Role of Pseudomonas aeruginosa PA4157in Quorum Sensing and Iron Transport Regulation

Pseudomonas aeruginosa, a Gram-negative opportunistic pathogen, is a pnmary contributing factor responsible for the morbidity and mortality in patients with cystic fibrosis. One of the trademarks of P. aeruginosa is its ability to resist antibiotics. P. aeruginosa does so in part through the LysR-type transcription factor, AmpR. To identify additional members of the AmpR regulon, a new algorithm called iterative enhancement of motifs was used to identify putative AmpR binding sites upstream of open reading frames in the P. aeruginosa genome. The surprising primary hit of this analysis was the promoter of an uncharacterized open reading frame, P A 415 7. P A 415 7 is located upstream ofthefep operon, which is known to be involved in iron acquisition. PA4157 shares high homology to the IclR family of transcriptional regulators which are known to regulate quorum sensing (QS), an elaborate cell-cell communication signaling system that uses quoromones. We postulated two hypotheses: 1) AmpR regulation of QS genes is mediated by PA4157, and 2) PA4157 may be involved in iron acquisition. To address the role of P A 415 7 we generated an in-frame chromosomal deletion of P A 415 7 in P. aeruginosa PA01 (PA0 PA4157). We compared PA0 PA4157 with its parent strain P A0 1 for its ability to produce quoromones using Chromobacterium violaceum as an indicator strain and LasA proteases using Staphylococcus aureus. We also tested its role in virulence using a Caenorhabditis elegans killing assay. Growth in iron-deficient media was also examined to determine if P A4157 has a potential role in iron uptake regulation. Our preliminary results suggest that P A 415 7 is not involved in quorum sensing regulation but does seem to exert a negative regulatory effect on iron uptake in P. aeruginosa P A0 1.

The international impact of productivity shocks

Even though many studies have confirmed the Feldstein-Horioka (1980) finding that savings and investment rates are highly correlated, there is no consensus on the major reason for this correlation. The purpose of this dissertation is to develop theoretical models and calibrate and simulate these to compare their implications to explain the observed time-series comovement between savings and investment in an attempt to show that this high correlation may stem from technological shocks.^ The dissertation is comprised of three studies. The first two studies construct overlapping-generations, two-economy models of saving and investment under conditions of perfect international capital mobility. The second study differs from the first by endogenizing the labor supply. Employing simulations, the models are used to generate time-series for savings and investment. These are then compared with the actual data for specific economies. The models show that productivity shocks produce a high correlation between savings and investment. Further, while the model with exogenous labor supply displays monotonic adjustment, the economy with endogenous labor supply adjusts cyclically.^ The third model, on the other hand, constructs a general equilibrium model for a small open economy. The study is based on two important elements: adjustment costs in investment and endogenous, recursive time preferences. Again, the simulation results show that the model generates, at least in a significant part of the adjustment path, a positive correlation between domestic savings and investment in response to a supply shock. ^

Essays on political economy

The first chapter analizes conditional assistance programs. They generate conflicting relationships between international financial institutions (IFIs) and member countries. The experience of IFIs with conditionality in the 1990s led them to allow countries more latitude in the design of their reform programs. A reformist government does not need conditionality and it is useless if it does not want to reform. A government that faces opposition may use conditionality and the help of pro-reform lobbies as a lever to counteract anti-reform groups and succeed in implementing reforms.^ The second chapter analizes economies saddled with taxes and regulations. I consider an economy in which many taxes, subsidies, and other distortionary restrictions are in place simultaneously. If I start from an inefficient laissez-faire equilibrium because of some domestic distortion, a small trade tax or subsidy can yield a first-order welfare improvement, even if the instrument itself creates distortions of its own. This may result in "welfare paradoxes". The purpose of the chapter is to quantify the welfare effects of changes in tax rates in a small open economy. I conduct the simulation in the context of an intertemporal utility maximization framework. I apply numerical methods to the model developed by Karayalcin. I introduce changes in the tax rates and quantify both the impact on welfare, consumption and foreign assets, and the path to the new steady-state values.^ The third chapter studies the role of stock markets and adjustment costs in the international transmission of supply shocks. The analysis of the transmission of a positive supply shock that originates in one of the countries shows that on impact the shock leads to an inmediate stock market boom enjoying the technological advance, while the other country suffers from depress stock market prices as demand for its equity declines. A period of adjustment begins culminating in a steady state capital and output level that is identical to the one before the shock. The the capital stock of one country undergoes a non-monotonic adjustment. The model is tested with plausible values of the variables and the numeric results confirm the predictions of the theory.^

Essays On Political Economy

The first chapter analizes conditional assistance programs. They generate conflicting relationships between international financial institutions (IFIs) and member countries. The experience of IFIs with conditionality in the 1990s led them to allow countries more latitude in the design of their reform programs. A reformist government does not need conditionality and it is useless if it does not want to reform. A government that faces opposition may use conditionality and the help of pro-reform lobbies as a lever to counteract anti-reform groups and succeed in implementing reforms. The second chapter analizes economies saddled with taxes and regulations. I consider an economy in which many taxes, subsidies, and other distortionary restrictions are in place simultaneously. If I start from an inefficient laissez-faire equilibrium because of some domestic distortion, a small trade tax or subsidy can yield a first-order welfare improvement, even if the instrument itself creates distortions of its own. This may result in "welfare paradoxes". The purpose of the chapter is to quantify the welfare effects of changes in tax rates in a small open economy. I conduct the simulation in the context of an intertemporal utility maximization framework. I apply numerical methods to the model developed by Karayalcin. I introduce changes in the tax rates and quantify both the impact on welfare, consumption and foreign assets, and the path to the new steady-state values. The third chapter studies the role of stock markets and adjustment costs in the international transmission of supply shocks. The analysis of the transmission of a positive supply shock that originates in one of the countries shows that on impact the shock leads to an inmediate stock market boom enjoying the technological advance, while the other country suffers from depress stock market prices as demand for its equity declines. A period of adjustment begins culminating in a steady state capital and output level that is identical to the one before the shock. The the capital stock of one country undergoes a non-monotonic adjustment. The model is tested with plausible values of the variables and the numeric results confirm the predictions of the theory.

Pairing Repeated Reading and Systematic Error Correction: Impact on Fluency of 18 Year Old Students on a Small Caribbean Island

This study investigates the impact of a combined treatment of Systematic Error Correction and Repeated Reading on reading rate and errors for 18 year olds with undiagnosed reading difficulties on a Caribbean Island. In addition to direct daily measures of reading accuracy, the Reading Self Perception Scale was administered to determine whether the intervention was associated with changes in the way the student perceives himself as a reader.