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Responses of bacterial communities to disturbance and restoration processes were investigated on alpine grassland soil. Bulk soil, rhizosphere soil and two soil separates, i.e. sand-size (2000-200 microm) and silt-size (50-2 microm) were sampled from undisturbed grassland soil to soil under restoration for 1 month, 1 year, 4 years and 13 years after disturbance. Automated ribosomal intergenic spacer analysis (ARISA) and restriction fragment length polymorphism (RFLP) of nifH gene pools were used to assay genetic structure of the bacterial communities and N2-fixing guild. According to the distribution of ARISA band length in bacterial phyla, the dominance of ARISA bands below 400 bp showed that Gram-positive bacteria would be predominant in the studied grassland soil when not disturbed. Disturbance affected the genetic structure of bacterial community and of N2-fixing guild in relation to their location within the selected habitats. Shifts in IGS and nifH profiles of bulk soil metagenome were larger than those observed from sand-size- and silt-size-fractions, accounting for 40-50% of the variance in the profiles. Restoration of the genetic structure of telluric bacteria community and N2-fixing populations was found to be influenced by the spatial heterogeneity of the soil and niche diversification. Particular bacterial genetic structure within distinct habitats were evidenced and must be defined as subdivisions of the meta-community of bulk soil. Scale of soil microbial diversity/stability relationships is discussed with special attention to disconnected bacterial habitat compared with whole soil with multiple niches. 相似文献
94.
Modular serine proteases are central to the complement cascade of the mammalian humoral immune system. These proteases form protein complexes through multi-domain interactions to achieve their proteolytic activity. We review the structural insights into complement initiation by auto-activation of the hetero-tetrameric proteases of the large danger-recognition protein complexes, amplification and labelling of particles by the formation and activity of C3 convertases, and regulation by convertase dissociation and degradation to prevent 'bystander' damage to healthy host cells and tissues. The data reveal that complex formation and large domain-domain rearrangements underlie the proteolytic reactions of the complement cascade, which enables the host to recognize and clear invading microbes and host debris from its blood and fluids surrounding tissues. 相似文献
95.
Stephanie J. Gros Nina Kurschat Astrid Drenckhan Thorsten Dohrmann Evelyn Forberich Katharina Effenberger Uta Reichelt Robert M. Hoffman Klaus Pantel Jussuf T. Kaifi Jakob R. Izbicki 《PloS one》2012,7(10)
A functional linkage of the structurally unrelated receptors HER2 and CXCR4 has been suggested for breast cancer but has not been evaluated for esophageal carcinoma. The inhibition of HER2 leads to a reduction of primary tumor growth and metastases in an orthotopic model of esophageal carcinoma. The chemokine receptor CXCR4 has been implicated in metastatic dissemination of various tumors and correlates with poor survival in esophageal carcinoma. The aim of this study was to investigate a correlation between the expression levels of HER2 and CXCR4 and to evaluate the involvemnent of CXCR4-expression in HER2-positive esophageal carcinoma. The effects of HER2-inhibition with trastuzumab and of CXCR4-inhibition with AMD3100 on primary tumor growth, metastatic homing, and receptor expression were evaluated in vitro and in an orthotopic model of metastatic esophageal carcinoma using MRI for imaging. The clinical relevance of HER2- and CXCR4-expression was examined in esophageal carcinoma patients. A significant correlation of HER2- and CXCR4-expression in primary tumor and metastases exists in the orthotopic model. Trastuzumab and AMD3100 treatment led to a significant reduction of primary tumor growth, metastases and micrometastases. HER2-expression was significantly elevated under AMD3100 treatment in the primary tumor and particularly in the metastases. The positive correlation between HER2- and CXCR4-expression was validated in esophageal cancer patients. The correlation of CXCR4- and HER2-expression and the elevation of HER2-expression and reduction of metastases through CXCR4-inhibition suggest a possible functional linkage and a role in tumor dissemination in HER2-positive esophageal carcinoma. 相似文献
96.
Sulphur-oxidizing extracellular bacteria in the gills of Mytilidae associated with wood falls 总被引:1,自引:0,他引:1
Six morphotypes of small mussels (Bivalvia: Mytilidae) were found attached to naturally sunken wood collected in the Bohol Sea (Philippines). These specimens are related to the large Bathymodiolus mussels that are found worldwide at cold seeps and hydrothermal vents. In these habitats, the mytilids harbour sulphur- and methane-oxidizing endosymbionts in their gills and depend on the energy and carbon provided by the symbionts. In this study, bacteria associated with the gills of wood-associated mussels are characterized using molecular and microscopic techniques. The existence of bacteria in the lateral zone of gill filaments in all specimens is demonstrated. Comparative analyses of 16S rRNA gene and adenosine 5'-phosphosulphate (APS) reductase gene sequences indicate that the bacteria are closely related to sulphur-oxidizing endosymbionts of Bathymodiolus. FISHs using specific probes confirm that sulphur oxidizers are by far the most abundant, if not the only bacteria present. Electron micrographs displayed mostly extracellular bacteria located between microvilli at the apical surface of host gill epithelial cells all along the lateral zone of each gill filament. In some specimens, occasional occurrence of intracellular bacteria with similar morphology was noted. This study provides the first molecular evidence for the presence of possible thiotrophic symbiosis in sunken wood ecosystems. With their epibiotic bacteria, wood-associated mussels display a less integrated type of interaction than described in their seep, vent and whale fall relatives. 相似文献
97.
Orelle C Gubellini F Durand A Marco S Lévy D Gros P Di Pietro A Jault JM 《Biochemistry》2008,47(8):2404-2412
ATP-binding cassette (ABC) transporters are involved in the transport of a wide variety of substrates, and ATP-driven dimerization of their nucleotide binding domains (NBDs) has been suggested to be one of the most energetic steps of their catalytic cycle. Taking advantage of the propensity of BmrA, a bacterial multidrug resistance ABC transporter, to form stable, highly ordered ring-shaped structures [Chami et al. (2002) J. Mol. Biol. 315, 1075-1085], we show here that addition of ATP in the presence of Mg2+ prevented ring formation or destroyed the previously formed rings. To pinpoint the catalytic step responsible for such an effect, two classes of hydrolysis-deficient mutants were further studied. In contrast to hydrolytically inactive glutamate mutants that behaved essentially as the wild-type, lysine Walker A mutants formed ring-shaped structures even in the presence of ATP-Mg. Although the latter mutants still bound ATP-Mg, and even slowly hydrolyzed it for the K380R mutant, they were most likely unable to undergo a proper NBD dimerization upon ATP-Mg addition. The ATP-driven dimerization step, which was still permitted in glutamate mutants and led to a stable conformation suitable to monitor the growth of 2D crystals, appeared therefore responsible for destabilization of the BmrA ring structures. Our results provide direct visual evidence that the ATP-induced NBD dimerization triggers a conformational change large enough in BmrA to destabilize the rings, which is consistent with the assumption that this step might constitute the "power stroke" for ABC transporters. 相似文献
98.
Patricia Cuellar-Mata Nada Jabado Jun Liu Wendy Furuya B Brett Finlay Philippe Gros Sergio Grinstein 《The Journal of biological chemistry》2002,277(3):2258-2265
Salmonella survive and replicate within mammalian cells by becoming secluded within specialized membrane-bound vacuoles inaccessible to the host defense mechanisms. Delayed acidification of the vacuole and its incomplete fusion with lysosomes have been implicated in intracellular Salmonella survival. Nramp1 confers to macrophages resistance to a variety of intracellular pathogens, including Salmonella, but its precise mode of action is not understood. We investigated whether Nramp1 affects the maturation and acidification of Salmonella-containing vacuoles (SCV). A mouse-derived macrophage line (RAW/Nramp1(-)) devoid of Nramp1 and therefore susceptible to infection was compared with isogenic clones stably transfected with Nramp1 (RAW/Nramp1(+)). Intravacuolar pH, measured in situ, was similar in Nramp1-expressing and -deficient cells. SCV acquired LAMP1 and fused with preloaded fluid-phase markers in both cell types. In contrast, although few vacuoles in RAW/Nramp1(-) acquired mannose 6-phosphate receptor, many more contained M6PR in RAW/Nramp1(+) cells. Shortly after closure, SCV in RAW/Nramp1(-) became inaccessible to extracellular markers, suggesting inability to fuse with newly formed endosomes. Expression of Nramp1 markedly increased the access to extracellularly added markers. We propose that Nramp1 counteracts the ability of Salmonella to become secluded in a compartment that limits access of bactericidal agents, allowing the normal degradative pathway of the macrophage to proceed. 相似文献
99.
We report here 1) the synthesis and properties of a new macromolecular carbonic anhydrase inhibitor, Prontosil-dextran, 2) its application to determine the localization of a previously described extracellular carbonic anhydrase in skeletal muscle, and 3) the application of a recently published histochemical technique using dansylsulfonamide to the same problem. Stable macromolecular inhibitors of molecular weights of 5,000, 100,000 and 1,000,000 were produced by covalently coupling the sulfonamide Prontosil to dextrans. Their inhibition constants towards bovine carbonic anhydrase II are 1-2 X 10(-7) M. The Prontosil-dextrans, PD 5,000, PD 100,000, and PD 1,000,000, were used in studies of the washout of H14CO3-) from the perfused rabbit hindlimb. This washout is slow due to the presence of an extracellular carbonic anhydrase and can be markedly accelerated by PD 5,000 but not by PD 100,000 and PD 1,000,000. Since PD 5,000 is accessible to the entire extracellular space and PD 100,000 and PD 1,000,000 are confined to the intravascular space, we conclude that the extracellular carbonic anhydrase of skeletal muscle is located in the interstitium. The histochemical studies show a strong staining of the sarcolemma of the muscle fibers with high oxidative capacity. It appears likely, therefore, that the extracellular carbonic anhydrase of skeletal muscle is associated with muscle plasma membranes with its active site directed toward the interstitial space. 相似文献
100.