bluuebunny/crossref_metadata_2025 huggingface dataset:
Dimensionality Effects in the Lifetime of Surface States
Authors: Kliewer J. , Berndt R. , Chulkov E. V. , Silkin V. M. , Echenique P. M. , Crampin S.
Published: July 2002

A long-standing discrepancy between experimental and theoretical values for the lifetimes of holes in the surface-state electron bands on noble metal surfaces is resolved; previous determinations of both are found to have been in error. The ability of the scanning tunneling microscope to verify surface quality before taking spectroscopic measurements is used to remove the effects of defect scattering on experimental lifetimes, found to have been a significant contribution to prior determinations. A theoretical treatment of inelastic electron-electron scattering is developed that explicitly includes intraband transitions within the surface state band. In our model, two-dimensional decay channels dominate the electron-electron interactions that contribute to the hole decay and are screened by the electron states of the underlying three-dimensional electron system.
Real-Time Observation of Adsorbate Atom Motion Above a Metal Surface
Authors: Petek Hrvoje , Weida Miles J. , Nagano Hisashi , Ogawa Susumu
Published: July 2002

The dynamics of cesium atom motion above the copper(111) surface following electronic excitation with light was studied with femtosecond (10
–15
seconds) time resolution. Unusual changes in the surface electronic structure within 160 femtoseconds after excitation, observed by time-resolved two-photon photoemission spectroscopy, are attributed to atomic motion in a copper–cesium bond-breaking process. Describing the change in energy of the cesium antibonding state with a simple classical model provides information on the mechanical forces acting on cesium atoms that are “turned on” by photoexcitation. Within 160 femtoseconds, the copper–cesium bond extends by 0.35 angstrom from its equilibrium value.
Extinct
129
I in Halite from a Primitive Meteorite: Evidence for Evaporite Formation in the Early Solar System
Authors: Whitby James , Burgess Ray , Turner Grenville , Gilmour Jamie , Bridges John
Published: July 2002

Halite crystals from the Zag H3-6 chondrite contain essentially pure (monoisotopic) xenon-129 (
129
Xe) produced in the early history of the solar system by the decay of short-lived iodine-129 (
129
I) (half-life = 15.7 million years). Correlated release of
129
Xe and
128
Xe, produced artificially from
127
I by neutron irradiation, corresponds to an initial (
129
I/
127
I) ratio of (1.35 ± 0.05) × 10
−4
, close to the most primitive early solar system value. If the
129
Xe was produced by in situ decay, then the halite formed from an aqueous fluid within 2 million years of the oldest known solar system minerals.
A Single Adenosine with a Neutral p
K
a
in the Ribosomal Peptidyl Transferase Center
Authors: Muth Gregory W. , Ortoleva-Donnelly Lori , Strobel Scott A.
Published: July 2002

Biochemical and crystallographic evidence suggests that 23
S
ribosomal RNA (rRNA) is the catalyst of peptide bond formation. To explore the mechanism of this reaction, we screened for nucleotides in
Escherichia coli
23
S
rRNA that may have a perturbed p
K
a
(where
K
a
is the acid constant) based on the pH dependence of dimethylsulfate modification. A single universally conserved A (number 2451) within the central loop of domain V has a near neutral p
K
a
of 7.6 ± 0.2, which is about the same as that reported for the peptidyl transferase reaction. In vivo mutational analysis of this nucleotide indicates that it has an essential role in ribosomal function. These results are consistent with a mechanism wherein the nucleotide base of A2451 serves as a general acid base during peptide bond formation.
A Calmodulin-Related Protein That Suppresses Posttranscriptional Gene Silencing in Plants
Authors: Anandalakshmi Radhamani , Marathe Rajendra , Ge Xin , Herr J. M. , Mau Christopher , Mallory Allison , Pruss Gail , Bowman Lewis , Vance Vicki B.
Published: July 2002

Posttranscriptional gene silencing (PTGS) is an ancient eukaryotic regulatory mechanism in which a particular RNA sequence is targeted and destroyed. The helper component–proteinase (HC-Pro) of plant potyviruses suppresses PTGS in plants. Using a yeast two-hybrid system, we identified a calmodulin-related protein (termed rgs-CaM) that interacts with HC-Pro. Here we report that rgs-CaM, like HC-Pro itself, suppresses gene silencing. Our work is the first report identifying a cellular suppressor of PTGS.
Imaging Precessional Motion of the Magnetization Vector
Authors: Acremann Y. , Back C. H. , Buess M. , Portmann O. , Vaterlaus A. , Pescia D. , Melchior H.
Published: July 2002

We report on imaging of three-dimensional precessional orbits of the magnetization vector in a magnetic field by means of a time-resolved vectorial Kerr experiment that measures all three components of the magnetization vector with picosecond resolution. Images of the precessional mode taken with submicrometer spatial resolution reveal that the dynamical excitation in this time regime roughly mirrors the symmetry of the underlying equilibrium spin configuration and that its propagation has a non-wavelike character. These results should form the basis for realistic models of the magnetization dynamics in a largely unexplored but technologically increasingly relevant time scale.
Tropical Climate at the Last Glacial Maximum Inferred from Glacier Mass-Balance Modeling
Authors: Hostetler Steven W. , Clark Peter U.
Published: July 2002

Model-derived equilibrium line altitudes (ELAs) of former tropical glaciers support arguments, based on other paleoclimate data, for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum (LGM). Relative to the present, LGM ELAs were maintained by air temperatures that were 3.5° to 6.6°C lower and precipitation that ranged from 63% wetter in Hawaii to 25% drier on Mt. Kenya, Africa. Our results imply the need for a ∼3°C cooling of LGM sea surface temperatures in the western Pacific warm pool. Sensitivity tests suggest that LGM ELAs could have persisted until 16,000 years before the present in the Peruvian Andes and on Papua, New Guinea.
A Four-Dimensional Generalization of the Quantum Hall Effect
Authors: Zhang Shou-Cheng , Hu Jiangping
Published: July 2002

We construct a generalization of the quantum Hall effect, where particles move in four dimensional space under a
SU
(2) gauge field. This system has a macroscopic number of degenerate single particle states. At appropriate integer or fractional filling fractions the system forms an incompressible quantum liquid. Gapped elementary excitation in the bulk interior and gapless elementary excitations at the boundary are investigated.
A 1998 Survey of Extended-Spectrum β-Lactamases in
Enterobacteriaceae
in France
Authors: De Champs C. , Sirot D. , Chanal C. , Bonnet R. , Sirot J. ,   the French Study Group
Published: July 2002

In a 3-month period in 1998, 79 consecutive isolates of
Enterobacteriaceae
producing an extended-spectrum β-lactamase (ESBL) were collected. ESBLs were predominantly TEM derivatives (74 of 79): TEM-24-like (40 isolates), TEM-3-like (29 isolates), TEM-21 (3 isolates), and TEM-4 and TEM-52 (1 isolate each). Four isolates produced SHV derivatives SHV-4 (three isolates) and SHV-5 (one isolate), and one strain produced a CTX-M-3 enzyme. The high proportion of TEM-24-like-producing
Enterobacter aerogenes
isolates (36 of 79) suggests the occurrence of an epidemic strain in France.
Updated Sequence Information and Proposed Nomenclature for
bla
TEM
Genes and Their Promoters
Authors: Leflon-Guibout V. , Heym B. , Nicolas-Chanoine M.-H.
Published: July 2002

The nucleotide sequences of 59
bla
TEM
genes encoding inhibitor-resistant TEM enzymes showed great genetic variability and were associated with different types of promoters. These findings led us to suggest an updated
bla
TEM
gene nomenclature based on the origin of the
bla
TEM
gene (
bla
TEM-1A
,
bla
TEM-1B
,
bla
TEM-1C
,
bla
TEM-1D
,
bla
TEM-1E
, and
bla
TEM-1F
) and the promoter type.
Polycationic Peptides as Prophylactic Agents against Methicillin-Susceptible or Methicillin-Resistant
Staphylococcus epidermidis
Vascular Graft Infection
Authors: Giacometti Andrea , Cirioni Oscar , Ghiselli Roberto , Goffi Luigi , Mocchegiani Federico , Riva Alessandra , Scalise Giorgio , Saba Vittorio
Published: July 2002

Several polycationic peptides isolated from animals, plants, and bacterial species possess a broad spectrum of antimicrobial activity. A rat model was used to investigate the efficacies of two peptides, ranalexin and buforin II, in the prevention of vascular prosthetic graft infections. The effect of peptide-soaked collagen-sealed Dacron was compared to that of rifampin-soaked collagen-sealed Dacron in the rat model of graft infection caused by methicillin-susceptible rifampin-susceptible
Staphylococcus epidermidis
and methicillin-resistant rifampin-susceptible
S. epidermidis
. Graft infections were established in the back subcutaneous tissue of 240 adult male Wistar rats by implantation of 1-cm
2
Dacron prostheses, followed by topical inoculation with 2 × 10
7
CFU of
S. epidermidis
. The study included a control group (no graft contamination), two contaminated groups that did not receive any antibiotic prophylaxis, two contaminated groups to which perioperative intraperitoneal cefazolin prophylaxis (30 mg/kg of body weight) was administered, six contaminated groups that received a peptide- or rifampin-soaked graft, and six contaminated groups that received a peptide- or rifampin-soaked graft and perioperative intraperitoneal cefazolin prophylaxis (30 mg/kg). The grafts were sterilely removed 7 days after implantation, and the infection was evaluated by using sonication and quantitative agar culture. Overall, the efficacies of the polycationic peptides against the methicillin-susceptible and methicillin-resistant strains were not significantly different from that of rifampin. Nevertheless, the combinations of ranalexin- and buforin II-coated grafts with cefazolin treatment demonstrated efficacies significantly higher than that of the combination of rifampin-coated grafts and cefazolin treatment against the methicillin-resistant strain.
Mutations in the Beginning of the
rpoB
Gene Can Induce Resistance to Rifamycins in both
Helicobacter pylori
and
Mycobacterium tuberculosis
Authors: Heep Markus , Rieger Ulrich , Beck Daniela , Lehn Norbert
Published: July 2002

A clinical isolate of
Helicobacter pylori
that developed resistance to rifabutin during therapy carried an
rpoB
gene that retained a wild-type cluster region sequence but had acquired a novel codon 149 (V149F) mutation. In transformation experiments, the mutation was shown to confer high-level rifabutin resistance. The equivalent mutation (V176F) was present in several resistant isolates of
Mycobacterium tuberculosis
.
Identification of the Novobiocin Biosynthetic Gene Cluster of
Streptomyces spheroides
NCIB 11891
Authors: Steffensky Marion , Mühlenweg Agnes , Wang Zhao-Xin , Li Shu-Ming , Heide Lutz
Published: July 2002

The novobiocin biosynthetic gene cluster from
Streptomyces spheroides
NCIB 11891 was cloned by using homologous deoxynucleoside diphosphate (dNDP)-glucose 4,6-dehydratase gene fragments as probes. Double-stranded sequencing of 25.6 kb revealed the presence of 23 putative open reading frames (ORFs), including the gene for novobiocin resistance,
gyrB
r
, and at least 11 further ORFs to which a possible role in novobiocin biosynthesis could be assigned. An insertional inactivation experiment with a dNDP-glucose 4,6-dehydratase fragment resulted in abolishment of novobiocin production, since biosynthesis of the deoxysugar moiety of novobiocin was blocked. Heterologous expression of a key enzyme of novobiocin biosynthesis, i.e., novobiocic acid synthetase, in
Streptomyces lividans
TK24 further confirmed the involvement of the analyzed genes in the biosynthesis of the antibiotic.
Effects of AIDS and Gender on Steady-State Plasma and Intrapulmonary Ethionamide Concentrations
Authors: Conte John E. , Golden Jeffrey A. , McQuitty Mari , Kipps Juliana , Lin Emil T. , Zurlinden Elisabeth
Published: July 2002

Ethionamide, 250 mg every 12 h for a total of nine doses, was administered to 40 adult volunteers (10 men with AIDS, 10 healthy men, 10 women with AIDS, and 10 healthy women). Blood was obtained for drug assay prior to administration of the first dose, 2 h after the last dose, and at the completion of standardized bronchoscopy and bronchoalveolar lavage, which were performed 4 h after the last dose. Ethionamide was measured in epithelial lining fluid (ELF) and alveolar cells (AC) using a new mass spectrometric method. The presence of AIDS or gender was without significant effect on the concentrations of ethionamide in plasma, AC, or ELF. Plasma concentrations (mean ± standard deviation [SD]) were 0.97 ± 0.65 and 0.65 ± 0.35 μg/ml at 2 and 4 h after the last dose, respectively, and both values were significantly greater than the concentration of ethionamide in AC (0.38 ± 0.47 μg/ml) (P< 0.05). The concentration of ethionamide was significantly greater in ELF (5.63 ± 3.8 μg/ml) than in AC or plasma at 2 and 4 h and was approximately 10 to 20 times the reported MIC for ethionamide-susceptible strains ofMycobacterium tuberculosis. For all 40 subjects, the ELF/plasma concentration ratios (mean ± SD) at 2 and 4 h were 8.7 ± 11.7 and 9.7 ± 5.6, respectively. We conclude that the absorption of orally administered ethionamide, as measured in this study, was not affected by gender or the presence of AIDS. Ethionamide concentrations were significantly greater in ELF than in plasma or AC, suggesting that substantial antimycobacterial activity resides in this compartment.
A Randomized Controlled Comparison of Azithromycin and Ofloxacin for Treatment of Multidrug-Resistant or Nalidixic Acid-Resistant Enteric Fever
Authors: Chinh Nguyen Tran , Parry Christopher M. , Ly Nguyen Thi , Ha Huynh Duy , Thong Mai Xuan , Diep To Song , Wain John , White Nicholas J. , Farrar Jeremy J.
Published: July 2002

To examine the efficacy and safety of short courses of azithromycin and ofloxacin for treating multidrug-resistant (MDR, i.e., resistant to chloramphenicol, ampicillin, and cotrimoxazole) and nalidixic acid-resistant enteric fever, azithromycin (1 g once daily for 5 days at 20 mg/kg/day) and ofloxacin (200 mg orally twice a day for 5 days at 8 mg/kg/day) were compared in an open randomized study in adults admitted to a hospital with uncomplicated enteric fever. A total of 88 blood culture-confirmed patients were enrolled in the study (86 with
Salmonella enterica
serovar Typhi and 2 with
S. enterica
serovar Paratyphi A). Of these, 44 received azithromycin and 44 ofloxacin. A total of 68 of 87 (78%) isolates were MDR serovar Typhi, and 46 of 87 (53%) were nalidixic acid resistant. The MIC
90
(range) of azithromycin was 8 (4 to 16) μg/ml for the isolates. The MIC
90
(range) of ofloxacin for the nalidixic acid-sensitive isolates was 0.03 (0.015 to 0.06) μg/ml and for the nalidixic acid-resistant isolates it was 0.5 (0.25 to 1.0) μg/ml. There was no significant difference in the overall clinical cure rate with ofloxacin and azithromycin (38 of 44 [86.4%] versus 42 of 44 [95.5%];
P
= 0.27) or in the patients infected with nalidixic acid-resistant typhoid (17 of 21 [81.0%] versus 24 of 25 [96.0%];
P
= 0.16). However, patients with nalidixic acid-resistant typhoid treated with ofloxacin had a longer fever clearance time compared with those treated with azithromycin (174 [60 to 264] versus 135 [72 to 186] h;
P
= 0.004) and had positive fecal cultures after the end of treatment (7 of 17 [41%] versus 0 of 19 [0%];
P
= 0.002). Both antibiotics were well tolerated. A 5-day course of azithromycin was effective for the treatment of enteric fever due to MDR and nalidixic-acid-resistant serovar Typhi, whereas the ofloxacin regimen chosen was less satisfactory for these strains.
A
soxRS
-Constitutive Mutation Contributing to Antibiotic Resistance in a Clinical Isolate of
Salmonella enterica
(Serovar Typhimurium)
Authors: Koutsolioutsou Anastasia , Martins Elizabeth A. , White D. G. , Levy S. B. , Demple Bruce
Published: July 2002

The
soxRS
regulon is activated by redox-cycling drugs such as paraquat and by nitric oxide. The >15 genes of this system provide resistance to both oxidants and multiple antibiotics. An association between clinical quinolone resistance and elevated expression of the
soxRS
regulon has been observed in
Escherichia coli
, but this association has not been explored for other enteropathogenic bacteria. Here we describe a
soxRS
-constitutive mutation in a clinical strain of
Salmonella enterica
(serovar Typhimurium) that arose with the development of resistance to quinolones during treatment. The elevated quinolone resistance in this strain derived from a point mutation in the
soxR
gene and could be suppressed in
trans
by multicopy wild-type
soxRS
. Multiple-antibiotic resistance was also transferred to a laboratory strain of
S. enterica
by introducing the cloned mutant
soxR
gene from the clinical strain. The results show that constitutive expression of
soxRS
can contribute to antibiotic resistance in clinically relevant
S. enterica.
Genetic Analyses of Mutations Contributing to Fluoroquinolone Resistance in Clinical Isolates of
Streptococcus pneumoniae
Authors: Weigel L. M. , Anderson G. J. , Facklam R. R. , Tenover F. C.
Published: July 2002

Twenty-one clinical isolates of
Streptococcus pneumoniae
showing reduced susceptibility or resistance to fluoroquinolones were characterized by serotype, antimicrobial susceptibility, and genetic analyses of the quinolone resistance-determining regions (QRDRs) of
gyrA
,
gyrB
,
parC
, and
parE
. Five strains were resistant to three or more classes of antimicrobial agents. In susceptibility profiles for gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, ofloxacin, sparfloxacin, and trovafloxacin, 14 isolates had intermediate- or high-level resistance to all fluoroquinolones tested except gemifloxacin (no breakpoints assigned). Fluoroquinolone resistance was not associated with serotype or with resistance to other antimicrobial agents. Mutations in the QRDRs of these isolates were more heterogeneous than those previously reported for mutants selected in vitro. Eight isolates had amino acid changes at sites other than ParC/S79 and GyrA/S81; several strains contained mutations in
gyrB
,
parE
, or both loci. Contributions to fluoroquinolone resistance by individual amino acid changes, including GyrB/E474K, ParE/E474K, and ParC/A63T, were confirmed by genetic transformation of
S. pneumoniae
R6. Mutations in
gyrB
were important for resistance to gatifloxacin but not moxifloxacin, and mutation of
gyrA
was associated with resistance to moxifloxacin but not gatifloxacin, suggesting differences in the drug-target interactions of the two 8-methoxyquinolones. The positions of amino acid changes within the four genes affected resistance more than did the total number of QRDR mutations. However, the effect of a specific mutation varied significantly depending on the agent tested. These data suggest that the heterogeneity of mutations will likely increase as pneumococci are exposed to novel fluoroquinolone structures, complicating the prediction of cross-resistance within this class of antimicrobial agents.
Pharmacokinetics, Safety, and Antiviral Effects of Hypericin, a Derivative of St. John's Wort Plant, in Patients with Chronic Hepatitis C Virus Infection
Authors: Jacobson Jeffrey M. , Feinman Lawrence , Liebes Leonard , Ostrow Nancy , Koslowski Victoria , Tobia Alfonso , Cabana Bernard E. , Lee Dong-Hun , Spritzler John , Prince Alfred M.
Published: July 2002

Hypericin is a natural derivative of the common St. Johns wort plant,Hypericum perforatum. It has in vitro activity against several viruses, including bovine diarrhea virus, a pestivirus with structural similarities to hepatitis C virus (HCV). We conducted a phase I dose escalation study to determine the safety and antiviral activity of hypericin in patients with chronic HCV infection. The first 12 patients received an 8-week course of 0.05 mg of hypericin per kg of body weight orally once a day; 7 patients received an 8-week course of 0.10 mg/kg orally once a day. At the end of the 8-week period of treatment, no subject had a change of plasma HCV RNA level of more than 1.0 log10. Five of 12 subjects receiving the 0.05-mg/kg/day dosing schedule and 6 of 7 subjects receiving the 0.10-mg/kg/day dosing schedule developed phototoxic reactions. No other serious adverse events associated with hypericin use occurred. The pharmacokinetic data revealed a long elimination half-life (mean values of 36.1 and 33.8 h, respectively, for the doses of 0.05 and 0.1 mg/kg) and mean area under the curve determinations of 1.5 and 3.1 μg/ml × hr, respectively. In sum, hypericin given orally in doses of 0.05 and 0.10 mg/kg/d caused considerable phototoxicity and had no detectable anti-HCV activity in patients with chronic HCV infection.
Differences in Antibiotic Resistance Patterns ofEnterococcus faecalisandEnterococcus faeciumStrains Isolated from Farm and Pet Animals
Authors: Butaye Patrick , Devriese Luc A. , Haesebrouck Freddy
Published: July 2002

The prevalence of acquired resistance in 146Enterococcus faeciumand 166Enterococcus faecalisstrains from farm and pet animals, isolated in 1998 and 1999 in Belgium, against antibiotics used for growth promotion and for therapy was determined. Acquired resistance against flavomycin and monensin, two antibiotics used solely for growth promotion, was not detected. Avoparcin (glycopeptide) resistance was found sporadically inE. faeciumonly. Avilamycin resistance was almost exclusively seen in strains from farm animals. Resistance rates were higher inE. faeciumstrains from broiler chickens than in strains from other animal groups with tylosin and virginiamycin and inE. faecalisas well as inE. faeciumstrains with narasin and bacitracin. Resistance against ampicillin was mainly found amongE. faeciumstrains from pets and was absent inE. faecalis. Tetracycline resistance occurred most often in strains from farm animals, while enrofloxacin resistance, only found inE. faecalis, occurred equally among strains from all origins. Resistance against gentamicin was very rare in broiler strains, whereas resistance rates were high in strains from other origins. It can be concluded that resistance against antibiotics used solely for growth promotion was more prevalent inE. faeciumstrains than inE. faecalisstrains. With few exceptions, resistance against the different categories of antibiotics was more prevalent in strains from farm animals than in those from pets.
Limonene Arrests Parasite Development and Inhibits Isoprenylation of Proteins in
Plasmodium falciparum
Authors: Moura Ivan Cruz , Wunderlich Gerhard , Uhrig Maria L. , Couto Alicia S. , Peres Valnice J. , Katzin Alejandro M. , Kimura Emı́lia A.
Published: July 2002

Isoprenylation is an essential protein modification in eukaryotic cells. Herein, we report that in
Plasmodium falciparum
, a number of proteins were labeled upon incubation of intraerythrocytic forms with either [
3
H]farnesyl pyrophosphate or [
3
H]geranylgeranyl pyrophosphate. By thin-layer chromatography, we showed that attached isoprenoids are partially modified to dolichol and other, uncharacterized, residues, confirming active isoprenoid metabolism in this parasite. Incubation of blood-stage
P. falciparum
treated with the isoprenylation inhibitor limonene significantly decreased the parasites' progression from the ring stage to the trophozoite stage and at 1.22 mM, 50% of the parasites died after the first cycle. Using Ras- and Rap-specific monoclonal antibodies, putative Rap and Ras proteins of
P. falciparum
were immunoprecipitated. Upon treatment with 0.5 mM limonene, isoprenylation of these proteins was significantly decreased, possibly explaining the observed arrest of parasite development.
Effects of Flavophospholipol on Resistance in Fecal
Escherichia coli
and Enterococci of Fattening P
Authors: van den Bogaard A. E. , Hazen M. , Hoyer M. , Oostenbach P. , Stobberingh E. E.
Published: July 2002

A “plasmid-curing effect” of multiresistant
Escherichia coli
by flavophospholipol, an antibiotic used as an antimicrobial growth promoter (AMGP) in animal feeds, has been reported to occur in vitro and in vivo under experimental conditions. In this study, the effect of flavophospholipol under field conditions was studied. The prevalence and degree (proportion of resistant strains to the total numbers present per gram of feces) of resistance of indicator bacteria,
E. coli
and enterococci, was determined in fecal samples from three groups of pigs that were fed a commercial finisher feed without any AMGP. Group A was the negative control group without any AMGP, group B received the same feed with 9 mg of flavophospholipol/kg of feed (study group), and group C received the same feed with 15 mg of avoparcin/kg (positive control). Fecal samples from each pig were collected at the start and at the end of the study and assessed for the prevalence and degree of resistance against antibiotics commonly used either for therapy in pig medicine or as an AMGP. Before the start of the study, all pigs were colonized with multiresistant
E. coli
by mixing three resistant pig isolates through their feed after disturbance of the colonization resistance of the intestinal flora by a 3-day course of lincomycin and spectinomycin. At the end of the study, the overall prevalence and degree of resistance of
E. coli
in the fecal flora had increased significantly in groups A and C but remained at the same level as at the start of the study in group B. The prevalence of vancomycin resistance was 44 and 41% in groups A and B, respectively, but only very low numbers of vancomycin-resistant enterococci (VRE) per gram of feces were found. In the avoparcin-fed group, the prevalence was 72%, and in 57% of the samples, more than 50% of all enterococci present were vancomycin resistant. The prevalence of resistant
Enterococcus faecalis
increased only in the flavophospholipol-exposed group, from 23% before the start of the study to 43% at the end of the study. It was concluded that flavophospholipol effectively suppressed the augmentation and dissemination of multiresistant
E. coli
in the intestinal flora of fattening pigs. Avoparcin use strongly selected for VRE carriage and excretion. Therefore, as neither flavophospholipol nor any related molecule is used therapeutically, no cross-resistance with therapeutic antibiotics exists and no transmissible resistance has been shown; the major decrease in resistance in intestinal
E. coli
of flavophospholipol-fed animals seemed to outweigh the small increase in the risk of transfer of flavophospholipol-resistant
E. faecalis
from animals to humans via the food chain.
Evidence of Active Efflux in Resistance to Ciprofloxacin and to Ethidium Bromide by
Mycoplasma hominis
Authors: Raherison S. , Gonzalez P. , Renaudin H. , Charron A. , Bébéar C. , Bébéar C. M.
Published: July 2002

The uptake of fluoroquinolones was characterized for the fluoroquinolone-susceptible strain PG21 of
Mycoplasma hominis
. Accumulation of fluoroquinolones appeared to occur by passive diffusion. Addition of arginine as the energizer significantly reduced the uptake of fluoroquinolones, suggesting the presence of an energy-dependent efflux process. Reserpine and orthovanadate, two multidrug pump inhibitors, increased significantly the ciprofloxacin (CIP) uptake. In contrast, such a strong effect was not observed for moxifloxacin and pefloxacin uptakes. Two ethidium bromide (EtBr)-resistant strains, selected in vitro, showed a resistance profile compatible with a multidrug-resistant phenotype, with increased MICs for the hydrophilic fluoroquinolones, CIP and norfloxacin, EtBr, and acriflavine. Taking the EtBr-resistant strain RB1La as a model, a significant decrease of the CIP and EtBr uptakes was observed compared to the reference strain PG21. In the presence of reserpine and orthovanadate, both inhibitors of ATP-dependent efflux pumps, the CIP uptake increased significantly, reaching approximately the same level as that of the susceptible strain. Similar results were obtained with EtBr uptake and efflux experiments. Our data suggest the presence of an active efflux system, possibly an ABC-type efflux pump, implicated in the resistance to CIP and unrelated compounds like EtBr in the human mycoplasma
M. hominis
.
Evolution of Thermotolerance in Hot Spring Cyanobacteria of the GenusSynechococcus
Authors: Miller Scott R. , Castenholz Richard W.
Published: July 2002

The extension of ecological tolerance limits may be an important mechanism by which microorganisms adapt to novel environments, but it may come at the evolutionary cost of reduced performance under ancestral conditions. We combined a comparative physiological approach with phylogenetic analyses to study the evolution of thermotolerance in hot spring cyanobacteria of the genusSynechococcus. Among the 20 laboratory clones ofSynechococcusisolated from collections made along an Oregon hot spring thermal gradient, four different 16S rRNA gene sequences were identified. Phylogenies constructed by using the sequence data indicated that the clones were polyphyletic but that three of the four sequence groups formed a clade. Differences in thermotolerance were observed for clones with different 16S rRNA gene sequences, and comparison of these physiological differences within a phylogenetic framework provided evidence that more thermotolerant lineages ofSynechococcusevolved from less thermotolerant ancestors. The extension of the thermal limit in these bacteria was correlated with a reduction in the breadth of the temperature range for growth, which provides evidence that enhanced thermotolerance has come at the evolutionary cost of increased thermal specialization. This study illustrates the utility of using phylogenetic comparative methods to investigate how evolutionary processes have shaped historical patterns of ecological diversification in microorganisms.
Cloning and Random Mutagenesis of theErwinia herbicola tyrRGene for High-Level Expression of Tyrosine Phenol-Lyase
Authors: Katayama Takane , Suzuki Hideyuki , Koyanagi Takashi , Kumagai Hidehiko
Published: July 2002

Tyrosine phenol-lyase (Tpl), which can synthesize 3,4-dihydroxyphenylalanine from pyruvate, ammonia, and catechol, is a tyrosine-inducible enzyme. Previous studies demonstrated that thetplpromoter ofErwinia herbicolais activated by the TyrR protein ofEscherichia coli. In an attempt to create a high-Tpl-expressing strain, we cloned thetyrRgene ofE. herbicolaand then randomly mutagenized it. Mutant TyrR proteins with enhanced ability to activatetplwere screened for by use of thelacreporter system inE. coli. The most increased transcription oftplwas observed for the strain with the mutanttyrRallele involving amino acid substitutions of alanine, cysteine, and glycine for valine-67, tyrosine-72, and glutamate-201, respectively. AtyrR-deficient derivative ofE. herbicolawas constructed and transformed with a plasmid carrying the mutanttyrRallele (V67A Y72C E201G substitutions). The resultant strain expressed Tpl without the addition of tyrosine to the medium and produced as much of it as was produced by the wild-type strain grown under tyrosine-induced conditions. The regulatory properties of the mutant TyrRV67A, TyrRY72C, TyrRE201G, and TyrRV67A Y72C E201Gproteins were examined in vivo. Interestingly, as opposed to the wild-type TyrR protein, the mutant TyrRV67Aprotein had a repressive effect on thetyrPpromoter in the presence of phenylalanine as the coeffector.
Quinolobactin, a New Siderophore of
Pseudomonas fluorescens
ATCC 17400, the Production of Which Is Repressed by the Cognate Pyoverdine
Authors: Mossialos Dimitris , Meyer Jean-Marie , Budzikiewicz Herbert , Wolff Ulrich , Koedam Nico , Baysse Christine , Anjaiah Vanamala , Cornelis Pierre
Published: July 2002

Transposon mutant strain 3G6 of
Pseudomonas fluorescens
ATCC 17400 which was deficient in pyoverdine production, was found to produce another iron-chelating molecule; this molecule was identified as 8-hydroxy-4-methoxy-quinaldic acid (designated quinolobactin). The pyoverdine-deficient mutant produced a supplementary 75-kDa iron-repressed outer membrane protein (IROMP) in addition to the 85-kDa IROMP present in the wild type. The mutant was also characterized by substantially increased uptake of
59
Fe-quinolobactin. The 75-kDa IROMP was produced by the wild type after induction by quinolobactin-containing culture supernatants obtained from the pyoverdine-negative mutant or by purified quinolobactin. Conversely, adding purified wild-type pyoverdine to the growth medium resulted in suppression of the 75-kDa IROMP in the pyoverdine-deficient mutant; however, suppression was not observed when
Pseudomonas aeruginosa
PAO1 pyoverdine, a siderophore utilized by strain 3G6, was added to the culture. Therefore, we assume that the quinolobactin receptor is the 75-kDa IROMP and that the quinolobactin-mediated iron uptake system is repressed by the cognate pyoverdine.
Cyt1A from
Bacillus thuringiensis
Synergizes Activity of
Bacillus sphaericus
against
Aedes aegypti
(Diptera: Culicidae)
Authors: Wirth Margaret C. , Federici Brian A. , Walton William E.
Published: July 2002

Bacillus sphaericus
is a mosquitocidal bacterium recently developed as a commercial larvicide that is used worldwide to control pestiferous and vector mosquitoes. Whereas
B. sphaericus
is highly active against larvae of
Culex
and
Anopheles
mosquitoes, it is virtually nontoxic to
Aedes aegypti
, an important vector species. In the present study, we evaluated the capacity of the cytolytic protein Cyt1A from
Bacillus thuringiensis
subsp.
israelensis
to enhance the toxicity of
B. sphaericus
toward
A. aegypti
. Various combinations of these two materials were evaluated, and all were highly toxic. A ratio of 10:1 of
B. sphaericus
to Cyt1A was 3,600-fold more toxic to
A. aegypti
than
B. sphaericus
alone. Statistical analysis showed this high activity was due to synergism between the Cyt1A toxin and
B. sphaericus
. These results suggest that Cyt1A could be useful in expanding the host range of
B. sphaericus
.
2,4,6-Trinitrotoluene Reduction by Carbon Monoxide Dehydrogenase from
Clostridium thermoaceticum
Authors: Huang Shouqin , Lindahl Paul A. , Wang Chuanyue , Bennett George N. , Rudolph Frederick B. , Hughes Joseph B.
Published: July 2002

Purified CO dehydrogenase (CODH) from
Clostridium thermoaceticum
catalyzed the transformation of 2,4,6-trinitrotoluene (TNT). The intermediates and reduced products of TNT transformation were separated and appear to be identical to the compounds formed by
C. acetobutylicum
, namely, 2-hydroxylamino-4,6-dinitrotoluene (2HA46DNT), 4-hydroxylamino-2,6-dinitrotoluene (4HA26DNT), 2,4-dihydroxylamino-6-nitrotoluene (24DHANT), and the Bamberger rearrangement product of 2,4-dihydroxylamino-6-nitrotoluene. In the presence of saturating CO, CODH catalyzed the conversion of TNT to two monohydroxylamino derivatives (2HA46DNT and 4HA26DNT), with 4HA26DNT as the dominant isomer. These derivatives were then converted to 24DHANT, which slowly converted to the Bamberger rearrangement product. Apparent

K
m

and
k
cat
values of TNT reduction were 165 ± 43 μM for TNT and 400 ± 94 s
−1
, respectively. Cyanide, an inhibitor for the CO/CO
2
oxidation/reduction activity of CODH, inhibited the TNT degradation activity of CODH.
Higher Diversity of
Rhizobium leguminosarum
Biovar viciae Populations in Arable Soils than in Grass Soils
Authors: Palmer K. M. , Young J. P. W.
Published: July 2002

The bacterial genetic diversity after long-term arable cultivation was compared with that under permanent grassland using replicated paired contrasts. Pea-nodulating
Rhizobium leguminosarum
populations were sampled from pairs of arable and grass sites at four locations in Yorkshire, United Kingdom. Isolates were characterized using both chromosomal (16S-23S ribosomal DNA internal transcribed spacer PCR-restriction fragment length polymorphism) and plasmid (group-specific
repC
PCR amplification) markers. The diversities of chromosomal types,
repC
profiles, and combined genotypes were calculated using richness in types (adjusted to equal sample sizes by rarefaction), Shannon-Wiener index, and Simpson's index. The relative differences in diversity within each pair of sites were similar for all three diversity measures. Chromosomal types,
repC
profiles, and combined genotypes were each more diverse in arable soils than in grass soils at two of the four locations. The other comparisons showed no significant differences. We conclude that rhizobial diversity can be affected by differences between these two management regimens. Multiple regression analyses indicated that lower diversity was associated with high potential nitrogen and phosphate levels or with acidity.
Effects of Metal Phytoextraction Practices on the Indigenous Community of Arbuscular Mycorrhizal Fungi at a Metal-Contaminated Landfill
Authors: Pawlowska Teresa E. , Chaney Rufus L. , Chin Mel , Charvat Iris
Published: July 2002

Phytoextraction involves use of plants to remove toxic metals from soil. We examined the effects of phytoextraction practices with three plant species (
Silene vulgaris
,
Thlaspi caerulescens
, and
Zea mays
) and a factorial variation of soil amendments (either an ammonium or nitrate source of nitrogen and the presence or absence of an elemental sulfur supplement) on arbuscular mycorrhizal (AM) fungi (Glomales, Zygomycetes) at a moderately metal-contaminated landfill located in St. Paul, Minn. Specifically, we tested whether the applied treatments affected the density of glomalean spores and AM root colonization in maize. Glomalean fungi from the landfill were grouped into two morphotypes characterized by either light-colored spores (LCS) or dark-colored spores (DCS). Dominant species of the LCS morphotype were
Glomus mosseae
and an unidentified
Glomus
sp., whereas the DCS morphotype was dominated by
Glomus constrictum
. The density of spores of the LCS morphotype from the phytoremediated area was lower than the density of these spores in the untreated landfill soil. Within the experimental area, spore density of the LCS morphotype in the rhizosphere of mycorrhizal maize was significantly higher than in rhizospheres of nonmycorrhizal
S. vulgaris
or
T. caerulescens
. Sulfur supplement increased vesicular root colonization in maize and exerted a negative effect on spore density in maize rhizosphere. We conclude that phytoextraction practices, e.g., the choice of plant species and soil amendments, may have a great impact on the quantity and species composition of glomalean propagules as well as on mycorrhiza functioning during long-term metal-remediation treatments.
Cloning of the Malic Enzyme Gene from
Corynebacterium glutamicum
and Role of the Enzyme in Lactate Metabolism
Authors: Gourdon Pierre , Baucher Marie-France , Lindley Nic D. , Guyonvarch Armel
Published: July 2002

Malic enzyme is one of at least five enzymes, known to be present in
Corynebacterium glutamicum
, capable of carboxylation and decarboxylation reactions coupling glycolysis and the tricarboxylic acid cycle. To date, no information is available concerning the physiological role of the malic enzyme in this bacterium. The
malE
gene from
C. glutamicum
has been cloned and sequenced. The protein encoded by this gene has been purified to homogeneity, and the biochemical properties have been established. Biochemical characteristics indicate a decarboxylation role linked to NADPH generation. Strains of
C. glutamicum
in which the
malE
gene had been disrupted or overexpressed showed no detectable phenotype during growth on either acetate or glucose, but showed a significant modification of growth behavior during lactate metabolism. The wild type showed a characteristic brief period of exponential growth on lactate followed by a linear growth period. This growth pattern was further accentuated in a
malE
-disrupted strain (
ΔmalE
). However, the strain overexpressing
malE
maintained exponential growth until all lactate had been consumed. This strain accumulated significantly larger amounts of pyruvate in the medium than the other strains.
Effect of Dissemination of 2,4-Dichlorophenoxyacetic Acid (2,4-D) Degradation Plasmids on 2,4-D Degradation and on Bacterial Community Structure in Two Different Soil Horizons
Authors: Dejonghe Winnie , Goris Johan , El Fantroussi Saïd , Höfte Monica , De Vos Paul , Verstraete Willy , Top Eva M.
Published: July 2002

Transfer of the 2,4-dichlorophenoxyacetic acid (2,4-D) degradation plasmids pEMT1 and pJP4 from an introduced donor strain,
Pseudomonas putida
UWC3, to the indigenous bacteria of two different horizons (A horizon, depth of 0 to 30 cm; B horizon, depth of 30 to 60 cm) of a 2,4-D-contaminated soil was investigated as a means of bioaugmentation. When the soil was amended with nutrients, plasmid transfer and enhanced degradation of 2,4-D were observed. These findings were most striking in the B horizon, where the indigenous bacteria were unable to degrade any of the 2,4-D (100 mg/kg of soil) during at least 22 days but where inoculation with either of the two plasmid donors resulted in complete 2,4-D degradation within 14 days. In contrast, in soils not amended with nutrients, inoculation of donors in the A horizon and subsequent formation of transconjugants (10
5
CFU/g of soil) could not increase the 2,4-D degradation rate compared to that of the noninoculated soil. However, donor inoculation in the nonamended B-horizon soil resulted in complete degradation of 2,4-D within 19 days, while no degradation at all was observed in noninoculated soil during 89 days. With plasmid pEMT1, this enhanced degradation seemed to be due only to transconjugants (10
5
CFU/g of soil), since the donor was already undetectable when degradation started. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes showed that inoculation of the donors was followed by a shift in the microbial community structure of the nonamended B-horizon soils. The new 16S rRNA gene fragments in the DGGE profile corresponded with the 16S rRNA genes of 2,4-D-degrading transconjugant colonies isolated on agar plates. This result indicates that the observed change in the community was due to proliferation of transconjugants formed in soil. Overall, this work clearly demonstrates that bioaugmentation can constitute an effective strategy for cleanup of soils which are poor in nutrients and microbial activity, such as those of the B horizon.
Role of
phaD
in Accumulation of Medium-Chain-Length Poly(3-Hydroxyalkanoates) in
Pseudomonas oleovorans
Authors: Klinke Stefan , de Roo Guy , Witholt Bernard , Kessler Birgit
Published: July 2002

Pseudomonas oleovorans
is capable of producing poly(3-hydroxyalkanoates) (PHAs) as intracellular storage material. To analyze the possible involvement of
phaD
in medium-chain-length (MCL) PHA biosynthesis, we generated a
phaD
knockout mutant by homologous recombination. Upon disruption of the
phaD
gene, MCL PHA polymer accumulation was decreased. The PHA granule size was reduced, and the number of granules inside the cell was increased. Furthermore, mutant cells appeared to be smaller than wild-type cells. Investigation of MCL PHA granules revealed that the pattern of granule-associated proteins was changed and that the predominant protein PhaI was missing in the mutant. Complementation of the mutant with a
phaD
-harboring plasmid partially restored the wild-type characteristics of MCL PHA production and fully restored the granule and cell sizes. Furthermore, PhaI was attached to the granules of the complemented mutant. These results indicate that the
phaD
gene encodes a protein which plays an important role in MCL PHA biosynthesis. However, although its main effect seems to be the stabilization of MCL PHA granules, we found that the PhaD protein is not a major granule-associated protein and therefore might act by an unknown mechanism involving the PhaI protein.
Role of Respiratory Nitrate Reductase in Ability of
Pseudomonas fluorescens
YT101 To Colonize the Rhizosphere of Maize
Authors: Ghiglione Jean-François , Gourbiere François , Potier Patrick , Philippot Laurent , Lensi Robert
Published: July 2002

Selection of the denitrifying community by plant roots (i.e., increase in the denitrifier/total heterotroph ratio in the rhizosphere) has been reported by several authors. However, very few studies to evaluate the role of the denitrifying function itself in the selection of microorganisms in the rhizosphere have been performed. In the present study, we compared the rhizosphere survival of the denitrifying
Pseudomonas fluorescens
YT101 strain with that of its isogenic mutant deficient in the ability to synthesize the respiratory nitrate reductase, coinoculated in nonplanted or planted soil. We demonstrated that under nonlimiting nitrate conditions, the denitrifying wild-type strain had an advantage in the ability to colonize the rhizosphere of maize. Investigations of the effect of the inoculum characteristics (density of the total inoculum and relative proportions of mutant and wild-type strains) on the outcome of the selection demonstrated that the selective effect of the plant was expressed only during the phase of bacterial multiplication and that the intensity of selection was dependent on the magnitude of this phase. Moreover, application of the de Wit replacement series technique to our results suggests that the advantage of the wild-type strain was maximal when the ratio between the two strains in the inoculum was close to 1:1. This work constitutes the first direct demonstration that the presence of a functional structural gene encoding the respiratory nitrate reductase confers higher rhizosphere competence to a microorganism.
Expression of Green Fluorescent Protein in
Streptococcus gordonii
DL1 and Its Use as a Species-Specific Marker in Coadhesion with
Streptococcus oralis
34 in Saliva-Conditioned Biofilms In Vitro
Authors: Aspiras Marcelo B. , Kazmerzak Karen M. , Kolenbrander Paul E. , McNab Roderick , Hardegen Neil , Jenkinson Howard F.
Published: July 2002

Streptococcus gordonii
is one of the predominant streptococci in the biofilm ecology of the oral cavity. It interacts with other bacteria through receptor-adhesin complexes formed between cognate molecules on the surfaces of the partner cells. To study the spatial organization of
S. gordonii
DL1 in oral biofilms, we used green fluorescent protein (GFP) as a species-specific marker to identify
S. gordonii
in a two-species in vitro oral biofilm flowcell system. To drive expression of
gfp
, we isolated and characterized an endogenous
S. gordonii
promoter,
PhppA
, which is situated upstream of the chromosomal
hppA
gene encoding an oligopeptide-binding lipoprotein. A chromosomal chloramphenicol acetyltransferase (
cat
) gene fusion with
PhppA
was constructed and used to demonstrate that
PhppA
was highly active throughout the growth of bacteria in batch culture. A promoterless 0.8-kb
gfp
(′
gfp
) cassette was PCR amplified from pBJ169 and subcloned to replace the
cat
cassette downstream of the
S. gordonii
-derived
PhppA
in pMH109-HPP, generating pMA1. Subsequently, the
PhppA-′gfp
cassette was PCR amplified from pMA1 and subcloned into pDL277 and pVA838 to generate the
Escherichia coli-S. gordonii
shuttle vectors pMA2 and pMA3, respectively. Each vector was transformed into
S. gordonii
DL1 aerobically to ensure GFP expression. Flow cytometric analyses of aerobically grown transformant cultures were performed over a 24-h period, and results showed that GFP could be successfully expressed in
S. gordonii
DL1 from
PhppA
and that
S. gordonii
DL1 transformed with the
PhppA-′gfp
fusion plasmid stably maintained the fluorescent phenotype. Fluorescent
S. gordonii
DL1 transformants were used to elucidate the spatial arrangement of
S. gordonii
DL1 alone in biofilms or with the coadhesion partner
Streptococcus oralis
34 in two-species biofilms in a saliva-conditioned in vitro flowcell system. These results show for the first time that GFP expression in oral streptococci can be used as a species-specific marker in model oral biofilms.