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971.
Weighardt H Kaiser-Moore S Schlautkötter S Rossmann-Bloeck T Schleicher U Bogdan C Holzmann B 《Journal of immunology (Baltimore, Md. : 1950)》2006,177(8):5623-5630
TLRs are considered important for the control of immune responses during endotoxic shock or polymicrobial sepsis. Signaling by TLRs may proceed through the adapter proteins MyD88 or TIR domain-containing adaptor inducinng IFN-beta. Both pathways can lead to the production of type I IFNs (IFN-alphabeta). In the present study, the role of the type I IFN pathway for host defense and immune pathology in sepsis was investigated using a model of mixed bacterial peritonitis. Systemic levels of IFN-alphabeta protein were markedly elevated during septic peritonitis. More detailed analyses revealed production of IFN-beta, but not IFN-alpha subtypes, and identified CD11b+ CD11c- macrophage-like cells as major producers of IFN-beta. The results further demonstrate that in IFN-alphabeta receptor I chain (IFNARI)-deficient mice, the early recruitment of neutrophils to the infected peritoneal cavity was augmented, most likely due to an increased local production of MCP-1 and leukotriene B4. In the absence of IFNARI, peritoneal neutrophils also exhibited enhanced production of reactive oxygen intermediates and elevated expression of Mac-1. Conversely, administration of recombinant IFN-beta resulted in reduced leukotriene B4 levels and decreased peritoneal neutrophil recruitment and activation. Analysis of the cytokine response to septic peritonitis revealed that IFNARI deficiency strongly attenuated late, but not early, hyperinflammation. In accordance with these findings, bacterial clearance and overall survival of IFNARI(-/-) mice were improved. Therefore, the present study reveals critical functions of the type I IFN pathway during severe mixed bacterial infections leading to sepsis. The results suggest that type I IFN exerts predominantly adverse effects under these conditions. 相似文献
972.
973.
Smirlis D Bisti SN Xingi E Konidou G Thiakaki M Soteriadou KP 《Molecular microbiology》2006,60(6):1457-1473
Episomal expression of Leishmania histone H1 sense mRNAs in Leishmania major promastigotes was found previously to result in overexpression of this molecule and to reduce parasite infectivity in vitro. Herein, we evaluated the in vivo infectivity of these transfectants, in BALB/c mice, and showed that it is dramatically reduced. No lesions were observed in this group of mice and this was associated with an extremely low number of parasites both in the footpad and in the draining lymph nodes. Interestingly, the transfectants-reduced infectivity was associated with a delay in their cell-cycle progression and differentiation to axenic amastigotes, assessed in vitro. Therefore, the dramatic reduction in their infectivity may be attributed to the above-mentioned phenotypic modifications. As the metazoan linker histone H1(0) homologue is known to delay cell-cycle progression in mammalian cells we investigated whether its Leishmania counterpart, which possesses homology to its C-terminal region, when expressed in mammalian cells may also affect their cell-cycle progression. It was thus shown that Leishmania histone H1 expressed in COS7 and NIH 3T3 cells, delays cell-cycle progression in these cells too. The latter strengthens the phenotype observed in Leishmania and provides evidence that critical functions of histone H1 molecules are conserved throughout evolution. 相似文献
974.
Abdallah AM Verboom T Hannes F Safi M Strong M Eisenberg D Musters RJ Vandenbroucke-Grauls CM Appelmelk BJ Luirink J Bitter W 《Molecular microbiology》2006,62(3):667-679
Mycobacterial genomes contain two unique gene families, the so-called PE and PPE gene families, which are highly expanded in the pathogenic members of this genus. Here we report that one of the PPE proteins, i.e. PPE41, is secreted by pathogenic mycobacteria, both in culture and in infected macrophages. As PPE41 lacks a signal sequence a dedicated secretion system must be involved. A single gene was identified in Mycobacterium marinum that showed strongly reduced PPE41 secretion. This gene was located in a gene cluster whose predicted proteins encode components of an ESAT-6-like secretion system. This cluster, designated ESX-5, is conserved in various pathogenic mycobacteria, but not in the saprophytic species Mycobacterium smegmatis. Therefore, different regions of this cluster were introduced in M. smegmatis. Only introduction of the complete ESX-5 locus resulted in efficient secretion of heterologously expressed PPE41. This PPE secretion system is also involved in the virulence of pathogenic mycobacteria, as the ESX-5 mutant of M. marinum was affected in spreading to uninfected macrophages. 相似文献
975.
976.
Kogut MH Swaggerty C He H Pevzner I Kaiser P 《Microbes and infection / Institut Pasteur》2006,8(7):1866-1874
977.
Shimane W. Makhabu Christina Skarpe Håkan Hytteborn Zenzele D. Mpofu 《Plant Ecology》2006,184(1):163-172
The way herbivores select what to eat is of considerable practical and theoretical interest, and has given rise to different theories and hypotheses. The plant vigour hypothesis predicts that herbivores feed preferentially on vigorous, i.e., large and/or fast-growing plants or plant parts. These predictions have previously primarily been tested on variation within plant species. Here we test whether differences in vigour among plant species in the same environment can explain differences in herbivore attack. We studied variation in browsing pressure by a guild of large herbivores on different woody species in an African savanna ecosystem. Shoot growth rate, annual shoot length, basal shoot diameter and annual shoot volume of 14 woody plant species were measured in the field. Plant species’ shoot vigour represented by the first PCA axis scores generated from the four shoot variables were then related to browsing pressure (% utilisation) on each of the species by native ungulates and elephant. Nutrient and fibre concentrations and tannin activity were also determined for the 14 woody plant species. We found ungulate browsing pressure to show a unimodal relationship with plant species’ shoot vigour. The heaviest browsing pressure was on plant species with shoots of intermediate vigour. We suggest that species with less vigorous shoots had low nutrient and high fibre concentrations and offered small bite sizes, whereas species with vigorous shoots had high nutrient concentrations but larger shoot diameters than the bite diameters of browsing ungulates. Elephant browsing pressure was not related to plant species’ shoot vigour. 相似文献
978.
Sylvia Toet Johannes H. C. Cornelissen Rien Aerts Richard S. P. van Logtestijn Miranda de Beus Rob Stoevelaar 《Plant Ecology》2006,182(1-2):27-40
We studied the effects of elevated CO2 (180–200 ppmv above ambient) on growth and chemistry of three moss species (Sphagnum palustre, S. recurvum and Polytrichum commune) in a lowland peatland in the Netherlands. Thereto, we conducted both a greenhouse experiment with both Sphagnum species and a field experiment with all three species using MiniFACE (Free Air CO2 Enrichment) technology during 3 years. The greenhouse experiment showed that Sphagnum growth was stimulated by elevated CO2 in the short term, but that in the longer term (≥1 year) growth was probably inhibited by low water tables and/or down-regulation
of photosynthesis. In the field experiment, we did not find significant changes in moss abundance in response to elevated
CO2, although CO2 enrichment appeared to reduce S. recurvum abundance. Both Sphagnum species showed stronger responses to spatial variation in hydrology than to increased atmospheric CO2 concentrations. Polytrichum was insensitive to changes in hydrology. Apart from the confounding effects of hydrology, the relative lack of growth response
of the moss species may also have been due to the relatively small increase in assimilated CO2 as achieved by the experimentally added CO2. We calculated that the added CO2 contributed at most 32% to the carbon assimilation of the mosses, while our estimates based on stable C isotope data even
suggest lower contributions for Sphagnum (24–27%). Chemical analyses of the mosses showed only small elevated CO2 effects on living tissue N concentration and C/N ratio of the mosses, but the C/N ratio of Polytrichum was substantially lower than those of the Sphagnum species. Continuing expansion of Polytrichum at the expense of Sphagnum could reduce the C sink function of this lowland Sphagnum peatland, and similar ones elsewhere, as litter decomposition rates would probably be enhanced. Such a reduction in sink
function would be driven mostly by increased atmospheric N deposition, water table regulation for agricultural purposes and
land management to preserve the early successional stage (mowing, tree and shrub removal), since these anthropogenic factors
will probably exert a greater control on competition between Polytrichum and Sphagnum than increased atmospheric CO2 concentrations. 相似文献
979.
Bacillus anthracis, a spore forming Gram-positive microbe, is the causative agent of anthrax. Although plasmid encoded factors such as lethal toxin (LeTx), edema toxin (EdTx), and gamma-poly-d-glutamic acid (PGA) capsule are known to be required for disease pathogenesis, B. anthracis genes that enable spore invasion, phagosomal escape and macrophage replication are still unknown. To establish transposon mutagenesis as a tool for the characterization of anthrax genes, we employed the mariner-based mini-transposon Bursa aurealis in B. anthracis strain Sterne 7702. B. aurealis carrying an erythromycin resistance cassette and its cognate transposase were delivered by transformation of two plasmids. B. aurealis transposition can be selected for by temperature shift to prevent plasmid replication and by screening colonies for erythromycin resistance. Using inverse polymerase chain reaction, DNA fragments of 129 random erythromycin-resistant transposon mutants were amplified and submitted to DNA sequence analysis. These studies demonstrate that B. aurealis inserts randomly into the genome of B. anthracis and can therefore be employed for finding genes involved in virulence. 相似文献
980.
A ribosomal RNA gene intergenic spacer based PCR and DGGE fingerprinting method for the analysis of specific rhizobial communities in soil 总被引:5,自引:0,他引:5
de Oliveira VM Manfio GP da Costa Coutinho HL Keijzer-Wolters AC van Elsas JD 《Journal of microbiological methods》2006,64(3):366-379
A direct molecular method for assessing the diversity of specific populations of rhizobia in soil, based on nested PCR amplification of 16S-23S ribosomal RNA gene (rDNA) intergenic spacer (IGS) sequences, was developed. Initial generic amplification of bacterial rDNA IGS sequences from soil DNA was followed by specific amplification of (1) sequences affiliated with Rhizobium leguminosarum "sensu lato" and (2) R. tropici. Using analysis of the amplified sequences in clone libraries obtained on the basis of soil DNA, this two-sided method was shown to be very specific for rhizobial subpopulations in soil. It was then further validated as a direct fingerprinting tool of the target rhizobia based on denaturing gradient gel electrophoresis (DGGE). The PCR-DGGE approach was applied to soils from fields in Brazil cultivated with common bean (Phaseolus vulgaris) under conventional or no-tillage practices. The community fingerprints obtained allowed the direct analysis of the respective rhizobial community structures in soil samples from the two contrasting agricultural practices. Data obtained with both primer sets revealed clustering of the community structures of the target rhizobial types along treatment. Moreover, the DGGE profiles obtained with the R. tropici primer set indicated that the abundance and diversity of these organisms were favoured under NT practices. These results suggest that the R. leguminosarum-as well as R. tropici-targeted IGS-based nested PCR and DGGE are useful tools for monitoring the effect of agricultural practices on these and related rhizobial subpopulations in soils. 相似文献