An Optimal Method of Iron Starvation of the Obligate Intracellular Pathogen, Chlamydia Trachomatis

Iron is an essential cofactor in a number of critical biochemical reactions, and as such, its acquisition, storage, and metabolism is highly regulated in most organisms. The obligate intracellular bacterium, Chlamydia trachomatis experiences a developmental arrest when iron within the host is depleted. The nature of the iron starvation response in Chlamydia is relatively uncharacterized because of the likely inefficient method of iron depletion, which currently relies on the compound deferoxamine mesylate (DFO). Inefficient induction of the iron starvation response precludes the identification of iron-regulated genes. This report evaluated DFO with another iron chelator, 2,2′-bipyridyl (Bpdl) and presented a systematic comparison of the two across a range of criteria. We demonstrate that the membrane permeable Bpdl was superior to DFO in the inhibition of chlamydia development, the induction of aberrant morphology, and the induction of an iron starvation transcriptional response in both host and bacteria. Furthermore, iron starvation using Bpdl identified the periplasmic iron-binding protein-encoding ytgA gene as iron-responsive. Overall, the data present a compelling argument for the use of Bpdl, rather than DFO, in future iron starvation studies of chlamydia and other intracellular bacteria

Grain Growth and mechanical processes in two-phased synthetic marbles and natural fault gouge

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.Microfiche copy available in Archives and Science.Vita.Includes bibliographies.by David LeClair Olgaard.Ph.D

Epigenetic Methylation of Parathyroid CaR and VDR Promoters in Experimental Secondary Hyperparathyroidism

Secondary hyperparathyroidism (s-HPT) in uremia is characterized by decreased expression in the parathyroids of calcium sensing (CaR) and vitamin D receptors (VDR). Parathyroid hormone (PTH) is normalized despite low levels of CaR and VDR after experimental reversal of uremia. The expression of CaR in parathyroid cultures decreases rapidly. Methylation of promoter regions is often detected during epigenetic downregulation of gene expression. Therefore, using an experimental rat model, we examined changes in methylation levels of parathyroid CaR and VDR promoters in vivo and in vitro. Methods. Uremia was induced by 5/6 nephrectomy. Melting temperature profiling of CaR and VDR PCR products after bisulfite treatment of genomic DNA from rat parathyroids was performed. Real-time PCR measured expression of PTH, CaR, VDR, and klotho genes in vitro. Results. Parathyroids from uremic rats had similar low levels of methylation in vivo and in vitro. In culture, a significant downregulation of CaR, VDR, and klotho within two hours of incubation was observed, while housekeeping genes remained stable for 24 hours. Conclusion. In uremic s-HPT and in vitro, no overall changes in methylation levels in the promoter regions of parathyroid CaR and VDR genes were found. Thus, epigenetic methylation of these promoters does not explain decreased parathyroid expression of CaR and VDR genes in uremic s-HPT

Exogenous BMP7 in aortae of rats with chronic uremia ameliorates expression of profibrotic genes, but does not reverse established vascular calcification

<div><p>Hyperphosphatemia and vascular calcification are frequent complications of chronic renal failure and bone morphogenetic protein 7 (BMP7) has been shown to protect against development of vascular calcification in uremia. The present investigation examined the potential reversibility of established uremic vascular calcification by treatment of uremic rats with BMP7. A control model of isogenic transplantation of a calcified aorta from uremic rats into healthy littermates examined whether normalization of the uremic environment reversed vascular calcification. Uremia and vascular calcification were induced in rats by 5/6 nephrectomy, high phosphate diet and alfacalcidol treatment. After 14 weeks severe vascular calcification was present and rats were allocated to BMP7, vehicle or aorta transplantation. BMP7 treatment caused a significant decrease of plasma phosphate to 1.56 ± 0.17 mmol/L vs 2.06 ± 0.34 mmol/L in the vehicle group even in the setting of uremia and high phosphate diet. Uremia and alfacalcidol resulted in an increase in aortic expression of genes related to fibrosis, osteogenic transformation and extracellular matrix calcification, and the BMP7 treatment resulted in a decrease in the expression of profibrotic genes. The total Ca-content of the aorta was however unchanged both in the abdominal aorta: 1.9 ± 0.6 μg/mg tissue in the vehicle group vs 2.2 ± 0.6 μg/mg tissue in the BMP7 group and in the thoracic aorta: 71 ± 27 μg/mg tissue in the vehicle group vs 54 ± 18 μg/mg tissue in the BMP7 group. Likewise, normalization of the uremic environment by aorta transplantation had no effect on the Ca-content of the calcified aorta: 16.3 ± 0.6 μg/mg tissue pre-transplantation vs 15.9 ± 2.3 μg/mg tissue post-transplantation. Aortic expression of genes directly linked to extracellular matrix calcification was not affected by BMP7 treatment, which hypothetically might explain persistent high Ca-content in established vascular calcification. The present results highlight the importance of preventing the development of vascular calcification in chronic kidney disease. Once established, vascular calcification persists even in the setting when hyperphosphatemia or the uremic milieu is abolished.</p></div

Effect of diagenesis on compaction of reservoir rocks

Predicting sediment porosity-depth trends and ultimately the quality of reservoir rocks requires an understanding of mechanical and chemical compaction mechanisms during diagenesis. In many siliciclastic sediments porosity versus depth profiles can be predicted from the sediment’s stress history. In carbonates such predictions are more difficult because chemical diagenesis is prevalent even within a few meters of the seafloor. We used a systematic laboratory approach to investigate the influence of early diagenesis in a meteoric environment on compaction of oolitic carbonates. Aggregates were synthesized in an autoclave from loosely packed natural aragonite ooids and fresh water, to mimic phreatic conditions. Time and temperature were used to control the degree of chemical diagenesis. Constant stress-rate, uniaxial strain compaction tests were performed on the aggregates to track mechanical properties as a function of chemical alteration. Samples were characterized before and after compaction with electron and optical microscopy, X-ray tomography, and X-ray diffraction. The aragonite ooids dissolved preferentially inwards from their rims, and blocky calcite precipitated in the original inter-ooid pore space with little change in porosity. This progression results in an inverted structure with moldic pores inside a foam-like structure of calcite. With deformation, all samples exhibited elastic to plastic compaction typical of granular aggregates. With increasing alteration, the elastic moduli appear to increase, the transition to plastic behavior occurs at progressively higher stresses, and the elastic-plastic transition becomes more abrupt. At high stresses the plastic behavior was similar for all samples. X-ray tomography with micron-scale resolution tracks grain displacement and void and cement compaction. These experiments and results help us understand the complexities of chemical-mechanical interactions during diagenesis and improve our ability to predict porosity changes with depth for basin modeling, reservoir quality prediction and reservoir management

A geophysical study of Mesquite Valley: Nevada-California border

This paper reports the results of a geophysical investigation of a sedimentary basin, Mesquite Valley, and its surrounding area in the Basin and Range province of the western United States. Mesquite Valley is located about 40 km south-southwest of Las Vegas, Nevada, and straddles the border between Nevada and California (Figure 1). It is surrounded on three sides by mountains in which Paleozoic sedimentary rocks and Precambrian granites and gneisses crop out (Figure 1) [Burchfiel et al., 1974; Durchfiel and Davis, 1971; Hewett, 1956]. Unlike most basins in the Basin and Range province, however, there are no clearly active, range-bounding normal faults, and, in general, the surrounding topography is more subdued than in the regions farther west or north