bluuebunny/crossref_metadata_2025_split huggingface dataset:
A mid‐Holocene environmental change in Amazonian savannas
Authors: De Toledo Mauro B. , Bush Mark B. 
Published: October 2006

AbstractAim  The main goal of this study was to investigate how climate and human activities may have influenced ecotonal areas of disjoint savannas within Brazilian Amazonia.Location  Eastern Brazilian Amazonia, Amapá State.Methods  The fossil pollen and charcoal records of two lakes in Amapá (Marcio and Tapera) were used to provide a Holocene palaeoecological history of eastern Amazonian savannas. Detrended correspondence analysis was used to enhance the patterns of sample distribution along the sediment core.Results  Even though sedimentary hiatuses were recognized in the sediment cores from both lakes, a marked change in vegetation from closed forests with swamp elements to open flooded savanna at c. 5000 yr bp was evident from the pollen record. Charcoal analysis revealed a pattern of increased accumulation of charred particles coincident with the establishment of savanna vegetation, suggesting higher fire frequency near the lakes. Because the timing of the sedimentary hiatus overlapped with the highest Holocene sea level, which would have increased the local water table preventing the lakes from drying out, we infer that both lakes used to depend heavily on flood waters, and the sedimentary gap was caused by reduced discharge from the Amazon River, due to a dry period in the Andes, when precipitation levels markedly decreased between 8000 and 5000 yr bp. The lack of Andean pollen (probably river transported) in the sediment record after this event and the existence of similar records near the study site make this interpretation more appealing. The resumption of sedimentation in Lake Marcio, contemporaneous with falling sea level and increasingly wet conditions in the Andes after 5000 yr bp, indicates that Holocene sea‐level variation did not play an important role in maintaining lake levels.Main conclusions  The study site recorded long‐term occupation by pre‐Columbian peoples. However, it is still unclear whether these disjoint savannas have an anthropogenic origin. Even though locally dry environmental conditions were inferred from both records, there is no evidence of a mid‐Holocene dry climate in eastern Amazonia. Instead, the Amapá record indicates a connection between Andean climate and eastern Amazonia, demonstrating the need for a better understanding of the impacts and magnitude of climate changes.
Pathogenesis and treatment of diabetic vascular disease – illustrated by two cases
Authors: SMITH U. , LAAKSO M. , ELIASSON B. , WESSLAU C. , BORÉN J. , WIKLUND O. , ATTVALL S. 
Published: October 2006

Abstract.This publication is a summary of the presentations given at the First JIM Grand Round held at the Sahlgrenska University Hospital on 15 March 2006. The Grand Round was based on two case reports; a patient with type 2 diabetes and pronounced macrovascular disease and another patient with early microvascular disease combined with the macrovascular complications. The pathogenesis of the vascular complications and the current treatment regimens were discussed in relation to the history and examinations performed in these patients.
A novel ligand bound ABC transporter, LolCDE, provides insights into the molecular mechanisms underlying membrane detachment of bacterial lipoproteins
Authors: Ito Yasuko , Kanamaru Kyoko , Taniguchi Naohiro , Miyamoto Shigehiko , Tokuda Hajime 
Published: October 2006

SummaryThe LolCDE complex of Escherichia coli belongs to the ABC transporter superfamily and initiates the lipoprotein sorting to the outer membrane by catalysing their release from the inner membrane. LolC and/or LolE, membrane subunits, recognize lipoproteins anchored to the outer surface of the inner membrane, while LolD hydrolyses ATP on its inner surface. We report here that ligand‐bound LolCDE can be purified from the inner membrane in the absence of ATP. Liganded LolCDE represents an intermediate of the release reaction and exhibits higher affinity for ATP than the unliganded form. ATP binding to LolD weakens the interaction between LolCDE and lipoproteins and causes their dissociation in a detergent solution, while lipoprotein release from membranes requires ATP hydrolysis. Liganded LolCDE thus reveals molecular events brought about through ATP binding and hydrolysis. LolCDE is the first example of an ABC transporter purified with tightly bound native substrates. A single molecule of lipoprotein is found to bind per molecule of the LolCDE complex.
An α‐(1,4)‐amylase is essential for α‐(1,3)‐glucan production and virulence in Histoplasma capsulatum
Authors: Marion Christopher L. , Rappleye Chad A. , Engle Jacquelyn T. , Goldman William E. 
Published: October 2006

Summary Histoplasma capsulatum is a dimorphic fungus that causes respiratory and systemic disease and is capable of surviving and replicating within macrophages. The virulence of Histoplasma has been linked to cell wall α‐(1,3)‐glucan; however, the role of this polysaccharide during infection, its organization within the cell wall, and its synthesis and regulation remain poorly understood. To identify genes involved in the biosynthesis of α‐(1,3)‐glucan, we employed a forward genetics strategy to isolate physically marked mutants with reduced α‐(1,3)‐glucan. Insertional mutants were generated in a virulent strain of H. capsulatum by optimization of Agrobacterium tumefaciens‐mediated transformation. Approximately 90% of these mutants possessed single insertions with no chromosomal rearrangements or deletions in the host genome. To confirm the role and specificity of identified candidate genes, we phenocopied the disrupted locus by either RNA interference or targeted gene deletion. Our findings indicate α‐(1,3)‐glucan production requires the function of the AMY1 gene product, a novel protein with homology to the α‐amylase family of glycosyl hydrolases, and UGP1, a UTP‐glucose‐1‐phosphate uridylyltransferase which synthesizes UDP‐glucose monomers. Loss of AMY1 function attenuated the ability of Histoplasma to kill macrophages and to colonize murine lungs.
RyhB small RNA modulates the free intracellular iron pool and is essential for normal growth during iron limitation in Escherichia coli
Authors: Jacques Jean‐François , Jang Soojin , Prévost Karine , Desnoyers Guillaume , Desmarais Maxime , Imlay James , Massé Eric 
Published: October 2006

SummaryThe small RNA RyhB has recently been shown to negatively regulate a number of mRNAs encoding dispensable iron‐using proteins in Escherichia coli. The resulting decrease in the synthesis of iron‐using proteins is thought to spare iron in order to ensure its availability for iron‐requiring proteins that are indispensable. Indeed, the expression of RyhB from a heterologous promoter activates the iron‐sensing repressor Fur, which suggests an increase in the pool of free intracellular iron (iron‐sparing). In accordance with these observations, we report here that RyhB expression increases the concentration of free intracellular iron, as shown by direct measurements of the metal in whole cells by electron paramagnetic resonance spectroscopy. Our data also suggest that iron‐sparing originates from rapid uptake of extracellular iron and not from already internalized metal. Furthermore, RyhB is shown to be essential for normal bacterial growth and survival during iron starvation, which is consistent with previous data describing the function of the small RNA. Overall, our data demonstrate that, by regulating synthesis of nonessential iron‐using proteins, the small RNA RyhB ensures that the iron is directed towards the iron‐requiring enzymes that are indispensable.
Prophages of Staphylococcus aureus Newman and their contribution to virulence
Authors: Bae Taeok , Baba Tadashi , Hiramatsu Keiichi , Schneewind Olaf 
Published: October 2006

SummaryFour prophages (φNM1–4) were identified in the genome of Staphylococcus aureus Newman, a human clinical isolate. φNM1, φNM2 and φNM4, members of the siphoviridae family, insert at different sites (poiA, downstream of isdB and geh) in the staphylococcal chromosome. φNM3, a β‐haemolysin (hlb) converting phage, encodes modulators of innate immune responses (sea, sak, chp and scn) in addition to other virulence genes. Replication of φNM1, φNM2 and φNM4 occurs in culture and during animal infection, whereas φNM3 prophage replication was not observed. Prophages were excised from the chromosome and S. aureus variants lacking φNM3 or φNM1, φNM2 and φNM4 displayed organ specific virulence defects in a murine model of abscess formation. S. aureus Newman lacking all four prophages was unable to cause disease, thereby revealing essential contributions of prophages to the pathogenesis of staphylococcal infections.
Increased expression and activity of urokinase‐type plasminogen activator during epileptogenesis
Authors: Lahtinen Laura , Lukasiuk Katarzyna , Pitkänen Asla 
Published: October 2006

AbstractOur recent large‐scale molecular profiling study revealed a sevenfold upregulation in the expression of urokinase‐type plasminogen activator (uPA) during epileptogenesis. uPA is a member of the plasminogen activation system, which is a major contributor to the reorganization of neuronal circuits after trauma. Here, we investigated the expression and activity of uPA in normal and epileptogenic rat hippocampus to test a hypothesis that the expression of uPA is altered in brain areas that undergo epilepsy‐related circuitry reorganization. Epileptogenesis was triggered by inducing status epilepticus (SE) with electrical stimulation of the amygdala in rats. Continuous video‐electroencephalogram recordings were used to monitor the development of SE and the occurrence of spontaneous seizures. Animals were killed at 1, 4 or 14 days after SE, and brains were processed for immunohistochemistry or protein extraction. Confocal microscopy analysis of double‐immunolabelled preparations indicated that SE triggered an increased expression of uPA in hippocampal astrocytes, neurons, white matter and blood vessels. Zymography revealed that the expression of uPA protein is associated with increased levels of enzymatically active uPA during epileptogenesis. uPA expression and enzymatic activity peaked within 1–4 days after SE, that is, before the occurrence of spontaneous seizures, and remained elevated for at least 2 weeks. These data suggest that uPA is involved in the reorganization of neuronal tissue during the epileptogenic process.
Injury‐induced axonal sprouting in the hippocampus is initiated by activation of trkB receptors
Authors: Dinocourt Céline , Gallagher Sandra E. , Thompson Scott M. 
Published: October 2006

AbstractPenetrating head injuries are often accompanied by the delayed development of post‐traumatic epilepsy. Schaffer collateral transection leads to axonal sprouting and hyperexcitability in area CA3 of hippocampal slice cultures. We used this model to test the hypothesis that the injury‐induced axonal sprouting results from increased neurotrophin signaling via trkB receptors near the lesion. Using rats and mice, we established that sprouting CA3 pyramidal cell axons are labeled with an antibody to the growth‐associated protein GAP‐43. We observed two‐ to threefold increases in the level of brain‐derived neurotrophic factor and trkB protein in area CA3 by 24–48 h after Schaffer collateral transection, preceding the onset of axonal sprouting. Finally, we demonstrated that injury‐induced axonal sprouting of GAP‐43‐immunoreactive axons is impaired in hippocampal slice cultures from mice expressing low levels of trkB receptors. We conclude that injury‐induced axonal sprouting is initiated by brain‐derived neurotrophic factor–trkB signaling and suggest that this process may be critical for the genesis of post‐traumatic epilepsy.
Striatum gray matter reduction in males with an overactive behavioral activation system
Authors: Barrós‐Loscertales A. , Meseguer V. , Sanjuán A. , Belloch V. , Parcet M. A. , Torrubia R. , Ávila C. 
Published: October 2006

AbstractUsing optimized voxel‐based morphometry, we studied the relationship between gray matter volume in brain areas associated with reward and scores on a behavioral activation system measure (the Sensitivity to Reward scale) in a sample of 50 male undergraduates. Voxel‐based morphometry analysis revealed a negative correlation between Sensitivity to Reward scores and gray matter volume in the dorsal striatum and prefrontal cortex. Results indicate that a reduced volume in the striatum might be associated with enhanced reward sensitivity and deficits in inhibitory control.
Relationship of opioid receptors with GABAergic neurons in the rat inferior colliculus
Authors: Tongjaroenbuangam W. , Jongkamonwiwat N. , Phansuwan‐Pujito P. , Casalotti S. O. , Forge A. , Dodson H. , Govitrapong P. 
Published: October 2006

AbstractThe inferior colliculus is a critical structure for processing auditory information and receives ascending and descending synaptic auditory projections. In addition to GABAergic and glutamatergic innervations, other neurotransmitter systems are also reported in the inferior colliculus, including opioid peptides. In the present study, the relative distribution of each type of opioid receptor, mu (MOR), delta (DOR) and kappa (KOR) within GABAergic neurons in the inferior colliculus was examined. GABA immunoreactivity was expressed by small, medium and large neurons and distributed in the central nucleus and the pericentral nucleus of the inferior colliculus. Immunostaining for MOR, DOR and KOR receptors was found in both disc‐shaped cells and stellate cells. Punctiform β‐endorphin immunolabelling was observed in the proximity of GABA‐positive neurons. Co‐localization of GABA and MOR receptors was observed in neurons and nerve terminals in the central nucleus, dorsal cortex and external cortex of the inferior colliculus. Quantification of the co‐localization patterns determined that a higher proportion of GABA neurons was associated with MOR receptors compared with KOR or DOR receptors.
Structure of Caribbean coral reef communities across a large gradient of fish biomass
Authors: Newman Marah J. H. , Paredes Gustavo A. , Sala Enric , Jackson Jeremy B. C. 
Published: October 2006

AbstractThe collapse of Caribbean coral reefs has been attributed in part to historic overfishing, but whether fish assemblages can recover and how such recovery might affect the benthic reef community has not been tested across appropriate scales. We surveyed the biomass of reef communities across a range in fish abundance from 14 to 593 g m−2, a gradient exceeding that of any previously reported for coral reefs. Increased fish biomass was correlated with an increased proportion of apex predators, which were abundant only inside large marine reserves. Increased herbivorous fish biomass was correlated with a decrease in fleshy algal biomass but corals have not yet recovered.
Spatial segregation of specialists and generalists in bird communities
Authors: Julliard Romain , Clavel Joanne , Devictor Vincent , Jiguet Frédéric , Couvet Denis 
Published: October 2006

AbstractEach species generally has a close relationship with one or more habitats and can therefore be classified as either specialist or generalist. We studied whether specialist and generalist species are spatially distributed independently of each other. Repeating the analysis for 100 of the most frequent terrestrial bird species recorded over the 10 000 sampled sites of the French Breeding Bird survey, we found that specialists were more abundant if the rest of the community was specialized, and that the inverse was also true. This pattern was far subtler than just a simple dichotomy: most species actually presented a maximum abundance at a value of community specialization similar to their own level of specialization. Bird communities appear very well defined along a specialist–generalist gradient. We believe this pattern becomes more apparent with habitat degradation. The consequences on both ecological services and community resilience may well be considerable.
Allometric scaling enhances stability in complex food webs
Authors: Brose Ulrich , Williams Richard J. , Martinez Neo D. 
Published: October 2006

AbstractClassic local stability theory predicts that complex ecological networks are unstable and are unlikely to persist despite empiricists’ abundant documentation of such complexity in nature. This contradiction has puzzled biologists for decades. While some have explored how stability may be achieved in small modules of a few interacting species, rigorous demonstrations of how large complex and ecologically realistic networks dynamically persist remain scarce and inadequately understood. Here, we help fill this void by combining structural models of complex food webs with nonlinear bioenergetic models of population dynamics parameterized by biological rates that are allometrically scaled to populations’ average body masses. Increasing predator–prey body mass ratios increase population persistence up to a saturation level that is reached by invertebrate and ectotherm vertebrate predators when being 10 or 100 times larger than their prey respectively. These values are corroborated by empirical predator–prey body mass ratios from a global data base. Moreover, negative effects of diversity (i.e. species richness) on stability (i.e. population persistence) become neutral or positive relationships at these empirical ratios. These results demonstrate that the predator–prey body mass ratios found in nature may be key to enabling persistence of populations in complex food webs and stabilizing the diversity of natural ecosystems.
Habitat effects on the relative importance of trait‐ and density‐mediated indirect interactions
Authors: Trussell Geoffrey C. , Ewanchuk Patrick J. , Matassa Catherine M. 
Published: October 2006

AbstractClassical views of trophic cascades emphasize the primacy of consumptive predator effects on prey populations to the transmission of indirect effects [density‐mediated indirect interactions (DMIIs)]. However, trophic cascades can also emerge without changes in the density of interacting species because of non‐consumptive predator effects on prey traits such as foraging behaviour [trait‐mediated indirect interactions (TMIIs)]. Although ecologists appreciate this point, measurements of the relative importance of each indirect predator effect are rare. Experiments with a three‐level, rocky shore food chain containing an invasive predatory crab (Carcinus maenas), an intermediate consumer (the snail, Nucella lapillus) and a basal resource (the barnacle, Semibalanus balanoides) revealed that the strength of TMIIs is comparable with, or exceeds, that of DMIIs. Moreover, the sign and strength of each indirect predator effect depends on whether it is measured in risky or refuge habitats. Because habitat shifts are often responsible for the emergence of TMIIs, attention to the sign and strength of these interactions in both habitats will improve our understanding of the link between individual behaviour and community dynamics.
Growth and mechanism of filamentous‐sulfur formation by Candidatus Arcobacter sulfidicus in opposing oxygen‐sulfide gradients
Authors: Sievert Stefan M. , Wieringa Elze B. A. , Wirsen Carl O. , Taylor Craig D. 
Published: October 2006

SummaryStudies were conducted in opposing gradients of oxygen and sulfide in microslide capillaries to (i) characterize the chemical microenvironment preferred by Candidatus Arcobacter sulfidicus, a highly motile, sulfur‐oxidizing bacterium that produces sulfur in filamentous form, and (ii) to develop a model describing the mechanism of filamentous‐sulfur formation. The highly motile microorganisms are microaerophilic, with swarms effectively aggregating within oxic‐anoxic interfaces by exhibiting a chemotactic response. The position of the band was found to be largely independent of the sulfide concentration as it always formed at the oxic‐anoxic interface. Flux calculations based on steady state gradients of oxygen and sulfide indicate that sulfide is incompletely oxidized to sulfur, in line with the formation of filamentous sulfur by these organisms. It is proposed that Candidatus Arcobacter sulfidicus effectively competes with other sulfur‐oxidizing bacteria in the environment by being able to tolerate higher concentrations of hydrogen sulfide (1–2 mM) and by possessing the ability to grow at very low oxygen concentrations (1–10 μM). The formation of mat‐like structures from filamentous sulfur appears to be a population mediated effort allowing these organisms to effectively colonize environments characterized by high sulfide, low oxygen and dynamic fluid movement.
Geographical variation in the ‘bottom‐up’ control of diversity: fleas and their small mammalian hosts
Authors: Krasnov Boris R. , Shenbrot Georgy I. , Khokhlova Irina S. , Poulin Robert 
Published: October 2006

ABSTRACTAim  We searched for signs of the ‘bottom‐up’ diversity effect in the association between fleas (Siphonaptera) and their small mammalian hosts (Rodentia, Insectivora and Lagomorpha). We asked (1) whether a strong dependence of flea species richness on host species richness is characteristic for both Palaeoarctic and Nearctic realms; (2) if yes, whether the ratio of host species per flea species along the host diversity gradient is similar between the Palaeoarctic and Nearctic; and (3) whether factors other than host species richness (i.e. geographical position, climate and landscape) might better explain variation in flea species richness than host species richness.Location The study used previously published data on species richness of fleas and their small mammalian hosts from 26 Palaeoarctic and 19 Nearctic regions.Methods  We regressed the number of flea species on the number of small mammal species across regions, separately for Palaeoarctic and Nearctic realms, using both non‐transformed data as well as data corrected for the confounding effects of host sampling effort and sampling area. To test whether flea species richness is determined by external factors unrelated to the host, we used stepwise multiple regressions of flea species richness against host species richness and parameters describing the geographical position, climate and relief of a region.Results  When non‐transformed data were analysed, flea species richness was positively correlated with host species richness in both the Palaeoarctic and Nearctic, although the slopes of the two regressions differed significantly. After removal of the confounding effects of host sampling effort and sampling area, Palaeoarctic flea species richness remained strongly positively correlated with host species richness, whereas in the Nearctic, flea species richness appeared to be completely independent of host species richness. Results of the multiple regressions using corrected data demonstrated that in the Palaeoarctic, flea species richness was correlated with both the number of host species and the mean altitude of the region, whereas in the Nearctic, flea species richness only tended to be weakly correlated with latitude (however, this correlation turned out to be non‐significant after Bonferroni correction).Main conclusions  We found evidence of bottom‐up control of flea diversity in the Palaeoarctic regions only, and not in the Nearctic. We explore several potential explanations for the different patterns observed in the two biogeographical realms, including differences in (1) levels of host specialization, (2) history of host–parasite associations and (3) landscape effects on flea diversification. We conclude that these factors combine to create different macroecological patterns in different biogeographical realms, and that diversity is not governed by the same forces everywhere.