bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of exchange‐rate volatility on foreign direct investment in Sub‐Saharan Africa
Authors: Kyereboah‐Coleman Anthony , Agyire‐Tettey Kwame F. 
Published: January 2008

PurposeThe present study aims at using a broader data set and longer time frame coupled with a relatively rigorous and robust methodology to examine the effect of real exchange rate volatility on foreign direct investment (FDI) in a small and developing country such as Ghana.Design/methodology/approachTime series data covering the period 1970‐2002 were used. ARCH and GARCH models were employed for the determination of real exchange rate volatility, and co‐integration and ECM were used to determine both the short‐ and the long‐term relationships.FindingsThe study showed that the volatility of the real exchange rate has a negative influence on FDI inflow and that the liberalization process has not led to a greater inflow of FDI in Ghana. It is also revealed that while both the stock of FDI and political factors are likely to attract FDI, most foreign investors do not consider the size of the market in making a decision to invest or otherwise in Ghana.Originality/valueThe main contribution of the study is its departure from the use of ratios in examining the effect of real exchange rate risk on FDI to a more rigorous and robust methodology, coupled with the fact that studies of this nature are virtually non‐existent in Ghana.
Risk minimization under budget constraints
Authors: Lee Kiseop 
Published: January 2008

PurposeThe purpose of this paper is to find the optimal hedging strategy when an investor has budget constraints on both the initial capital and the future cash flow.Design/methodology/approachThe paper follows the utility minimization of the total cost, using convex utility functions on both initial capital and future cash flows.FindingsClosed‐form solutions of optimal hedging strategies are found in some specific but popular cases. It is also found that this method corresponds to the local risk minimization method in quadratic hedging.Research limitations/implicationsHedging strategies are calculated for only two popular choices. One may want to calculate hedging strategies for other popular utility functions such as power utility or HARA utility.Practical implicationsWhen a trader has some budget constraint in both initial capital and future cash flows, this paper gives a simple alternative.Originality/valueBudget constraints on both initial capital and future cash flow are new to this kind of study. Connection to the local risk minimization strategy is original too.
Variation in Prokaryotic Community Composition as a Function of Resource Availability in Tidal Creek Sediments
Authors: Edmonds Jennifer W. , Weston Nathanial B. , Joye Samantha B. , Moran Mary Ann 
Published: January 2008

ABSTRACT

In anaerobic coastal sediments, hydrolytic and/or fermentative bacteria degrade polymeric material and produce labile intermediates, which are used by terminal metabolizers to complete the conversion of organic material to CO
2
. We used molecular approaches to evaluate the response of two bacterial terminal metabolizer groups from a coastal tidal creek sediments, sulfate reducers and methanogens, to controlled changes in carbon resource supply. Tidal creek sediment bioreactors were established in April and August 2004. For each date, intact sediment sections were continuously supplied with flowthrough seawater that was either unamended or amended with the high-molecular-weight polysaccharide dextran. Biogeochemical data indicate that the activity of fermenting bacteria and the terminal metabolizers was limited by organic carbon supply during both experiments, with a significant increase in net volatile fatty acid (VFA) production and rates of sulfate reduction and methanogenesis following dextran addition. Community composition (measured by using terminal restriction fragment length polymorphism analysis, and functional gene [
dsrA, mcrA
] clone libraries) changed from April to August. However, community composition was not different between amended and unamended cores within each month, despite the change in resource level. Moreover, there was no relationship between community richness and evenness with resource level. This lack of variation in community composition with C addition could be attributed to the dynamic environment these sediment communities experience in situ. Fluctuations in VFA concentrations are most likely very high, so that the dominant bacterial species must be able to outcompete other species at both high and low resource levels.
Two Different Tetracycline Resistance Mechanisms, Plasmid-Carried
tet
(L) and Chromosomally Located Transposon-Associated
tet
(M), Coexist in
Lactobacillus sakei
Rits 9
Authors: Ammor Mohammed Salim , Gueimonde Miguel , Danielsen Morten , Zagorec Monique , van Hoek Angela H. A. M. , de los Reyes-Gavilán Clara G. , Mayo Baltasar , Margolles Abelardo 
Published: January 2008

ABSTRACT

Lactobacillus sakei
is extensively used as functional starter culture in fermented meat products. One of the safety criteria of a starter culture is the absence of potentially transferable antibiotic resistance determinants. However, tetracycline-resistant
L. sakei
strains have already been observed. In this paper, we show that tetracycline resistance in
L. sakei
Rits 9, a strain isolated from Italian Sola cheese made from raw milk, is mediated by a transposon-associated
tet
(M) gene coding for a ribosomal protection protein and a plasmid-carried
tet
(L) gene coding for a tetracycline efflux pump. pLS55, the 5-kb plasmid carrying the
tet
(L) gene, is highly similar to the pMA67 plasmid recently described for
Paenibacillus larvae
, a species pathogenic to honeybees. pLS55 could be transferred by electroporation into the laboratory strain
L. sakei
23K. While the
L. sakei
23K transformant containing pLS55 displayed an intermediate tetracycline resistance level (MIC, <32 μg/ml),
L. sakei
Rits 9, containing both tetracycline-resistant determinants, had a MIC of <256 μg/ml, suggesting that Tet L and Tet M confer different levels of resistance in
L. sakei
. Remarkably, in the absence of tetracycline, a basal expression of both genes was detected for
L. sakei
Rits 9. In addition, subinhibitory concentrations of tetracycline affected the expression patterns of
tet
(M) and
tet
(L) in different ways: the expression of
tet
(M) was induced only at high tetracycline concentrations, whereas the expression of
tet
(L) was up-regulated at lower concentrations. This is the first time that two different mechanisms conferring resistance to tetracycline are characterized for the same strain of a lactic acid bacterium.
Identification of
Campylobacter jejuni
Genes Involved in the Response to Acidic pH and Stomach Transit
Authors: Reid Anne N. , Pandey Reenu , Palyada Kiran , Naikare Hemant , Stintzi Alain 
Published: January 2008

ABSTRACT

Campylobacter jejuni
causes food- and waterborne gastroenteritis, and as such it must survive passage through the stomach in order to reach the gastrointestinal tract. While little is known about how
C. jejuni
survives transit through the stomach, its low infectious dose suggests it is well equipped to sense and respond to acid shock. In this study, the transcriptional profile of
C. jejuni
NCTC 11168 was obtained after the organism was exposed to in vitro and in vivo (piglet stomach) acid shock. The observed down-regulation of genes encoding ribosomal proteins likely reflects the need to reshuffle energy toward the expression of components required for survival. Acid shock also caused
C. jejuni
to up-regulate genes involved in stress responses. These included heat shock genes as well as genes involved in the response to oxidative and nitrosative stress. A role for the chaperone
clpB
in acid resistance was confirmed in vitro. Some genes showed expression patterns that were markedly different in vivo and in vitro, which likely reflects the complexity of the in vivo environment. For instance, transit through the stomach was characterized by up-regulation of genes that encode products that are involved in the use of nitrite as a terminal electron acceptor and down-regulation of genes that are involved in capsular polysaccharide expression. In conclusion, this study has enabled us to understand how
C. jejuni
modulates gene expression in response to acid shock in vitro and to correlate this with gene expression profiles of
C. jejuni
as it transits through the host stomach.
Identification of
Campylobacter jejuni
Genes Contributing to Acid Adaptation by Transcriptional Profiling and Genome-Wide Mutagenesis
Authors: Reid Anne N. , Pandey Reenu , Palyada Kiran , Whitworth Lisa , Doukhanine Evgueni , Stintzi Alain 
Published: January 2008

ABSTRACT

In order to cause disease, the food- and waterborne pathogen
Campylobacter jejuni
must face the extreme acidity of the host stomach as well as cope with pH fluctuations in the intestine. In the present study,
C. jejuni
NCTC 11168 was grown under mildly acidic conditions mimicking those encountered in the intestine. The resulting transcriptional profiles revealed how this bacterium fine-tunes gene expression in response to acid stress. This adaptation involves the differential expression of respiratory pathways, the induction of genes for phosphate transport, and the repression of energy generation and intermediary metabolism genes. We also generated and screened a transposon-based mutant library to identify genes required for wild-type levels of growth under mildly acidic conditions. This screen highlighted the important role played by cell surface components (flagella, the outer membrane, capsular polysaccharides, and lipooligosaccharides) in the acid stress response of
C. jejuni
. Our data also revealed that a limited correlation exists between genes required for growth under acidic conditions and genes differentially expressed in response to acid. To gain a comprehensive picture of the acid stress response of
C. jejuni
, we merged transcriptional profiles obtained from acid-adapted cells and cells subjected to acid shock. Genes encoding the transcriptional regulator PerR and putative oxidoreductase subunits Cj0414 and Cj0415 were among the few up-regulated under both acid stress conditions. As a Cj0415 mutant was acid sensitive, it is likely that these genes are crucial to the acid stress response of
C. jejuni
and consequently are important for host colonization.
Sexual Reproduction as the Cause of Heat Resistance in the Food Spoilage Fungus
Byssochlamys spectabilis
(Anamorph
Paecilomyces variotii
)
Authors: Houbraken Jos , Varga János , Rico-Munoz Emilia , Johnson Shawn , Samson Robert A. 
Published: January 2008

ABSTRACT

Paecilomyces variotii
is a common cosmopolitan species that is able to spoil various food- and feedstuffs and is frequently encountered in heat-treated products. However, isolates from heat-treated products rarely form ascospores. In this study we examined by using molecular techniques and mating tests whether this species can undergo a sexual cycle and form ascospores. The population structure of this species was examined by analyzing the nuclear ribosomal internal transcribed spacer 1 (ITS1) and ITS2 and the 5.8S rRNA gene, as well as partial β-tubulin, actin, and calmodulin gene sequences. Phylogenetic analyses revealed that
P. variotii
is a highly variable species. Partition homogeneity tests revealed that
P. variotii
has a recombining population structure. In addition to sequence analyses, mating experiments indicated that
P. variotii
is able to form ascomata and ascospores in culture in a heterothallic manner. The distribution of MAT1-1 and MAT1-2 genes showed a 1:1 ratio in the progeny of the mating experiments. From the sequence analyses and mating data we conclude that
P. variotii
is the anamorph of
Talaromyces spectabilis
and that it has a biallelic heterothallic mating system. Since
Paecilomyces
sensu stricto anamorphs group within
Byssochlamys
, a new combination
Byssochlamys spectabilis
is proposed.
Water Deficit as a Driver of the Mutualistic Relationship between the Fungus
Trichoderma harzianum
and Two Wheat Genotypes
Authors: Donoso Eduardo P. , Bustamante Ramiro O. , Carú Margarita , Niemeyer Hermann M. 
Published: January 2008

ABSTRACT

The aim of this study was to assess the occurrence of mutualistic interactions between the fungus
Trichoderma harzianum
and two wheat genotypes,
Triticum aestivum
cv. Talhuén and
T. turgidum
subsp.
durum
cv. Alifén, and the extent to which water deficit affected these interactions. Two wheat genotypes were cultivated in the presence or absence of
T. harzianum
and in the presence or absence of water deficit.
T. harzianum
was in turn cultivated in the presence or absence of wheat plants and in the presence or absence of water deficit. To evaluate the plant-fungus interactions, the root volume, dry biomass, and fecundity of wheat were determined, as was the population growth rate of the fungus.
Trichoderma harzianum
exerted a positive effect only on plants subjected to water deficit. The population growth rate of
T. harzianum
was negative in the absence of wheat plants and reached its highest level in the presence of plants under conditions of water deficit. These results confirm the occurrence of a mutualistic interaction between wheat and
T. harzianum
and show that it is asymmetric and context dependent.
Isolation and Characterization of Human Intestinal Bacteria Capable of Transforming the Dietary Carcinogen 2-Amino-1-Methyl-6-Phenylimidazo[4,5-
b
]Pyridine
Authors: Vanhaecke Lynn , Vercruysse Filip , Boon Nico , Verstraete Willy , Cleenwerck Ilse , De Wachter Marjan , De Vos Paul , van de Wiele Tom 
Published: January 2008

ABSTRACT

2-Amino-1-methyl-6-phenylimidazo[4,5-
b
]pyridine (PhIP) is a carcinogenic heterocyclic aromatic amine formed in meat products during cooking. Although the formation of hazardous PhIP metabolites by mammalian enzymes has been extensively reported, research on the putative involvement of the human intestinal microbiota in PhIP metabolism remains scarce. In this study, the in vitro conversion of PhIP into its microbial derivate, 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3′,2′:4,5]imidazo[1,2-
a
]pyrimidin-5-ium chloride (PhIP-M1), by fecal samples from 18 human volunteers was investigated. High-performance liquid chromatography analysis showed that all human fecal samples transformed PhIP but with efficiencies ranging from 1.8 to 96% after 72 h of incubation. Two PhIP-transforming strains, PhIP-M1-a and PhIP-M1-b, were isolated from human feces and identified by fluorescent amplified fragment length polymorphism and
pheS
sequence analyses as
Enterococcus faecium
strains. Some strains from culture collections belonging to the species
E. durans
,
E. avium
,
E. faecium
, and
Lactobacillus reuteri
were also able to perform this transformation. Yeast extract, special peptone, and meat extract supported PhIP transformation by the enriched
E. faecium
strains, while tryptone, monomeric sugars, starch, and cellulose did not. Glycerol was identified as a fecal matrix constituent required for PhIP transformation. Abiotic synthesis of PhIP-M1 and quantification of the glycerol metabolite 3-hydroxypropionaldehyde (3-HPA) confirmed that the anaerobic fermentation of glycerol via 3-HPA is the critical bacterial transformation process responsible for the formation of PhIP-M1. Whether it is a detoxification is still a matter of debate, since PhIP-M1 has been shown to be cytotoxic toward Caco-2 cells but is not mutagenic in the Ames assay.
NADH Availability Limits Asymmetric Biocatalytic Epoxidation in a Growing Recombinant
Escherichia coli
Strain
Authors: Bühler Bruno , Park Jin-Byung , Blank Lars M. , Schmid Andreas 
Published: January 2008

ABSTRACT

Styrene can efficiently be oxidized to (
S
)-styrene oxide by recombinant
Escherichia coli
expressing the styrene monooxygenase genes
styAB
from
Pseudomonas
sp. strain VLB120. Targeting microbial physiology during whole-cell redox biocatalysis, we investigated the interdependency of styrene epoxidation, growth, and carbon metabolism on the basis of mass balances obtained from continuous two-liquid-phase cultures. Full induction of
styAB
expression led to growth inhibition, which could be attenuated by reducing expression levels. Operation at subtoxic substrate and product concentrations and variation of the epoxidation rate via the styrene feed concentration allowed a detailed analysis of carbon metabolism and bioconversion kinetics. Fine-tuned
styAB
expression and increasing specific epoxidation rates resulted in decreasing biomass yields, increasing specific rates for glucose uptake and the tricarboxylic acid (TCA) cycle, and finally saturation of the TCA cycle and acetate formation. Interestingly, the biocatalysis-related NAD(P)H consumption was 3.2 to 3.7 times higher than expected from the epoxidation stoichiometry. Possible reasons include uncoupling of styrene epoxidation and NADH oxidation and increased maintenance requirements during redox biocatalysis. At epoxidation rates of above 21 μmol per min per g cells (dry weight), the absence of limitations by O
2
and styrene and stagnating NAD(P)H regeneration rates indicated that NADH availability limited styrene epoxidation. During glucose-limited growth, oxygenase catalysis might induce regulatory stress responses, which attenuate excessive glucose catabolism and thus limit NADH regeneration. Optimizing metabolic and/or regulatory networks for efficient redox biocatalysis instead of growth (yield) is likely to be the key for maintaining high oxygenase activities in recombinant
E. coli
.
Vanadium Requirements and Uptake Kinetics in the Dinitrogen-Fixing Bacterium
Azotobacter vinelandii
Authors: Bellenger J. P. , Wichard T. , Kraepiel A. M. L. 
Published: January 2008

ABSTRACT

Vanadium is a cofactor in the alternative V-nitrogenase that is expressed by some N
2
-fixing bacteria when Mo is not available. We investigated the V requirements, the kinetics of V uptake, and the production of catechol compounds across a range of concentrations of vanadium in diazotrophic cultures of the soil bacterium
Azotobacter vinelandii
. In strain CA11.70, a mutant that expresses only the V-nitrogenase, V concentrations in the medium between 10
−8
and 10
−6
M sustain maximum growth rates; they are limiting below this range and toxic above.
A. vinelandii
excretes in its growth medium micromolar concentrations of the catechol siderophores azotochelin and protochelin, which bind the vanadate oxoanion. The production of catechols increases when V concentrations become toxic. Short-term uptake experiments with the radioactive isotope
49
V show that bacteria take up the V-catechol complexes through a regulated transport system(s), which shuts down at high V concentrations. The modulation of the excretion of catechols and of the uptake of the V-catechol complexes allows
A. vinelandii
to precisely manage its V homeostasis over a range of V concentrations, from limiting to toxic.
Molecular Structure and Transferability of Tn
1546
-Like Elements in
Enterococcus faecium
Isolates from Clinical, Sewage, and Surface Water Samples in Iran
Authors: Talebi M. , Pourshafie M. R. , Katouli M. , Möllby R. 
Published: January 2008

ABSTRACT

The molecular structure and transferability of Tn
1546
in 143 vancomycin-resistant
Enterococcus faecium
(VREF) isolates obtained from patients (
n
= 49), surface water (
n
= 28), and urban and hospital sewage (
n
= 66) in Tehran, Iran, were investigated. Molecular characterization of Tn
1546
elements in
vanA
VREF was performed using a combination of restriction fragment length polymorphism analysis and DNA sequencing of the internal PCR fragments of
vanA
transposons. Long-PCR amplification showed that the molecular size of Tn
1546
elements varied from 10.8 to 12.8 kb. The molecular analysis of Tn
1546
showed that 45 isolates (31.5%) harbored a deletion/mutation upstream from nucleotide 170. No horizontal transfer of Tn
1546
was observed following filter-mating conjugation with these isolates. Nevertheless, the rates of transferability for other isolates were 10
−5
to 10
−6
per donor. Insertion sequences IS
1216V
and IS
1542
were present in 103 (72%) and 138 (96.5%) of the isolates, respectively. The molecular analysis of Tn
1546
elements resulted in three genomic organizations. The genomic organization lineage 1 was dominated by the isolates from clinical samples (3.4%), lineage 2 was dominated mostly by sewage isolates (24.5%), and lineage 3 contained isolates obtained from all sources (72.1%). The genetic diversity determined using pulsed-field gel electrophoresis (PFGE) revealed a single
E. faecium
clone, designated 44, which was common to the samples obtained from clinical specimens and hospital and municipal sewage. Furthermore, the results suggest that lineage 3 Tn
1546
was highly disseminated among our enterococcal isolates in different PFGE patterns.
Role of
Campylobacter jejuni
Respiratory Oxidases and Reductases in Host Colonization
Authors: Weingarten Rebecca A. , Grimes Jesse L. , Olson Jonathan W. 
Published: January 2008

ABSTRACT

Campylobacter jejuni
is the leading cause of human food-borne bacterial gastroenteritis. The
C. jejuni
genome sequence predicts a branched electron transport chain capable of utilizing multiple electron acceptors. Mutants were constructed by disrupting the coding regions of the respiratory enzymes nitrate reductase (
napA
::Cm), nitrite reductase (
nrfA
::Cm), dimethyl sulfoxide, and trimethylamine
N
-oxide reductase (termed Cj0264::Cm) and the two terminal oxidases, a cyanide-insensitive oxidase (
cydA
::Cm) and
cbb3
-type oxidase (
ccoN
::Cm). Each strain was characterized for the loss of the associated enzymatic function in vitro. The strains were then inoculated into 1-week-old chicks, and the cecal contents were assayed for the presence of
C. jejuni
2 weeks postinoculation.
cydA
::Cm and Cj0264c::Cm strains colonized as well as the wild type;
napA
::Cm and
nrfA
::Cm strains colonized at levels significantly lower than the wild type. The
ccoN
::Cm strain was unable to colonize the chicken; no colonies were recovered at the end of the experiment. While there appears to be a role for anaerobic respiration in host colonization, oxygen is the most important respiratory acceptor for
C. jejuni
in the chicken cecum.
Heavy-Metal and Benzalkonium Chloride Resistance of
Listeria monocytogenes
Isolates from the Environment of Turkey-Processing Plants
Authors: Mullapudi S. , Siletzky R. M. , Kathariou S. 
Published: January 2008

ABSTRACT

The resistance of
Listeria monocytogenes
to cadmium and arsenic has been used extensively for strain subtyping. However, limited information is available on the prevalence of such resistance among isolates from the environment of food-processing plants. In addition, it is not known whether the resistance of such isolates to heavy metals may correlate with resistance to quaternary ammonium compounds extensively used as disinfectants in the food-processing industry. In this study, we characterized 192
L. monocytogenes
isolates (123 putative strains) from the environment of turkey-processing plants in the United States for resistance to cadmium and arsenic and to the quaternary ammonium disinfectant benzalkonium chloride (BC). Resistance to cadmium was significantly more prevalent among strains of serotypes 1/2a (or 3a) and 1/2b (or 3b) (83% and 74%, respectively) than among strains of the serotype 4b complex (19%). Resistance to BC was encountered among 60% and 51% of the serotype 1/2a (or 3a) and 1/2b (or 3b) strains, respectively, and among 7% of the strains of the serotype 4b complex. All BC-resistant strains were also resistant to cadmium, although the reverse was not always the case. In contrast, no correlation was found between BC resistance and resistance to arsenic, which overall was low (6%). Our findings suggest that the processing environment of turkey-processing plants may constitute a reservoir for
L. monocytogenes
harboring resistance to cadmium and to BC and raise the possibility of common genetic elements or mechanisms mediating resistance to quaternary ammonium disinfectants and to cadmium in
L. monocytogenes
.