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建(构)筑物下盾构掘进施工隆沉控制  [PDF]
王辉
铁道工程学报 , 2011,
Abstract: ?研究目的:目前国家和地方还没有盾构穿越建(构)筑物的隆沉控制标准,以及在盾构推进施工过程中地表隆沉多少才不会影响建(构)筑物的正常使用。在软土层地质条件下根据盾构机设备和施工参数的技术要求,研究新型同步注浆浆液配合比、初凝时间、注入量以及二次双液浆注配合比注入量。分析研究推进过程中盾构机为中心的不同位置的隆沉。研究结论:在室内理论配合比的基础上,结合施工现场操作和使用,确定了满足施工技术要求的准厚浆配合比,根据现场地面监测数据每环注入3.75m3准厚浆和1.2m3双液浆,能控制地面沉降在10mm内。根据现场监测数据显示,管片刚拖出盾尾时地面变化值最大,同步注浆量要足,二次注浆能有效控制后期沉降。建(构)筑物隆沉在-16~+4mm范围基本没有影响。
《大禹治水图》玉山与扬州建隆寺  [PDF]
王明发
东南文化 , 2000,
Abstract: ????本文通过文献记载认为《大禹治水图》玉山是在扬州建隆寺琢制而成,而且建隆寺具有场所、交通、环境、情感等多种有利因素被选为两淮地区的大型琢玉场所。
青藏高原隆升的历史背景和机因  [PDF]
陈国达
大地构造与成矿学 , 1997,
Abstract: 青藏高原自中、上新世大幅度的隆升、形成,是亚洲大陆壳体演化-运动历史中,与地洼构造活动有直接关系的重大事件之一。对青藏高原形成的原因,运用历史一动力大地构造学的研究方法,从多方面的资料综合分析,可以得到较为合理的解释。根据上地壳结构、历史背景、占植物区、地热活动状态等资料,对隆升运动的物质基础、物理因素、内动力和外动力因素;及其对壳体演化一运动史的制约等的综合分析,表明青藏高原的隆升运动发生于亚洲大陆接纳印度外来壳体的过程完结之后,是在另一次和另一种地壳运动中出现的。从力学上说是在碰撞力及后继挤压力已衰退,又经青藏统一古地台形成、以垂向运动占主导的稳定区阶段的间断之后,再度转入活动区阶段,由于多方面的挤压力才开始发生的,是属于另一个壳体演化阶段和另一个应力场的产物。在造山带的性质上,隆升事件是在印度壳体与中亚壳体汇聚接合已经完成,印度大陆已成为亚洲大陆的一部分,并且碰撞造山力及其后继厂力都已为地台型地壳运动所代替之后,才由于大陆内部的地洼型造山作用所致的。
The luxS mutation causes loosely-bound biofilms in Shewanella oneidensis
Agnes M Bodor, Lothar J?nsch, Josef Wissing, Irene Wagner-D?bler
BMC Research Notes , 2011, DOI: 10.1186/1756-0500-4-180
Abstract: Here, we provide further evidence regarding the metabolic role of a luxS mutation in S. oneidensis. We constructed a luxS mutant and compared its phenotype to a wild type control with respect to its ability to remove AI-2 from the medium, expression of secreted proteins and biofilm formation. We show that S. oneidensis has a cell-dependent mechanism by which AI-2 is depleted from the medium by uptake or degradation at the end of the exponential growth phase. As AI-2 depletion is equally active in the luxS mutant and thus does not require AI-2 as an inducer, it appears to be an unspecific mechanism suggesting that AI-2 for S. oneidensis is a metabolite which is imported under nutrient limitation. Secreted proteins were studied by iTraq labelling and liquid chromatography mass spectrometry (LC-MS) detection. Differences between wild type and mutant were small. Proteins related to flagellar and twitching motility were slightly up-regulated in the luxS mutant, in accordance with its loose biofilm structure. An enzyme related to cysteine metabolism was also up-regulated, probably compensating for the lack of the LuxS enzyme. The luxS mutant developed an undifferentiated, loosely-connected biofilm which covered the glass surface more homogenously than the wild type control, which formed compact aggregates with large voids in between.The data confirm the role of the LuxS enzyme for biofilm growth in S. oneidensis and make it unlikely that AI-2 has a signalling role in this organism.Shewanella oneidensis is a Gram-negative Gammaproteobacterium isolated from the sediment of fresh water habitats [1], and occasionally from water columns and clinical specimens [2]. The most investigated characteristic of S. oneidensis is its ability to use a broad spectrum of electron acceptors [3]. In our previous study, Shewanella species were shown to produce autoinducer-2, proposed to be a universal signal molecule in bacteria [4], and to contain its synthesis gene, luxS [5]. As S. oneidens
Bifidobacteria Exhibit LuxS-Dependent Autoinducer 2 Activity and Biofilm Formation  [PDF]
Zhongke Sun, Xiang He, Vincenzo F. Brancaccio, Jing Yuan, Christian U. Riedel
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088260
Abstract: Autoinducer-2 (AI-2) molecules are one class of signalling molecules involved in gene regulation dependent on population density in a mechanism commonly referred to as quorum sensing (QS). AI-2 is produced by the methylthioadenosine/S-adenosyl-homocyste?inenucleosidase LuxS. In the present study, we characterise the function of bifidobacterial LuxS proteins to address the question whether these economically important bacteria are able to perform QS communication. All publically available genome sequences of bifidobacteria harbour putative luxS genes. The deduced amino acid sequences are well conserved in the genus and show good homology to the LuxS protein of the prototypical AI-2 producer Vibrio harveyi. The luxS genes of three bifidobacterial strains were successfully expressed in AI-2-negative Escherichia coli DH5α. Supernatants of these recombinant E. coli strains contained significant AI-2 activity. In initial experiments, we failed to detect AI-2 activity in supernatants of bifidobacteria grown in MRSc. High concentration of glucose as well as acidic pH had strong inhibitory effects on AI-2 activity. AI-2 activity could be detected when lower volumes of supernatants were used in the assay. Homologous overexpression of luxS in Bifidobacterium longum NCC2705 increased AI-2 levels in the supernatant. Furthermore, over-expression of luxS or supplementation with AI-2-containing supernatants enhanced biofilm formation of B. longum NCC2705. Collectively, these results suggest that bifidobacteria indeed harbour functional luxS genes that are involved in the production of AI-2-like molecules. To the best of our knowledge, this represents the first report on AI-2 activity produced by bifidobacteria. Self-produced AI-2 activity as well as AI-2-like molecules of other bacteria of the intestinal tract may have a regulatory function in biofilm formation and host colonization by bifidobacteria.
luxS Mutant Regulation: Quorum Sensing Impairment or Methylation Disorder?  [PDF]
Qian Wang,Zhiyan He,Yuejian Hu,Yuntao Jiang,Rui Ma,Zisheng Tang,Jingping Liang,Zheng Liu,Zhengwei Huang
Sensors , 2012, DOI: 10.3390/s120506176
Abstract: AI-2–mediated quorum sensing has been identified in various bacteria, including both Gram-negative and Gram-positive species, and numerous phenotypes have been reported to be regulated by this mechanism, using the luxS-mutant strain. But the AI-2 production process confused this regulatory function; some considered this regulation as the result of a metabolic change, which refers to an important metabolic cycle named activated methyl cycle (AMC), caused by luxS-mutant simultaneously with the defect of AI-2. Herein we hypothesized that the quorum sensing system—not the metabolic aspect—is responsible for such a regulatory function. In this study, we constructed plasmids infused with sahH and induced protein expression in the luxS-mutant strain to make the quorum-sensing system and metabolic system independent. The biofilm-related genes were investigated by real-time polymerase chain reaction (PCR), and the results demonstrated that the quorum-sensing completed strain restored the gene expression of the defective strain, but the metabolically completed one did not. This evidence supported our hypothesis that the autoinducer-2-mediated, quorum-sensing system, not the AMC, was responsible for luxS mutant regulation.
Functional correlation of bacterial LuxS with their quaternary associations: interface analysis of the structure networks
Moitrayee Bhattacharyya, Saraswathi Vishveshwara
BMC Structural Biology , 2009, DOI: 10.1186/1472-6807-9-8
Abstract: The protein structure networks (PSN) are constructed and graph theoretical analysis is performed on the structures obtained from X-ray crystallography and on the modelled ones. The interfaces, which are known to contain the active site, are characterized from the PSNs of these homodimeric proteins. The key features presented by the protein interfaces are investigated for the classification of the proteins in relation to their function. From our analysis, structural interface motifs are identified for each class in our dataset, which showed distinctly different pattern at the interface of LuxS for the probiotics and some extremophiles. Our analysis also reveals potential sites of mutation and geometric patterns at the interface that was not evident from conventional sequence alignment studies.The structure network approach employed in this study for the analysis of dimeric interfaces in LuxS has brought out certain structural details at the side-chain interaction level, which were elusive from the conventional structure comparison methods. The results from this study provide a better understanding of the relation between the luxS gene and its functional role in the prokaryotes. This study also makes it possible to explore the potential direction towards the design of inhibitors of LuxS and thus towards a wide range of antimicrobials.Quorum sensing is a widespread mechanism of intercellular communication among bacteria controlling its gene expression as a function of cell density. Two major quorum sensing pathways, with characteristic signalling molecules, AI-1 and AI-2, have been identified[1]. LuxS is one of the principal components in the biosynthetic pathway of AI-2, the universal signal for bacterial inter-species communication. In some organisms, quorum sensing by LuxS has been shown to have a profound effect on pathogenicity by affecting toxin production or flagellar morphogenesis and hence motility and colonization. However, in some other species it has no dir
Transcriptional and Post-Transcriptional Regulation of the Escherichia coli luxS mRNA; Involvement of the sRNA MicA  [PDF]
Klas I. Udekwu
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0013449
Abstract: The small RNA (sRNA) MicA has been shown to post-transcriptionally regulate translation of the outer membrane protein A (OmpA) in Escherichia coli. It uses an antisense mechanism to down-regulate OmpA protein synthesis and induce mRNA degradation. MicA is genomically localized between the coding regions of the gshA and luxS genes and is divergently transcribed from its neighbours. Transcription of the luxS gene which originates within or upstream of the MicA sequence would thus be complementary to the sRNA. LuxS regulation is as yet unclear.
2D proteome analysis initiates new Insights on the Salmonella Typhimurium LuxS protein
Gwendoline Kint, Kathleen AJ Sonck, Geert Schoofs, David De Coster, Jos Vanderleyden, Sigrid CJ De Keersmaecker
BMC Microbiology , 2009, DOI: 10.1186/1471-2180-9-198
Abstract: Differential proteome analysis of wildtype S. Typhimurium versus a luxS mutant revealed relatively few changes beyond the known effect on phase 2 flagellin. However, two highly differentially expressed protein spots with similar molecular weight but differing isoelectric point, were identified as LuxS whereas the S. Typhimurium genome contains only one luxS gene. This observation was further explored and we show that the S. Typhimurium LuxS protein can undergo posttranslational modification at a catalytic cysteine residue. Additionally, by constructing LuxS-βla and LuxS-PhoA fusion proteins, we demonstrate that S. Typhimurium LuxS can substitute the cognate signal peptide sequences of β-lactamase and alkaline phosphatase for translocation across the cytoplasmic membrane in S. Typhimurium. This was further confirmed by fractionation of S. Typhimurium protein extracts, followed by Western blot analysis.2D-DIGE analysis of a luxS mutant vs. wildtype Salmonella Typhimurium did not reveal new insights into the role of AI-2/LuxS in Salmonella as only a small amount of proteins were differentially expressed. However, subsequent in depth analysis of the LuxS protein itself revealed two interesting features: posttranslational modification and potential translocation across the cytoplasmic membrane. As the S. Typhimurium LuxS protein does not contain obvious signal motifs, it is speculated that LuxS is a new member of so called moonlighting proteins. These observations might have consequences in future studies on AI-2 quorum signaling in S. Typhimurium.Several bacteria utilize a cell-cell communication system called quorum sensing to coordinate diverse behaviors in response to population density [1]. This quorum sensing process is based on the generation of small signaling molecules by means of specific synthases. These signaling molecules accumulate into the extracellular environment and when a certain threshold concentration is reached, the bacteria detect and respond to th
Deep Sequencing of Porphyromonas gingivalis and Comparative Transcriptome Analysis of a LuxS Mutant  [PDF]
Takanori Hirano,David A. C. Beck,Murray Hackett,Richard J. Lamont
Frontiers in Cellular and Infection Microbiology , 2012, DOI: 10.3389/fcimb.2012.00079
Abstract: Porphyromonas gingivalis is a major etiological agent in chronic and aggressive forms of periodontal disease. The organism is an asaccharolytic anaerobe and is a constituent of mixed species biofilms in a variety of microenvironments in the oral cavity. P. gingivalis expresses a range of virulence factors over which it exerts tight control. High-throughput sequencing technologies provide the opportunity to relate functional genomics to basic biology. In this study we report qualitative and quantitative RNA-Seq analysis of the transcriptome of P. gingivalis. We have also applied RNA-Seq to the transcriptome of a ΔluxS mutant of P. gingivalis deficient in AI-2-mediated bacterial communication. The transcriptome analysis confirmed the expression of all predicted ORFs for strain ATCC 33277, including 854 hypothetical proteins, and allowed the identification of hitherto unknown transcriptional units. Twelve non-coding RNAs were identified, including 11 small RNAs and one cobalamin riboswitch. Fifty-seven genes were differentially regulated in the LuxS mutant. Addition of exogenous synthetic 4,5-dihydroxy-2,3-pentanedione (DPD, AI-2 precursor) to the ΔluxS mutant culture complemented expression of a subset of genes, indicating that LuxS is involved in both AI-2 signaling and non-signaling dependent systems in P. gingivalis. This work provides an important dataset for future study of P. gingivalis pathophysiology and further defines the LuxS regulon in this oral pathogen.
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