bluuebunny/crossref_metadata_2025 huggingface dataset:
The countering of overgeneralization
Authors: HOWE CHRISTINE J.
Published: November 2002

Commenting on Goldberg's (1995) ‘construction grammar’, Tomasello (1998) proposes a model of language acquisition in which children move from highly specific utterance–event pairings to abstract, verb-general structures. Despite their many strengths, models of this kind predict considerably more overgeneralization of the argument structures of verbs than seems to occur. In recognition of this, the paper explains (and supports with data from a previously unpublished study of 44 children aged 2;0 to 4;4) how processes which are side effects of the emergence of the verb form class could counter the overgeneralizing tendencies. It is argued that these processes are consistent not just with the model proposed by Tomasello but also (in large part) with the grammatical theory developed by Goldberg.
What's the difference between ‘toilet paper’ and ‘paper toilet’? French-English bilingual children's crosslinguistic transfer in compound nouns
Authors: NICOLADIS ELENA
Published: November 2002

Bilingual acquisition can shed light on the cues children use in acquiring language. The purpose of this paper was to examine whether frequency, ambiguity or language dominance could explain crosslinguistic transfer in compound nouns. Crosslinguistic transfer would appear in the form of compound reversals. 25 monolingual English children between the ages of three and four years and 25 age-matched French-English bilingual children were asked to create and indicate their understanding of novel compound nouns. In production, the bilingual children reversed compounds in English more often than the monolingual children but equally often in French and English. In comprehension, there were no differences between groups. These results cannot be explained by any previous explanation of transfer. Implications for the theory of language acquisition are discussed.
Pitch modification when interacting with elders: Japanese women with and without experience with infants
Authors: MASATAKA NOBUO
Published: November 2002

Twenty Japanese-speaking twenty-six- to twenty-seven-year-old women were recorded as they conversed with an infant, an elder, or another young adult. When their utterances were acoustically compared among the three settings with regard to prosodic characteristics, elevated pitch and increased pitch range were found when their speech was directed to both the infant and the elder as compared to when it was directed to the young adult. The degree to which such modifications occurred was greater in those women who were experienced with children than in those women who were not experienced. Moreover, the degree of the modification showed a highly positive correlation in each participant when the speech was directed to the infant and when it was directed to the elder. Prosodic modifications of speech styles to infants and to elders are both exaggerated consistently through the experience with children.
Triangle-Freeness is Hard to Detect
Authors: JUKNA S. , SCHNITGER G.
Published: November 2002

We show that recognizing the K3-freeness and K4-freeness of graphs is hard, respectively, for
two-player nondeterministic communication protocols using exponentially many partitions
and for nondeterministic syntactic read-r times branching programs.

The key ingredient is a generalization of a colouring lemma, due to Papadimitriou and
Sipser, which says that for every balanced red—blue colouring of the edges of the complete
n-vertex graph there is a set of εn2 triangles, none of which is monochromatic, such that
no triangle can be formed by picking edges from different triangles. We extend this lemma
to exponentially many colourings and to partial colourings.
The breast cancer resistance protein protects against a major chlorophyll-derived dietary phototoxin and protoporphyria
Authors: Jonker Johan W. , Buitelaar Marije , Wagenaar Els , van der Valk Martin A. , Scheffer George L. , Scheper Rik J. , Plösch Torsten , Kuipers Folkert , Elferink Ronald P. J. Oude , Rosing Hilde , Beijnen Jos H. , Schinkel Alfred H.
Published: November 2002

The breast cancer resistance protein (BCRP/ABCG2) is a member of the ATP-binding cassette family of drug transporters and confers resistance to various anticancer drugs. We show here that mice lacking Bcrp1/Abcg2 become extremely sensitive to the dietary chlorophyll-breakdown product pheophorbide a, resulting in severe, sometimes lethal phototoxic lesions on light-exposed skin. Pheophorbide a occurs in various plant-derived foods and food supplements. Bcrp1 transports pheophorbide a and is highly efficient in limiting its uptake from ingested food.Bcrp1−/−mice also displayed a previously unknown type of protoporphyria. Erythrocyte levels of the heme precursor and phototoxin protoporphyrin IX, which is structurally related to pheophorbide a, were increased 10-fold. Transplantation with wild-type bone marrow cured the protoporphyria and reduced the phototoxin sensitivity ofBcrp1−/−mice. These results indicate that humans or animals with low or absent BCRP activity may be at increased risk for developing protoporphyria and diet-dependent phototoxicity and provide a striking illustration of the importance of drug transporters in protection from toxicity of normal food constituents.
Identification of endoglin as a functional marker that defines long-term repopulating hematopoietic stem cells
Authors: Chen Chang-Zheng , Li Min , de Graaf David , Monti Stefano , Göttgens Berthold , Sanchez Maria-Jose , Lander Eric S. , Golub Todd R. , Green Anthony R. , Lodish Harvey F.
Published: November 2002

We describe a strategy to obtain highly enriched long-term repopulating (LTR) hematopoietic stem cells (HSCs) from bone marrow side-population (SP) cells by using a transgenic reporter gene driven by a stem cell enhancer. To analyze the gene-expression profile of the rare HSC population, we developed an amplification protocol termed “constant-ratio PCR,” in which sample and control cDNAs are amplified in the same PCR. This protocol allowed us to identify genes differentially expressed in the enriched LTR-HSC population by oligonucleotide microarray analysis using as little as 1 ng of total RNA. Endoglin, an ancillary transforming growth factor β receptor, was differentially expressed by the enriched HSCs. Importantly, endoglin-positive cells, which account for 20% of total SP cells, contain all the LTR-HSC activity within bone marrow SP. Our results demonstrate that endoglin, which plays important roles in angiogenesis and hematopoiesis, is a functional marker that defines LTR HSCs. Our overall strategy may be applicable for the identification of markers for other tissue-specific stem cells.
Discovery of chemical inhibitors of the selective transfer of lipids mediated by the HDL receptor SR-BI
Authors: Nieland Thomas J. F. , Penman Marsha , Dori Limor , Krieger Monty , Kirchhausen Tomas
Published: November 2002

The high-density lipoprotein (HDL) receptor, scavenger receptor, class B, type I (SR-BI), mediates both the selective uptake of lipids, mainly cholesterol esters, from HDL to cells and the efflux of cholesterol from cells to lipoproteins. The mechanism underlying these lipid transfers is distinct from classic receptor-mediated endocytosis, but it remains poorly understood. To investigate SR-BI's mechanism of action and
in vivo
function, we developed a high-throughput screen to identify small molecule inhibitors of SR-BI-mediated lipid transfer in intact cells. We identified five compounds that in the low nanomolar to micromolar range block lipid transport (BLTs), both selective uptake and efflux. The effects of these compounds were highly specific to the SR-BI pathway, because they didn't interfere with receptor-mediated endocytosis or with other forms of intracellular vesicular traffic. Surprisingly, all five BLTs enhanced, rather than inhibited, HDL binding by increasing SR-BI's binding affinity for HDL (decreased dissociation rates). Thus, the BLTs provide strong evidence for a mechanistic coupling between HDL binding and lipid transport and may serve as a starting point for the development of pharmacologically useful modifiers of SR-BI activity and, thus, HDL metabolism.
KaiA-stimulated KaiC phosphorylation in circadian timing loops in cyanobacteria
Authors: Iwasaki Hideo , Nishiwaki Taeko , Kitayama Yohko , Nakajima Masato , Kondo Takao
Published: November 2002

Cyanobacterial clock proteins KaiA and KaiC are proposed as positive and negative regulators in the autoregulatory circadiankaiBCexpression, respectively. Here, we show that activation ofkaiBCexpression bykaiArequires KaiC, suggesting a positive feedback control in the cyanobacterial clockwork. We found that robust circadian phosphorylation of KaiC. KaiA was essential forin vivoKaiC phosphorylation and activatedin vitroKaiC autophosphorylation. These effects of KaiA were attenuated by thekaiA2long period mutation. Both the long period phenotype and the abnormal KaiC phosphorylation in this mutant were suppressed by a previously undocumentedkaiCmutation. We propose that KaiA-stimulated circadian KaiC phosphorylation is important for circadian timing.
Infection of a human hepatoma cell line by hepatitis B virus
Authors: Gripon Philippe , Rumin Sylvie , Urban Stephan , Le Seyec Jacques , Glaise Denise , Cannie Isabelle , Guyomard Claire , Lucas Josette , Trepo Christian , Guguen-Guillouzo Christiane
Published: November 2002

Among numerous established human hepatoma cell lines, none has been shown susceptible to hepatitis B virus (HBV) infection. We describe here a cell line, called HepaRG, which exhibits hepatocyte-like morphology, expresses specific hepatocyte functions, and supports HBV infection as well as primary cultures of normal human hepatocytes. Differentiation and infectability are maintained only when these cells are cultured in the presence of corticoids and dimethyl sulfoxide. The specificity of this HBV infection model was ascertained by both the neutralization capacity of HBV-envelope protein-specific antibodies and the competition with an envelope-derived peptide. HepaRG cells therefore represent a tool for deciphering the mechanism of HBV entry. Moreover, their close resemblance to normal human hepatocytes makes them suitable for many applications including drug metabolism studies.
Statistical learning of new visual feature combinations by infants
Authors: Fiser József , Aslin Richard N.
Published: November 2002

The ability of humans to recognize a nearly unlimited number of unique visual objects must be based on a robust and efficient learning mechanism that extracts complex visual features from the environment. To determine whether statistically optimal representations of scenes are formed during early development, we used a habituation paradigm with 9-month-old infants and found that, by mere observation of multielement scenes, they become sensitive to the underlying statistical structure of those scenes. After exposure to a large number of scenes, infants paid more attention not only to element pairs that cooccurred more often as embedded elements in the scenes than other pairs, but also to pairs that had higher predictability (conditional probability) between the elements of the pair. These findings suggest that, similar to lower-level visual representations, infants learn higher-order visual features based on the statistical coherence of elements within the scenes, thereby allowing them to develop an efficient representation for further associative learning.
Intracerebroventricular corticotropin-releasing factor increases limbic glucose metabolism and has social context-dependent behavioral effects in nonhuman primates
Authors: Strome Elissa M. , Wheler G. H. Trevor , Higley J. Dee , Loriaux D. Lynn , Suomi Stephen J. , Doudet Doris J.
Published: November 2002

Corticotropin-releasing factor (CRF) is a neuropeptide involved in integrating the behavioral, autonomic, and hormonal responses to stress within the central nervous system. Patients suffering from depression have abnormal activity in stress responsive brain regions and elevated cerebrospinal fluid CRF. The DSM-IV criteria for major depressive disorder include behavioral changes such as depressed mood, anhedonia, and psychomotor agitation/retardation. We studied the effects of 434 μg of CRF given intracerebroventricularly over 40 min in group and individually housed monkeys to examine the role of elevated levels of central CRF on behavior. CRF elicited a wide range of behaviors, which fell into three broad categories: anxiety-like, depressive-like, and externally oriented. Externally oriented behaviors decreased, and anxiety-like behaviors increased regardless of how the animals were housed. Interestingly, increased depressive-like behaviors were only observed when the animals were socially housed. In a separate experiment, we examined the effects of the same dose of CRF on the regional cerebral glucose metabolism of lightly anesthetized monkeys by using positron emission tomography and [
18
F]fluorodeoxyglucose. CRF infusion increased glucose metabolism in the pituitary/infundibulum, the amygdala, and hippocampus. These results indicate that increased central CRF tone affects primate behavior in a context-dependent manner, and that it activates limbic and stress-responsive regions. The fact that intracerebroventricular CRF increases depressive-like behavior in socially housed animals and increases activity in limbic brain regions may help explain the behavioral and metabolic alterations in humans with affective disorders, and this model could therefore have significant value in the development of novel antidepressant treatments.
Structure and function from the circadian clock protein KaiA of
Synechococcus elongatus
: A potential clock input mechanism
Authors: Williams Stanly B. , Vakonakis Ioannis , Golden Susan S. , LiWang Andy C.
Published: November 2002

In the cyanobacterium
Synechococcus elongatus
(PCC 7942) the proteins KaiA, KaiB, and KaiC are required for circadian clock function. We deduced a circadian clock function for KaiA from a combination of biochemical and structural data. Both KaiA and its isolated carboxyl-terminal domain (KaiA180C) stimulated KaiC autophosphorylation and facilitated attenuation of KaiC autophosphorylation by KaiB. An amino-terminal domain (KaiA135N) had no function in the autophosphorylation assay. NMR structure determination showed that KaiA135N is a pseudo-receiver domain. We propose that this pseudo-receiver is a timing input-device that regulates KaiA stimulation of KaiC autophosphorylation, which in turn is essential for circadian timekeeping.
Low-magnesium calcite produced by coralline algae in seawater of Late Cretaceous composition
Authors: Stanley Steven M. , Ries Justin B. , Hardie Lawrence A.
Published: November 2002

Shifts in the Mg/Ca ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 108years. Since Cambrian time, skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates. Here we report on experiments showing that the ambient Mg/Ca ratio actually governs the skeletal mineralogy of some simple organisms. In modern seas, coralline algae produce skeletons of high-Mg calcite (>4 mol % MgCO3). We grew three species of these algae in artificial seawaters having three different Mg/Ca ratios. All of the species incorporated amounts of Mg into their skeletons in proportion to the ambient Mg/Ca ratio, mimicking the pattern for nonskeletal precipitation. Thus, the algae calcified as if they were simply inducing precipitation from seawater through their consumption of CO2for photosynthesis; presumably organic templates specify the calcite crystal structure of their skeletons. In artificial seawater with the low Mg/Ca ratio of Late Cretaceous seas, the algae in our experiments produced low-Mg calcite (<4 mol % MgCO3), the carbonate mineral formed by nonskeletal precipitation in those ancient seas. Our results suggest that many taxa that produce high-Mg calcite today produced low-Mg calcite in Late Cretaceous seas.
Gaussian curvature and the equilibrium among bilayer cylinders, spheres, and discs
Authors: Jung H.-T. , Lee S. Y. , Kaler E. W. , Coldren B. , Zasadzinski J. A.
Published: November 2002

In mixtures of cetyltrimethylammonium bromide (CTAB) and sodium perfluorooctanoate (FC
7
) in aqueous solution, novel bilayer cylinders with hemispherical end caps and open, flat discs coexist with spherical unilamellar vesicles, apparently at equilibrium. Such equilibrium among bilayer cylinders, spheres, and discs is only possible for systems with a spontaneous curvature,
R
o
, and a positive Gaussian curvature modulus, κ̄. We have measured the size distributions of the spherical vesicles, cylinders, and discs by using cryo-electron microscopy; a simple analysis of this length distribution allows us to independently determine that the mean curvature modulus, κ ≈ 5 ± 1 k
B
T and κ̄ ≈ 2 ± 1 k
B
T. This is one of the few situations in which
R
o
, κ, and κ̄ can be determined from the same experiment. From a similar analysis of the disk size distribution, we find that the edges of the discs are likely stabilized by excess CTAB. The fraction of discs, spherical vesicles, and cylinders depends on the CTAB/FC
7
mole ratio: increasing CTAB favors discs, while decreasing CTAB favors cylinders. This control over aggregate shape with surfactant concentration may be useful for the design of templates for polymerization, mesoporous silicates, etc.
Transcriptional profiling of a mouse model for Rett syndrome reveals subtle transcriptional changes in the brain
Authors: Tudor Matthew , Akbarian Schahram , Chen Richard Z. , Jaenisch Rudolf
Published: November 2002

The
Mecp2
gene has been shown to be mutated in most cases of human Rett syndrome, and mouse models deleted for the ortholog have been generated. Lineage-specific deletion of the gene indicated that the Rett-like phenotype is caused by
Mecp2
deficiency in neurons. Biochemical evidence suggests that
Mecp2
acts as a global transcriptional repressor, predicting that mutant mice should have genome-wide transcriptional deregulation. We tested this hypothesis by comparing global gene expression in wild-type and
Mecp2
mutant mice. The results of numerous microarray analyses revealed no dramatic changes in transcription even in mice displaying overt disease symptoms, although statistical power analyses of the data indicated that even a small number of relatively subtle changes in transcription would have been detected if present. However, a classifier consisting of a combined small set of genes was able to distinguish between mutant and wild-type samples with high accuracy. This result suggests that
Mecp2
deficiency leads to subtle gene expression changes in mutant brains which may be associated with the phenotypic changes observed.
Two isoforms of the Notch antagonist Hairless are produced by differential translation initiation
Authors: Maier Dieter , Nagel Anja C. , Preiss Anette
Published: November 2002

The Notch-signaling pathway controls cellular differentiation, including proliferation and cell death in all higher metazoans (including flies and men). Signal transduction through activated Notch involves the CSL group of transcriptional regulators. Notch signals need to be tightly regulated, and in
Drosophila
they are antagonized by the Hairless (H) protein. H silences the activity of Notch target genes by transforming the
Drosophila
CSL protein, Suppressor of Hairless [Su(H)], from a transcriptional activator into a repressor while recruiting one of the corepressors dCtBP or Groucho. The H protein has a calculated molecular mass of ≈110 kDa and contains several functional domains apart from the two small corepressor-binding domains. However, although there is no indication for alternative splicing, two Hairless protein isoforms, H
p120
and H
p150
, are observed throughout development. Here, we show that the smaller isoform derives from an internal ribosome entry site (IRES) within the ORF. The IRES is active in a heterologous assay and contains an essential, conserved structural element. The two Hairless isoforms have residual activity
in vivo
which is, however, reduced compared to a combination of both, which implies that both protein isoforms are necessary for WT function. In larval tissues, translation of the two isoforms is cell-cycle regulated: whereas the H
p150
isoform is translated during interphase, H
p120
is enriched during mitosis. Thus, the presence of either H isoform throughout the cell cycle allows efficient inhibition of Notch-regulated cell proliferation.
Gene expression profiling of isogenic cells with different
TP53
gene dosage reveals numerous genes that are affected by
TP53
dosage and identifies
CSPG2
as a direct target of p53
Authors: Yoon Heejei , Liyanarachchi Sandya , Wright Fred A. , Davuluri Ramana , Lockman Janet C. , de la Chapelle Albert , Pellegata Natalia S.
Published: November 2002

TP53
does not fully comply with the Knudson model [Knudson, A. G., Jr. (1971)
Proc. Natl. Acad. Sci. USA
68, 820–823] in that a reduction of constitutional expression of p53 may be sufficient for tumor predisposition . This finding suggests a gene-dosage effect for p53 function. To determine whether
TP53
gene dosage affects the transcriptional regulation of target genes, we performed oligonucleotide-array gene expression analysis by using human cells with wild-type p53 (p53 +/+), or with one (p53 +/−), or both (p53 −/−)
TP53
alleles disrupted by homologous recombination. We identified 35 genes whose expression is significantly correlated to the dosage of
TP53
. These genes are involved in a variety of cellular processes including signal transduction, cell adhesion, and transcription regulation. Several of them are involved in neurogenesis and neural crest migration, developmental processes in which p53 is known to play a role. Motif search analysis revealed that of the genes highly expressed in p53 +/+ and +/− cells, several contain a putative p53 consensus binding site (bs), suggesting that they could be directly regulated by p53. Among those genes, we chose
CSPG2
(which encodes versican) for further study because it contains a
bona fide
p53 bs in its first intron and its expression highly correlates with
TP53
dosage. By using
in vitro
and
in vivo
assays, we showed
CSPG2
to be directly transactivated by p53. In conclusion, we developed a strategy to demonstrate that many genes are affected by
TP53
gene dosage for their expression. We report several candidate genes as potential downstream targets of p53 in nonstressed cells. Among them,
CSPG2
is validated as being directly transactivated by p53. Our method provides a useful tool to elucidate additional mechanisms by which p53 exerts its functions.
Early stages of energy transduction by myosin: Roles of Arg in Switch I, of Glu in Switch II, and of the salt-bridge between them
Authors: Onishi Hirofumi , Ohki Takashi , Mochizuki Naoki , Morales Manuel F.
Published: November 2002

On the basis of the crystallographic snapshots of Rayment and his collaborators [Fisher, A. J., Smith, C. A., Thoden, J. B., Smith, R., Sutoh, K., Holden, H. M., & Rayment, I. (1995)
Biochemistry
34, 8960–8972], we have understood some basic principles about the early stages of myosin catalysis, namely, ATP is drawn into the active site, over which the cleft closes. Catalyzed hydrolysis occurs, and the first product (orthophosphate) is released from the backdoor of the cleft. In the cleft-closing process, the active site incidentally signals its movement to a particular remote tryptophan residue, Trp-512. In this work, we expand on some of these ideas to rationalize the behavior of a mutated system in action. From the behavior of recombinant myosin systems in which Arg-247 and Glu-470 were substituted in several ways, we draw the conclusions that (
i
) the force between Arg-247 and γ-phosphate of ATP may assist in closing the cleft, and incidentally in signaling to the remote Trp, and (
ii
) in catalysis, Glu-470 is involved in holding the lytic H
2
O (w
1
). We also propose that w
1
and also a second water, w
2
, enter into a structure that bridges Glu-470 and the γ-phosphate of bound ATP, and at the same time positions w
1
for its in-line hydrolytic attack.
Frequent deletions and down-regulation of micro- RNA genes
miR15
and
miR16
at 13q14 in chronic lymphocytic leukemia
Authors: Calin George Adrian , Dumitru Calin Dan , Shimizu Masayoshi , Bichi Roberta , Zupo Simona , Noch Evan , Aldler Hansjuerg , Rattan Sashi , Keating Michael , Rai Kanti , Rassenti Laura , Kipps Thomas , Negrini Massimo , Bullrich Florencia , Croce Carlo M.
Published: November 2002

Micro-RNAs (
miR
genes) are a large family of highly conserved noncoding genes thought to be involved in temporal and tissue-specific gene regulation. MiRs are transcribed as short hairpin precursors (≈70 nt) and are processed into active 21- to 22-nt RNAs by Dicer, a ribonuclease that recognizes target mRNAs via base-pairing interactions. Here we show that
miR15
and
miR16
are located at chromosome 13q14, a region deleted in more than half of B cell chronic lymphocytic leukemias (B-CLL). Detailed deletion and expression analysis shows that
miR15
and
miR16
are located within a 30-kb region of loss in CLL, and that both genes are deleted or down-regulated in the majority (≈68%) of CLL cases.
Mitogen-activated protein kinase signaling in postgermination arrest of development by abscisic acid
Authors: Lu C. , Han M.-H. , Guevara-Garcia A. , Fedoroff N. V.
Published: November 2002

Abscisic acid (ABA) mediates plant responses to environmental stress, particularly to water status. During germination, the embryo emerges from dormancy as the ABA concentration declines. Exposure to exogenous ABA during germination arrests development rapidly, but reversibly, enabling seedlings to withstand early water stress without loss of viability. Postgermination proteolytic degradation of the essential ABI5 transcription factor is interrupted by perception of an increase in ABA concentration, leading to ABI5 accumulation and reactivation of embryonic genes. Making use of the ABA-hypersensitive
hyl1
mutant of
Arabidopsis
, we show that the ABA signal is transmitted to the transcriptional apparatus through mitogen-activated protein kinase signaling.
The hemochromatosis protein HFE inhibits iron export from macrophages
Authors: Drakesmith Hal , Sweetland Emma , Schimanski Lisa , Edwards Jon , Cowley Diana , Ashraf Mubeen , Bastin Judy , Townsend Alain R. M.
Published: November 2002

Hereditary hemochromatosis (HH) is a disorder of iron metabolism caused by common mutations in the gene
HFE
. The HFE protein binds to transferrin receptor-1 (TfR1) in competition with transferrin, and
in vitro
, reduces cellular iron by reducing iron uptake. However,
in vivo
, HFE is strongly expressed by liver macrophages and intestinal crypt cells, which behave as though they are relatively iron-deficient in HH. These latter observations suggest, paradoxically, that expression of wild-type HFE may lead to iron accumulation in these specialized cell types. Here we show that wild-type HFE protein raises cellular iron by inhibiting iron efflux from the monocyte/macrophage cell line THP-1, and extend these results to macrophages derived from healthy individuals and HH patients. In addition, we find that the HH-associated mutant H41D has lost the ability to inhibit iron release despite binding to TfR1 as well as wild-type HFE. Finally, we show that the ability of HFE to block iron release is not competitively inhibited by transferrin. We conclude that HFE has two mutually exclusive functions, binding to TfR1 in competition with Tf, or inhibition of iron release.
Classical optics and light pressure in spherical laser plasmas
Authors: P Mulser  , C van Kessel
Published: November 2002

The propagation of light in spherical geometry is treated on the basis of the wave equation. Analytical formulae for classical reflection from pellets and plane targets under normal incidence are presented and the maximum electric field increase in smooth density profiles is determined. Density profile distortions due to light pressure and their influence on pellet compression are discussed in a steady-state model.
Self‐directed work teams in a post‐apartheid gold mine: perspectives from the rock face
Authors: Sizwe Phakathi Timothy
Published: November 2002

Increasing international competition requires companies to empower and develop the skills of workers at the lower levels. This paper will show how implementing change from below through self‐directed teamwork enhances the understanding of the changing nature of work and the relationship between work and training. The case study of African Gold Mine (a pseudonym of one of the world’s deepest gold mines) illustrates the South African gold mining industry’s attempt to create a twenty‐first century workforce through self‐directed work team (SDWT) training conducted within the mine. However, underground participatory research reveals that in the workplace, organisational constraints hinder the effective implementation of SDWT training. In order to cope with these organizational constraints and inefficiencies, workers resort to planisa; “they make a plan”. In other words, they “get on and get by” underground through improvising and the team’s self‐initiated action. This paper argues that planisa is part of the existing occupational culture of miners and is an embryonic form of teamwork. Any strategy to increase the productivity of mineworkers must draw on these experiences.
Identification of an Iron-Regulated, Hemin-Binding Outer Membrane Protein inSinorhizobium meliloti
Authors: Battistoni Federico , Platero Raúl , Duran Rosario , Cerveñansky Carlos , Battistoni Julio , Arias Alicia , Fabiano Elena
Published: November 2002

Rhizobia are soil bacteria that are able to establish symbiotic associations with leguminous hosts. In iron-limited environments these bacteria can use iron present in heme or heme compounds (hemoglobin, leghemoglobin). Here we report the presence inSinorhizobium melilotiof an iron-regulated outer membrane protein that is able to bind hemin but not hemoglobin. Protein assignment was done by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Tryptic peptides correlated with the mass measurements obtained accounted for 54% of the translated sequence of a putative heme receptor gene present in the chromosome ofS. meliloti1021. The results which we obtained suggest that this protein (designated ShmR forSinorhizobiumheme receptor) is involved in high-affinity heme-mediated iron transport.
Prevalence of
Campylobacter jejuni
,
Campylobacter lari
, and
Campylobacter coli
in Different Ecological Guilds and Taxa of Migrating Birds
Authors: Waldenström Jonas , Broman Tina , Carlsson Inger , Hasselquist Dennis , Achterberg René P. , Wagenaar Jaap A. , Olsen Björn
Published: November 2002

A total of 1,794 migrating birds trapped at a coastal site in southern Sweden were sampled for detection of
Campylobacter
spp. All isolates phenotypically identified as
Campylobacter jejuni
and a subset of those identified as non-
C. jejuni
were identified to the species level by PCR-based techniques.
C. jejuni
was found in 5.0% of the birds,
Campylobacter lari
was found in 5.6%, and
Campylobacter coli
was found in 0.9%. An additional 10.7% of the tested birds were infected with hippurate hydrolysis-negative
Campylobacter
spp. that were not identified to the species level. The prevalence of
Campylobacter
spp. differed significantly between ecological guilds of birds. Shoreline-foraging birds feeding on invertebrates and opportunistic feeders were most commonly infected (76.8 and 50.0%, respectively). High prevalence was also shown in other ground-foraging guilds, i.e., ground-foraging invertebrate feeders (11.0%), ground-foraging insectivores (20.3%), and plant-eating species (18.8%). Almost no
Campylobacter
spp. were found in ground-foraging granivores (2.3%), arboreal insectivores (0.6%), aerial insectivores (0%), or reed- and herbaceous plant-foraging insectivores (3.5%). During the autumn migration, a high proportion of samples from juveniles were positive (7.1% in passerines, 55.0% in shorebirds), indicating transmission on the breeding grounds or during the early part of migration. Prevalence of
Campylobacter
spp. was associated with increasing body mass among passerine bird species. Furthermore, prevalence was higher in short-distance migrants wintering in Europe than in long-distance migrants wintering in Africa, the Middle East, or Asia. Among ground-foraging birds of the Muscicapidae, those of the subfamily Turdinae (i.e.,
Turdus
spp.) showed a high prevalence of
Campylobacter
spp., while the organism was not isolated in any member of the subfamily Muscicapinae (i.e.,
Erithacus
and
Luscinia
). The prevalence of
Campylobacter
infection in wild birds thus seems to be linked to various ecological and phylogenetic factors, with great variations in carriership between different taxa and guilds.
Cryptosporidium
and
Giardia
Recoveries in Natural Waters by Using Environmental Protection Agency Method 1623
Authors: DiGiorgio Carol L. , Gonzalez David A. , Huitt Christopher C.
Published: November 2002

Relatively few studies have examined recoveries from source waters by using Environmental Protection Agency method 1623 with organism spike doses that are environmentally realistic and at turbidity levels commonly found in surface waters. In this study, we evaluated the filtration capacities and recovery efficiencies of the Gelman Envirochek (standard filter) and the Gelman Envirochek high-volume (HV) sampling capsules under environmental conditions. We also examined the performance of method 1623 under ambient conditions with matrix spike experiments using 10 organisms/liter. Under turbid conditions, the HV capsule filtered approximately twice the volume filtered by the standard filter, but neither could filter 10 liters without clogging. In low-turbidity waters, oocyst, but not cyst, recoveries were significantly higher when the HV capsule was used. In turbid waters, organism recoveries were lower than those in nonturbid waters and were not significantly different for the different filters. When the HV capsule was used,
Cryptosporidium
recoveries ranged from 36 to 75%, and
Giardia
recoveries ranged from 0.5 to 53%. For both organisms, recoveries varied significantly by site. Turbidity could explain variation in
Giardia
recoveries (
r
2
= 0.80) but not variation in
Cryptosporidium
recoveries (
r
2
= 0.16). The inconsistent recoveries across sites suggested that the background matrix of the ambient water affected recovery by method 1623. A control sample collected at the height of the winter rainy season detected one organism, highlighting the difficulty of using this method to accurately measure pathogen abundance under natural conditions. Our findings support the use of the HV filter under field conditions but suggest that designing a cost-effective and statistically valid monitoring program to evaluate sources and loads of protozoan pathogens may be difficult.
Aquaporin Expression Correlates with Freeze Tolerance in Baker's Yeast, and Overexpression Improves Freeze Tolerance in Industrial Strains
Authors: Tanghe An , Van Dijck Patrick , Dumortier Françoise , Teunissen Aloys , Hohmann Stefan , Thevelein Johan M.
Published: November 2002

Little information is available about the precise mechanisms and determinants of freeze resistance in baker's yeast,
Saccharomyces cerevisiae
. Genomewide gene expression analysis and Northern analysis of different freeze-resistant and freeze-sensitive strains have now revealed a correlation between freeze resistance and the aquaporin genes
AQY1
and
AQY2
. Deletion of these genes in a laboratory strain rendered yeast cells more sensitive to freezing, while overexpression of the respective genes, as well as heterologous expression of the human aquaporin gene
hAQP1
, improved freeze tolerance. These findings support a role for plasma membrane water transport activity in determination of freeze tolerance in yeast. This appears to be the first clear physiological function identified for microbial aquaporins. We suggest that a rapid, osmotically driven efflux of water during the freezing process reduces intracellular ice crystal formation and resulting cell damage. Aquaporin overexpression also improved maintenance of the viability of industrial yeast strains, both in cell suspensions and in small doughs stored frozen or submitted to freeze-thaw cycles. Furthermore, an aquaporin overexpression transformant could be selected based on its improved freeze-thaw resistance without the need for a selectable marker gene. Since aquaporin overexpression does not seem to affect the growth and fermentation characteristics of yeast, these results open new perspectives for the successful development of freeze-resistant baker's yeast strains for use in frozen dough applications.
Distribution of Human Virus Contamination in Shellfish from Different Growing Areas in Greece, Spain, Sweden, and the United Kingdom
Authors: Formiga-Cruz M. , Tofiño-Quesada G. , Bofill-Mas S. , Lees D. N. , Henshilwood K. , Allard A. K. , Conden-Hansson A.-C. , Hernroth B. E. , Vantarakis A. , Tsibouxi A. , Papapetropoulou M. , Furones M. D. , Girones R.
Published: November 2002

Viral pollution in shellfish has been analyzed simultaneously across a wide range of geographical regions, with emphasis on the concomitant variations in physicochemical characteristics and social features. The methods for sample treatment and for the detection of human enteric viruses were optimized by the participating laboratories. The second part of this study involves the selection of a protocol for virus detection, which was validated by analyzing the distribution and concentration of human viral pathogens under diverse conditions during an 18-month period in four European countries. Shellfish-growing areas from diverse countries in the north and south of Europe were defined and studied, and the microbiological quality of the shellfish was analyzed. Human adenovirus, Norwalk-like virus, and enterovirus were identified as contaminants of shellfish in all the participating countries. Hepatitis A virus was also isolated in all areas except Sweden. The seasonal distribution of viral contamination was also described. Norwalk-like virus appeared to be the only group of viruses that demonstrated seasonal variation, with lower concentrations occurring during warm months. The depuration treatments currently applied were shown to be adequate for reducing
Escherichia coli
levels but ineffective for the elimination of viral particles. The human adenoviruses detected by PCR correlate with the presence of other human viruses and could be useful as a molecular index of viral contamination in shellfish.
Phylogenetic and Kinetic Diversity of Aerobic Vinyl Chloride-Assimilating Bacteria from Contaminated Sites
Authors: Coleman Nicholas V. , Mattes Timothy E. , Gossett James M. , Spain Jim C.
Published: November 2002

Aerobic bacteria that grow on vinyl chloride (VC) have been isolated previously, but their diversity and distribution are largely unknown. It is also unclear whether such bacteria contribute to the natural attenuation of VC at chlorinated-ethene-contaminated sites. We detected aerobic VC biodegradation in 23 of 37 microcosms and enrichments inoculated with samples from various sites. Twelve different bacteria (11
Mycobacterium
strains and 1
Nocardioides
strain) capable of growth on VC as the sole carbon source were isolated, and 5 representative strains were examined further. All the isolates grew on ethene in addition to VC and contained VC-inducible ethene monooxygenase activity. The
Mycobacterium
strains (JS60, JS61, JS616, and JS617) all had similar growth yields (5.4 to 6.6 g of protein/mol), maximum specific growth rates (0.17 to 0.23 day
−1
), and maximum specific substrate utilization rates (9 to 16 nmol/min/mg of protein) with VC. The
Nocardioides
strain (JS614) had a higher growth yield (10.3 g of protein/mol), growth rate (0.71 day
−1
), and substrate utilization rate (43 nmol/min/mg of protein) with VC but was much more sensitive to VC starvation. Half-velocity constant (

K
s

) values for VC were between 0.5 and 3.2 μM, while

K
s

values for oxygen ranged from 0.03 to 0.3 mg/liter. Our results indicate that aerobic VC-degrading microorganisms (predominantly
Mycobacterium
strains) are widely distributed at sites contaminated with chlorinated solvents and are likely to be responsible for the natural attenuation of VC.
Identification and Characterization of Novel Surface Proteins in
Lactobacillus johnsonii
and
Lactobacillus gasseri
Authors: Ventura Marco , Jankovic Ivana , Walker D. Carey , Pridmore R. David , Zink Ralf
Published: November 2002

We have identified and sequenced the genes encoding the aggregation-promoting factor (APF) protein from six different strains of
Lactobacillus johnsonii
and
Lactobacillus gasseri
. Both species harbor two
apf
genes,
apf1
and
apf2
, which are in the same orientation and encode proteins of 257 to 326 amino acids. Multiple alignments of the deduced amino acid sequences of these
apf
genes demonstrate a very strong sequence conservation of all of the genes with the exception of their central regions. Northern blot analysis showed that both genes are transcribed, reaching their maximum expression during the exponential phase. Primer extension analysis revealed that
apf1
and
apf2
harbor a putative promoter sequence that is conserved in all of the genes. Western blot analysis of the LiCl cell extracts showed that APF proteins are located on the cell surface. Intact cells of
L. johnsonii
revealed the typical cell wall architecture of S-layer-carrying gram-positive eubacteria, which could be selectively removed with LiCl treatment. In addition, the amino acid composition, physical properties, and genetic organization were found to be quite similar to those of S-layer proteins. These results suggest that APF is a novel surface protein of the
Lactobacillus acidophilus
B-homology group which might belong to an S-layer-like family.
Response of Ants to a Deterrent Factor(s) Produced by the Symbiotic Bacteria of Entomopathogenic Nematodes
Authors: Zhou Xinsheng , Kaya Harry K. , Heungens Kurt , Goodrich-Blair Heidi
Published: November 2002

The production of an ant-deterrent factor(s) (ADF) by
Xenorhabdus nematophila
and
Photorhabdus luminescens
, the symbiotic bacteria of the nematodes
Steinernema carpocapsae
and
Heterorhabditis bacteriophora
, respectively, was examined. In addition to an in vivo assay in which bacteria were tested for their ability to produce ADF within insect cadavers (M.E. Baur, H. K. Kaya, and D. R. Strong, Biol. Control 12:231-236, 1998), an in vitro microtiter dish assay was developed to monitor ADF activity produced by bacteria grown in cultures. Using these methods, we show that ADF activity is present in the supernatants of bacterial cultures, is filterable, heat stable, and acid sensitive, and passes through a 10-kDa-pore-size membrane. Thus, ADF appears to be comprised of a small, extracellular, and possibly nonproteinaceous compound(s). The amount of ADF repellency detected depends on the ant species being tested, the sucrose concentration (in vitro assays), and the strain, form, and age of the ADF-producing bacteria. These findings demonstrate that the symbiotic bacteria of some species of entomopathogenic nematodes produce a compound(s) that deters scavengers such as ants and thus could protect nematodes from being eaten during reproduction within insect cadavers.
Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry of Lipopeptide Biosurfactants in Whole Cells and Culture Filtrates of
Bacillus subtilis
C-1 Isolated from Petroleum Sludge
Authors: Vater Joachim , Kablitz Bärbel , Wilde Christopher , Franke Peter , Mehta Neena , Cameotra Swaranjit Singh
Published: November 2002

An innovative method was developed for rapid sensitive detection and efficient structural characterization of lipopeptide biosurfactants by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry by using whole microbial cells and crude culture filtrates as targets in combination with surface tension measurements. This was done for a bacterial strain that was isolated from petroleum sludge and efficiently produces biosurfactants. This organism was identified by using biochemical, physiological, and genetic parameters as a
Bacillus subtilis
strain, designated
B. subtilis
C-1. This assignment was supported by a mass spectrometric investigation of the secondary metabolite spectrum determined by whole-cell MALDI-TOF mass spectrometry, which revealed three lipopeptide complexes, the surfactins, the iturins, and the fengycins, which are well-known biosurfactants produced by
B. subtilis
strains. These compounds were structurally characterized by in situ structure analysis by using postsource decay MALDI-TOF mass spectrometry. The isoforms were separated by miniaturized high-resolution reversed-phase high-performance liquid chromatography for mass spectrometric characterization. Iturin compounds which contain unusual fatty acid components were detected.
Coexistence of Multiple Proteobacterial Endosymbionts in the Gills of the Wood-Boring Bivalve
Lyrodus pedicellatus
(Bivalvia: Teredinidae)
Authors: Distel Daniel L. , Beaudoin David J. , Morrill Wendy
Published: November 2002

Wood-boring bivalves of the family Teredinidae (commonly called shipworms) are known to harbor dense populations of gram-negative bacteria within specialized cells (bacteriocytes) in their gills. These symbionts are thought to provide enzymes, e.g., cellulase and dinitrogenase, which assist the host in utilizing wood as a primary food source. A cellulolytic, dinitrogen-fixing bacterium,
Teredinibacter turnerae
, has been isolated from the gill tissues of numerous teredinid bivalves and has been proposed to constitute the sole or predominant symbiont of this bivalve family. Here we demonstrate that one teredinid species,
Lyrodus pedicellatus
, contains at least four distinct bacterial 16S rRNA types within its gill bacteriocytes, one of which is identical to that of
T. turnerae
. Phylogenetic analyses indicate that the three newly detected ribotypes are derived from gamma proteobacteria that are related to but distinct (>6.5% sequence divergence) from
T. turnerae.
In situ hybridizations with 16S rRNA-directed probes demonstrated that the pattern of occurrence of symbiont ribotypes within bacteriocytes was predictable and specific, with some bacteriocytes containing two symbiont ribotypes. However, only two of the six possible pairwise combinations of the four ribotypes were observed to cooccur within the same host cells. The results presented here are consistent with the existence of a complex multiple symbiosis in this shipworm species.