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911.
912.
In the pathogenic bacterium Bacillus anthracis, virulence requires induced expression of the anthrax toxin and capsule genes. Elevated CO2/bicarbonate levels, an indicator of the host environment, provide a signal ex vivo to increase expression of virulence factors, but the mechanism underlying induction and its relevance in vivo are unknown. We identified a previously uncharacterized ABC transporter (BAS2714-12) similar to bicarbonate transporters in photosynthetic cyanobacteria, which is essential to the bicarbonate induction of virulence gene expression. Deletion of the genes for the transporter abolished induction of toxin gene expression and strongly decreased the rate of bicarbonate uptake ex vivo, demonstrating that the BAS2714-12 locus encodes a bicarbonate ABC transporter. The bicarbonate transporter deletion strain was avirulent in the A/J mouse model of infection. Carbonic anhydrase inhibitors, which prevent the interconversion of CO2 and bicarbonate, significantly affected toxin expression only in the absence of bicarbonate or the bicarbonate transporter, suggesting that carbonic anhydrase activity is not essential to virulence factor induction and that bicarbonate, and not CO2, is the signal essential for virulence induction. The identification of this novel bicarbonate transporter essential to virulence of B. anthracis may be of relevance to other pathogens, such as Streptococcus pyogenes, Escherichia coli, Borrelia burgdorferi, and Vibrio cholera that regulate virulence factor expression in response to CO2/bicarbonate, and suggests it may be a target for antibacterial intervention. 相似文献
913.
Filip Morin Marina Antonina Zoe Panova Magali Schweizer Marlene Wiechmann Nicole Eliassen Per Sundberg Lili Cluzel-Burgalat Irina Polovodova Asteman 《Environmental microbiology》2023,25(11):2321-2337
The problem of invasive species is a well-studied one, but knowledge of free-living unicellular eukaryotic invasive species is lacking. A potentially invasive foraminifer (Rhizaria), Nonionella sp. T1, was recently discovered in the Skagerrak and its fjords. Digital polymerase chain reaction (dPCR) was applied to track the spread of this non-indigenous species using a new dPCR assay (T1-1). The use of dPCR appears highly complementary to traditional hand picking of foraminiferal shells from the sediment, and is far less time-consuming. This study indicates that Nonionella sp. T1 has bypassed the outer Skagerrak strait, instead becoming established in Swedish west coast fjords, constituting up to half of the living foraminiferal community in fjord mouth areas. The ecology of Nonionella sp. T1 and its potential invasive impacts are still largely unknown, but it appears to be an opportunist using several energy sources such as nitrate respiration and kleptoplasty along with a possibly more efficient reproductive strategy to gain an advantage over the native foraminiferal species. Future ecological studies of Nonionella sp. T1 could be aided by dPCR and the novel Nonionella sp. T1-specific T1-1 assay. 相似文献
914.
915.
Christophe Thomazo Daniele L. Pinti Vincent Busigny Magali Ader Ko Hashizume Pascal Philippot 《Comptes Rendus Palevol》2009,8(7):665-678
The search for early Earth biological activity is hindered by the scarcity of the rock record. The very few exposed sedimentary rocks have all been affected by secondary processes such as metamorphism and weathering, which might have distorted morphological microfossils and biogenic minerals beyond recognition and have altered organic matter to kerogen. The search for biological activity in such rocks therefore relies entirely on chemical, molecular or isotopic indicators. A powerful tool used for this purpose is the stable isotope signature of elements related to life (C, N, S, Fe). It provides key informations not only on the metabolic pathways operating at the time of the sediment deposition, but more globally on the biogeochemical cycling of these elements and thus on the Earth's surface evolution. Here, we review the basis of stable isotope biogeochemistry for these isotopic systems. Rather than an exhaustive approach, we address some examples to illustrate how they can be used as biosignatures of early life and as proxies for its environment, while keeping in mind what their limitations are. We then focus on the covariations among these isotopic systems during the Archean time period to show that they convey important information both on the evolution of the redox state of the terrestrial surface reservoirs and on co-occurring ecosystems in the Archean. 相似文献
916.
Francisco Azuaje Frédérique Léonard Magali Rolland-Turner Yvan Devaux Daniel R Wagner 《Theoretical biology & medical modelling》2011,8(1):7
Background
We investigated an algorithmic approach to modelling angiogenesis controlled by vascular endothelial growth factor (VEGF), the anti-angiogenic soluble VEGF receptor 1 (sVEGFR-1) and adenosine (Ado). We explored its feasibility to test angiogenesis-relevant hypotheses. We illustrated its potential to investigate the role of Ado as an angiogenesis modulator by enhancing VEGF activity and antagonizing sVEGFR-1. 相似文献917.
918.
919.
Molecular phylogenetics gives new insights into the taxonomy of foraminifera, independent of their morphology. After a survey of the present knowledge on how molecular phylogeny can contribute to foraminiferal taxonomy, we present an applied example. The comparison of ribosomal DNA (rDNA) sequences belonging to the SSU (Small Subunit) and LSU (Large Subunit) genes of Pseudoeponides falsobeccarii with other similar sequences of rotaliids available in GenBank shows that this species actually belongs to the genus Ammonia, because it groups inside the other Ammonia sequences instead of forming a distinct clade. Moreover, Ammonia falsobeccarii forms a clade well separated from other Ammonia phylotypes, meaning that it can be considered as a distinct species, and not as an ecophenotype of one of the other Ammonia species. 相似文献
920.
Osteoarthritis (OA), a paramount cause of physical disability for which there is no definitive cure, is mainly characterized by the gradual loss of the articular cartilage. Current nonsurgical and reconstructive surgical therapies have not met success in reversing the OA phenotype so far. Gene transfer approaches allow for a long‐term and site‐specific presence of a therapeutic agent to re‐equilibrate the metabolic balance in OA cartilage and may consequently be suited to treat this slow and irreversible disorder. The distinct stages of OA need to be respected in individual gene therapy strategies. In this context, molecular therapy appears to be most effective for early OA. A critical step forward has been made by directly transferring candidate sequences into human articular chondrocytes embedded within their native extracellular matrix via recombinant adeno‐associated viral vectors. Although extensive studies in vitro attest to a growing interest in this approach, data from animal models of OA are sparse. A phase I dose‐escalating trial was recently performed in patients with advanced knee OA to examine the safety and activity of chondrocytes modified to produce the transforming growth factor β1 via intra‐articular injection, showing a dose‐dependent trend toward efficacy. Proof‐of‐concept studies in patients prior to undergoing total knee replacement may be privileged in the future to identify the best mode of translating this approach to clinical application, followed by randomized controlled trials. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献