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21.
Keith B. Gido Nathan R. Franssen David L. Propst 《Environmental Biology of Fishes》2006,75(2):197-207
Synopsis Spatial patterns of resource use by small-bodied fishes in the San Juan River were examined using stable isotopes. Using δ15N of fishes as an index of trophic position, our data suggest both native and non-native fishes primarily consumed macro-invertebrates.
The δ13C of these fishes further suggested a detritus-based food web, from which most species fed on chironomids in low-velocity
habitats. A two-way ANOVA revealed a significant interaction between trophic level of fish species and longitudinal position
in the river. This interaction was primarily attributed to a decline in trophic level of non-native red shiner Cyprinella lutrensis, relative to other species, in upstream reaches of the river. In addition, ANCOVA results suggest trophic position of fishes
was dependent on channel type (primary vs. secondary), as there was less variability in resource use in secondary channels.
These data provided a spatial framework of trophic interactions that can be used to predict the outcome of management actions.
Overall, we confirmed high overlap in resource used between native and non-native fishes. However, spatial variation in trophic
interactions both longitudinally and laterally in the river present a challenge to resource managers attempting to managing
entire river systems. 相似文献
22.
N. W. J. T. Heinsman M. C. R. Franssen A. van der Padt R. M. Boom K. van't Riet Ae. de Groot 《Biocatalysis and Biotransformation》2002,20(5):297-309
Branched chain fatty acids (BCFAs) are fatty acids substituted with alkyl groups. Many of them are chiral and therefore occur in two enantiomeric forms. This review describes their occurrence in Nature, their biosynthesis, their properties as flavours, and their enzymatic kinetic resolution. Many lipases are able to separate the enantiomers of BCFAs, in hydrolysis, esterification or transesterification reactions. Very often, the stereoselectivity of these reactions is remarkably high, even when the chiral carbon atom is remote from the carboxylic acid group. 相似文献
23.
N. W. J. T. Heinsman P. L. J. van der Weide A. van der Padt M. C. R. Franssen R. M. Boom K. van't Riet 《Biocatalysis and Biotransformation》2002,20(6):429-436
The bench scale Novozym 435 ® catalysed esterification of 4-methyloctanoic acid with ethanol was studied at 35°C. Esterification in a batch reactor (molar ratio of 1:8 (acid:EtOH)) resulted in the isolation of the enantiomerically enriched product (ee p =81%) and substrate (ee s =93%). In order to integrate reaction and separation, liquid-vapour equilibria calculations were performed showing that an excess of ethanol results in a very low ester fraction in the vapour phase. Since this is undesirable for an integrated process of reaction and product removal, a repeated batch reaction was performed using a molar ratio of 10:1 (acid:EtOH). After six cycles (45% conversion) the ee of 4-methyloctanoic acid ethyl ester turned out to be 80%. For different E values the ee p was calculated for batch and repeated batch reactions. It was shown that in all cases the ee p was higher for the repeated batch reaction. However, the product is not enantiopure since the E value of the reaction is rather low at the low ethanol concentration used. An alternative approach would be the continuous separation of the product during the reaction. A mathematical model was developed to describe esterification in a packed bed reactor integrated with product separation. This model shows that integration of reaction and product removal in advance is not suitable either to obtain an enantiomerically pure product. Since the optimal reaction conditions (high ethanol concentration) and the optimal separation system (low ethanol concentration) do not match in this reaction, the preference is given to the batch reaction at high ethanol concentrations because in that case the highest enantioselectivity of the enzyme is obtained. 相似文献
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26.
Courtney M. Franssen Michael Tobler Rüdiger Riesch Francisco J. García de León Ralph Tiedemann Ingo Schlupp Martin Plath 《Aquatic Ecology》2008,42(4):685-692
A prominent trade-off in life history theory and evolution balances the costs of reproduction with those of basic somatic
needs. Hence, reproductive efforts may be reduced in environments where additional energy is required for somatic maintenance.
Here, we investigated male sperm stores in Atlantic mollies (Poecilia mexicana) from a sulfidic cave and several sulfidic and non-sulfidic surface habitats. We found significant differences among populations
in the number of sperm stripped per male, which was also correlated with differences in gonad weights. The largest sperm stores
were detected in males from non-sulfidic surface creeks, while males from a partially sulfidic surface system had lower sperm
counts, and males from completely sulfidic systems, surface as well as subterranean, had even fewer available sperm. We conclude
that the extreme environmental conditions in sulfidic habitats appear to constrain male sperm production, since hydrogen sulfide
as a naturally occurring toxin requires energy-demanding adaptations. Furthermore, we examined sperm counts of lab-reared
cave and surface mollies in response to energy limitation. Males from stock populations were placed under high and low food
treatments for a 2-week period and then stripped of sperm. Sperm counts of surface mollies tended to be reduced by low food
availability, whereas sperm counts of cave mollies did not significantly vary between food treatments, which likely points
towards a higher starvation resistance in cave mollies. 相似文献
27.
Michael CW Chan Renee WY Chan Wendy CL Yu Carol CC Ho WH Chui CK Lo Kit M Yuen Yi Guan John M Nicholls JS Malik Peiris 《Respiratory research》2009,10(1):102
Background
Highly pathogenic avian influenza (HPAI) H5N1 virus is entrenched in poultry in Asia and Africa and continues to infect humans zoonotically causing acute respiratory disease syndrome and death. There is evidence that the virus may sometimes spread beyond respiratory tract to cause disseminated infection. The primary target cell for HPAI H5N1 virus in human lung is the alveolar epithelial cell. Alveolar epithelium and its adjacent lung microvascular endothelium form host barriers to the initiation of infection and dissemination of influenza H5N1 infection in humans. These are polarized cells and the polarity of influenza virus entry and egress as well as the secretion of cytokines and chemokines from the virus infected cells are likely to be central to the pathogenesis of human H5N1 disease.Aim
To study influenza A (H5N1) virus replication and host innate immune responses in polarized primary human alveolar epithelial cells and lung microvascular endothelial cells and its relevance to the pathogenesis of human H5N1 disease.Methods
We use an in vitro model of polarized primary human alveolar epithelial cells and lung microvascular endothelial cells grown in transwell culture inserts to compare infection with influenza A subtype H1N1 and H5N1 viruses via the apical or basolateral surfaces.Results
We demonstrate that both influenza H1N1 and H5N1 viruses efficiently infect alveolar epithelial cells from both apical and basolateral surface of the epithelium but release of newly formed virus is mainly from the apical side of the epithelium. In contrast, influenza H5N1 virus, but not H1N1 virus, efficiently infected polarized microvascular endothelial cells from both apical and basolateral aspects. This provides a mechanistic explanation for how H5N1 virus may infect the lung from systemic circulation. Epidemiological evidence has implicated ingestion of virus-contaminated foods as the source of infection in some instances and our data suggests that viremia, secondary to, for example, gastro-intestinal infection, can potentially lead to infection of the lung. HPAI H5N1 virus was a more potent inducer of cytokines (e.g. IP-10, RANTES, IL-6) in comparison to H1N1 virus in alveolar epithelial cells, and these virus-induced chemokines were secreted onto both the apical and basolateral aspects of the polarized alveolar epithelium.Conclusion
The predilection of viruses for different routes of entry and egress from the infected cell is important in understanding the pathogenesis of influenza H5N1 infection and may help unravel the pathogenesis of human H5N1 disease. 相似文献28.
29.
Poornima Gopal Niki L Reynaert Jean L J M Scheijen Casper G Schalkwijk Frits M E Franssen Emiel F M Wouters Erica P A Rutten 《Respiratory research》2014,15(1):24
Rationale
Plasma soluble Receptor for Advanced Glycation End Product (sRAGE) is considered as a biomarker in COPD. The contribution of endogenous sRAGE (esRAGE) to the pool of plasma sRAGE and the implication of both markers in COPD pathogenesis is however not clear yet. The aim of the current study was therefore to measure plasma levels of esRAGE comparative to total sRAGE in patients with COPD and a control group. Further, we established the relations of esRAGE and total sRAGE with disease specific characteristics such as lung function and DLCO, and with different circulating AGEs.Methods
Plasma levels of esRAGE and sRAGE were measured in an 88 patients with COPD and in 55 healthy controls. FEV1 (%predicted) and FEV1/VC (%) were measured in both groups; DLCO (%predicted) was measured in patients only. In this study population we previously reported that the AGE Nϵ-(carboxymethyl) lysine (CML) was decreased, Nϵ-(carboxyethyl) lysine (CEL) increased and pentosidine was not different in plasma of COPD patients compared to controls.Results
Plasma esRAGE (COPD: 533.9 ± 412.4, Controls: 848.7 ± 690.3 pg/ml; p = 0.000) was decreased in COPD compared to controls. No significant correlations were observed between plasma esRAGE levels and lung function parameters or plasma AGEs. A positive correlation was present between esRAGE and total sRAGE levels in the circulation. Confirming previous findings, total sRAGE (COPD: 512.6 ± 403.8, Controls: 1834 ± 804.2 pg/ml; p < 0.001) was lower in patients compared to controls and was positively correlated FEV1 (r = 0.235, p = 0.032), FEV1/VC (r = 0.218, p = 0.047), and DLCO (r = 0.308, p = 0.006). sRAGE furthermore did show a significant positive association with CML (r = 0.321, p = 0.003).Conclusion
Although plasma esRAGE is decreased in COPD patients compared to controls, only total sRAGE showed a significant and independent association with FEV1, FEV1/VC and DLCO, indicating that total sRAGE but not esRAGE may serve as marker of COPD disease state and severity. 相似文献30.
In their natural habitat, the peripheral nerve, Schwann cells (SCs) form nicely aligned pathways (also known as the bands of Büngner) that guide regenerating axons to their targets. Schwann cells that are implanted in the lesioned spinal cord fail to align in pathways that could support axon growth but form cellular clusters that exhibit only limited intermingling with the astrocytes and meningeal cells (MCs) that are present in the neural scar. The formation of cell clusters can be studied in co-cultures of SCs and MCs. In these co-cultures SCs form cluster-like non-overlapping cell aggregates with well-defined boundaries. There are several indications that neuropilins (NRPs) play an important role in MC-induced SC aggregation. Both SCs and MCs express NRP1 and NRP2 and SCs express the NRP ligands Sema3B, C and E while MCs express Sema3A, C, E and F. We now demonstrate that in SC-MC co-cultures, siRNA mediated knockdown of NRP2 in SCs decreased the formation of SC clusters while these SCs maintained their capacity to align in bands of Büngner-like columnar arrays. Unexpectedly, knockdown of NRP1 expression resulted in a significant increase in SC aggregation. These results suggest that a reduction in NRP2 expression may enhance the capacity of implanted SCs to interact with MCs that invade a neural scar formed after a lesion of the spinal cord. 相似文献