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1
Moreno, Ana Carolina Ramos. "Caracterização molecular do gene fliC de Escherichia coli enterotoxigênica pela análise de seu polimorfismo de restrição". Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/9/9136/tde-04022015-091115/.
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Neste estudo, mostramos a possibilidade de identificação dos AgH de ETEC pela caracterização molecular do gene fliC pela análise de seu polimorfismo de restrição. Um único alelo de fliC de ETEC foi encontrado para cada antígeno flagelar, utilizando-se a endonuclease RsaI, com exceção do H21. Além de cepas móveis, isolados imóveis também puderam ser caracterizados por essa técnica molecular. A alta tipabilidade da PCR-RFLP foi comprovada por meio de sua aplicação não só a amostras de ETEC com AgH previamente desconhecidos, mas também a outras linhagens de E. coli. Observamos que após identificação do antígeno flagelar das amostras de ETEC pela PCR-RFLP, a determinação do antígeno somático pôde ser direcionada, diminuindo assim, o número de anti-soros utilizados para a pesquisa do AgO. A técnica de PCR-RFLP, em nosso estudo, mostrou uma sensibilidade de 83% e 100% de especificidade. Esta técnica foi mais rápida na identificação do AgH de E. coli (2 dias) em comparação à sorologia clássica (7 ou mais dias, dependendo da motilidade da cepa). Acreditamos que o método de soroaglutinação para determinação do AgH será substituído rapidamente pela PCR-RFLP. Contudo, a soro aglutinação não poderá ser totalmente dispensada em curto prazo. No futuro, com o perfil molecular obtido dos alelos de cepas procedentes de estudos epidemiológicos, novos padrões serão definidos para as cepas diarreiogênicas de E. coli, permitindo o abandono da sorologia para AgH.In this study, we showed that the H antigens of ETEC can be characterised by restriction analysis of the polymorphism of the fliC gene. Only one allele of the fliC gene of ETEC was found for each flagellar antigen when restriction endonuclease RsaI was used, with the exception of H21 . Additionally, non-motile strains could also be characterised using this molecular technique. The high typeability of this technique was demonstrated by the fact that it can not only be applied to ETEC samples with previously unknown H antigens but also to all other lineages belonging to the E. coli species. Moreover, the determination of the somatic antigen was guided by the identification of the flagellar antigen of ETEC strains by PCR-RFLP, thus reducing the number of anti-AgO sera used. In this study, the PCR-RFLP technique showed a sensitivity of 83% and a specificity of 100%. This technique proved to be quicker for the identification of the E. coli AgH, taking 2 days to complete, in comparison to the 7 or more days necessary when using classic serotyping. We believe that the determination of the AgH by seroagglutination will soon be substituted by the PCR-RFLP technique. However, serotyping will still have to be used in the short run, for further studies involving PCR-RFLP must be carried out. In the future, with the determination of the molecular profiles of alleles of strains obtained in epidemiological studies, new patterns will have been described for the diarrhoeagenic strains of E. coli, thus permitting the abandonment of AgH serotyping for good.
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Kaczanowska, Magdalena. "Study of the link between translation termination and ribosome biogenesis /". Stockholm : Institutionen för genetik, mikrobiologi och toxikologi, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-288.
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Brown, Angela. "An ecotoxicogenomic study in Escherichia coli K12-MG1655". Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417436.
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Liu, Guowen. "A study of the Escherichia coli cell cycle". Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/12440.
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The ftsK gene of Escherichia coli encodes a 147kDa peptide, which consists of three distinct domains; namely a conserved N-terminal domain, a proline and glutamine rich region, and a C-terminal domain with consensus nucleotide-binding pocket (Begg et al., 1995). The N-terminus is essential for cell division (Begg et al., 1995; Draper et al 1998; Wang and Lutkenhaus 1998) and targets the whole protein to the septum (Yu et al., 1998 and Wang and Lutkenhaus, 1998). It was found in this thesis that depletion of the C-terminal domain resulted in the appearance of cells with abnormally located chromosomes and also in cell division-dependent SOS induction. Further study in this thesis showed that it was required only for chromosomal dimer resolution. The phenomenon of cell division-dependent SOS induction in FtsK-depleted GLC600 cells suggested that chromosome partition mutants should have continuous SOS induction. A study of the mutants obtained in this way showed that the RuvABC proteins, which are required for the resolution of recombination intermediates, are involved in chromosome partition. Over-expression of RuvAB could cause inhibition of cell division even in recA- cells, slow down the elongation of chromosome replication and cause the repression of transcription of cell division genes in the 2min region of the E. coli chromosome. To confirm that cell division and chromosome replication are coupled, nalidixic acid treatment and thymine starvation were used to block chromosome replication and it was found that cell division was coupled with chromosome replication at the level of transcription. It was also found that over-expression of DsbB, a protein required for protein disulfide bond formation in E. coli (Bardwell et al., 1993), resulted in the loss of the rod shape of E. coli cells. Over-expression of another gene named friL caused inhibition of cell division at a very early stage. It is proposed that FriL might be a regulator of cell division.
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Jepson, Alys Katherine. "E. coli motility and growth : a biophysical study". Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/10484.
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This thesis comprises two parts, both concerned with the study of Escherichia coli bacterial suspensions. The first part investigates E. coli motility whilst the second part explores E. coli growth in the presence of the antimicrobial peptide pexiganan. In Part 1 I measure the three-dimensional diffusion of non-motile cells in an active suspension of E. coli, using Differential Dynamic Microscopy (DDM). It is found that tracer diffusivity is enhanced linearly as a function of the bath activity, defined as the product of the number density of active bacteria and their average speed. The absolute enhancement is measured to be 1:8 ± 0:1 times smaller that that published previously in the vicinity of a surface, in agreement with theoretical predictions of enhanced diffusion by far-field advection. The diffusivities of non-motile mutants with and without paralysed flagella are enhanced to the same extent, despite a difference in hydrodynamic radii. In addition, the protocol for growing, preparing and measuring motile E. coli is optimised using DDM. In Part 2 I investigate how E. coli density in liquid media supplemented with pexiganan influences the measurement of its Minimum Inhibitory Concentration (MIC). Growth curves, peptide bioassays and single cell microscopy are used. It is found that population density drops rapidly when pexiganan is introduced, but regrowth occurs within 24 hours at sub-MIC concentrations. The shape of the density curve is explained by peptide depletion linked to cell death and immediate recovery of cells exposed to the peptide. As expected from these findings, the system displays a substantial inoculum effect, quantified with a fitted power law. Substantial variation is seen between replicate MIC assays; an inherent property of the system which derives from the drop to small numbers of viable cells before regrowth. Finally, I show that DDM measurements of E. coli motility in antimicrobial peptides can provide an alternative, high-throughput density curve.
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Maderbocus, Riyaz. "A study of outer membrane biogenesis in E. coli". Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4098/.
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The outer membrane (OM) of Escherichia coli is an essential organelle. The OM allows E. coli to interact with its environment and has a critical function as a barrier to prevent the entry of toxic molecules into the cell. The OM is composed of phospholipids, lipoproteins, outer membrane β-barrel proteins (OMPs) and lipopolysaccharide (LPS). The correct ratio of these components is needed to ensure proper OM barrier function is maintained. Assembly of OMPs is performed by the Bam (β-barrel assembly machinery) complex, lipoproteins by the Lol (Localisation of lipoproteins) pathway and LPS by the Lpt (LPS transport) pathway. The factors responsible for the assembly of phospholipids at the OM are unknown. This study presents two key areas in understanding OM biogenesis. Firstly, a comprehensive mutagenesis screen was performed on the Bam complex member BamE. This analysis along with the structure of BamE has indicated crucial regions for BamE function. Secondly, we have performed a structure and function analysis on the previously uncharacterised protein, YraP. The structure of YraP has been solved and represents a novel fold. Additionally, we have obtained some functional evidence that suggest that YraP is involved in phospholipid biogenesis in the OM.
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Zheng, Yunan. "Study of Allosteric Regulation of Escherichia coli Aspartate Transcarbamoylase". Thesis, Boston College, 2013. http://hdl.handle.net/2345/3683.
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Thesis advisor: Evan R. KantrowitzFor nearly 60 years the ATP activation and the CTP inhibition of Escherichia coli aspartate transcarbamoylase (ATCase) has been the textbook example of allosteric regulation. We present kinetic data and 5 X-ray structures determined in the absence and presence of a Mg2+ concentration within the physiological range. In the presence of 2 mM divalent cations (Mg2+, Ca2+, Zn2+) CTP does not significantly inhibit the enzyme while the allosteric activation by ATP is enhanced. The data suggest that the actual allosteric inhibitor in vivo of ATCase is the combination of CTP, UTP and a M2+ cation and the actual allosteric activator is ATP and M2+ or ATP, GTP and M2+. The structural data reveals that two NTPs can bind to each allosteric site with a Mg2+ ion acting as a bridge between the triphosphates. Thus the regulation of ATCase is far more complex than previously believed and calls many previous studies into question. The X-ray structures reveal the catalytic chains undergo essentially no alternations, however, several regions of the regulatory chains undergo significant structural changes. Most significant is that the N-terminal regions of the regulatory chains exist in different conformations in the allosterically activated and inhibited forms of the enzyme. Here, a new model of allosteric regulation is proposed
Thesis (MS) — Boston College, 2013
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Hidalgo, González Ricardo. "Infrared spectroelectrochemical study of E. coli NiFe hydrogenase 1". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:2cd6fb00-ba61-4697-9fef-64d395db29e0.
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This thesis investigates the catalytic mechanism of NiFe hydrogenases. The specific enzyme studied in this work, E. coli Hyd-1, is an efficient catalyst for H2 oxidation even in the presence of O2. A method for studying the chemistry of the active site of this enzyme, under catalytic conditions, is developed. The combination of IR spectroscopy with protein film electrochemistry in situ is demonstrated. This was achieved by adsorbing the hydrogenase on a high surface area carbon nanoparticle electrode; and by the design of a spectroelectrochemical flow cell that provides efficient mass transport conditions. A complete redox characterisation of the active site for a hydrogenase immobilised on a carbon electrode is described for the first time. The study of the effect of pH on the distribution of redox states demonstrates the existence of a pH equilibrium between the Ni-C and the Ni-L states. It is shown that the active site responds to the pH of the external solution, and that the increase in pH acts as a driving force that removes the proton further away from the active site. Studies under electrocatalytic conditions provides direct evidence of intermediates of the catalytic cycle. The role of Ni-SI, Ni-R, and Ni-C is confirmed. Furthermore, Ni-L is detected under turnover conditions and therefore shown to be an important intermediate in the cycle. The detection of different protonation states of Ni-L and Ni-R is proposed to provide information on the transport of the protons as they start to move away from the active site. In the investigation of O2 inhibition, Ni-B (detected spectroscopically) is directly related to the loss in activity upon the attack of O2 for the first time. Also, the formation of solely Ni-B from the reaction with O2 (no other O2-damaged species are detected) provides further evidence on the ability of O2-tolerant hydrogenases of having an effective mechanism for dealing with O2 tolerance. A thorough study on the interaction of CO with Hyd-1 proves unequivocally that this O2-tolerant hydrogenase does bind CO, and that CO does inhibit its catalytic activity (both H2 and H+ reduction). This helps clarify how CO interacts with O2-tolerant hydrogenases. Overall, the work in this thesis contributed to the understanding of key mechanistic aspects in O2-tolerant hydrogenases. The technique for combining protein film electrochemistry with IR spectroscopy in situ shall provide valuable opportunities for providing new insight into the mechanisms of hydrogenases and other metalloenzymes that bind small molecules.
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Pg, Hj Besar Dk Hjh Siti Norainna. "Engaging higher education students with social media : MIB module case study". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/engaging-higher-education-students-with-social-mediamib-module-case-study(a3b1b263-7e9d-44ec-a9cc-93f7840c4f31).html.
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This thesis reports on a study which investigated the application of social media in teaching Malay Islamic Monarchy (MIB) in a University of Brunei. The aim was to complement the on-campus delivery of this module, encourage student engagement and produce more active than passive learners. However, tensions existed between social media and the content of the course because of the potential of social media to drown and influence Bruneian Malay cultures and Islamic beliefs in a way that is not consistent with MIB. A questionnaire to 362 undergraduate students at the University of Brunei Darussalam taking the PB1501 MIB module in the semester 1 2012/2013 provided an initial sense of social media use and expectations. Six MIB teachers were also selected to represent different perspective of using social media in MIB module. Furthermore, the observation of ten MIB Facebook groups spaces and content analysis of ten MIB Facebook groups' transcripts produced information on teaching and learning activities as well as findings as to how teachers facilitate student engagement. The findings of the study indicate that whilst social media is a tool that should be able to solve the pedagogical problems in the MIB course, at the same time cultural obstacles are perceived by some teachers in this particular setting, impacting on its acceptance. Findings suggest that the implementation of social media such as Facebook in order to solve a pedagogical problem have raised tensions in this specific cultural environment. The research also shows the MIB teachers have mixed feelings about the fact that social media could complement MIB education. A way of conceiving the tensions between these issues is provided by the Technological Pedagogical Content Knowledge (TPACK) framework developed by Koehler and Mishra (2009), which is used to understand teacher decisions with respect to MIB, MIB pedagogy and social media (TPACK). This shows the connections and interactions between the content of MIB, the MIB pedagogy and social media.
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Huen, Shing-yan Michael. "A mechanistic study of lambdaphage-mediated recombination in E. coli". Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B35321854.
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Huen, Shing-yan Michael y 禤承恩. "A mechanistic study of lambdaphage-mediated recombination in E. coli". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B35321854.
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Roxas, Jennifer Lising y Jennifer Lising Roxas. "Novel Virulence Strategies of Enteropathogenic Escherichia Coli: An Integrated Study". Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625671.
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Enteropathogenic Escherichia coli (EPEC) is a Gram-negative bacteria responsible for significant morbidity and mortality in young children. EPEC elaborates a type III secretion system (T3SS), which translocates bacterial effector proteins into the host intestinal epithelial cell. To this date, 23 effector proteins are known to be secreted by EPEC. Over the past two decades, traditional studies uncovered the functions of some of these effector proteins. While there was an initial rise in the EPEC effector function discoveries, we now observe a plateau in the identification of host-EPEC interactions. Thus, the aim of my dissertation is to define novel virulence strategies in EPEC pathogenesis, and to demonstrate how traditional reductionist and global systems biology approaches can be utilized in uncovering functions of individual effectors, as well as the complex interplay of effectors in modulating host functions. Specifically, we defined the novel cytoprotective function of a T3SS effector EspZ. We further illustrated the complex interplay of EPEC effectors by defining how EPEC utilizes EspZ and EspF to dynamically regulate the prosurvival epidermal growth factor receptor signaling pathway. Finally, by integrating comparative proteomics and traditional reductionist approaches, we identified a novel function for EspH, and defined the mechanism by which EspH perturbs epithelial cell structure and function.
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Kedzierski, Mateusz Kacper. "Study of the relative domain stability of a two-domain E. coli MFS transporter, GlpT". Thesis, King's College London (University of London), 2018. https://kclpure.kcl.ac.uk/portal/en/theses/study-of-the-relative-domain-stability-of-a-twodomain-ecoli-mfs-transporter-glpt(616a8bbb-e141-4339-87b2-200a5f5475be).html.
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Members of the Major Facilitator Superfamily (MFS) make up the largest family of secondary active transporters, they mediate a diverse set of functions by controlling the movement of ions and small molecules across cell membranes. Members of the MFS share a set of common structural motifs consisting of transmembrane ɑ-helical segments. The glycerol-3-phosphate transporter (GlpT), is an example of an MFS transporter with 12 α-helices ordered into two domains. Recent study on MFS transporter LacY, has implied an increased stability localized to the vicinity of the first helices of the protein. If this observation is found in other MFS proteins it could suggest a folding principle for other MFS transporters, whereby the first helix of the protein is acting as a stable unit that supports the process of folding. The inherent magnified stability of the helix 1 may also aid in other cellular events, where transporters or receptors are integrated into the membrane by anchoring to the membrane as well as becoming part of the unit that first penetrates the membrane leaflet. This work is focused on the stability analysis via alanine substitutions along the first alpha helix of the first domain of GlpT, compared to similar and corresponding mutations along the first helix of its second domain. The transporters stability is estimated by unfolding assays coupled with the decrease of secondary structure as measured by circular dichroism spectroscopy. Additional methods such as fluorescence spectroscopy, temperature denaturation and ligand binding assays have also been used in order to gain deeper understanding of the nature of the GlpT unfolding and its helical stability.
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John, Chukwuemeka K., Jaan H. Pu, M. Pandey y R. Moruzzi. "Impacts of sedimentation on rainwater quality: case study at Ikorodu of Lagos, Nigeria". IWA, 2021. http://hdl.handle.net/10454/18450.
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YesThis study investigated the impact of sedimentation on rainwater storage system using a case study at the Ikorodu area of Lagos state, a rural area in Nigeria. In this investigation, the proportions of Escherichia coli (E. coli) that were settleable (due to sedimentation) and those that were at the free phase have been studied. Water samples were collected from different depths in the inspected rainwater storage tank at two different periods (i.e. rainy and dry periods) for 20 days. The samples collected from these periods have been analysed for physical and microbial measures before passing it through the serial filters with pore sizes of 500 μm, 100 μm, 10 μm and 1.5 μm to measure the retained particle mass. From the results, it was observed that: (1) the water quality at the free-phase zone was better than that at the tank’s bottom; (2) the settleable bacteria rapidly sinked to bottom; (3) the correlation of turbidity, E. coli and total suspended solids (TSS) for all the rain events showed a relatively high Pearson’s coefficient of 0.9 to one another; and (4) over 70% of settling TSS occurred within first 36 hours. Finally, it has been found that the physical sedimentation process can significantly reduce the microbial measures.
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Pliotas, Christos. "Using biophysical techniques to study the mechanism of ligand-gated potassium efflux systems (KEF) from bacteria". Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=165422.
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The ligand-gated potassium channels KefC and KefB of Escherichia coli are critical components in protecting cells from toxic electrophiles. Potassium efflux through these channels is coupled to a decrease in cytoplasmic pH which in turn reduces the damage to DNA by electrophiles. KefC and KefB are both inhibited by cytoplasmic glutathione and activated by glutathione adducts, such as ESG, formed by conjugation of glutathione with electrophilic compounds. Robust membrane purification protocols were developed to isolate both the wild type full-length KefC and KefB and the mutants required for biophysical analysis. In vivo K+ measurements were performed to ensure that all of the constructs used were fully functional. Structural and functional analysis used electron paramagnetic resonance (EPR) and stead state emission fluorescence measurements in vivo, on wild type and mutated full-length proteins to elucidate the gating mechanism and test the model generated from crystallographic data. In particular, EPR spectroscopy combined with site-directed spin labelling revealed a substantial conformational change and thus provided the first insight into coupling between sensing and gating. Steady state fluorescence spectroscopy was used to precisely measure binding affinities for both activating and inhibitory ligands and characterise nucleotide binding to KefC. Finally, a variety of chemically diverse glutathione adducts was tested on KefC in vitro to elucidate the mechanism by which these ligands initiate K+ flux through the associated transmembrane domain.
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Magennis, Marisa. "The dynamics of adaptation in fluctuating environments : an experimental evolution study with Escherichia coli". Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/17853.
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Resource conditions in nature can fluctuate markedly and how organisms adapt to survive in these conditions is of great interest in the fields of evolutionary biology and ecology. Experimental evolution using microbes has been shown to be effective in answering general evolutionary questions. Using this technique, I studied the bacterium Escherichia coli adapting to fluctuating environments to investigate the evolution of growth traits and the dynamics of adaptation. My results have provided general insight into bacterial adaptation which may allow for better prediction of growth trait evolution in a range of conditions. (1) I have shown that evolution in both predictable and unpredictable environments resulted in the evolution of a reduced lag phase, an increased growth rate and a higher maximum population size. My results suggest that bacteria do not adapt to conditions by anticipating the timing of the resource renewal. (2) I found that a trade-off exists for evolved populations between a reduced lag phase and a higher mortality rate in all environments, and propose this as an explanation as to why some bacteria retain a lag phase. (3) I show that the dynamics of adaptation do not differ between populations adapted to conditions which involved varying periods of time in stationary phase between transfers. There seem to be different mutations for different traits, with mutations to the lag reducing first, followed by growth rate, and finally population size. These findings highlight the dynamics of growth trait evolution in environments in which a complex interplay exists between reproducing and growing faster than competitors, and being able to survive in starvation conditions.
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Sonnenfield, Jean Marie. "Study of the StpA protein from Salmonella typhimurium and Escherichia coli". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389027.
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Pickering, David Jonathan. "A study of the enzymology of DNA ligase from Escherichia coli". Thesis, University of Hull, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395429.
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Irvine, Helen Patricia. "A metabolic engineering approach to study overflow metabolism in E. coli". Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1444751/.
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Aerobic fermentations of Escherichia coli grown with glucose accumulate organic acids in the culture medium. These by-products of glucose metabolism are synthesised and excreted when the glucose uptake rate is greater than its conversion to biomass and carbon dioxide. Acetate is the most abundant overflow metabolite produced in aerobic cultures of E. coli. Its production is strain and media specific, being greatest in dense nutrient-rich cultures. In industrial fermentations, E. coli is widely employed for production of recombinant proteins. However, acetate excretion reduces process efficiency by lowering cell growth rate, and decreasing the amount of substrate carbon converted to recombinant protein product. This thesis describes the construction of three plasmid vectors designed to express antisense RNA targeted against phosphotransacetylase and acetate kinase, which convert acetyl CoA to acetate. Antisense RNA was used as a metabolic engineering tool in this study, to enable examination of the central carbon flux distribution before, during and after enzyme downregulation. The aim was to decrease expression of these enzymes in E. coli, and thus decrease acetate production. E. coli MG1655 was transformed with a) a plasmid construct encoding an antisense RNA fragment, b) two compatible plasmids encoding different antisense RNA fragments. The resulting strains were cultivated in a 2L bioreactor, and the effect of antisense RNA expression evaluated. Assays to monitor the enzyme activities of phosphotransacetylase and acetate kinase were conducted, along with metabolite analysis to determine organic acid excretion profiles. Flux balance analysis, which is a method of modelling metabolism, was applied to the central carbon pathways in E. coli to provide insight into the partitioning of internal carbon fluxes. Information about the mechanisms used by E. coli to cope with partial shutdown of the acetate synthesis pathway was gained by comparing the flux distribution of a control strain with an antisense RNA-expressing strain.
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Mulcahy, Marian P. B. "A genetic and molecular study of phenylalanine transport in Escherichia coli". Thesis, University of Dundee, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.655207.
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Kemp, Elizabeth Helen. "A study of the ompT gene of Escherichia coli K-12". Thesis, University of Warwick, 1988. http://wrap.warwick.ac.uk/109990/.
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The ompT gene of E. coll encodes a 40 kd outer membrane protein (OmpT) which, in vitro, exhibits proteolytic activity towards the ferric-enterochelin receptor protein. In this study the ompT gene was cloned from E. coli K-12 on a 4.3 kb EcoRI DNA-Fragment. Subcloning of this fragment, in conjunction with maxi-cell analysis, demonstrated that ompT was located on a 1.5 kb Pstl-Smal DNA fragment. DNA sequence analysis revealed that the Pstl-Smal fragment contained an open reading frame (ORF) of 951 bp, the latter having a coding capacity of 35.6 kd. This deduced molecular weight was somewhat smaller than the molecular weight of 42 kd estimated by SDS-PAGE for pro-OmpT. Potential -10 and -35 promoter consensus sequences were identified upstream from the ompT coding region as was a putative ribosome binding site. A DNA sequence showing homology to a consensus sequence present in the putative promoter regions of iron- regulated genes, was also located upstream from the ompT coding region. With regard to the deduced amino acid sequence of OmpT, a potential signal sequence was found at the amino-terminal of the protein which could direct export from the cell cytoplasm. The protein was also examined for amino acid sequences displaying homology to other outer membrane proteins, but none were identified. OmpT-phoA gene fusions were constructed in order to assess the ability of the ompT transcription/translation initiation signals to drive the expression of cloned heterologous genes in E. coli. OmpT-PhoA fusion proteins were indeed produced and these were exported to the periplasm of the cell. Synthesis of the chimeric proteins was found to be 5-6 fold higher at 37°C than at 30°C which seemed to reflect the normal temperature-dependent production of the OmpT protein. Both ompT-lacZ operon and protein fusions were also created in an attempt to define the stage at which temperature affected the synthesis of OmpT. Studies indicated that this occurred at some post-transcriptional step. The effect of the envZ allele on the expression of ompT was also investigated. This mutation appeared to reduce the level of transcription of ompT as Indicated by studies using the ompT-phoA and ompT-lacZ fusions.
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Zamarreño, Beas Jordi. "Study of molecular mechanisms allowing E. coli to resist against antibiotics". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0581/document.
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La résistance aux antibiotiques est devenue un problème de santé publique majeur. Comprendre les mécanismes moléculaires menant à la résistance aux antibiotiques et ceux qui permettent la sensibilisation est capital pour trouver des nouvelles manières de combattre les bactéries multirésistantes. La concentration intracellulaire en antibiotiques est un paramètre clé qui influe sur la sensibilité bactérienne aux antibiotiques. Au cours de ma thèse, j'ai étudié trois mécanismes différents modulant la concentration intracellulaire d'antibiotiques chez E. coli.Tout d'abord, j'ai montré que RavA, une ATPase AAA+, et son partenaire ViaA, sensibilisent E. coli aux aminoglycosides en augmentant la concentration intracellulaire d'antibiotiques. Contrairement au modèle actuellement en vigueur dans la littérature, j'ai montré que RavA et ViaA ne requièrent ni les machineries de biogénèse des centres Fe-S, ni les complexes respiratoires contenant des centres Fe-S pour sensibiliser E. coli aux aminoglycosides. Un nouveau modèle sera discuté.Enfin, dans une étude en collaboration avec l'équipe de Nassos Typas qui a analysé à très large échelle l'effet des antibiotiques en combinaison avec différentes molécules, j'ai étudié les combinaisons ayant un effet antagoniste avec les aminoglycosides. En réalisant des tests d'import de gentamicine avec 8 combinaisons différentes, j'ai montré que l'effet antagoniste était dû à une diminution de la concentration intracellulaire de gentamicine dans 7 des 8 combinaisons antagonistes testéesAntimicrobial resistance is becoming an issue of major public health concern. Understanding the molecular mechanisms leading to antibiotic resistance or sensitization is of major interest to find out new manners to fight superbugs. Modulation of intracellular concentration of antibiotics is one of the most frequent processes leading to antibiotics resistance. My thesis focused on studying three different mechanisms that modulate intracellular antibiotic concentration in E. coli.First, I showed that RavA, an AAA+ ATPase, and its VWA-containing partner, ViaA, sensitize Escherichia coli to aminoglycosides by increasing the intracellular concentrations of the drug. In physiological conditions, the RavA-ViaA aminoglycosides sensitization occurred in anaerobic conditions. To understand the molecular mechanism of such effect I developed genetic approach. I showed that in contrast to what was previously thought, RavA and ViaA acted neither with Fe-S cluster biogenesis machineries (ISC and SUF) nor with Fe-S cluster-containing respiratory complexes. Alternative model will be discussed.Last, in a collaborative work that analysed the effect of almost 3,000 dose- resolved combinations of antibiotics, I focused on drugs antagonizing aminoglycosides. The antagonistic drug combinations identified were highly conserved in six strains from three Gram-negative pathogens, E. coli, Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa. By performing aminoglycosides uptake assays with 8 different drug-gentamicin combinations, I showed that for 7 out of the 8 antagonistic combinations tested, a decreased in the intracellular concentration of aminoglycosides occurred
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Stegmeier, Johannes Friedrich. "Study of Omp85 family proteins YaeT and YtfM and multidrug export machineries in Escherichia coli". Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980586682.
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Monaghan, Áine Marie. "Investigations on the serotypes and virulence profiles of non-O157 Shiga-toxin producing Escherichia coli (STEC) and Enteropathogenic Escherichia coli (EPEC) isolated from bovine farms and abattoirs". Thesis, Ulster University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.695311.
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This study focuses on emerging E. coil serotypes and has developed methods for the isolation and identification of non-0157 STEC and EPEC. A basal medium for the isolation of these pathogens was developed as well as a serogroup specific PCR assay for the detection of the 02 serogroup. These culture and molecular based techniques have proven to be valuable in the detection, identification, and epidemiological investigation of these groups of emerging pathogens. These methods were applied to 1) a farm study, whereby samples (faecal and soil) and 2) an abattoir study, whereby samples (hide and carcass) were analysed for the presence of non-0157 STEC and EPEC. Isolates were subsequently characterised in terms of serotype/serogroup and virulence markers. The data generated by this work has illustrated the extent of non-0157 STEC and EPEC contamination in the farm and abattoir environments, thus providing scientific background upon which control strategies may be based.
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Ying, Wang Li. "Study of the transport mechanism of the melibiose permease from Escherichia coli". Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/377470.
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El transportador de melibiosa d'Escherichia coli (MelB) pot utilitzar l'energia electroquímica tant de H+, Na+ o Li+ per transportar la melibiosa a l'interior de les cèl·lules en contra del seu gradient de concentració. La MelB és una proteïna de 473 aminoàcids disposats en 12 hèlices transmembrana, amb els extrems N- i C-terminal situats al costat citoplàsmic. Mitjançant l'ús de mètodes espectroscòpics i bioquímics, hem analitzat el paper d'alguns aminoàcids en el bucle 7-8/final d'hèlix VII, que conté diversos aminoàcids aromàtics altament conservats, així com dos residus carregats negativament. Aplicant tècniques de mutagènesi, es van obtenir mutants individuals en què cada aminoàcid s'ha canviat a cisteïna excepte Ser-259, que també es va canviar a alanina. L'espectroscòpia de fluorescència va mostrar que els mutants dels aminoàcids conservats Tyr-256, Tyr-257, Phe-258 i Tyr-260 no uneixen substrats, i els espectres de diferència d'infrarojos de Y256C i Y260C van confirmar l’absència d’unió al substrat. Simulacions de dinàmica molecular van mostrar que aquests residus aromàtics formen part d'un bloc d’interaccions hidrofòbiques que jugaria un paper destacat en el mecanisme de transport. D'altra banda, els espectres de fluorescència i de diferència d’infraroig van demostrar que el mutant Cys del residu Asp-266 i del restant aminoàcid aromàtic del bucle 7-8 Phe-268 són capaços d'unir sodi i melibiosa en una forma semblant a la MelB nativa (Cless). Altres mutants de cisteïna (S259C, S259A, V261C, G263C, D264C, A265C i L267C) del bucle 7-8/final d'hèlix VII mostren una capacitat d'unió similar a Cless. Aquests resultats suggereixen que els aminoàcids conservats Tyr-256, Tyr-257, Phe-Tyr-258 i 260 tenen un paper estructural important en el mecanisme de transport de la MelB.The melibiose transporter from Escherichia coli (MelB) can use the electrochemical energy of either H+, Na+ or Li+ to transport the melibiose to the cell interior against its concentration gradient. MelB is a protein of 473 amino acids arranged in 12 transmembrane helices, with the N- and C-terminus located in the cytoplasmic side. By using spectroscopic and biochemical methods, we have analyzed the role of some amino acids in the loop 7-8/end of helix VII, which contains several highly conserved aromatic amino acids as well as two negatively charged residues. Applying mutagenesis techniques, we obtained single mutants in which each amino acid has been changed to cysteine except Ser-259 also changed to alanine. Fluorescence spectroscopy showed that mutants of the conserved amino acids Tyr-256, Tyr-257, Phe-258 and Tyr-260 did not exhibit substrate binding, and the infrared difference spectra of Y256C and Y260C also showed no substrate binding. Molecular dynamics simulation experiments pointed out that these aromatic residues make part of a hydrophobic lock that would play a significant role in the transport mechanism. On the other hand, infrared difference and fluorescence spectra demonstrated that the Cys mutant of Asp-266 and the remaining aromatic amino acid of loop 7-8 Phe-268 are able to bind sodium and melibiose in a similar way as the wild type MelB (Cless). Other cysteine mutants (S259C, S259A, V261C, G263C, D264C, A265C and L267C) of the loop 7-8/end of helix VII show similar binding capacity as Cless. These results suggest that the conserved amino acids Tyr-256, Tyr-257, Phe-258 and Tyr-260 have an important structural role in the MelB transport mechanism.
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Zheng, Dongling. "Studies of Escherichia coli promoters : mutational study and in vitro transcriptional profiling". Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403445.
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Nandal, Anjali. "Molecular-genetic study of novel aspects of iron regulation in Escherichia coli". Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434113.
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Lewanczyk, M. M. "Study of uropathogenic Escherichia coli host-pathogen interactions using novel infection models". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3020536/.
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Coombs, Anne-Marie. "A study of near-ultraviolet radiation induced oxidative damage in Escherichia coli". Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380929.
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Månsson, Lisa. "Visualizing the dynamic interplay between the host and bacterial pathogen : a real-time study of renal infection /". Stockholm, 2007. http://diss.kib.ki.se/2007/978-91-7357-218-7/.
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Banakhr, Fahd. "Proof of principle non-invasive pulsed electric field study (measurement and experiments)". Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12020.
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Pulsed electric field (PEF) technology applied to food processing was firstly used in the late 1960s. The currently available systems use either conventional Blumlein generators or generators similar to those found in radar power sources to produce the required high voltage pulses. The liquid to be processed is passed through a number of treatment chambers or cells which each contain a pair of electrodes in contact with the liquid. An electric field is thereby applied to the liquid, leading to the technology being termed invasive and it can be used only with liquid food. A novel and non-invasive PEF technology for use in the food processing industry is introduced and investigated in this thesis. The technology represents a novel way of performing PEF treatment. A proof of concept arrangement uses two ceramic cylinders mounted inside the non-invasive PEF cell with a gap of 3 mm between them. A displacement current of the order of mA passes through the non-invasive PEF cell during treatment, as compared with the kA of current usually produced during an invasive treatment. The low current is not only economic in electric energy but also maintains a low food temperature, which implicitly maintains food flavour. In the thesis the electro-optic Kerr effect technique is used to perform accurately the PEF measurement and convincingly prove that strong electric fields are present. Two Kerr water cells were designed and used to determine the Kerr constant for water, since the data presented in the literature is unreliable. The first Kerr water cell uses a pair of Bruce profile stainless steel electrodes and the second a pair of parallel plate stainless steel electrodes. An electro-static solver (Maxwell software) was used to determine the electric field distribution and to calculate the electric field integral to accurately determine the Kerr constant for water. Water samples containing the E-coli bacteria were prepared and filled in the non-invasive PEF cell by the Flavometrix Company. Eight PEF experiments were successfully performed during this research programme and the results show unequivocally that the novel noninvasive technique is effective in significantly reducing the initial concentration of E-coli bacteria. This opens the door for the future design of an industrial prototype.
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Tie, Cuijuan. "Kinetics and dynamics study on the allosteric pathway of phosphofructokinase from Escherichia coli". Diss., Texas A&M University, 2008. http://hdl.handle.net/1969.1/85900.
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Phosphofructokinase from Escherichia coli (EcPFK) is allosterically regulated by MgADP and phosphoenolpyruvate (PEP), which act to activate or inhibit, respectively, by changing the substrate (Fru-6-P) affinity of the enzyme. Both ligands bind to the same allosteric site in EcPFK. Therefore, the questions we want to address are how these two molecules regulate EcPFK and how the allosteric signal is propagated throughout the enzyme. EcPFK has 28 potential site-site interactions. These interactions in turn derive from multiple copies of 6 potentially unique homotropic interactions and 4 potentially unique heterotropic interactions. Making hybrid tetramer of EcPFK is used to isolate a single heterotropic interaction. To improve the yield of the 1:3 hybrid, the in vivo hybrid formation method was developed. Four heterotropic interactions were isolated by this manner and re-evaluated. The same kinetics characteristics were obtained for each 1:3 hybrid from both the in vivo and in vitro method. To address the question of how the allosteric signal is transmitted throughout EcPFK, we identified residues (G184, Asp59 and S157) that are important for the allosteric regulation for both PEP inhibition and MgADP activation. The impact of each mutation on individual interaction is unique and also suggests that the structural basis for PEP inhibition is different from that for MgADP activation. Most importantly, since the sum of each heterotropic interaction with a modification in only one subunit is equal to the total heterotropic interaction with a modification in all four subunits, this result indicates that the heterotropic allosteric signal transmission is realized in a single subunit. The 23Ã heterotropic interaction, which contributes the most to the PEP inhibition, was chosen to study the dynamic properties. Fluorescence was used to study the dynamic perturbations of the 23Ã interaction upon ligand binding. Taking advantage of the hybrid formation strategy and the tryptophan-shift mutagenesis method, a tryptophan residue can be placed at different individual locations throughout the native subunit containing the 23Ã heterotropic interaction. The steady-state anisotropy and lifetime measurement at each tryptophan position indicate that the 23Ã allosteric interaction involves the perturbation of side-chain dynamics both near and quite far away from the respective ligand binding sites.
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Sentek, Mina. "Cult Buildings In Aceramic Neolithic Southeast Anatolia: A Case Study Of Nevali Cori". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607137/index.pdf.
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First settlements in Southeast Anatolia begun to appear as early as 10000 BC. Among all the unanswered questions about this early period, cult-related activities and cult buildings are widely studied due to their nature, which has strong connections with the social organization and early symbolism.
During the last decade, Southeast Anatolia has provided new evidence for this early stage of development in human history. This study aims to examine cult buildings that have common characteristicshow they were treated and distributed. The settlement of Nevali Ç
ori and its cult building is taken as an example and studied in detail. Other cult buildings with the same or similar architectural features are included in this study in order to discuss the roots, the distribution and the continuity of this Aceramic Neolithic tradition.
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Ghatak, Archana. "Rapid kinetics study of the nuclease activity of RecBCD enzyme from Escherichia coli". College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3388.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Riordan, Denise Catherine Rose. "A study on the survival of Escherichia coli O157:H7 in fermented meat". Thesis, University of Ulster, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264692.
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Wang, X. "NMR study of the Escherichia coli 70S ribosome particle using residual dipolar couplings". Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1388785/.
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The ribosome is the 2.5-MDa complex that is responsible for production of biologically active polypeptide chains. Crystallographic and cryo-EM studies have revealed the intricate motions of the ribosome during protein synthesis, but less is known about the highly dynamic regions such as L7/L12 stalk protein, which has an important role during this process. Moreover, there is currently very little structural information on the dynamic nascent polypeptide chain (NC), which during its progressive emergence from the ribosome has its first opportunity to acquire structure, folding in a co-translational manner. While the formation of tertiary structure occurs outside of the ribosomal exit tunnel while the NC remains tethered there is little understanding of how this process takes place. NMR spectroscopy, which has the ability to report on both residue-specific structure and dynamics at atomic resolution, has previously been applied to report on mobile regions of the ribosome, such as the L7/L12 stalk protein, and more recently, to the study of co-translational folding of ribosome-nascent chain complexes (RNC). For example, chemical shift studies of RNCs of an immunoglobulin domain (ddFLN-Dom5), have revealed a dynamic RNC capable of adopting the native fold. The motional properties of both L7/L12 and the NC therefore permit the application of NMR strategies, such as residual dipolar couplings (RDC), to derive direct three-dimensional structural information. RDCs encode detailed structural information in the form of distance-independent bond-vector orientations, and can be exploited for both structured and unstructured proteins. This thesis describes steps towards the development of RDC techniques for probing the structural and dynamic properties of RNCs. Initial application to the L7/L12 stalk protein was used as the foundation for subsequent studies of RNCs. Alignment in phage enabled a set of RDCs to be measured for both ribosome-bound and isolated L7/L12, yielding the first direct structural information on the L7/L12 protein in its ribosome-bound form. The application of RDCs to the study of RNCs required extensive development of the strategy for the production of isotopically-labelled RNCs, which resulted in significant improvements in both the yield and quality of the final RNC samples. The RDC study of a model RNC, Dom5+110, highlighted the inherent challenges associated with the finite sample lifetime, low sample concentration and restricted mobility of the RNC. These were addressed with the study of the intrinsically disordered alpha-Syn-RNC, which enabled the measurement of N-H RDCs. A potential interaction between the alpha-Syn NC and the ribosome prevented acquisition of RDCs for all residues, but further studies are underway to improve the quality of the spectra with a view to obtain the complete set of RDC data. Together these data provide a solid foundation for an RDC methodology for application to the ribosome and RNCs, and will enable more detailed structural and dynamical studies of the emerging nascent chain.
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Drage, Lauren Kathryn Letitia. "A longitudinal study of long-term Escherichia coli colonisation of the elderly bladder". Thesis, University of Newcastle upon Tyne, 2017. http://hdl.handle.net/10443/3558.
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Urinary tract infections (UTIs) are the second most common cause of infection worldwide, making them a huge economic burden. People can carry diagnostic loads of bacteria within the bladder without experiencing any symptoms, this is asymptomatic bacteriuria (ABU). ABU prevalence increases with age, with around 19% of those over 60 being susceptible. ABU can reactivate sporadically, causing symptomatic episodes, known as recurrence. Current treatment is with antibiotics, either short courses or prophylaxis. Guidelines state to only treat symptomatic episodes. However, UTI symptoms are often diffuse and unclear, especially in older people. Thus, ABU is inappropriately treated in up to 52% of cases, encouraging antibiotic resistance. Better ways of discriminating between symptomatic and asymptomatic cases are needed. This would allow for more efficient treatment and patient management. To improve understanding of ABU, a longitudinal clinical pilot study was performed. For 6 months, every 2 weeks a urine sample and symptom questionnaire was collected from 30 patients over 65 who were clinically diagnosed with recurrent UTIs. The aim was to analyse potential changes in the host response and the colonising bacteria around periods of symptoms to see if distinct urinary profiles could be seen between symptomatic and asymptomatic states. Allowing for analysis into potential predictive biomarkers for symptoms. Uropathogenic Escherichia coli (UPEC) is known to cause the majority of UTIs, thus was the bacterial focus for this project. The study firstly allowed us to test the feasibility of such a demanding study design. It was possible to fully recruit to the study with all 30 patients completing its entirety, thus suggesting such a design could be repeated or scaled up in the future. The study produced a large database of bacterial isolates as well as urine samples. Urines were measured for a wide range of immune response proteins. Despite varying levels of immune activation, UPEC was able to evade host-defences and thrive in the bladder long-term. The study showed that ABU patients can carry significant bacterial loads of UPEC, even with antibiotics, questioning the advantages of prophylactic treatment of ABU patients. No distinct host or bacterial profile was identified between symptomatic states. No biomarkers could be seen to predict symptomatic episodes in these patients. However, what was observed was an unexpected level of dynamic variability within individuals and across the patient cohort.
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Simpkin, David. "The anaerobic fumarate reductase of Escherichia coli : a study of its prosthetic groups". Thesis, University of St Andrews, 1986. http://hdl.handle.net/10023/14389.
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The prosthetic groups of the respiratory fumarate reductase from Escherichia coli have been studied by electron paramagnetic resonance. The iron-sulphur clusters of this enzyme were characterised in membranes from a strain of E. coli with amplified expression of the fumarate reductase. Two ferredoxin centres, paramagnetic in the reduced state (FR1 & FR2, Em -50mV & -280mV) were shown to be present at the same concentration as the flavin, together with a centre paramagnetic in the oxidised state (FR3, Em -30mV), present at the same concentration. Another ferredoxin signal was observed in reduced membranes at 1/10th the concentration of the other centres. The relaxation processes of the iron-sulphur centres were characterised and shown to be similar to those reported for other iron-sulphur centres. These relaxation processes changed when more than one centre was paramagnetic, indicating interaction between the centres, which were characterised between FR1 & FR2, and FR1 & FR3, by the observed changes in e.p.r. properties. Estimates of the distances between centres were made from these observed changes. The orientation of the g-tensors of the iron-sulphur centres was studied in membrane multilayers, both from a wild-type strain and a strain with amplified expression of the enzyme. The iron-sulphur clusters were shown to have distinct orientations in both cases, with the amplified strain producing crystalline multilayers. The interactions between the iron-sulphur centres were shown to have an angular dependence and thus to be magnetic dipole-dipole interactions. The location of the iron-sulphur centres was studied using the exogenous paramagnetic probe dysprosium(III), and they were all shown to be on the cytoplasmic aspect of the cell membrane. The catalytic site of fumarate reduction was also located as cytoplasmic, by the use of mutant strains of coli, and inhibitors of the dicarboxylic acid porter. The iron-sulphur centres were shown to be located deep within the catalytic subunits of the enzyme. The flavin moiety of fumarate reductase was characterised in the isolated enzyme by e. p. r. The semiquinone form of the flavin was shown to be stable in the physiological pH range and to have an Em7 of -12mV (n = 2). Interaction between the semiquinone and FR1 was shown and characterised.
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Pham, Christopher K. "The Study of the Regulon of OxyR in Escherichia coli and Porphyromonas gingivalis". VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4155.
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The facultative anaerobe, Escherichia coli and the obligate anaerobe, Porphyromonas gingivalis are two bacteria that reside in our body. Although they reside in separate environments, they are both subject to hydrogen peroxide stress and have mechanisms to regulate the stress. OxyR is the primary transcriptional regulator/sensor of oxidative stress response caused by hydrogen peroxide. OxyR in P. gingivalis is not well-characterized compared to OxyR in E. coli. We sought to characterize and compare the two forms of OxyR in order to gain a better understanding of the protein. We determined the oligomeric state of both proteins: primarily a tetramer for E. coli and primarily a tetramer for P. gingivalis OxyR.. We demonstrated DNA binding with E. coli OxyR, indicating purification of the functional form of E. coli OxyR.Through pulldown assays we discovered potential novel binding targets, mobB for E. coli OxyR and PG1209 for P. gingivalis OxyR. Many of the other targets corresponded to intergenic regions within genes, which may pertain to small RNAs or small proteins. These results show that OxyR in E. coli and P. gingivalis has novel function and properties indicating an expanded role in addition to the well-characterized oxidative stress response.
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Kanamaru, Sojun. "Molecular epidemiological study of a putative virulence factor USP in uropathogenic Escherichia coli". Kyoto University, 2007. http://hdl.handle.net/2433/135724.
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Rothery, Richard A. "An in situ study of cytochrome bd : a ubiquinol oxidase of Escherichia coli". Thesis, University of St Andrews, 1989. http://hdl.handle.net/10023/14392.
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An in situ study was conducted of the cytochrome bd ubiquinol:oxygen oxidoreductase (cytochrome b558-b595-d) of Escherichia coli grown anaerobically on glycerol with fumarate as respiratory oxidant. Nitrite reacts with and is reduced by the oxidase, resulting in the formation of NO adducts to haems b595 and d. The kinetics of formation of these species indicate that the affinity of haem d for nitrite is higher than that of haem b595. CO also binds to the oxidase, resulting in the formation of CO adducts to haems d and b595. Binding titrations indicate that the affinity of haem d for CO is higher than that of haem b595. The steady state kinetics of the oxidase reaction in the presence of nitrite or CO are cooperative with respect to oxygen binding, suggesting that both haems d and b595 are involved in the reduction of oxygen. E.p.r. studies of the ferric oxidase indicate the presence of two high spin haem signals, one rhombic and one axial, which are assigned to haems b595 and d, respectively. These signals titrate potentiometrically with midpoint potentials similar to those published on the basis of optically followed titrations for haems b595 and d. The high spin ferric haem spectra are affected by oxygen, CO, cyanide, and pH. A low spin ferric haem signal is observed at g=3.3 and is assigned to haem b558. The sidedness with respect to the cytoplasmic membrane of ligand binding haems of the oxidase was determined by investigating the effect of the exogenous paramagnetic probe DyEDTA on the e.p.r. properties of the ferrous haems d-NO and b595-NO. These haems are located towards the inner aspect of the cytoplasmic membrane at around 8 and 12A° below the surface, respectively. Overall, the data supports a functional model for cytochrome bd with two oxygen binding sites, haems d and b595, forming the binuclear centre of the oxidase reaction. Possible mechanisms of this reaction are discussed.
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Pernestig, Anna-Karin. "The study of the Escherichia coli BarA-UvrY two-component system and its ability to sense the environment /". Stockholm, 2002. http://diss.kib.ki.se/2003/91-7349-474-7.
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Chow, I.-Ting. "Functional study of ClpB95 and ClpB80, the alternative translation products of the E. coli clpB transcript /". Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9842.
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Leal, Junior Luiz Carlos. "Tessitura sobre discursos acerca de resolução de problemas e seus pressupostos filosóficos em educação matemática : cosi è, se vi pare /". Rio Claro, 2018. http://hdl.handle.net/11449/157077.
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Orientador: Lourdes de la Rosa OnuchicBanca: Arthur Belford Powell
Banca: Rosana Giaretta Sguerra Miskulin
Banca: Silvanio de Andrade
Banca: Simone Moura Queiroz
Resumo: Práticas de Resolução de Problemas são problematizadas nesta pesquisa na forma de uma tessitura. Elas estão articuladas em torno de um estudo analítico acerca do tema Resolução de Problemas e de seus pressupostos filosóficos. Considerando-se a falta de explicitação e objetivação destes pressupostos teórico-filosóficos que amparam práticas em Resolução de Problemas, objetiva-se realizar um estudo analítico acerca dos discursos que permeiam, engendram, potencializam e põem em funcionamento práticas, teorias, teorizações e outros discursos sobre a Resolução de Problemas tanto no cenário nacional quanto internacional. Para tanto, procedemos a análise do discurso, pautada pela arqueogenealogia de Michel Foucault enquanto uma caixa de ferramentas, para compor uma análise com o corpus desta pesquisa, que consiste em entrevistas, questionários, artigos, livros, teses, dissertações e demais materiais acadêmicos. Uma questão diretriz a ser trabalhada nessa tessitura é: Como e quais pressupostos filosóficos operam, tessem ou põem em funcionamento discursos presentes nas pesquisas em Resolução de Problemas? Bem como seus desdobramentos sobre práticas discursivas relacionadas ao tema. Desse modo, observamos que há momentos, movimentos, práticas e discursos que possuem uma fundamentação teórica bastante consistente com os pressupostos filosóficos que lhes dão suporte. Por outro lado, há aqueles que não têm preocupações críveis com a teoria, residindo na práxis enquanto eixo estruturador de... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Problem Solving practices are problematized in this research in the form of a "tessiture" . They are articulated around an analytical study on the subject of Problem Solving and its philosophical tenants. Considering the lack of conceptual understanding of the theoretical - philosophical presuppositions that bear on practices in Problem Solving, we aim to carry out an analytical study of the discourses th at permeate, engender and potentiate elements as: practices, theories, theorizations and other discourses on Problem Solving both on the national and international scene, besides running them . In order to do so, we proceeded to Michel Foucault's discourse analysis based on archaeogenealogy, as a tool box, to compose an analysis with the corpus of this research, which consists of interviews, questionnaires, articles, books, theses, dissertations and other academic materials. A guiding question to be addressed in this " tessiture" is: How and which philosophical presuppositions work or running discourses present in the researches in Problem Solving? As well as its implications on discursive practices related to the theme. Thus, we observe that there are moments, movements, practices and discourses that have a theoretical foundation very consistent with the philosophical tenants that support them. On the other hand, there are those who do not have credible concerns with theory, residing in praxis as the structuring axis of their practices in Problem Solving. There are situat... (Complete abstract click electronic access below)
Doutor
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Mariano, Valeria. "A study of tetracycline resistant Escherichia coli in impala (Aepyceros melampus) and their water sources". Diss., Pretoria : [s.n.], 2008. http://upetd.up.ac.za/thesis/available/etd-02192009-140903/.
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劉淦光. "Study of Escherichia coli RNA degradosome". Thesis, 2000. http://ndltd.ncl.edu.tw/handle/17710397564225441872.
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楊奇凌. "Expression study of escherichia coli recO gene". Thesis, 1993. http://ndltd.ncl.edu.tw/handle/24684901128974668548.
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FANG, SHU-SHENG y 房樹生. "Study of natural transformation in escherichia coli". Thesis, 1993. http://ndltd.ncl.edu.tw/handle/87345770981270388128.
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Po-ChuenHsu y 許博淳. "Functional study of an Escherichia coli protease". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/23823351648468425605.
Texto completoResumen
碩士國立成功大學
分子醫學研究所
104
Escherichia coli are one of the most common gram-negative bacteria that cause bacteremia and urinary tract infections. Antibiotic treatment is the traditional way to manage the E. coli-caused infections. Due to the rapid emergence of antibiotic-resistant strains, developing novel strategies against such diseases becomes critical. The E. coli protease, Rep, is a potential target for developing the new antimicrobial strategies, because deletion of rep increased the sensitivity to multiple antibiotics, and decreased pathogenic E. coli’s ability to survive in the bloodstream. Also, the E. coli rep mutant exhibit a growth defect under the combined low osmotic and high temperature stresses. Characterizing the function of Rep would facilitate the development of alternative antibacterial strategies. In this study, we utilize E. coli proteome chip assay to screen for the potential Rep substrates. The E. coli proteome chip assay revealed that 100 E. coli proteins might be the substrate of Rep. Among these 100 possible substrates, 13 of them could be cleaved by the Rep protease in vitro. Further, one of them, ECK1083, was shown to contribute to the growth defect of the E. coli rep mutant under the combined osmotic and high temperature stresses, because the eck1083 deletion in the rep mutant partially rescued the growth defect. To assess whether ECK1083 accumulates in the rep mutant, we constructed the strains with eck1083-3xFlag at the chromosomal locus of eck1083 to allow the detection of the ECK1083 protein with the anti-Flag antibody. Since ECK1083 has been identified as an inner membrane protein, the membrane fraction from the wild-type and rep mutant strains were isolated under the combined osmotic and high temperature stresses condition. The level of ECK1083 in the membrane fraction was measured by western blot analysis. The level of ECK1083 in the rep mutant was significantly higher than that in the wild-type strain. Also, the mRNA level of eck1083 in the rep mutant was similar to that of the wild-type strain. These results suggested that the lack of Rep-mediated degradation cause the accumulation of ECK1083 in the E. coli rep mutant and that the accumulation may contribute the growth defect under the combined osmotic and high temperature stresses.
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Lee, Che-Hui y 李則輝. "Study on Magnetic Tunnel Junction with Spin-valve Structure NiFe/CoFe/AlO/CoFe/NiFe/FeMn". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/43025971596481317018.
Texto completoResumen
碩士國立臺灣大學
物理學研究所
91
Comparing to the pseudo spin valve magnetic tunnel junction (MTJ), the spin valve MTJ provides a better spin configuration for clearer and more definite antiparallel state. In this work, the FeMn-based spin valve MTJs (top spin valve & bottom spin valve) are prepared to investigate the magnetic properties and the tunnel magnetoresistance. We discuss several critical factors for fabricating high quality spin valve MTJ, for example: bias field, buffer layer, annealing effect, and etc. The structure and composition of MTJs are examined with cross-sectional images generated by high-resolution transmission electron microscopy, energy dispersive X-ray spectrometer, and electron energy loss spectrometer. The microscopic images prove that we already have high quality pseudo spin valve MTJs. The magnetic and electric properties of the spin valve MTJ are measured by magneto-optical Kerr effect and four-probe method, respectively. In the bottom spin valve experiment, the thickness of pinned layer affects the bias field directly, and buffer layer provides a texture, which is determined by x-ray diffraction, for NiFe/FeMn growth. For proper annealing temperature, the post annealing effect improves the interface condition and barrier quality, resulting in a higher tunnel magnetoresistance ratio. In the top spin valve experiment, we discuss the post annealing effect at different dwelling temperatures. A value of 42% was achieved for the tunnel magnetoresistance ratio in the top spin valve structure.