4 results
Bioleaching of ilmenite and basalt in the presence of iron-oxidizing and iron-scavenging bacteria
- Jesica U. Navarrete, Ian J. Cappelle, Kimberlin Schnittker, David M. Borrok
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- Journal:
- International Journal of Astrobiology / Volume 12 / Issue 2 / April 2013
- Published online by Cambridge University Press:
- 11 December 2012, pp. 123-134
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Bioleaching has been suggested as an alternative to traditional mining techniques in extraterrestrial environments because it does not require extensive infrastructure and bulky hardware. In situ bioleaching of silicate minerals, such as those found on the moon or Mars, has been proposed as a feasible alternative to traditional extraction techniques that require either extreme heat and/or substantial chemical treatment. In this study, we investigated the biotic and abiotic leaching of basaltic rocks (analogues to those found on the moon and Mars) and the mineral ilmenite (FeTiO3) in aqueous environments under acidic (pH ∼ 2.5) and circumneutral pH conditions. The biological leaching experiments were conducted using Acidithiobacillus ferrooxidans, an iron (Fe)-oxidizing bacteria, and Pseudomonas mendocina, an Fe-scavenging bacteria. We found that both strains were able to grow using the Fe(II) derived from the tested basaltic rocks and ilmenite. Although silica leaching rates were the same or slightly less in the bacterial systems with A. ferrooxidans than in the abiotic control systems, the extent of Fe, Al and Ti released (and re-precipitated in new solid phases) was actually greater in the biotic systems. This is likely because the Fe(II) leached from the basalt was immediately oxidized by A. ferrooxidans, and precipitated into Fe(III) phases which causes a change in the equilibrium of the system, i.e. Le Chatelier's principle. Iron(II) in the abiotic experiment was allowed to build up in solution which led to a decrease in its overall release rate. For example, the percentage of Fe, Al and Ti leached (dissolved + reactive mineral precipitates) from the Mars simulant in the A. ferrooxidans experimental system was 34, 41 and 13% of the total Fe, Al and Ti in the basalt, respectively, while the abiotic experimental system released totals of only 11, 25 and 2%. There was, however, no measurable difference in the amounts of Fe and Ti released from ilmenite in the experiments with A. ferrooxidans versus the abiotic controls. P. mendocina scavenged some Fe from the rock/mineral substrates, but the overall amount of leaching was small (<2% of total Fe in rocks) when compared with the acidophilic systems. Although the mineralogy of the tested basaltic rocks was roughly similar, the surface areas of the lunar and Mars simulants varied greatly and thus were possible factors in the overall amount of metals released. Overall, our results indicate that the presence of bacteria does not increase the overall silica leaching rates of basaltic rocks; however, the presence of A. ferrooxidans does lead to enhanced release of Fe, Al and Ti and subsequent sequestration of Fe (and other metals) in Fe(III)-precipitates.
185 - Herpes Simplex Viruses 1 and 2
- from Part XXIII - Specific Organisms – Viruses
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- By David W. Kimberlin, University of Alabama at Birmingham School of Medicine, Richard J. Whitley, University of Alabama at Birmingham
- Edited by David Schlossberg
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- Book:
- Clinical Infectious Disease
- Published online:
- 05 March 2013
- Print publication:
- 12 May 2008, pp 1275-1280
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Summary
THE VIRUS
Herpesviruses are generally defined as large enveloped virions with an icosapentahedral nucleocapsid consisting invariably of 162 capsomeres arranged around a double-stranded DNA core. The two antigenically distinct types of herpes simplex virus (HSV) are HSV-1 and HSV-2. Considerable homology exists between the HSV-1 and HSV-2 genomes, with most of the polypeptides specified by one viral type being antigenically related to polypeptides of the other viral type. Although this results in considerable cross-reactivity between the HSV-1 and HSV-2 glycoproteins (g), unique antigenic determinants allow for differentiation between these two viruses (eg, gG-1 and gG-2). Surrounding the viral genome and nucleocapsid is a tightly adherent membrane known as the tegument. A lipid envelope containing the viral glycoproteins loosely surrounds the tegument.
PATHOLOGY AND PATHOGENESIS
Cutaneous HSV infection causes ballooning of infected epithelial cells, with nuclear degeneration, loss of intact cellular membranes, and the formation of multinucleated giant cells. Ultimately, cells lyse and release clear fluid containing large quantities of virus, with subsequent accumulation of cellular debris and inflammatory cells between the epidermal and dermal layers. Multinucleated giant cells are usually present at the base of the vesicle. An intense inflammatory response extends from the base of the vesicle into the dermis, producing the erythema that classically surrounds a cluster of HSV vesicles. As the lesions heal, vesicular fluid becomes purulent as more inflammatory cells are recruited to the site of infection. Scab formation then follows.
64 - Antiviral therapy of HSV-1 and -2
- from Part VI - Antiviral therapy
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- By David W. Kimberlin, Department of Pediatrics, University of Alabama at Birmingham, AL, USA, Richard J. Whitley, Department of Pediatrics, University of Alabama at Birmingham, AL, USA
- Edited by Ann Arvin, Stanford University, California, Gabriella Campadelli-Fiume, Università degli Studi, Bologna, Italy, Edward Mocarski, Emory University, Atlanta, Patrick S. Moore, University of Pittsburgh, Bernard Roizman, University of Chicago, Richard Whitley, University of Alabama, Birmingham, Koichi Yamanishi, University of Osaka, Japan
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- Book:
- Human Herpesviruses
- Published online:
- 24 December 2009
- Print publication:
- 16 August 2007, pp 1153-1174
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Summary
Introduction
The discovery of effective antiviral agents has been facilitated by advances in the fields of molecular biology and virology. In the pre-antiviral era, the widely held belief was that any therapeutically meaningful interference with viral replication would destroy the host cell upon which viral replication was dependent. A growing understanding of host cell–virus interactions and viral replication, however, has led to the development of safe and effective antivirals. These agents act by impeding entry of viruses into host cells; interfering with viral assembly, release, or de-aggregation; inhibiting transcription or replication of the viral genome; or interrupting viral protein synthesis.
Antiviral agents can be used to treat disease (a therapeutic strategy), to prevent infection (a prophylactic strategy), or to prevent disease (a preemptive strategy). Prophylaxis refers to the administration of an agent to patients at risk of contracting infection (e.g., acyclovir given to HSV-seropositive renal transplant recipients). Pre-emptive treatment refers to the administration of a drug after there is evidence of infection, but before there is evidence of disease (e.g., ganciclovir given to bone marrow transplant recipients with positive CMV culture, but no symptoms of infection).
The effectiveness of antiviral therapy sometimes is limited by the development of antiviral resistance. Antiviral drug resistance has increased in parallel with the expanded use of, and indications for, antiviral therapy. Resistance most commonly occurs in patients with chronic and/or progressive infections who have been exposed to prolonged or repeated courses of therapy.
9 - State-controlled procurement and the obsidian workshops of Teotihuacán, Mexico
- Jonathon E. Ericson, Barbara A. Purdy
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- Book:
- Prehistoric Quarries and Lithic Production
- Published online:
- 04 August 2010
- Print publication:
- 26 July 1984, pp 97-106
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Summary
The inhabitants of Teotihuacán, a major pre-Hispanic urban center, imported huge quantities of obsidian from the Sierra de las Navajas region 50 km to the northeast. Within the city this material was distributed in a highly equitable fashion among the numerous workshops. Trace-element analysis reveals that each workshop area included material from a number of distinct loci of exploitation in the source region. These data indicate that the obsidian was exploited and transported to Teotihuacán through a procurement network organized and maintained by the Teotihuacán state. With the collapse of the state about a.d. 750, the flow of Navajas material into Teotihuacán largely ceased.
Introduction
Teotihuacán, one of the two largest urban centers in the pre-Hispanic New World, lies a short distance northeast of Mexico City. At its height, about a.d. 200–600, it had a population of 150,000 and controlled much of the central Mexico region (Bernal 1966; Millon 1973). At that time it must have been importing enormous quantities of raw materials, both to supply its own huge population and to fuel the widespread trade network that it dominated. This raises a number of questions about the mechanisms involved in the exploitation and transportation of these resources. It is important to determine the role played by the Teotihuacán state in procurement, the scope and stability of the networks that were established, and the effects of these networks on the political and economic structures of both Teotihuacán and the source regions.