 Is Required for Infectious Growth in
Magnaporthe grisea
Authors: Mehrabi Rahim , Ding Shengli , Xu Jin-Rong
Published: March 2008

Magnaporthe grisea
is a model fungus for studying fungus-plant interactions. Two mitogen-activated protein (MAP) kinase genes,
PMK1
and
MPS1
, have been implicated in regulating plant infection processes in
M. grisea
. However, transcription factors activated by these MAP kinases are not well studied. In this study we functionally characterized the
MIG1
gene that encodes a MADS-box transcription factor homologous to
Saccharomyces cerevisiae
Rlm1. In yeast two-hybrid assays,
MIG1
interacts with
MPS1
, suggesting that
MIG1
may function downstream from the
MPS1
pathway. The
mig1
deletion mutant had a normal growth rate and formed melanized appressoria, but it was nonpathogenic and failed to infect rice leaves through wounds. Appressoria formed by the
mig1
mutant developed penetration pegs and primary infectious hyphae, but further differentiation of the secondary infectious hyphae inside live plant cells was blocked. However, the
mig1
mutant formed infectious hypha-like structures in heat-killed plant cells or cellophane membranes. In transformants expressing the
MIG1
-
GFP
fusion, green fluorescent protein (GFP) signals were not detectable in vegetative hyphae and conidiophores. Mig1-GFP was localized to nuclei in conidia, appressoria, and infectious hyphae. Deletion of the MADS box had no effect on the expression and localization of the
MIG1-GFP
fusion but eliminated its ability to complement the
mig1
mutant. These results suggest that
MIG1
may be required for overcoming plant defense responses and the differentiation of secondary infectious hyphae in live plant cells. The MADS-box domain is essential for the function of
MIG1
but dispensable for its nuclear localization, which may be associated with the activation of
MIG1
by
MPS1
during conidiation and plant infection.
Schizosaccharomyces pombe
Hst4 Functions in DNA Damage Response by Regulating Histone H3 K56 Acetylation
Authors: Haldar Devyani , Kamakaka Rohinton T.
Published: March 2008

The packaging of eukaryotic DNA into chromatin is likely to be crucial for the maintenance of genomic integrity. Histone acetylation and deacetylation, which alter chromatin accessibility, have been implicated in DNA damage tolerance. Here we show that
Schizosaccharomyces pombe
Hst4, a homolog of histone deacetylase Sir2, participates in S-phase-specific DNA damage tolerance. Hst4 was essential for the survival of cells exposed to the genotoxic agent methyl methanesulfonate (MMS) as well as for cells lacking components of the DNA damage checkpoint pathway. It was required for the deacetylation of histone H3 core domain residue lysine 56, since a strain with a point mutation of its catalytic domain was unable to deacetylate this residue in vivo. Hst4 regulated the acetylation of H3 K56 and was itself cell cycle regulated. We also show that MMS treatment resulted in increased acetylation of histone H3 lysine 56 in wild-type cells and
hst4
Δ mutants had constitutively elevated levels of histone H3 K56 acetylation. Interestingly, the level of expression of Hst4 decreased upon MMS treatment, suggesting that the cell regulates access to the site of DNA damage by changing the level of this protein. Furthermore, we find that the phenotypes of both K56Q and K56R mutants of histone H3 were similar to those of
hst4
Δ mutants, suggesting that proper regulation of histone acetylation is important for DNA integrity. We propose that Hst4 is a deacetylase involved in the restoration of chromatin structure following the S phase of cell cycle and DNA damage response.
Ultrastructural Characterization of the Prokaryotic Symbiosis in “Chlorochromatium aggregatum”
Authors: Wanner Gerhard , Vogl Kajetan , Overmann Jörg
Published: March 2008

The phototrophic consortium “Chlorochromatium aggregatum” currently represents the most highly developed interspecific association of bacteria and consists of green sulfur bacteria, so-called epibionts, surrounding a central, motile, chemotrophic bacterium. In order to identify subcellular structures characteristic of this symbiosis, consortia were studied by a combination of high-resolution analytical scanning electron microscopy, transmission electron microscopy, and three-dimensional reconstruction and image analyses. Epibionts are interconnected and to a lesser extent are also connected with the central bacterium, by electron-dense, hair-like filaments. In addition, numerous periplasmic tubules extend from the outer membrane of the central bacterium and are in direct contact with the outer membrane of the epibionts. In each epibiont cell, the attachment site to the central bacterium is characterized by the absence of chlorosomes and an additional 17-nm-thick layer (epibiont contact layer [ECL]) attached to the inner side of the cytoplasmic membrane. The ECL is only occasionally observed in pure cultures of the epibiont, where it occurs in about 10 to 20% of the free-living cells. A striking feature of the central bacterium is the presence of one or two hexagonally packed flat crystals (central bacterium crystal [CBC]) per cell. The CBC reaches 1 μm in length, is 35 nm thick, and consists of bilayers of subunits with a spacing of 9 nm. A detailed model for consortia is presented, summarizing our conclusions regarding (i) cohesion of the cells, (ii) common periplasmic space between the central bacterium and the epibiont, (iii) ECL as a symbiosis-specific structure, and (iv) formation of the interior paracrystalline structures, central bacterium membrane layer, and CBC.
Evidence that AphB, Essential for the Virulence of
Vibrio vulnificus
, Is a Global Regulator
Authors: Jeong Hee Gon , Choi Sang Ho
Published: March 2008

The
Vibrio vulnificus aphB
mutant was significantly less virulent than the wild type and was impaired in motility and adherence to host cells. Microarray analysis revealed that AphB of
V. vulnificus
(AphB

Vv

) influences the expression of over 10% of the
V. vulnificus
genome. The combined results indicated that AphB

Vv

is a global regulator contributing to the pathogenesis of
V. vulnificus
.
Fine-Tuning of Galactoglucan Biosynthesis in
Sinorhizobium meliloti
by Differential WggR (ExpG)-, PhoB-, and MucR-Dependent Regulation of Two Promoters
Authors: Bahlawane Christelle , Baumgarth Birgit , Serrania Javier , Rüberg Silvia , Becker Anke
Published: March 2008

Depending on the phosphate concentration encountered in the environment
Sinorhizobium meliloti
2011 synthesizes two different exopolysaccharides (EPS). Galactoglucan (EPS II) is produced under phosphate starvation but also in the presence of extra copies of the transcriptional regulator WggR (ExpG) or as a consequence of a mutation in
mucR
. The galactoglucan biosynthesis gene cluster contains the operons
wga
(
expA
),
wge
(
expE
),
wgd
(
expD
), and
wggR
(
expG
). Two promoters, differentially controlled by WggR, PhoB, and MucR, were identified upstream of each of these operons. The proximal promoters of the
wga
,
wge
, and
wgd
transcription units were constitutively active when separated from the upstream regulatory sequences. Promoter activity studies and the positions of predicted PhoB and WggR binding sites suggested that the proximal promoters are cooperatively induced by PhoB and WggR. MucR was shown to strongly inhibit the distal promoters and bound to the DNA in the vicinity of the distal transcription start sites. An additional inhibitory effect on the distal promoter of the structural galactoglucan biosynthesis genes was identified as a new feature of WggR in a
mucR
mutant. A regulatory model of the fine-tuning of galactoglucan production is proposed.
Opine-BasedAgrobacteriumCompetitiveness: Dual Expression Control of the Agrocinopine Catabolism (acc) Operon by Agrocinopines and Phosphate Levels
Authors: Kim H. Stanley , Yi Hyojeong , Myung Jaehee , Piper Kevin R. , Farrand Stephen K.
Published: March 2008

Agrobacterium tumefaciensstrain C58 can transform plant cells to produce and secrete the sugar-phosphate conjugate opines agrocinopines A and B. The bacterium then moves in response to the opines and utilizes them as exclusive sources of carbon, energy, and phosphate via the functions encoded by theaccoperon. These privileged opine-involved activities contribute to the formation of agrobacterial niches in the environment. We found that the expression of theaccoperon is induced by agrocinopines and also by limitation of phosphate. The main promoter is present in front of the first gene,accR, which codes for a repressor. This operon structure enables efficient repression when opine levels are low. The promoter contains two putative operators, one overlapping the −10 sequence and the other in the further upstream from it; two partly overlapped putativephoboxes between the two operators; and two consecutive transcription start sites. DNA fragments containing either of the operators bound purified repressor AccR in the absence of agrocinopines but not in the presence of the opines, demonstrating the on-off switch of the promoter. Induction of theaccoperon can occur under low-phosphate conditions in the absence of agrocinopines and further increases when the opines also are present. Such opine-phosphate dual regulatory system of the operon may ensure maximum utilization of agrocinopines when available and thereby increase the chances of agrobacterial survival in the highly competitive environment with limited general food sources.
Cold Shock Exoribonuclease R (VacB) Is Involved in
Aeromonas hydrophila
Pathogenesis
Authors: Erova Tatiana E. , Kosykh Valeri G. , Fadl Amin A. , Sha Jian , Horneman Amy J. , Chopra Ashok K.
Published: March 2008

In this study, we cloned and sequenced a virulence-associated gene (
vacB
) from a clinical isolate SSU of
Aeromonas
hydrophila
. We identified this gene based on our recently annotated genome sequence of the environmental isolate ATCC 7966
T
of
A. hydrophila
and the
vacB
gene of
Shigella flexneri
. The
A. hydrophila
VacB protein contained 798 amino acid residues, had a molecular mass of 90.5 kDa, and exhibited an exoribonuclease (RNase R) activity. The RNase R of
A. hydrophila
was a cold-shock protein and was required for bacterial growth at low temperature. The
vacB
isogenic mutant, which we developed by homologous recombination using marker exchange mutagenesis, was unable to grow at 4°C. In contrast, the wild-type (WT)
A. hydrophila
exhibited significant growth at this low temperature. Importantly, the
vacB
mutant was not defective in growth at 37°C. The
vacB
mutant also exhibited reduced motility, and these growth and motility phenotype defects were restored after complementation of the
vacB
mutant. The
A. hydrophila
RNase R-lacking strain was found to be less virulent in a mouse lethality model (70% survival) when given by the intraperitoneal route at as two 50% lethal doses (LD
50
). On the other hand, the WT and complemented strains of
A. hydrophila
caused 80 to 90% of the mice to succumb to infection at the same LD
50
dose. Overall, this is the first report demonstrating the role of RNase R in modulating the expression of
A. hydrophila
virulence.
Catalytic Mechanism of Cyclic Di-GMP-Specific Phosphodiesterase: a Study of the EAL Domain-Containing RocR fromPseudomonas aeruginosa
Authors: Rao Feng , Yang Ye , Qi Yaning , Liang Zhao-Xun
Published: March 2008

EAL domain proteins are the major phosphodiesterases for maintaining the cellular concentration of second-messenger cyclic di-GMP in bacteria. Given the pivotal roles of EAL domains in the regulation of many bacterial behaviors, the elucidation of their catalytic and regulatory mechanisms would contribute to the effort of deciphering the cyclic di-GMP signaling network. Here, we present data to show that RocR, an EAL domain protein that regulates the expression of virulence genes and biofilm formation inPseudomonas aeruginosaPAO-1, catalyzes the hydrolysis of cyclic di-GMP by using a general base-catalyzed mechanism with the assistance of Mg2+ion. In addition to the five essential residues involved in Mg2+binding, we propose that the essential residue E352functions as a general base catalyst assisting the deprotonation of Mg2+-coordinated water to generate the nucleophilic hydroxide ion. The mutation of other conserved residues caused various degree of changes in thekcatorKm, leading us to propose their roles in residue positioning and substrate binding. With functions assigned to the conserved groups in the active site, we discuss the molecular basis for the lack of activity of some characterized EAL domain proteins and the possibility of predicting the phosphodiesterase activities for the vast number of EAL domains in bacterial genomes in light of the catalytic mechanism.
Mutations in
pimE
Restore Lipoarabinomannan Synthesis and Growth in a
Mycobacterium smegmatis lpqW
Mutant
Authors: Crellin Paul K. , Kovacevic Svetozar , Martin Kirstee L. , Brammananth Rajini , Morita Yasu S. , Billman-Jacobe Helen , McConville Malcolm J. , Coppel Ross L.
Published: March 2008

Lipoarabinomannans (LAMs) and phosphatidylinositol mannosides (PIMs) are abundant glycolipids in the cell walls of all corynebacteria and mycobacteria, including the devastating human pathogen
Mycobacterium tuberculosis
. We have recently shown that
M. smegmatis
mutants of the lipoprotein-encoding
lpqW
gene have a profound defect in LAM biosynthesis. When these mutants are cultured in complex medium, spontaneous bypass mutants consistently evolve in which LAM biosynthesis is restored at the expense of polar PIM synthesis. Here we show that restoration of LAM biosynthesis in the
lpqW
mutant results from secondary mutations in the
pimE
gene. PimE is a mannosyltransferase involved in converting AcPIM4, a proposed branch point intermediate in the PIM and LAM biosynthetic pathways, to more polar PIMs. Mutations in
pimE
arose due to insertion of the mobile genetic element ISMsm1 and independent point mutations that were clustered in predicted extracytoplasmic loops of this polytopic membrane protein. Our findings provide the first strong evidence that LpqW is required to channel intermediates such as AcPIM4 into LAM synthesis and that loss of PimE function results in the accumulation of AcPIM4, bypassing the need for LpqW. These data highlight new mechanisms regulating the biosynthetic pathways of these essential cell wall components.
Stabilization of pSW100 fromPantoea stewartiiby the F Conjugation System
Authors: Lin Mei-Hui , Liu Shih-Tung
Published: March 2008

Plasmid pSW100 is 1 of the 13 plasmids fromPantoea stewartiisubsp.stewartiiSW2 which has a replicon that resembles that of ColE1. This work uses a pSW100 derivative, pSW140K, to study how the pSW100 replicon is stably maintained in its hosts. Our results indicate that although pSW140K is stable inEscherichia coliHB101, the plasmid is rapidly lost in anotherE. colistrain, DH5α, indicating that the genetic background of anE. colistrain affects the stability of pSW140K. Mutagenesis ofE. coliHB101 with EZ::TN  revealed that mutations intraC,traF,traG,traN, andtraV, which encode the components of the sex pilus assembly, reduce plasmid stability. Furthermore, this work identified that a 38-bp region located immediately upstream of the RNAII promoter is critical to the maintenance of plasmid stability inE. coliHB101. TraC binds to the region, and in addition, deleting the region destabilizes the plasmid. Furthermore, inserting this 38-bp fragment into a plasmid that contains the minimal replicon from pSW200 stabilizes the plasmid inE. coliHB101. Fluorescence in situ hybridization and immunofluorescence staining also revealed that derivatives of pSW100, pSW128A, and TraC are colocalized in cells, suggesting that pSW100 may use the sex pilus assembly as a partition apparatus to ensure the even distribution of the plasmid during cell division, which may thus maintain the plasmid's stability.
Proteins Found in a CikA Interaction Assay Link the Circadian Clock, Metabolism, and Cell Division in
Synechococcus elongatus
Authors: Mackey Shannon R. , Choi Jong-Soon , Kitayama Yohko , Iwasaki Hideo , Dong Guogang , Golden Susan S.
Published: March 2008

Diverse organisms time their cellular activities to occur at distinct phases of Earth's solar day, not through the direct regulation of these processes by light and darkness but rather through the use of an internal biological (circadian) clock that is synchronized with the external cycle. Input pathways serve as mechanisms to transduce external cues to a circadian oscillator to maintain synchrony between this internal oscillation and the environment. The circadian input pathway in the cyanobacterium
Synechococcus elongatus
PCC 7942 requires the kinase CikA. A
cikA
null mutant exhibits a short circadian period, the inability to reset its clock in response to pulses of darkness, and a defect in cell division. Although CikA is copurified with the Kai proteins that constitute the circadian central oscillator, no direct interaction between CikA and either KaiA, KaiB, or KaiC has been demonstrated. Here, we identify four proteins that may help connect CikA with the oscillator. Phenotypic analyses of null and overexpression alleles demonstrate that these proteins are involved in at least one of the functions—circadian period regulation, phase resetting, and cell division—attributed to CikA. Predictions based on sequence similarity suggest that these proteins function through protein phosphorylation, iron-sulfur cluster biosynthesis, and redox regulation. Collectively, these results suggest a model for circadian input that incorporates proteins that link the circadian clock, metabolism, and cell division.
Concerted Action of Lactate Oxidase and Pyruvate Oxidase in Aerobic Growth of
Streptococcus pneumoniae
: Role of Lactate as an Energy Source
Authors: Taniai Hiroaki , Iida Ken-ichiro , Seki Masanori , Saito Mitsumasa , Shiota Susumu , Nakayama Hiroaki , Yoshida Shin-ichi
Published: March 2008

Streptococcus pneumoniae
was shown to possess lactate oxidase in addition to well-documented pyruvate oxidase. The activities of both H
2
O
2
-forming oxidases in wild-type cultures were detectable even in the early exponential phase of growth and attained the highest levels in the early stationary phase. For each of these oxidases, a defective mutant was constructed and compared to the parent regarding the dynamics of pyruvate and lactate in aerobic cultures. The results obtained indicated that the energy-yielding metabolism in the wild type could be best described by the following scheme. (i) As long as glucose is available, approximately one-fourth of the pyruvate formed is converted to acetate by the sequential action of pyruvate oxidase and acetate kinase with acquisition of additional ATP; (ii) the rest of the pyruvate is reduced by lactate dehydrogenase to form lactate, with partial achievement of redox balance; (iii) the lactate is oxidized by lactate oxidase back to pyruvate, which is converted to acetate as described above; and (iv) the sequential reactions mentioned above continue to occur as long as lactate is present. As predicted by this model, exogenously added lactate was shown to increase the final growth yield in the presence of both oxidases.
The Virulence Regulator Sae ofStaphylococcus aureus:Promoter Activities and Response to Phagocytosis-Related Signals
Authors: Geiger Tobias , Goerke Christiane , Mainiero Markus , Kraus Dirk , Wolz Christiane
Published: March 2008

The two-component system SaeRS ofStaphylococcus aureusis closely involved in the regulation of major virulence factors. However, little is known about the signals leading tosaeRSactivation. A total of four overlapping transcripts (T1 to T4) from three different transcription starting points are expressed in thesaeoperon. We used a β-galactosidase reporter assay to characterize the putative promoter regions within thesaeRSupstream region. The main transcript T2 is probably generated by endoribonucleolytic processing of the T1 transcript. Only two distinct promoter elements (P1 and P3) could be detected within thesaeRSupstream region. The P3 promoter, upstream ofsaeRS, generates the T3 transcript, includes acis-acting enhancer element and is repressed bysaeRS. The most distal P1 promoter is strongly autoregulated, activated byagr, and repressed by sigma factor B. In strain Newman a mutation within the histidine kinase SaeS leads to a constitutively activatedsaesystem. Evaluation of different external signals revealed that the P1 promoter in strain ISP479R and strain UAMS-1 is inhibited by low pH and high NaCl concentrations but activated by hydrogen peroxide. The most prominent induction of P1 was observed at subinhibitory concentrations of α-defensins in variousS. aureusstrains, with the exception of strain ISP479R and strain COL. P1 was not activated by the antimicrobial peptides LL37 and daptomycin. In summary, the results indicate that the sensor molecule SaeS is activated by alteration within the membrane allowing the pathogen to react to phagocytosis related effector molecules.
Regulation of theBacillus subtilis yciCGene and Insights into the DNA-Binding Specificity of the Zinc-Sensing Metalloregulator Zur
Authors: Gabriel Scott E. , Miyagi Faith , Gaballa Ahmed , Helmann John D.
Published: March 2008

TheBacillus subtilisZur protein regulates zinc homeostasis by repressing at least 10 genes in response to zinc sufficiency. One of these genes,yciC, encodes an abundant protein postulated to function as a metallochaperone. Here, we used a genetic approach to identify thecis-acting elements andtrans-acting factors contributing to the tight repression ofyciC. Initial studies led to the identification of onlytrans-acting mutations, and, when the selection was repeated using a transposon library, all recovered mutants contained insertionally inactivatedzur. Using azurmerodiploid strain, we obtained twocis-acting mutations that contained large deletions in theyciCregulatory region. We demonstrate that theyciCregulatory region contains two functional Zur boxes: a primary site (C2) overlapping a σApromoter ∼200 bp upstream ofyciCand a second site near the translational start point (C1). Zur binds to both of these sites to mediate strong, zinc-dependent repression ofyciC. Deletion studies indicate that either Zur box is sufficient for repression, although repression by Zur bound to C2 is more efficient. Binding studies demonstrate that both sites bind Zur with high affinity. Sequence alignment of these and previously described Zur boxes suggest that Zur recognizes a more extended operator than other Fur family members. We used synthetic oligonucleotides to identify bases critical for DNA binding by Zur. Unlike Fur and PerR, which bind efficiently to sequences containing a core 7-1-7 repeat element, Zur requires a 9-1-9 inverted repeat for high-affinity binding.
The GTPase CpgA Is Implicated in the Deposition of the Peptidoglycan Sacculus in
Bacillus subtilis
Authors: Absalon Cédric , Hamze Kassem , Blanot Didier , Frehel Claude , Carballido-Lopez Rut , Holland Barry I. , van Heijenoort Jean , Séror Simone J.
Published: March 2008

Depletion of the
Bacillus subtilis
GTPase CpgA produces abnormal cell shapes, nonuniform deposition of cell wall, and five- to sixfold accumulation of peptidoglycan precursors. Nevertheless, the inherent structure of the cell wall appeared mostly unchanged. The results are consistent with CpgA being involved in coordinating normal peptidoglycan deposition.
Four weeks’ corticosteroid inhalation does not augment maximal power output in endurance athletes
Authors: Kuipers H , Hullenaar G A C Van’t , Pluim B M , Overbeek S E , De Hon O , Van Breda E J , Van Loon L C
Published: March 2008

Objective:

To assess possible ergogenic properties of corticosteroid administration.

Design:

A balanced, double-blind, placebo-controlled design was used.

Participants:

28 well-trained cyclists and rowers.

Intervention:

4 weeks’ daily inhalation of 800 μg budesonide or placebo.

Main outcome measurements:

The subjects performed three incremental cycle ergometer tests until exhaustion, before and after 2 and 4 weeks of placebo or budesonide administration, to measure maximal power output (Wmax). Once a week they filled in a profile of mood state (POMS) questionnaire.

Results:

There was no significant difference in Wmaxbetween the placebo (376 (SD 25) W) and the corticosteroid group (375 (36) W) during the preintervention test, and there were no significant changes in either group after 2 and 4 weeks of intervention. No effect of the intervention on mood state was found.

Conclusion:

4 weeks of corticosteroid or placebo inhalation in healthy, well-trained athletes did not affect maximal power output or mood state. Hence no ergogenic properties of 4 weeks’ corticosteroid administration could be demonstrated, which corroborates previous studies of short-term corticosteroid administration.
Septic arthritis in a native joint due toAnaerococcus prevotii
Authors: Jain S , Bui V , Spencer C , Yee L
Published: March 2008

A 37-year-old injecting drug user presented with signs and symptoms of septic arthritis.Staphylococcus aureuswas grown from his blood cultures. Despite treatment with flucloxacillin and fusidic acid his condition continued to deteriorate. Echocardiography showed no signs of endocarditis. Culture of his knee aspirate grewAnaerococcus prevotiiafter 5 days of incubation. Metronidazole was added to his treatment regime. A collection of pus (800 ml) was drained from the right thigh andA prevotiiwas isolated. His condition improved gradually and he was subsequently transferred to a drug rehabilitation unit after completing his antibiotic course. The importance of anaerobic streptococci in septic arthritis, as a very rare cause, is highlighted.
Amelogenin positive cells scattered in the interstitial component of odontogenic fibromas
Authors: Kabasawa Y , Nagumo K , Takeda Y , Kawashima N , Okada N , Omura K , Yamaguchi A , Katsube K
Published: March 2008

Background:

Odontogenic tumours are often biphasic, consisting of epithelial and interstitial components, with an origin that is not well understood. Odontogenic fibromas are rich in mesenchymal component, but also have many epithelial nests.

Aims:

To investigate the origin of this tumour by immunohistochemistry.

Methods:

The expression of several odontogenic and epithelial markers, including amelogenin, was investigated by immunofluorescent studies.

Results:

Immunohistochemical analysis showed that epithelial nests exhibited E-cadherin expression, but not amelogenin. Amelogenin positive cells were scattered in the fibrous tissue, which did not exhibit epithelial marker expression except for epithelial membrane antigen. In one case that had received a test biopsy before whole resection of tumour, amelogenin positive cells were distributed in the regenerating mucosal epithelium or subepithelial tissue.

Conclusions:

Results indicate that amelogenin positive cells of odontogenic fibromas have an epithelial origin and may have the potential for epithelial mesenchymal transition, which has not to date been investigated in benign tumours.
The distribution of Saxifraga ferruginea and the problem of refugia in northwestern North America
Authors: Randhawa A. S. , Beamish Katherine I.
Published: March 2008

Saxifraga ferruginea ranges over that part of northwestern North America which was glaciated in late Pleistocene time. A survey of chromosome numbers within the species places diploids south of the ice margin and, in a few locations, inside the margin. Elsewhere only polyploids have been found. The distribution of diploids and polyploids supports the reality of refugia on Kodiak Island and the Queen Charlotte Islands.It is proposed that polyploids evolved either before or during recession of the ice and that they rather than the diploids were the colonizers of the newly open disturbed terrain.
The fine structure of two rust fungi, Puccinia helianthi and Melampsora lini
Authors: Coffey Michael D. , Palevitz Barry A. , Allen Paul J.
Published: March 2008

The parasitic phase of the uredial stage of rust fungus infection is characterized by the formation of a specialized structure—the haustorium. The haustorial neck contains a band of darkly staining wall material, the length of which is dependent on the fungal species. In older infected tissues a collar sometimes develops at the site of penetration. In such cells, the host plasmalemma appears to double back on itself between the collar and the haustorial neck. The mitochondria of the haustorium contain many plate-like cristae and, less frequently, concentric whorls of membranes. Cytoplasmic microtubules are also observed in both the neck and body of the haustorium. Centriolar plaques are found appressed to the nuclear envelopes in both the hyphae and haustoria. They frequently consist of two amorphous regions which are connected by a rod-shaped, layered structure. The septal pore of the intercellular hyphae contains a plug of electron-transparent material. Surrounding it is a matrix of dense amorphous cytoplasm devoid of organelles which is bordered by a hemispherical array of microbodies containing crystals. Axenic cultures of Melampsora lini mycelium were examined and found to contain similar septal pore regions. These cultures also show some differences from the parasitic hyphae. The septa-associated microbodies in these cells appear to derive from an aggregate of tubular endoplasmic reticulum cisternae. Their mitochondria differ from those of the intercellular hyphae in having more and longer, plate-like cristae and a denser staining matrix. They therefore represent a type intermediate between those of the intercellular hyphae and the haustoria. The pseudoparenchymatous stroma of the axenic cultures contains cells of widely divergent ages. Some are young as determined by their dense cytoplasmic contents and large lobed nuclei. However, others are older, with large vacuoles and many lipid bodies. In some cases they have thick cell walls consisting of many layers.
La recherche qui éclaire les guides sur l’activité physique au Canada : introductionCet article est tiré d’un supplément intitulé Advancing physical activity measurement and guidelines in Canada: a scientific review and evidence-based foundation for the future of Canadian physical activity guidelines (Favoriser les lignes directrices et la mesure de l’activité physique au Canada: examen scientifique et justification selon les données probantes pour l’avenir des lignes directrices de l’activité physique canadienne) publié par Physiologie appliquée, nutrition et métabolisme et la Revue canadienne de santé publique. On peut aussi mentionner Appl. Physiol. Nutr. Metab. 32 (Suppl. 2F) ou Can. J. Public Health 98 (Suppl. 2).
Authors: Tremblay Mark S. , Shephard Roy J. , Brawley Lawrence R.
Published: March 2008

La Société canadienne de physiologie de l’exercice (SCPE), en collaboration avec Santé Canada et d’autres organismes, a publié en 1998 le premier guide d’activité physique canadien à l’intention des adultes ; d’autres guides conçus spécifiquement à l’intention des aînés et des enfants ont vu le jour en 1999 et 2002 respectivement. La recherche en sciences de l’activité physique (recherche fondamentale, sur le comportement, sur la relation dose–effet, en épidémiologie, en promotion de la santé et en évaluation de l’activité physique) ne cesse de progresser depuis. Une revue détaillée de la littérature s’avère donc pertinente pour vérifier si les directives et les guides sont toujours d’actualité ou nécessitent d’être mis à jour. Cet article énumère selon une approche chronologique les événements justifiant la préparation de ce numéro spécial pour la revue incluant une prise de position et un aperçu du contenu et de son organisation. Puis, en guise d’introduction aux autres articles, on y lit une brève discussion sur les objectifs des directives et des guides, sur les issues anticipées aux plans biologiques, psychologiques et comportementaux et sur les modalités de suivi.
Effects of summer frosts and subsequent shade on foliage gas exchange in peatland tamarack and black spruce
Authors: Dang Q. L. , Lieffers V. J. , Rothwell R. L.
Published: March 2008

In this study, we examined the effect of summer frost on light-saturated net photosynthesis (Pnet) and related parameters in 20-year-old black spruce (Piceamariana (Mill.) B.S.P.) and tamarack (Larixlaricina (Du Roi) K. Koch) at a peatland site in central Alberta. Summer frosts were simulated in the field using a self-contained freezing chamber. Some trees were shaded from direct sunlight after freezing. Shaded trees received about 20% of full sunlight at midday. We found that the response of photosynthesis consisted of two phases: a depression phase, where photosynthesis declined progressively, and a recovery phase, where photosynthesis recovered gradually. The length of the depression phase varied with species but not with the degree of freezing. For both species, depression in Pnet was primarily related to decreased mesophyll conductance to CO2, and a full recovery of Pnet took more than 11 days. Post-frost shade enhanced recovery in Pnet after a −3.5 °C frost in tamarack, but had no detectable effect after a −6 °C frost in tamarack or a −3 °C frost in black spruce.
MAGNETIC PROPERTIES OF NANOCRYSTALLINE CO-FERRITE FILMS DEPOSITED ON SINGLE-CRYSTAL SiO2 SUBSTRATES USING PULSED LASER DEPOSITION
Authors: YIN J. H. , DING J. , LIU B. H. , MIAO X. S. , YI J. B. , CHEN J. S.
Published: March 2008

Co-ferrite films were prepared using pulsed laser deposition with both post-annealing and in situ heating processes. Magnetic properties of these films were studied in the function of temperature, film thickness, and substrate. The films using post-annealing processes exhibited isotropic microstructure, and the coercivity showed no obvious magnetic anisotropy and no strong dependence on film thickness. Co-ferrite films using in situ heating exhibited (111) highly textured structure and possessed perpendicular anisotropy as well as large coercivity. The preferential texture and magnetic anisotropy were closely associated with substrate temperature and thickness. Perpendicular Hc over 12.5 kOe was obtained in the 33 nm Co-ferrite film deposited on single crystal quartz substrate at 550°C. The high coercivity and perpendicular coercivity may be attributed to the nanocrystalline grain, textured orientation, and large residual strain in these films since large residual strain may induce strong stress anisotropy.
A STUDY ON THERMO-OPTIC EFFECT OF β POLY(VINYLIDENE FLUORIDE) THIN FILMS PREPARED BY SOLUTION CASTING METHOD
Authors: XI YINGXUE , FAN HUIQING , LIU WEIGUO , YANG CHEN , NIU XIAOLING
Published: March 2008

The Poly(vinylidene) fluoride (PVDF) thin films with a high content of β-phase were prepared by controlling heat-treatment temperature using casting from the poled solvents. The crystallite microstructure of thin films was depicted by the techniques of X-ray diffraction and FTIR. The results showed that heat treatment was favorable for inducing the β- and γ-phase formation of PVDF. The β phase films were obtained with heat treatment at temperatures ranging from 60°C to 120°C and annealing at 120°C after casting from DMF. The thermo-optical effect of β phase PVDF films was investigated using a spectroscopic ellipsometer. At temperatures ranging from 20°C to 100°C, the refractive index of PVDF was negatively correlated with the temperature between 350 and 1500 nm. The value of the t.o. coefficient of PVDF films was calculated at all temperatures. The maximum value of the t.o. coefficient was about 3.3 × 10-4/°C at the ascending stage of temperature and 3.0 × 10-4/°C at the descending stage of temperature. Therefore, it is possible to use the thermo-optic effect of the β phase PVDF for long wavelength infrared imaging.
Estrogen, nitric oxide, and hypertension differentially modulate agonist-induced contractile responses in female transgenic (mRen2)27 hypertensive rats
Authors: Brosnihan K. Bridget , Li Ping , Figueroa Jorge P. , Ganten Detlev , Ferrario Carlos M.
Published: March 2008

Clinical trials revealed that estrogen may result in cardiovascular risk in patients with coronary heart disease, despite earlier studies demonstrating that estrogen provided cardiovascular protection. It is possible that the preexisting condition of hypertension and the ability of estrogen to activate the renin-angiotensin system could confound its beneficial effects. Our hypothesis is that the attenuation of estrogen to agonist-induced vasoconstrictor responses through the activation of nitric oxide (NO) synthase (NOS) is impaired by hypertension. We investigated the effects of 17β-estradiol (E2) replacement in normotensive Sprague-Dawley (SD) and (mRen2)27 hypertensive transgenic (TG) rats on contractile responses to three vasoconstrictors, angiotensin II (ANG II), serotonin (5-HT), and phenylephrine (PE), and on the modulatory role of vascular NO to these responses. The aorta was isolated from ovariectomized SD and TG rats treated chronically with 5 mg E2or placebo (P). The isometric tension of the aortic rings was measured in organ chambers, and endothelial NOS (eNOS) in the rat aorta was detected using Western blot analysis. E2treatment increased eNOS expression in the SD and TG aorta and reduced ANG II- and 5-HT- but not PE-induced contractions in SD and TG rats. The inhibition of NOS with Nω-nitro-l-arginine methyl ester enhanced ANG II-, 5-HT-, and PE-induced contractions in P-treated and ANG II and PE responses in E2-treated SD and TG rats. Only the responses to 5-HT were augmented in hypertensive rats. In conclusion, this study shows that the preexisting condition of hypertension augmented the vascular responsiveness of 5-HT, whereas the attenuation of estrogen by ANG II and 5-HT vascular responses was not impaired by hypertension. The adrenergic agonist was unresponsive to estrogen treatment. The contribution of NO as a factor contributing to the relative refractoriness of the vascular responses is dependent on the nature of the vasoconstrictor and/or the presence of estrogen.