bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular beam epitaxy growth and characterization of broken-gap (type II) superlattices and quantum wells for midwave-infrared laser diodes
Authors: Hasenberg T. C. , Day P. S. , Shaw E. M. , Magarrell D. J. , Olesberg J. T. , Yu C. , Boggess Thomas F. , Flátte M. E.
Published: July 2002

We have developed a broken-gap (type II) quantum well active region for midwave infrared interband lasers which exhibits a significantly increased Auger lifetime over that of previous designs.
Extremely Large Variations of Atmospheric
14
C Concentration During the Last Glacial Period
Authors: Beck J. Warren , Richards David A. , Lawrence R. , Edwards  , Silverman Bernard W. , Smart Peter L. , Donahue Douglas J. , Hererra-Osterheld Sofia , Burr George. S. , Calsoyas Leal , Timothy A. J. , Jull  , Biddulph Dana
Published: July 2002

A long record of atmospheric
14
C concentration, from 45 to 11 thousand years ago (ka), was obtained from a stalagmite with thermal-ionization mass-spectrometric
230
Th and accelerator mass-spectrometric
14
C measurements. This record reveals highly elevated Δ
14
C between 45 and 33 ka, portions of which may correlate with peaks in cosmogenic
36
Cl and
10
Be isotopes observed in polar ice cores. Superimposed on this broad peak of Δ
14
C are several rapid excursions, the largest of which occurs between 44.3 and 43.3 ka. Between 26 and 11 ka, atmospheric Δ
14
C decreased from ∼700 to ∼100 per mil, modulated by numerous minor excursions. Carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle.
Massive Expansion of Marine Archaea During a Mid-Cretaceous Oceanic Anoxic Event
Authors: Kuypers Marcel M. M. , Blokker Peter , Erbacher Jochen , Kinkel Hanno , Pancost Richard D. , Schouten Stefan , Sinninghe Damsté Jaap S.
Published: July 2002

Biogeochemical and stable carbon isotopic analysis of black-shale sequences deposited during an Albian oceanic anoxic event (∼112 million years ago) indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine, nonthermophilic archaea. The carbon-13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically. Their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event. Indeed, the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in Earth history at which certain hyperthermophilic archaea adapted to low-temperature environments.
HST and VLT Investigations of the Fragments of Comet C/1999 S4 (LINEAR)
Authors: Weaver H. A. , Sekanina Z. , Toth I. , Delahodde C. E. , Hainaut O. R. , Lamy P. L. , Bauer J. M. , A'Hearn M. F. , Arpigny C. , Combi M. R. , Davies J. K. , Feldman P. D. , Festou M. C. , Hook R. , Jorda L. , Keesey M. S. W. , Lisse C. M. , Marsden B. G. , Meech K. J. , Tozzi G. P. , West R.
Published: July 2002

At least 16 fragments were detected in images of comet C/1999 S4 (LINEAR) taken on 5 August 2000 with the Hubble Space Telescope (HST) and on 6 August with the Very Large Telescope (VLT). Photometric analysis of the fragments indicates that the largest ones have effective spherical diameters of about 100 meters, which implies that the total mass in the observed fragments was about 2 × 10
9
kilograms. The comet's dust tail, which was the most prominent optical feature in August, was produced during a major fragmentation event, whose activity peaked on UT 22.8 ± 0.2 July 2000. The mass of small particles (diameters less than about 230 micrometers) in the tail was about 4 × 10
8
kilograms, which is comparable to the mass contained in a large fragment and to the total mass lost from water sublimation after 21 July 2000 (about 3 × 10
8
kilograms). HST spectroscopic observations during 5 and 6 July 2000 demonstrate that the nucleus contained little carbon monoxide ice (ratio of carbon monoxide to water is less than or equal to 0.4%), which suggests that this volatile species did not play a role in the fragmentation of C/1999 S4 (LINEAR).
Josephson Junction Arrays with Bose-Einstein Condensates
Authors: Cataliotti F. S. , Burger S. , Fort C. , Maddaloni P. , Minardi F. , Trombettoni A. , Smerzi A. , Inguscio M.
Published: July 2002

We report on the direct observation of an oscillating atomic current in a one-dimensional array of Josephson junctions realized with an atomic Bose-Einstein condensate. The array is created by a laser standing wave, with the condensates trapped in the valleys of the periodic potential and weakly coupled by the interwell barriers. The coherence of multiple tunneling between adjacent wells is continuously probed by atomic interference. The square of the small-amplitude oscillation frequency is proportional to the microscopic tunneling rate of each condensate through the barriers and provides a direct measurement of the Josephson critical current as a function of the intermediate barrier heights. Our superfluid array may allow investigation of phenomena so far inaccessible to superconducting Josephson junctions and lays a bridge between the condensate dynamics and the physics of discrete nonlinear media.
Glacial-to-Holocene Redistribution of Carbonate Ion in the Deep Sea
Authors: Broecker Wallace S. , Clark Elizabeth
Published: July 2002

We have reconstructed the glacial-age distribution of carbonate ion concentration in the deep waters of the equatorial ocean on the basis of differences in weight between glacial and Holocene foraminifera shells picked from a series of cores spanning a range of water depth on the western Atlantic's Ceara Rise and the western Pacific's Ontong Java Plateau. The results suggest that unlike today's ocean, sizable vertical gradients in the carbonate ion concentration existed in the glacial-age deep ocean. In the equatorial Pacific, the concentration increased with depth, and in the Atlantic, it decreased with depth. In addition, the contrast between the carbonate ion concentration in deep waters produced in the northern Atlantic and deep water in the Pacific appears to have been larger than in today's ocean.
Submillimeter Evidence for the Coeval Growth of Massive Black Holes and Galaxy Bulges
Authors: Page M. J. , Stevens J. A. , Mittaz J. P. D. , Carrera F. J.
Published: July 2002

The correlation, found in nearby galaxies, between black hole mass and stellar bulge mass implies that the formation of these two components must be related. Here we report submillimeter photometry of eight x-ray–absorbed active galactic nuclei that have luminosities and redshifts characteristic of the sources that produce the bulk of the accretion luminosity in the universe. The four sources with the highest redshifts are detected at 850 micrometers, with flux densities between 5.9 and 10.1 millijanskies, and hence are ultraluminous infrared galaxies. If the emission is from dust heated by starbursts, then the majority of stars in spheroids were formed at the same time as their central black holes built up most of their mass by accretion. This would account for the observed demography of massive black holes in the local universe. The skewed rate of submillimeter detection with redshift is consistent with a high redshift epoch of star formation in radio-quiet active galactic nuclei, similar to that seen in radio galaxies.
Fraud and Ethics Charges Hit Stroke Drug Trial
Authors: Enserink Martin
Published: July 2002

Amsterdam, the Netherlands—The Second European Stroke Prevention Study, a major clinical trial of a drug to prevent repeat strokes, has become mired in controversy. A paper describing promising results from the trial, published earlier this month, was originally turned down by
The Lancet
in part because of ethical concerns over the use of placebos, and it has been further tainted by allegations that fabricated data led to the disqualification of information on more than 400 patients.
Shape-Changing Crystals Get Shiftier
Authors: Service Robert F.
Published: July 2002

A talented family of materials has gained some even more gifted members. Piezoelectric crystals have the unique ability to swell or shrink when zapped with electricity, as well as give off a jolt of juice themselves when compressed or pulled apart. Now, by varying the recipe for these materials, researchers have found new ones that display an effect up to 10 times larger than that of current family members.
Calculated Pulse Widths and Spectra of a Single Sonoluminescing Bubble
Authors: Moss William C. , Clarke Douglas B. , Young David A.
Published: July 2002

A sonoluminescing bubble has been modeled as a thermally conducting, partially ionized, two-component plasma. The model shows that the measured picosecond pulse widths are due to electron conduction and the rapidly changing opacity of the plasma and that these mechanisms are also responsible for the absence of an “afterglow” subsequent to the sonoluminescence flash while the hot bubble expands and cools. The calculated spectra for sonoluminescing nitrogen and argon bubbles suggest that a sonoluminescing air bubble probably contains only argon, in agreement with a recent theoretical analysis.
The Source of Green Light Emission Determined from a Heavy-Ion Storage Ring Experiment
Authors: Kella D. , Vejby-Christensen L. , Johnson P. J. , Pedersen H. B. , Andersen L. H.
Published: July 2002

The final electronic states of oxygen atoms formed by dissociative recombination of O
2
+
with cold electrons have been measured by an imaging technique at a heavy-ion storage ring. The
3
P
,
1
D
, and
1
S
quantum yield for O
2
+
in the vibrational ground level was found to be 0.86, 1.09, and 0.05, respectively. The yield of the
1
S
state, which is responsible for the 5577 angstrom green light from upper planetary atmospheres, was more than an order of magnitude larger than the theoretical value used in atmospheric models. The results may help refine the models of the chemistry and dynamics of the ionosphere and provide guidance for further quantum-chemistry calculations.
Response of the African Monsoon to Orbital Forcing and Ocean Feedbacks in the Middle Holocene
Authors: Kutzbach J. E. , Liu Z.
Published: July 2002

Simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the Northern Hemisphere 6000 years ago could have increased tropical Atlantic sea surface temperatures in late summer. The simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern Africa by more than 25 percent, compared with the middle Holocene simulation with prescribed modern sea surface temperatures, and provided better agreement with paleorecords of enhanced monsoons.
Inhibition of Brain G
z
GAP and Other RGS Proteins by Palmitoylation of G Protein α Subunits
Authors: Tu Yaping , Wang Jun , Ross Elliott M.
Published: July 2002

Palmitoylation of the α subunit of the guanine nucleotide-binding protein G
z
inhibited by more than 90 percent its response to the guanosine triphosphatase (GTPase)–accelerating activity of G
z
GAP, a G
z
-selective member of the regulators of G-protein signaling (RGS) protein family of GTPase-activating proteins (GAPs). Palmitoylation both decreased the affinity of G
z
GAP for the GTP-bound form of Gα
z
by at least 90 percent and decreased the maximum rate of GTP hydrolysis. Inhibition was reversed by removal of the palmitoyl group by dithiothreitol. Palmitoylation of Gα
z
also inhibited its response to the GAP activity of Gα-interacting protein (GAIP), another RGS protein, and palmitoylation of Gα
i1
inhibited its response to RGS4. The extent of inhibition of G
z
GAP, GAIP, RGS4, and RGS10 correlated roughly with their intrinsic GAP activities for the Gα target used in the assay. Reversible palmitoylation is thus a major determinant of G
z
deactivation after its stimulation by receptors, and may be a general mechanism for prolonging or potentiating G-protein signaling.
Earth's Background Free Oscillations
Authors: Suda Naoki , Nawa Kazunari , Fukao Yoshio
Published: July 2002

Earth's free oscillations were considered to be transient phenomena occurring after large earthquakes. An analysis of records of the IDA (International Deployment of Accelerometers) gravimeter network shows that Earth is freely oscillating at an observable level even in seismically inactive periods. The observed oscillations are the fundamental spheroidal modes at frequencies between 2 and 7 millihertz. Numerical modeling indicates that these incessant excitations cannot be explained by stacked effects of a large number of small earthquakes. The observed “background” free oscillations represent some unknown dynamic process of Earth.
Major Bacterial Contribution to Marine Dissolved Organic Nitrogen
Authors: McCarthy Matthew D. , Hedges John I. , Benner Ronald
Published: July 2002

Next to N
2
gas, the largest pool of reduced nitrogen in the ocean resides in the enormous reservoir of dissolved organic nitrogen (DON). The chemical identity of most of this material, and the mechanisms by which it is cycled, remain fundamental questions in contemporary oceanography. Amino acid enantiomeric ratios in the high molecular weight fraction of DON from surface and deep water in three ocean basins show substantial enrichment in
d
enantiomers of four amino acids. The magnitude and pattern of these
d
/
l
enrichments indicate that peptidoglycan remnants derived from bacterial cell walls constitute a major source of DON throughout the sea. These observations suggest that structural properties of specific bacterial biopolymers, and the mechanisms for their accumulation, are among the central controls on long-term cycling of dissolved organic nitrogen in the sea.
Catalytic Plasticity of Fatty Acid Modification Enzymes Underlying Chemical Diversity of Plant Lipids
Authors: Broun Pierre , Shanklin John , Whittle Ed , Somerville Chris
Published: July 2002

Higher plants exhibit extensive diversity in the composition of seed storage fatty acids. This is largely due to the presence of various combinations of double or triple bonds and hydroxyl or epoxy groups, which are synthesized by a family of structurally similar enzymes. As few as four amino acid substitutions can convert an oleate 12-desaturase to a hydroxylase and as few as six result in conversion of a hydroxylase to a desaturase. These results illustrate how catalytic plasticity of these diiron enzymes has contributed to the evolution of the chemical diversity found in higher plants.
Electrical Conductivity in the Precambrian Lithosphere of Western Canada
Authors: Boerner D. E. , Kurtz R. D. , Craven J. A. , Ross G. M. , Jones F. W. , Davis W. J.
Published: July 2002

The subcrustal lithosphere underlying the southern Archean Churchill Province (ACP) in western Canada is at least one order of magnitude more electrically conductive than the lithosphere beneath adjacent Paleoproterozoic crust. The measured electrical properties of the lithosphere underlying most of the Paleoproterozoic crust can be explained by the conductivity of olivine. Mantle xenolith and geological mapping evidence indicate that the lithosphere beneath the southern ACP was substantially modified as a result of being trapped between two nearly synchronous Paleoproterozoic subduction zones. Tectonically induced metasomatism thus may have enhanced the subcrustal lithosphere conductivity of the southern ACP.
Regulation of the Mammalian Pineal by Non-rod, Non-cone, Ocular Photoreceptors
Authors: Lucas Robert J. , Freedman Melanie S. , Muñoz Marta , Garcia-Fernández José-M. , Foster Russell G.
Published: July 2002

In mammals, ocular photoreceptors mediate an acute inhibition of pineal melatonin by light. The effect of rod and cone loss on this response was assessed by combining the
rd
mutation with a transgenic ablation of cones (
cl
) to produce mice lacking both photoreceptor classes. Despite the loss of all known retinal photoreceptors,
rd/rd cl
mice showed normal suppression of pineal melatonin in response to monochromatic light of wavelength 509 nanometers. These data indicate that mammals have additional ocular photoreceptors that they use in the regulation of temporal physiology.
Broad-Spectrum Mildew Resistance in
Arabidopsis thaliana
Mediated by
RPW8
Authors: Xiao Shunyuan , Ellwood Simon , Calis Ozer , Patrick Elaine , Li Tianxian , Coleman Mark , Turner John G.
Published: July 2002

Plant disease resistance (
R
) genes control the recognition of specific pathogens and activate subsequent defense responses. We show that the
Arabidopsis thaliana
locus
RESISTANCE TO POWDERY MILDEW8
(
RPW8
) contains two naturally polymorphic, dominant
R
genes,
RPW8.1
and
RPW8.2
, which individually control resistance to a broad range of powdery mildew pathogens. Although the predicted RPW8.1 and RPW8.2 proteins are different from the previously characterized
R
proteins, they induce localized, salicylic acid–dependent defenses similar to those induced by
R
genes that control specific resistance. Apparently, broad-spectrum resistance mediated by
RPW8
uses the same mechanisms as specific resistance.
Comparative Pharmacodynamics of Gatifloxacin and Ciprofloxacin in an In Vitro Dynamic Model: Prediction of Equiefficient Doses and the Breakpoints of the Area under the Curve/MIC Ratio
Authors: Vostrov Sergey N. , Kononenko Olga V. , Lubenko Irene Y. , Zinner Stephen H. , Firsov Alexander A.
Published: July 2002

To demonstrate the impact of the pharmacokinetics of gatifloxacin (GA) relative to those of ciprofloxacin (CI) on the antimicrobial effect (AME), the killing and regrowth kinetics of two differentially susceptible clinical isolates each of
Staphylococcus aureus
,
Escherichia coli
, and
Klebsiella pneumoniae
were studied. With each organism, a series of monoexponential pharmacokinetic profiles of GA (half-life [
t
1/2
], 7 h) and CI (
t
1/2
= 4 h) were simulated to mimic different single doses of GA and two 12-h doses of CI. The respective eightfold ranges of the ratios of the area under the concentration-time curve (AUC) to the MIC were 58 to 466 and 116 to 932 (μg · h/ml)/(μg/ml). The species- and strain-independent linear relationships observed between the intensity of AME (

I
E

) and log AUC/MIC were not superimposed for GA and CI (
r
2
= 0.99 in both cases). The predicted AUC/MIC ratio for GA that might be equivalent to a clinically relevant AUC/MIC breakpoint for CI was estimated to be 102 rather than 125 (μg · h/ml)/(μg/ml). The respective MIC breakpoints were 0.32 μg/ml (for a 400-mg dose of GA) and 0.18 μg/ml (for two 500-mg doses of CI). On the basis of the

I
E

-log AUC/MIC relationships, equiefficient 24-h doses (
D
24h
s) of GA and CI were calculated for hypothetical strains of
S. aureus
,
E. coli
, and
K. pneumoniae
for which the MICs were equal to the MICs at which 50% of isolates are inhibited. To provide an “acceptable”

I
E

equal to 200 (log CFU/ml) · h, i.e., the

I
E

provided by AUC/MIC of 125 (μg · h/ml)/(μg/ml) for ciprofloxacin, the
D
24h
s of GA for all three organisms were much lower (115, 30, and 60 mg) than the clinically proposed 400-mg dose. Although the usual dose of CI (two doses of 500 mg) would be in excess for
E. coli
and
K. pneumoniae
(
D
24h
= two doses of 40 mg and two doses of 115 mg, respectively), even the highest clinical dose of CI (two doses of 750 mg) might be insufficient for
S. aureus
(
D
24h
, > two doses of 1,000 mg). The method of generalization of data obtained with specific organisms to other representatives of the same species described in the present report might be useful for prediction of the AMEs of new quinolones.
Comparative In Vitro Activities of Linezolid, Quinupristin-Dalfopristin, Moxifloxacin, and Trovafloxacin against Erythromycin-Susceptible and -Resistant Streptococci
Authors: Betriu Carmen , Redondo Montserrat , Palau M. Luisa , Sánchez Ana , Gómez María , Culebras Esther , Boloix Ana , Picazo Juan J.
Published: July 2002

The in vitro activities of the new agents linezolid, quinupristin-dalfopristin, moxifloxacin, and trovafloxacin were determined and compared with those of penicillin, clindamycin, and four macrolides against 53 erythromycin-resistant
Streptococcus pneumoniae
, 117
S. pyogenes
(64 erythromycin-susceptible and 53 -resistant), and 101
S. agalactiae
(53 erythromycin-susceptible and 48 -resistant) isolates. Differentiation of macrolide resistance phenotypes was performed by the double-disk method. The genetic basis for macrolide resistance in 52 strains was also determined. The M phenotype was found in 84.9, 6.3, and 1.9% of
S. pyogenes
,
S. agalactiae
, and
S. pneumoniae
isolates, respectively. These strains were susceptible to miocamycin and clindamycin. Strains with the inducible phenotype accounted for 27.1% of
S. agalactiae
isolates and 9.4% each of
S. pyogenes
and
S. pneumoniae
isolates. All erythromycin-resistant isolates were also resistant to the 14- and 15-membered macrolides tested. Strains with all three phenotypes were susceptible to ≤2 μg of linezolid per ml. Quinupristin-dalfopristin exhibited good in vitro activity against all strains, irrespective of their resistance to erythromycin (MICs at which 90% of the isolates tested were inhibited [MIC
90
s], 0.2 to 1 μg/ml). Against the erythromycin-resistant
S. pyogenes
and
S. agalactiae
strains, moxifloxacin and trovafloxacin were the most active agents (MIC
90
s, 0.1 μg/ml). The new antimicrobials evaluated may be alternative agents to treat infections caused by macrolide-resistant as well as macrolide-susceptible streptococci.
In Vitro Activities of a New Ketolide, ABT-773, Alone and in Combination with Amoxicillin, Metronidazole, or Tetracycline against
Helicobacter pylori
Authors: Pendland Susan L. , Prause Jennifer L. , Neuhauser Melinda M. , Boyea Nicole , Hackleman Jodi M. , Danziger Larry H.
Published: July 2002

The in vitro activity of ABT-773, a new ketolide, was compared with those of clarithromycin, amoxicillin, metronidazole, and tetracycline against 15 strains of
Helicobacter pylori
. The MIC of ABT-773 at which 90% of isolates were inhibited was 0.25 μg/ml, which was 3 dilutions higher than that of the most active agent, clarithromycin. Synergy and antagonism were not seen with any combinations. Additive activity was seen with tetracycline, metronidazole, and amoxicillin in 100, 60, and 40% of the combinations, respectively.
Pharmacokinetics of Cefepime during Continuous Renal Replacement Therapy in Critically Ill Patients
Authors: Malone Rebecca S. , Fish Douglas N. , Abraham Edward , Teitelbaum Isaac
Published: July 2002

The pharmacokinetics of cefepime were studied in 12 adult patients in intensive care units during continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodiafiltration (CVVHDF) with a Multiflow60 AN69HF 0.60-m2polyacrylonitrile hollow-fiber membrane (Hospal Industrie, Meyzieu, France). Patients (mean age, 52.0 ± 13.0 years [standard deviation]; mean weight, 96.7 ± 18.4 kg) received 1 or 2 g of cefepime every 12 or 24 h (total daily doses of 1 to 4 g/day) by intravenous infusion over 15 to 30 min. Pre- and postmembrane blood (serum) samples and corresponding ultrafiltrate or dialysate samples were collected 1, 2, 4, 8, and 12 or 24 h (depending on dosing interval) after completion of the drug infusion. Drug concentrations were measured using validated high-performance liquid chromatography methods. Mean systemic clearance (CLS) and elimination half-life (t1/2) of cefepime were 35.9 ± 6.0 ml/min and 12.9 ± 2.6 h during CVVH versus 46.8 ± 12.4 ml/min and 8.6 ± 1.4 h during CVVHDF, respectively. Cefepime clearance was substantially increased during both CVVH and CVVHDF, with membrane clearance representing 40 and 59% of CLS, respectively. The results of this study confirm that continuous renal replacement therapy contributes substantially to total CLSof cefepime and that CVVHDF appears to remove cefepime more efficiently than CVVH. Cefepime doses of 2 g/day (either 2 g once daily or 1 g twice daily) appear to achieve concentrations adequate to treat most common gram-negative pathogens (MIC ≤ 8 μg/ml) during CVVH or CVVHDF.
Restoration of Vancomycin Susceptibility in
Enterococcus faecalis
by Antiresistance Determinant Gene Transfer
Authors: Torres Viera C. , Tsiodras S. , Gold H. S. , Coakley E. P. G. , Wennersten C. , Eliopoulos G. M. , Moellering R. C. , Inouye R. T.
Published: July 2002

We assessed the ability of gene transfer to reverse vancomycin resistance in class A (VanA) glycopeptide-resistant
Enterococcus faecalis
. Recombinant shuttle vectors containing a
vanH
promoter-
vanA
antisense gene cassette fully restored vancomycin susceptibility through a combined transcriptional activator binding domain decoy and inducible
vanA
antisense RNA effect.
Pseudomonas aeruginosa
Reveals High Intrinsic Resistance to Penem Antibiotics: Penem Resistance Mechanisms and Their Interplay
Authors: Okamoto Kiyomi , Gotoh Naomasa , Nishino Takeshi
Published: July 2002

Pseudomonas aeruginosa
exhibits high intrinsic resistance to penem antibiotics such as faropenem, ritipenem, AMA3176, sulopenem, Sch29482, and Sch34343. To investigate the mechanisms contributing to penem resistance, we used the laboratory strain PAO1 to construct a series of isogenic mutants with an impaired multidrug efflux system MexAB-OprM and/or impaired chromosomal AmpC β-lactamase. The outer membrane barrier of PAO1 was partially eliminated by inducing the expression of the plasmid-encoded
Escherichia coli
major porin OmpF. Susceptibility tests using the mutants and the OmpF expression plasmid showed that MexAB-OprM and the outer membrane barrier, but not AmpC β-lactamase, are the main mechanisms involved in the high intrinsic penem resistance of PAO1. However, reducing the high intrinsic penem resistance of PAO1 to the same level as that of penem-susceptible gram-negative bacteria such as
E. coli
required the loss of either both MexAB-OprM and AmpC β-lactamase or both MexAB-OprM and the outer membrane barrier. Competition experiments for penicillin-binding proteins (PBPs) revealed that the affinity of PBP 1b and PBP 2 for faropenem were about 1.8- and 1.5-fold lower, than the respective affinity for imipenem. Loss of the outer membrane barrier, MexAB, and AmpC β-lactamase increased the susceptibility of PAO1 to almost all penems tested compared to the susceptibility of the AmpC-deficient PAO1 mutants to imipenem. Thus, it is suggested that the high intrinsic penem resistance of
P. aeruginosa
is generated from the interplay among the outer membrane barrier, the active efflux system, and AmpC β-lactamase but not from the lower affinity of PBPs for penems.
Cofactor Regeneration by a Soluble Pyridine Nucleotide Transhydrogenase for Biological Production of Hydromorphone
Authors: Boonstra Birgitte , Rathbone Deborah A. , French Christopher E. , Walker Edward H. , Bruce Neil C.
Published: July 2002

We have applied the soluble pyridine nucleotide transhydrogenase of
Pseudomonas fluorescens
to a cell-free system for the regeneration of the nicotinamide cofactors NAD and NADP in the biological production of the important semisynthetic opiate drug hydromorphone. The original recombinant whole-cell system suffered from cofactor depletion resulting from the action of an NADP
+
-dependent morphine dehydrogenase and an NADH-dependent morphinone reductase. By applying a soluble pyridine nucleotide transhydrogenase, which can transfer reducing equivalents between NAD and NADP, we demonstrate with a cell-free system that efficient cofactor cycling in the presence of catalytic amounts of cofactors occurs, resulting in high yields of hydromorphone. The ratio of morphine dehydrogenase, morphinone reductase, and soluble pyridine nucleotide transhydrogenase is critical for diminishing the production of the unwanted by-product dihydromorphine and for optimum hydromorphone yields. Application of the soluble pyridine nucleotide transhydrogenase to the whole-cell system resulted in an improved biocatalyst with an extended lifetime. These results demonstrate the usefulness of the soluble pyridine nucleotide transhydrogenase and its wider application as a tool in metabolic engineering and biocatalysis.
A Protein Disulfide Isomerase Gene Fusion Expression System That Increases the Extracellular Productivity of
Bacillus brevis
Authors: Kajino Tsutomu , Ohto Chikara , Muramatsu Masayoshi , Obata Shusei , Udaka Shigezo , Yamada Yukio , Takahashi Haruo
Published: July 2002

We have developed a versatile
Bacillus brevis
expression and secretion system based on the use of fungal protein disulfide isomerase (PDI) as a gene fusion partner. Fusion with PDI increased the extracellular production of heterologous proteins (light chain of immunoglobulin G, 8-fold; geranylgeranyl pyrophosphate synthase, 12-fold). Linkage to PDI prevented the aggregation of the secreted proteins, resulting in high-level accumulation of fusion proteins in soluble and biologically active forms. We also show that the disulfide isomerase activity of PDI in a fusion protein is responsible for the suppression of the aggregation of the protein with intradisulfide, whereas aggregation of the protein without intradisulfide was prevented even when the protein was fused to a mutant PDI whose two active sites were disrupted, suggesting that another PDI function, such as chaperone-like activity, synergistically prevented the aggregation of heterologous proteins in the PDI fusion expression system.
Sexuality and Genetic Identity in the
Agaricus
Section
Arvenses
Authors: Calvo-Bado Leo , Noble Ralph , Challen Mike , Dobrovin-Pennington Andreja , Elliott Tim
Published: July 2002

Twelve wild collections and one commercial strain were used to characterize breeding systems and to develop molecular identities in the
Arvenses
section of the genus
Agaricus
, which includes the “horse mushroom”
A. arvensis
. Two morphotypes were identified based on macro- and micromorphological features. However, not all collections could be delimited by conventional taxonomic characters. Sequencing of the small subunit intergenic spacer (ITS) region (368 to 370 bp) of the rRNA genes clearly resolved the 13 collections into two clusters consistent with the identified morphotypes. Single-spore progenies and mating type testers were established and used to test intra- and interstock compatibility. The two compatibility groups identified were consistent with ITS clusters. Compatibility group I stocks readily interbred within the constraints of a unifactorial heterothallic system with a multiallelic mating type factor. Compatibility group II had a more restricted breeding pattern, and interactions were difficult to predict on the basis of mating type. Morphological data, ITS sequences, and the ability to interbreed suggest that these collections are part of a complex of interrelated species. Single-spore, homokaryotic isolates from both compatibility groups were able to fruit in compost culture, and two of the collections may represent natural homokaryotic fruiting. We conclude that species from the section
Arvenses
have versatile unifactorial heterothallic life cycles that permit both interbreeding and homokaryotic fruiting.
Glutathione-Dependent Conversion of
N
-Ethylmaleimide to the Maleamic Acid by
Escherichia coli
: an Intracellular Detoxification Process
Authors: McLaggan D. , Rufino H. , Jaspars M. , Booth I. R.
Published: July 2002

The electrophile
N
-ethylmaleimide (NEM) elicits rapid K
+
efflux from
Escherichia coli
cells consequent upon reaction with cytoplasmic glutathione to form an adduct,
N
-ethylsuccinimido-
S
-glutathione (ESG) that is a strong activator of the KefB and KefC glutathione-gated K
+
efflux systems. The fate of the ESG has not previously been investigated. In this report we demonstrate that NEM and
N
-phenylmaleimide (NPM) are rapidly detoxified by
E. coli
. The detoxification occurs through the formation of the glutathione adduct of NEM or NPM, followed by the hydrolysis of the imide bond after which
N
-substituted maleamic acids are released.
N
-Ethylmaleamic acid is not toxic to
E. coli
cells even at high concentrations. The glutathione adducts are not released from cells, and this allows glutathione to be recycled in the cytoplasm. The detoxification is independent of new protein synthesis and NAD
+
-dependent dehydrogenase activity and entirely dependent upon glutathione. The time course of the detoxification of low concentrations of NEM parallels the transient activation of the KefB and KefC glutathione-gated K
+
efflux systems.
Isolation of a Pandemic O3:K6 Clone of a
Vibrio parahaemolyticus
Strain from Environmental and Clinical Sources in Thailand
Authors: Vuddhakul Varaporn , Chowdhury Ashrafazzuman , Laohaprertthisan Varaporn , Pungrasamee Punnee , Patararungrong Nuanjira , Thianmontri Pongpaga , Ishibashi Masanori , Matsumoto Chiho , Nishibuchi Mitsuaki
Published: July 2002

Application of an immunomagnetic enrichment method selective for
Vibrio parahaemolyticus
serovar K6 allowed isolation of a strain belonging to the pandemic O3:K6 clone of
V. parahaemolyticus
from fresh shellfish not implicated in a clinical case in southern Thailand. Arbitrarily primed PCR profiles of this strain, clinical O3:K6 strains isolated from sporadic diarrhea cases in the same area, and a standard pandemic O3:K6 strain were indistinguishable.
Development and Application of Small-Subunit rRNA Probes for Assessment of Selected
Thiobacillus
Species and Members of the Genus
Acidiphilium
Authors: Peccia Jordan , Marchand Eric A. , Silverstein Joann , Hernandez Mark
Published: July 2002

Culture-dependent studies have implicated sulfur-oxidizing bacteria as the causative agents of acid mine drainage and concrete corrosion in sewers.
Thiobacillus
species are considered the major representatives of the acid-producing bacteria in these environments. Small-subunit rRNA genes from all of the
Thiobacillus
and
Acidiphilium
species catalogued by the Ribosomal Database Project were identified and used to design oligonucleotide DNA probes. Two oligonucleotide probes were synthesized to complement variable regions of 16S rRNA in the following acidophilic bacteria:
Thiobacillus ferrooxidans
and
T. thiooxidans
(probe Thio820) and members of the genus
Acidiphilium
(probe Acdp821). Using
32
P radiolabels, probe specificity was characterized by hybridization dissociation temperature (

T
d

) with membrane-immobilized RNA extracted from a suite of 21 strains representing three groups of bacteria. Fluorochrome-conjugated probes were evaluated for use with fluorescent in situ hybridization (FISH) at the experimentally determined

T
d

s. FISH was used to identify and enumerate bacteria in laboratory reactors and environmental samples. Probing of laboratory reactors inoculated with a mixed culture of acidophilic bacteria validated the ability of the oligonucleotide probes to track specific cell numbers with time. Additionally, probing of sediments from an active acid mine drainage site in Colorado demonstrated the ability to identify numbers of active bacteria in natural environments that contain high concentrations of metals, associated precipitates, and other mineral debris.
Physical and Metabolic Interactions of
Pseudomonas
sp. Strain JA5-B45 and
Rhodococcus
sp. Strain F9-D79 during Growth on Crude Oil and Effect of a Chemical Surfactant on Them
Authors: Van Hamme Jonathan D. , Ward Owen P.
Published: July 2002

Methods to enhance crude oil biodegradation by mixed bacterial cultures, for example, (bio)surfactant addition, are complicated by the diversity of microbial populations within a given culture. The physical and metabolic interactions between
Rhodococcus
sp. strain F9-D79 and
Pseudomonas
sp. strain JA5-B45 were examined during growth on Bow River crude oil. The effects of a nonionic chemical surfactant, Igepal CO-630 (nonylphenol ethoxylate), also were evaluated. Strain F9-D79 grew attached to the oil-water interface and produced a mycolic acid-containing capsule. Crude oil emulsification and surface activity were associated with the cellular fraction. Strain JA5-B45 grew in the aqueous phase and was unable to emulsify oil, but cell-free supernatants mediated kerosene-water emulsion formation. In coculture, stable emulsions were formed and strain JA5-B45 had an affinity for the capsule produced by strain F9-D79. Igepal CO-630 inhibited F9-D79 cells from adhering to the interface, and cells grew dispersed in the aqueous phase as 0.5-μm cocci rather than 2.5-μm rods. The surfactant increased total petroleum hydrocarbon removal by strain JA5-B45 from 4 to 22% and included both saturated compounds and aromatics. In coculture, TPH removal increased from 13 to 40% following surfactant addition. The culture pH normally increased from 7.0 to between 7.5 and 8.5, although addition of Igepal CO-630 to F9-D79 cultures resulted in a drop to pH 5.5. We suggest a dual role for the nonylphenol ethoxylate surfactant in the coculture: (i) to improve hydrocarbon uptake by strain JA5-B45 through emulsification and (ii) to prevent strain F9-D79 from adhering to the oil-water interface, indirectly increasing hydrocarbon availability. These varied effects on hydrocarbon biodegradation could explain some of the known diversity of surfactant effects.
Assessment of the Genetic Diversity among Strains of
Xanthomonas cynarae
by Randomly Amplified Polymorphic DNA Analysis and Development of Specific Characterized Amplified Regions for the Rapid Identification of
X. cynarae
Authors: Trébaol Gaëlle , Manceau Charles , Tirilly Yves , Boury Stéphane
Published: July 2002

The randomly amplified polymorphic DNA (RAPD) method was used to investigate the genetic diversity in
Xanthomonas cynarae
, which causes bacterial bract spot disease of artichoke. This RAPD analysis was also intended to identify molecular markers characteristic of this species, in order to develop PCR-based markers which can be used to detect this pathogenic bacterium in artichoke fields. Among the 340 RAPD primers tested, 40 were selected on their ability to produce reproducible and reliable fingerprints in our genetic background. These 40 primers produced almost similar patterns for the 37
X. cynarae
strains studied, different from the fingerprints obtained for other
Xanthomonas
species and other xanthomonad-like bacteria isolated from artichoke leaves. Therefore,
X. cynarae
strains form a homogeneous genetic group. However, a little DNA polymorphism within this species was observed and the collection of
X. cynarae
isolates was divided into two groups (one containing three strains, the second one including all other strains). Out of seven RAPD markers characteristic of
X. cynarae
that were cloned, four did not hybridize to the genomic DNA of strains belonging to other
Xanthomonas
species. These four RAPD markers were converted into PCR markers (specific characterized amplified regions [SCARs]); they were sequenced, and a PCR primer pair was designed for each of them. Three derived SCARs are good candidates to develop PCR-based tests to detect
X. cynarae
in artichoke fields.
Interception of Small Particles by Flocculent Structures, Sessile Ciliates, and the Basic Layer of a Wastewater Biofilm
Authors: Eisenmann Heinrich , Letsiou Ioanna , Feuchtinger Anette , Beisker Wolfgang , Mannweiler Ernst , Hutzler Peter , Arnz Patrik
Published: July 2002

We investigated attachment processes of hydrophobic and hydrophilic particles (diameter = 1 μm) to mature biofilms grown on clay marbles in a sequencing batch biofilm reactor. During a treatment cycle with filtered wastewater containing different fluorescent beads, the progression of particle density in various biofilm compartments (carrier biofilm, basic biofilm layer, biofilm flocs, and sessile ciliates) was determined by flow cytometry, confocal laser scanning microscopy and automated image analysis. Particles were almost completely removed from wastewater by typical processes of particle retention: up to 58% of particles attached to clay marbles, up to 15% were associated with suspended flocs, and up to 10% were ingested by sessile ciliates. Ingestion of particles by ciliates was exceptionally high immediately after wastewater addition (1,200 particles grazer
−1
h
−1
) and continued until approximately 14% of the water had been cleared by ciliate filter feeding. Most probably, ciliate bioturbation increases particle sorption to the basic biofilm. Backwashing of the reactor detached pieces of biofilm and thus released approximately 50% of the particles into rinsing water. Clay marbles in the upper part of the reactor were more efficiently abraded than in the lower part. No indications for selective attachment of the applied hydrophobic and hydrophilic beads were found. As a consequence of interception patterns, organisms at elevated biofilm structures are probably major profiteers of wastewater particles; among them, ciliates may be of major importance because of their highly active digestive food vacuoles.
Standardization ofNeisseria meningitidisSerogroup B Colorimetric Serum Bactericida Assay
Authors: Rodríguez Tamara , Lastre Miriam , Cedré Barbara , Campo Judith del , Bracho Gustavo , Zayas Caridad , Taboada Carlos , Díaz Miriam , Sierra Gustavo , Pérez Oliver
Published: July 2002

The correlate of protection for serogroup B meningococci is not currently known, but for serogroup C it is believed to be the serum bactericidal assay (SBA). The current SBAs are labor intensive and the variations in protocols among different laboratories make interpretation of results difficult. A colorimetric SBA (cSBA), based on the ability ofNeisseria meningitidisserogroup B to consume glucose, leading to acid production, was standardized by using group B strain Cu385-83 as the target. The cSBA results were compared to those obtained for a traditional colony-counting microassay (mSBA). Glucose and bromocresol purple pH indicator were added to the medium in order to estimate growth of cSBA target cell survivors through color change. Different variants of the assay parameters were optimized: growth of target cells (Mueller Hinton agar plates), target cell number (100 CFU/per well), and human complement source used at a final concentration of 25%. After the optimization, three other group B strains (H44/76, 490/91, and 511/91) were used as targets for the cSBA. The selection of the assay parameters and the standardization of cSBA were done with 13 sera from vaccinated volunteers. The titers were determined as the higher serum dilution that totally inhibited the bacterial growth marked by the color invariability of the pH indicator. This was detected visually as well as spectrophotometrically and was closely related to a significant difference in the growth of target cell survivors determined using Student’sttest. Intralaboratory reproducibility was ±1 dilution. The correlation between bactericidal median titers and specific immunoglobulin G serum concentration by enzyme immunoassay was high (r= 0.910,P< 0.01). The bactericidal titers generated by the cSBA and the mSBA were nearly identical, and there was a high correlation between the two assays (r= 0.974,P< 0.01). The standardized cSBA allows easy, fast, and efficient evaluation of samples.
Resected Human Colonic Tissue: New Model for Characterizing Adhesion of Lactic Acid Bacteria
Authors: Ouwehand Arthur C. , Salminen Seppo , Tölkkö Satu , Roberts Peter , Ovaska Jari , Salminen Eeva
Published: July 2002

Adhesion to the intestinal mucosa is one of the main selection criteria for probiotic strains. The adhesion of commonly used probiotic strains to human intestinal tissue pieces and mucus was assessed. The strains tested adhered to the intestinal tissue at low levels and adhered to the intestinal mucus at higher levels.
Inclusion Fluorescent-Antibody Test as a Screening Assay for Detection of Antibodies toChlamydia pneumoniae
Authors: Tapia Olga , Slepenkin Anatoly , Sevrioukov Evgueni , Hamor Kathi , de la Maza Luis M. , Peterson Ellena M.
Published: July 2002

A study was conducted to determine the ability of the inclusion immunofluorescence assay (inclusion IFA) to act as a screening test to detect samples with antibodies toChlamydia pneumoniae; microimmunofluorescence (MIF) was used as the “gold standard.” In addition, the inclusion IFA was compared using HEp-2 cells infected with eitherC. pneumoniaeCM-1 orChlamydia trachomatisserovar E. A total of 331 serum samples representing a range of MIF titers were evaluated. The sensitivities of the inclusion IFA for detecting samples withC. pneumoniaeMIF titers of ≥16 were 96.9 and 74.8% withC. pneumoniae-andC. trachomatis-infected cells, respectively. For samples with an elevatedC. pneumoniaeMIF titer of ≥512, the sensitivities of theC. pneumoniae-andC. trachomatis-based inclusion IFA were 97.0 and 8.8%, respectively. These results suggest that the inclusion IFA is not a genus-specific test, as evidenced by the failure of theC. trachomatis-infected cells to detect a significant number of samples withC. pneumoniaeantibodies. Samples that had elevatedC. pneumoniaeinclusion IFA and MIF titers but that were found negative (titer, <16) by theC. trachomatisinclusion IFA were further tested by an in vitro neutralization assay for functional antibodies that might not have been detected by the serological assays. The in vitro neutralization results corroborated the serological results in that all seven sera tested had a neutralization titer forC. pneumoniae(range, 20 to 225), while all but one failed to have any effect on the infectivity ofC. trachomatisserovar E. While theC. pneumoniaeinclusion IFA had a high sensitivity for detecting chlamydial antibodies, depending on whether it was used as a screening test for detecting samples with low (≥16) or elevated (≥512) MIF titers, its specificity ranged from 53.4 to 77.1%. In conclusion, the inclusion IFA withC. pneumoniae-infected cells was best suited as a sensitive screening test for identifying specimens with elevated MIF titers (those associated with a possible acute infection withC. pneumoniae).
Vitamin A Levels and Immunity in Humans
Authors: Jason Janine , Archibald Lennox K. , Nwanyanwu Okey C. , Sowell Anne L. , Buchanan Ian , Larned Joshua , Bell Michael , Kazembe Peter N. , Dobbie Hamish , Jarvis William R.
Published: July 2002

In animal studies, vitamin A deficiency induces a shift from type 2 (humoral) to type 1 (cellular) cytokines; there are no similar data for humans. Control of human immunodeficiency virus (HIV) andMycobacterium tuberculosisinfections requires type 1 cytokine (cellular) immunity. These infections and vitamin A deficiency are highly prevalent in Africa. We therefore examined the interactions among serum vitamin A levels, immune parameters, HIV infection status,Mycobacterium bovisBCG vaccine scarring (as an indicator of a type 1 cytokine profile), and clinical findings for 70 hospitalized children in Malawi, Africa. Directly conjugated monoclonal antibodies and flow cytometry were used to assess cell-specific cytokine production by peripheral blood monocytes and lymphocyte subpopulations. The statistical techniques employed included nonparametric statistics and logistic regression analyses. Thirty percent of the participants had severe vitamin A deficiency (<10 μg/dl), 34% had moderate deficiency (10 to <20 μg/dl), and 36% had normal levels (≥20 μg/dl). Vitamin A levels were lower for HIV-positive than for HIV-negative children (median, 10 and 17 μg/dl, respectively). Vitamin A-deficient children (<20 μg/dl) were more likely than non-vitamin A-deficient children to have higher proportions of natural killer (NK) cells (median, 8.3 and 5.2%, respectively) and lower ratios of interleukin-10-producing monocytes to tumor necrosis factor alpha-producing monocytes after induction (median, 1.0 and 2.3, respectively). Vitamin A-deficient children were also more likely than non-vitamin A-deficient children to exhibit respiratory symptoms (47% versus 12%) and visible BCG vaccine scars (83% versus 48%), which are indicative of a type 1 response to vaccination. Vitamin A status did not vary with gender, age, incidence of malaria parasitemia, blood culture positivity, or rates of mortality (6% of vitamin A-deficient children died versus 20% of non-vitamin A-deficient children). Lower vitamin A levels were associated with a relative type 1 cytokine dominance and proportionately more NK cells, both of which may be somewhat beneficial to persons who are exposed to HIV,M. tuberculosis, or other type 1 pathogens.