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51.
52.
Mol O Oudhuis WC Oud RP Sijbrandi R Luirink J Harms N Oudega B 《Journal of molecular microbiology and biotechnology》2001,3(1):135-142
K88 fimbriae are ordered polymeric protein structures at the surface of enterotoxigenic Escherichia coli cells. Their production and assembly requires a molecular chaperone located in the periplasm (FaeE) and a molecular usher located in the outer membrane (FaeD). FaeC is the tip component of the K88 fimbriae. We studied the expression of the subcloned faeC gene, the subcellular localization of FaeC and its interaction with the chaperone and the outer membrane usher. In the absence of the chaperone or the usher, FaeC could not be detected in E. coli cells harbouring the faeC gene and its ribosome binding site under contol of the IPTG inducible lpp/lac promoter/operator. The expression of FaeC was detectable in the presence of chaperone FaeE, but a direct interaction between the chaperone and FaeC was not found. The expression of FaeC was also detectable in cells co-expressing the outer membrane usher FaeD. Overexpression of FaeC after changing the faeC ribosome binding site appeared to induce lethality. Expression of subcloned FaeC in the absence of FaeE or FaeD could be detected when faeC was cloned under the tight control of the ara promoter/operator and when lethality induction was avoided. The direct interaction of FaeC with outer membranes containing the usher FaeD was studied by cell fractionation, isopycnic sucrose density gradient centrifugation, SDS-PAGE and immunoblotting. FaeC was found to bind to outer membranes containing FaeD or a FaeD-PhoA hybrid construct containing 215 amino-terminal residues of FaeD. This binding was not observed when control outer membranes without FaeD were used. No other K88 specific proteins were required for this interaction. The direct interaction between FaeC and FaeD in the outer membranes was shown by affinity blotting experiments. FaeE was not required for this interaction. Together these data indicate that the minor fimbrial subunit FaeC, unlike FaeG, H and F, does not have a strong interaction with the chaperone FaeE in the E. coli periplasm, but directly binds to the outer membrane molecular usher FaeD. 相似文献
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An improved technique, viz., maceration with cellulase and pectinase, was applied in order to obtain chromosome preparations of botanical material suitable for fluorescence microscopy. The application of this method to Petunia hybrida allows the individual distinction of all chromosomes in mitosis. The following three criteria are required for this distinetion: the centromere index, the relative length, and the fluorescence intensity pattern after staining with Quinacrine. A standard karyogram is drawn up to render possible a comparison with other Petunia material. 相似文献
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Alena S Gsell Lisette N de Senerpont Domis Koen JF Verhoeven Ellen van Donk Bastiaan W Ibelings 《The ISME journal》2013,7(10):2057-2059
Contrary to expectation, populations of clonal organisms are often genetically highly diverse. In phytoplankton, this diversity is maintained throughout periods of high population growth (that is, blooms), even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes. Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms. Here, we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure. The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure, whereas the within group dispersion did not change under low parasite pressure. Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts. 相似文献
57.
Bastiaan J. van Nierop Hans C. van Assen Elza D. van Deel Leonie B. P. Niesen Dirk J. Duncker Gustav J. Strijkers Klaas Nicolay 《PloS one》2013,8(2)
Background
Left ventricular (LV) and right ventricular (RV) function have an important impact on symptom occurrence, disease progression and exercise tolerance in pressure overload-induced heart failure, but particularly RV functional changes are not well described in the relevant aortic banding mouse model. Therefore, we quantified time-dependent alterations in the ventricular morphology and function in two models of hypertrophy and heart failure and we studied the relationship between RV and LV function during the transition from hypertrophy to heart failure.Methods
MRI was used to quantify RV and LV function and morphology in healthy (n = 4) and sham operated (n = 3) C57BL/6 mice, and animals with a mild (n = 5) and a severe aortic constriction (n = 10).Results
Mice subjected to a mild constriction showed increased LV mass (P<0.01) and depressed LV ejection fraction (EF) (P<0.05) as compared to controls, but had similar RVEF (P>0.05). Animals with a severe constriction progressively developed LV hypertrophy (P<0.001), depressed LVEF (P<0.001), followed by a declining RVEF (P<0.001) and the development of pulmonary remodeling, as compared to controls during a 10-week follow-up. Myocardial strain, as a measure for local cardiac function, decreased in mice with a severe constriction compared to controls (P<0.05).Conclusions
Relevant changes in mouse RV and LV function following an aortic constriction could be quantified using MRI. The well-controlled models described here open opportunities to assess the added value of new MRI techniques for the diagnosis of heart failure and to study the impact of new therapeutic strategies on disease progression and symptom occurrence. 相似文献58.
Philipp Mahlknecht Stefan Kiechl Bastiaan R. Bloem Johann Willeit Christoph Scherfler Arno Gasperi Gregorio Rungger Werner Poewe Klaus Seppi 《PloS one》2013,8(7)
Background
Although gait disorders are common in the elderly, the prevalence and overall burden of these disorders in the general community is not well defined.Methods
In a cross-sectional investigation of the population-based Bruneck Study cohort, 488 community-residing elderly aged 60–97 years underwent a thorough neurological assessment including a standardized gait evaluation. Gait disorders were classified according to an accepted scheme and their associations to falls, neuropsychological measures, and quality of life were explored.Results
Overall, 32.2% (95% confidence interval [CI] 28.2%–36.4%) of participants presented with impaired gait. Prevalence increased with age (p<0.001), but 38.3% (95%CI 30.1%–47.3%) of the subjects aged 80 years or older still had a normally preserved gait. A total of 24.0% (95%CI 20.4%–28.0%) manifested neurological gait disorders, 17.4% (14.3%–21.0%) non-neurological gait problems, and 9.2% (6.9%–12.1%) a combination of both. While there was no association of neurological gait disorders with gender, non-neurological gait disorders were more frequent in women (p = 0.012). Within the group of neurological gait disorders 69.2% (95%CI 60.3%–76.9%) had a single distinct entity and 30.8% (23.1%–39.7%) had multiple neurological causes for gait impairment. Gait disorders had a significant negative impact on quantitative gait measures, but only neurological gait disorders were associated with recurrent falls (odds ratio 3.3; 95%CI 1.4–7.5; p = 0.005 for single and 7.1; 2.7–18.7; p<0.001 for multiple neurological gait disorders). Finally, we detected a significant association of gait disorders, in particular neurological gait disorders, with depressed mood, cognitive dysfunction, and compromised quality of life.Conclusions
Gait disorders are common in the general elderly population and are associated with reduced mobility. Neurological gait disorders in particular are associated with recurrent falls, lower cognitive function, depressed mood, and diminished quality of life. 相似文献59.
Evolution of fitnesses and allele frequencies in a population with spatially heterogeneous selection pressures 总被引:2,自引:0,他引:2
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The level of gene flow considerably influences the outcome of evolutionary processes in structured populations with spatial heterogeneity in selection pressures; low levels of gene flow may allow local adaptation whereas high levels of gene flow may oppose this process thus preventing the stable maintenance of polymorphism. Indeed, proportions of fitness space that successfully maintain polymorphism are substantially larger in spatially heterogenous populations with lower to moderate levels of gene flow when compared to single-deme models. Nevertheless, the effect of spatial heterogeneity on the evolutionary construction of polymorphism is less clear. We have investigated the levels of polymorphism resulting from a simple two-deme construction model, which incorporates recurrent mutation as well as selection. We further compared fitness properties, stability of equilibria, and frequency distribution patterns emerging from the construction approach and compared these to the static fitness-space approach. The construction model either promotes or constrains the level of polymorphisms, depending on the levels of gene flow. Comparison of the fitness properties resulting from both approaches shows that they maintain variation in different parts of fitness space. The part of fitness space resulting from construction is more stable than that implied by the ahistoric fitness-space approach. Finally, the equilibrium allele-frequency distribution patterns vary substantially with different levels of gene flow, underlining the importance of correctly sampling spatial structure if these patterns are to be used to estimate population-genetic processes. 相似文献
60.
Bruce Schoelitsz Bastiaan G. Meerburg Willem Takken 《Entomologia Experimentalis et Applicata》2019,167(1):14-26
Households are mini‐ecosystems that provide a variety of conditions in which a variety of insect species can develop. Whether these insects are considered pests, largely depends on the perception, attitudes, and knowledge of the human inhabitants of the house. If considered unacceptable, residents can attempt to manage the insects themselves, or hire a professional. A pest management professional can provide a quick‐fix solution, often relying on the sole use of insecticides, or a sustainable solution through integrated pest management (IPM). In this review, it is discussed how the public's perception, attitudes, and knowledge affect the implementation of IPM in the household through the following steps: inspection, identification, establishment of a threshold level, pest control, and evaluation of effectiveness. Furthermore, recent and novel developments within the fields of inspection, identification, and pest control that allow to address pest infestations more effectively are described and their implementation in the household environment is discussed. In general, pest management in the household environment is reactive instead of pro‐active. The general public lacks the knowledge of the pest insects’ biology to identify the species, perform a proper inspection and identify causes of pest presence, as well as the knowledge of the available tools for monitoring and pest control. The percentage of individuals that seek professional aid in identification and pest control is relatively low. Moreover, the perception of and attitudes towards household insects generally result in low threshold levels. Current developments of methods for monitoring, identification, and control of insect pests in the household environment are promising, such as DNA barcoding, matrix‐assisted laser desorption/ionization time‐of‐flight and RNA interference. Efforts should be strengthened to alter the perception and attitude, and increase the knowledge of the non‐professional stakeholders, so that correct pest management decisions can be taken. 相似文献