Iron restriction induces preferential down-regulation of H2-consuming over H2-evolving reactions during fermentative growth of Escherichia coli

<p>Abstract</p> <p>Background</p> <p><it>Escherichia coli </it>synthesizes three anaerobically inducible [NiFe]-hydrogenases (Hyd). All three enzymes have a [NiFe]-cofactor in the large subunit and each enzyme also has an iron-sulfur-containing small subunit that is required for electron transfer. In order to synthesize functionally active Hyd enzymes iron must be supplied to the maturation pathways for both the large and small subunits. The focus of this study was the analysis of the iron uptake systems required for synthesis of active Hyd-1, Hyd-2 and Hyd-3 during fermentative growth.</p> <p>Results</p> <p>A transposon-insertion mutant impaired in hydrogenase enzyme activity was isolated. The mutation was in the <it>feoB </it>gene encoding the ferrous iron transport system. The levels of both hydrogen-oxidizing enzymes Hyd-1 and Hyd-2 as determined by specific in-gel activity staining were reduced at least 10-fold in the mutant after anaerobic fermentative growth in minimal medium, while the hydrogen-evolving Hyd-3 activity was less severely affected. Supplementation of the growth medium with ferric iron, which is taken up by e.g. the siderophore enterobactin, resulted in phenotypic complementation of the <it>feoB </it>mutant. Growth in rich medium demonstrated that a mutant lacking both the ferrous iron transport system and enterobactin biosynthesis (<it>entC</it>) was devoid of Hyd-1 and Hyd-2 activity but retained some hydrogen-evolving Hyd-3 activity. Analysis of crude extracts derived from the <it>feoB entC </it>double null mutant revealed that the large subunits of the hydrogen-oxidizing enzymes Hyd-1 and Hyd-2 were absent. Analysis of <it>lacZ </it>fusions demonstrated, however, that expression of the <it>hya</it>, <it>hyb </it>and <it>hyc </it>operons was reduced only by maximally 50% in the mutants compared with the wild type.</p> <p>Conclusions</p> <p>Our findings demonstrate that the ferrous iron transport system is the principal route of iron uptake for anaerobic hydrogenase biosynthesis, with a contribution from the ferric-enterobactin system. Hydrogen-oxidizing enzyme function was abolished in a <it>feoB entC </it>double mutant and this appears to be due to post-translational effects. The retention of residual hydrogen-evolving activity, even in the <it>feoB entC </it>double null mutant suggests that sufficient iron can be scavenged to synthesize this key fermentative enzyme complex in preference to the hydrogen-uptake enzymes.</p

Quantum holonomies in photonic waveguide systems

The thesis at hand deals with the emergence of quantum holonomies in systems of coupled waveguides. Several proposals for their realisation in arrays of laser-written fused-silica waveguides are presented, including experimental results. I develop an operator-theoretic framework for the photon-number independent description of these optical networks. Finally, quantum holonomies will be embedded into schemes for measurement-based quantum computation, with the aim of approximating Jones polynomials.Die vorliegende Arbeit untersucht die Konzipierung von Quantenholonomien in Systemen gekoppelter Wellenleiter. Eine Vielzahl möglicher Realisierungen mittels lasergeschriebener Wellenleiter in Quarzglas wird präsentiert und zugehörige experimentelle Ergebnisse erläutert. Die Entwicklung einer operatortheoretischen Darstellung für die photonenzahlunabhängige Beschreibung dieser optischen Netzwerke wird vorgenommen. Abschließend werden Quantenholonomien für die messinduzierte Quantenberechnung von Jones-Polynomen verwendet

A COMPARISON OF LOWER BODY ANGLES BETWEEN FREE HIGH PULLS AND A FIXED HIGH PULL APPARATUS

The majority of strength and conditioning programs for athletes are based on the Olympic lifting exercises. Olympic lifts generate explosive power through the lower body (Armstrong, 1993). There appears to be a relationship between resistance training exercises and bar path kinematics (Souza, Schimada, & Koontz, 2002). The resistance training program at the university used in this study had a piece of equipment called the Cormax ® Smith Machine Plus. The Cormax® Smith Machine Plus utilizes a barbell that is set in tracks which does not allow any horizontal bar movement. It also has a piston system that allows the athlete to throw and release the barbell. The pistons support the barbell and allows it to slowly drop back to the starting postion. The researchers were interested if the technique using this piece of equipment would be similar to the technique that is used with free weight high pulls. Therefore, the purpose of this study was to examine the lower body joint kinematics between the two methods of completing a high pull

Particle-Number Threshold for Non-Abelian Geometric Phases

When a quantum state traverses a path, while being under the influence of a gauge potential, it acquires a geometric phase that is often more than just a scalar quantity. The variety of unitary transformations that can be realised by this form of parallel transport depends crucially on the number of particles involved in the evolution. Here, we introduce a particle-number threshold (PNT) that assesses a system's capabilities to perform purely geometric manipulations of quantum states. This threshold gives the minimal number of particles necessary to fully exploit a system's potential to generate non-Abelian geometric phases. Therefore, the PNT might be useful for evaluating the resource demands of a holonomic quantum computer. We benchmark our findings on bosonic systems relevant to linear and nonlinear quantum optics

Power properties if invariant tests for spatial autocorrelation in linear regression

This paper derives some exact power properties of tests for spatial autocorrelation in the context of a linear regression model. In particular, we characterize the circumstances in which the power vanishes as the autocorrelation increases, thus extending the work of Krämer (2005). More generally, the analysis in the paper sheds new light on how the power of tests for spatial autocorrelation is affected by the matrix of regressors and by the spatial structure. We mainly focus on the problem of residual spatial autocorrelation, in which case it is appropriate to restrict attention to the class of invariant tests, but we also consider the case when the autocorrelation is due to the presence of a spatially lagged dependent variable among the regressors. A numerical study aimed at assessing the practical relevance of the theoretical results is include

Correlation and reliability of the Zone-Quick Phenol Red Thread Tear Test to dry eye symptoms

Purpose: In the past, optometry has relied on such tests as the Schirmer Test to diagnose dry eye syndrome. New methods such as the Zone-Quick Phenol Red Thread Test (PRTT) have been developed to identify dry eye patients. This project is designed to test the correlation of the PRTT to dry eye symptoms as well as test/retest reliability. Methods: Of 120 randomly chosen young, pathology free optometry students, 54 test subjects (108 eyes) were placed into either a control group or a symptomatic group based upon their responses to a detailed dry eye questionnaire. Both eyes were tested according to PRTT protocol, resulting in a wet thread length measurement in mm. Measurements of less than 10 mm were considered a dry result, while lengths 20 nun or greater were considered normal. Results: A statistically significant difference (p=0.003) in mean wet thread length was found between the two groups. Based on mean wet thread lengths, all 27 subjects in the control group were classified as normal by the PRTT, while only 2 of 27 subjects in the symptomatic group were correctly classified as \u27dry. Intra-trial and inter-trial correlation testing was variable, ranging from r=0.19 to r=0.76. Conclusions: The results of this study suggest that the PRTT may be inadequate as a diagnostic test for dry eye syndrome in the normal population. Statistical analysis revealed poor repeatability between trials and inconsistent correlation between eyes. The gold standard for accurate diagnosis of dry eye syndrome remains a detailed questionnaire combined with extensive case history

Expanding the substrates for a bacterial hydrogenlyase reaction

Escherichia coli produces enzymes dedicated to hydrogen metabolism under anaerobic conditions. In particular, a formate hydrogenlyase (FHL) enzyme is responsible for the majority of hydrogen gas produced under fermentative conditions. FHL comprises a formate dehydrogenase (encoded by fdhF) linked directly to [NiFe]-hydrogenase-3 (Hyd-3), and formate is the only natural substrate known for proton reduction by this hydrogenase. In this work, the possibility of engineering an alternative electron donor for hydrogen production has been explored. Rational design and genetic engineering led to the construction of a fusion between Thermotoga maritima ferredoxin (Fd) and Hyd-3. The Fd-Hyd-3 fusion was found to evolve hydrogen when co-produced with T. maritima pyruvate :: ferredoxin oxidoreductase (PFOR), which links pyruvate oxidation to the reduction of ferredoxin. Analysis of the key organic acids produced during fermentation suggested that the PFOR/Fd-Hyd-3 fusion system successfully diverted pyruvate onto a new pathway towards hydrogen production

Exploring the directionality of <i>Escherichia coli </i>formate hydrogenlyase:a membrane-bound enzyme capable of fixing carbon dioxide to organic acid

During mixed‐acid fermentation Escherichia coli produces formate, which is initially excreted out the cell. Accumulation of formate, and dropping extracellular pH, leads to biosynthesis of the formate hydrogenlyase (FHL) complex. FHL consists of membrane and soluble domains anchored within the inner membrane. The soluble domain comprises a [NiFe] hydrogenase and a formate dehydrogenase that link formate oxidation directly to proton reduction with the release of CO (2) and H(2). Thus, the function of FHL is to oxidize excess formate at low pH. FHL subunits share identity with subunits of the respiratory Complex I. In particular, the FHL membrane domain contains subunits (HycC and HycD) that are homologs of NuoL/M/N and NuoH, respectively, which have been implicated in proton translocation. In this work, strain engineering and new assays demonstrate unequivocally the nonphysiological reverse activity of FHL in vivo and in vitro. Harnessing FHL to reduce CO (2) to formate is biotechnologically important. Moreover, assays for both possible FHL reactions provide opportunities to explore the bioenergetics using biochemical and genetic approaches. Comprehensive mutagenesis of hycC did not identify any single amino acid residues essential for FHL operation. However, the HycD E199, E201, and E203 residues were found to be critically important for FHL function