No description available.

No description available.

M.Sc. / The leaching of chalcopyrite (CuFeS2) concentrate in a ferrous iron promoted aerobic/anaerobic controlled low potential sulphate system was investigated by using the duel metabolic (aerobic ferrous iron oxidation and anaerobic ferric iron reduction) capabilities of Ferroplasma JTC 3. The experimental work conducted in this study was divided in three sections. The first section focussed on the identification and phylogenetic classification of Ferroplasma JTC 3, first identified amongst a mixed microbial population in a 55 oC pyrite concentrate-fed bioreactor operated at Johannesburg Technology Centre (BHP Billiton, JTC). Based on the 16S rDNA sequence and the phylogenetic analysis, Ferroplasma JTC 3 represents a new species member under the genus of Ferroplasma. The optimal growth temperature of Ferroplasma JTC 3 was determined at approximately 53 oC (moderate thermophile). The second section of this study focussed on the isolation, basic metabolism and growth conditions of Ferroplasma JTC 3, specifically directed towards the chalcopyrite leaching related experimental work. An important aspect of this study was to compare low potential chalcopyrite leaching (potential below 400 mV vs. Ag/AgCl) against high potential chalcopyrite bioleaching (potential above 600 mV vs. Ag/AgCl) in terms of the rate of copper extraction. Microbial growth and the rate of ferrous iron oxidation are essential in order to maintain a high potential during an extended leach period, which was typically the case in the high potential chalcopyrite leaching experiments performed during this study. Ferroplasma JTC 3 required yeast extract as sole carbon source (chemo-heterotrophic) for growth via aerobic ferrous iron oxidation. Taking into account no carbon dioxide enrichment via aeration, chemo-autotrophic growth by means of ferrous iron oxidation was poor with carbon dioxide as sole carbon source. The anaerobic metabolism of Ferroplasma JTC 3 was utilized in assisting with solution potential control during the low potential chalcopyrite leaching work. The anaerobic metabolism enabled the reduction of ferric iron (decrease redox potential) in the presence of elemental sulphur and yeast extract. Elemental sulphur was shown to be a requirement for Ferroplasma JTC 3 assisted ferric iron reduction, which was not influenced by different ferrous/ferric iron based redox potentials. The third section covers the main focus of this study, which was the low potential leaching of chalcopyrite in combination with the metabolic capabilities of Ferroplasma JTC 3. The major challenge of low potential chalcopyrite leaching in an acidic environment is maintaining the solution potential below the critical upper limit (400 mV vs. Ag/AgCl) of the low potential window for prolonged periods of time. The reason is the slow chemical oxidation of ferrous iron in the presence of oxygen, which increases the leach solution potential above the critical upper limit before complete copper dissolution is obtained. The aim of this study was to maintain a low solution potential environment in a bioreactor via a programmable electronic gas control system, capable of creating an aerobic environment until the solution potential would reach the upper low potential limit (400 mV vs. Ag/AgCl) due to ferrous iron oxidation (chemically or via Ferroplasma JTC 3) and then switch to an anaerobic environment. During the anaerobic environment, the aim was to decrease the solution potential to a lower potential set point via chalcopyrite oxidation by ferric iron (ferric iron reduction) and by employing the ferric iron reduction metabolism of Ferroplasma JTC 3. With the particular aerobic/anaerobic solution potential control system, in conjunction with the metabolic capabilities of Ferroplasma JTC 3, the solution potential could be controlled within the critical low potential region, but no chalcopyrite leaching could be obtained during the anaerobic phase. The lack of chalcopyrite leaching during the anaerobic phase was due to inability of ferric iron to act as oxidant of chalcopyrite after the mineral was pre-leached in the preceding aerobic phase. The “oxidative acid leach” mechanism was identified as the dominant leach reaction that prevailed during the aerobic low potential stage in each of the aerobic/anaerobic control experiments conducted, in which oxygen acts as oxidant of chalcopyrite (electron acceptor) in the presence of protons (H+) (acidic environment), instead of ferric iron in an acid environment. The “boundary potential”, which is the maximum solution where no electron flow occurred to the ferrous/ferric couple from “pre-leached” chalcopyrite, was identified in the region of 450 mV (Ag/AgCl). Under the experimental conditions within this study, the leaching of chalcopyrite within the aerobic phase of the aerobic/anaerobic control experiments was superior to the Ferroplasma JTC 3 mediated high potential leaching, but complete copper dissolution could not be obtained with the combined aerobic and anaerobic system. Ferric iron precipitation as a function of pH was proposed as a tool for solution potential control, instead of controlling the potential by limiting oxygen to the leach system. In controlling the solution potential via pH, almost complete copper dissolution from chalcopyrite was obtained, while maintaining the solution potential below the critical upper limit of the low potential region.

The naturally occurring monoterpene 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octane 1, commonly named 1,8-cineole and the major component in the leaf oil of many eucalypts, exhibits bioactivity, being potentially antimicrobial and pesticidal. A range of derivatives of 1,8-cineole and its naturally occurring isomeric analogue 1,4-cineole 2, 1-isopropyl-4-methyl-7-oxabicyclo[2.2.1]heptane, were synthesised. High-cineole eucalyptus oil, 1,8-cineole and the 1,8- and 1,4-cineole derivatives were shown to have a dose dependent pre-emergence and post-emergence herbicidal activity against radish (Raphanus sativus var. Long Scarlet), and annual ryegrass (Lolium rigidum) in laboratory bioassays. A postulated increase in activity of the ester derivatives due to metabolic cleavage into their bioactive hydroxy-cineole and carboxylic acid portions after uptake by the plant was not observed. The role of mallee eucalypts in the rehabilitation of degraded farmland in the Western Australian wheat belt, uses of eucalyptus oil and the bioactivity of essential oils and naturally occurring terpenes, with particular emphasis on eucalyptus oil and 1,8-cineole, were reviewed. The review encompasses allelopathic and herbicidal activity, insecticidal, acaricidal and antimicrobial activity. 1,8-Cineole compounds functionalised at position 3 of the cyclohexane ring and the 1,4-cineole derivatives were chemically synthesised whilst 2-endo-hydroxy-1,8-cineole was obtained as the primary metabolite of a novel bacterium grown on 1,8-cineole as sole carbon source. The bacteria were isolated by inoculating liquid growth medium containing 1,8-cineole as carbon source with aliquots of deionised water in which eucalyptus leaves had been stirred. Sequencing of its 16S rRNA gene identified the bacteria as belonging to the order Sphingomonadales, family Sphingomonadaceae and genus Sphingomonas. Growth curves for the bacterium are described and a metabolic pathway for the microbial degradation of 1,8-cineole is confirmed. Bacteria were cultured on a 20 L scale to provide sufficient 2-endo-hydroxy-1,8-cineole for the herbicidal bioassays.

Thesis (Ph. D.)--Washington State University, December 2009. / Title from PDF title page (viewed on Dec. 11, 2009). "School of Molecular Biosciences." Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 203-215). Available also in a digital version from Dissertation Abstracts.

Contaminated surficial sediments represent a potential point of entry into the food web for environmental pollutants that are toxic to fish, wildlife, and humans. One approach for managing polluted sediments is in situ capping, the placement of clean fill material, such as sand, atop the polluted sediments. A cap stabilizes the underlying sediment and physically separates pollutants from benthic organisms that inhabit the sediment/water interface. Additionally, a sediment cap can be amended with sorbents to sequester hydrophobic organic chemicals. While the physical processes affecting contaminant transport in sediment caps are readily modeled, fate and transport processes mediated by sediment bacteria are location-specific and thus highly uncertain. Laboratory bench-scale tests were employed to aid in the design of a sediment cap in Onondaga Lake. Recognizing the importance of bacterial activity beneath the benthic zone for affecting the risks of contaminant exposure, anaerobic processes were emphasized. A combination of batch and column tests were used to determine whether (1) bacteria in sediments were capable of biotransforming methylated and chlorinated benzenes, (2) the ability to biotransform the contaminants of interest would be translated from the sediments to a sand cap, (3) the rate of biogenic gas production in sediments would threaten the integrity of a sand cap, and (4) the contribution of gas-phase contaminant transport to the overall transport of contaminants from the sediments was significant. The apparent anaerobic biotransformation of toluene in a sand cap was supported by detection of a genetic biomarker for anaerobic toluene degradation, the development of substantial biomass in the sand column, apparent anaerobic biotransformation of toluene in sediment slurries, and the concomitant reduction of iron in the sand column. The dissimilarity in bacterial community composition between sediment and sand cap samples suggests that contaminant biotransformation capability cannot be predicted from community analysis. For sediments that failed to demonstrate biotransformation potential, amending a sand column with organophilic clay proved effective at retarding transport of the contaminants of interest. This work advances methods for characterizing bacterial processes in sediments and demonstrates the potential for anaerobic biotransformation of organic contaminants in sand caps. / text

The Deilmann Tailings Management Facility (DTMF) at Key Lake in northern Saskatchewan, Canada, is an active deposition site for uranium tailings and it has been in operation since 1996. In terms of geochemical stability of the tailings, a ferrihydrite secondary phase is utilized for the sequestration of contaminants, such as As, Ni, Mo, and Se, under alkaline and highly oxic conditions. Arsenic is highly abundant in the DTMF tailings and the principal environmental concern is the possibility for leaching of ferrihydrite-attached As into the surrounding environment. Microorganisms can proliferate in a broad range of habitats and their activities are key factors in determining fate and transport of contaminants in various environments. This thesis attempts to obtain insights into the biogeochemical processes that may occur during the early phase of the DTMF’s history that could potentially become significant over extended periods of time that run from 100’s to 1000’s of years. Hence, a primary focus was to characterize microbial diversity and extrapolate their potential functional roles as well as their potential to chemically alter the Eh and ferrihydrite, which are the primary controlling conditions within the DTMF tailings and in the mineral secondary phase, respectively. To achieve these goals, two molecular techniques (clone library construction and Ion Torrent sequencing), a range of conventional culture-based techniques, metabolic assays addressing metabolic transformation and resistance to metals/metalloids, microscopic technique (Confocal Laser Scanning Microscope), spectroscopic analyses (Scanning Transmission X-ray Microscope) and bench-scale microcosm assays were carried out. Culture-dependent and -independent methods revealed that the most prevalent microbial groups in the water column, tailings mass and at the tailings-water interface affiliated into phyla (e.g., Proteobacteria, Actinobacteria, Firmicutes and Bacteriodetes) that have previously been detected at uranium-, heavy metal- and complex hydrocarbon-contaminated sites. Phylotypes closely related to well-characterized sulfate-, thiosulfate- and iron-reducing bacteria (e.g., Desulfosporosinus, Dethiobacter, Geoalkalibacter, Ralstonia, Georgfuchsia) were also detected at low frequency, with the exception of the tailings-water interface where sequences closely related to Desulfosporosinus were abundant. The readily culturable heterotrophs (e.g., Pseudomonas, Arthrobacter, Massilia, Hydrogenophaga, Polaromonas, Bacillus) retrieved from the tailings exhibited reducing/oxidizing capabilities as well as high tolerance to metal/metalloids. Bench scale microcosm assays showed that heterotrophs native to the DTMF site could not only reduce ferrihydrite but could also create highly reducing (< -300 mV) conditions within the tailings amenable to strict anaerobic bacteria such as Desulfosporosinus. STXM image analyses confirmed the presence of reduced iron in close proximity to bacterial cells in biofilm grown in situ and in microcosm tailings, strongly suggesting that ferrihydrite served as electron acceptor during microbial processes. Reduced iron detected in situ also indicated that microscale iron reduction could occur even though macroscale DTMF chemistry remained oxidizing. Overall, the nature of microbial community present in the DMTF system strongly indicated that complex hydrocarbons (e.g., kerosene) discharged into the tailings during processing could potentially support microbial processes that involve Fe and S cycling and that this process could become significant over extended period of times, contributing to arsenic escape into the environment.

No description available.

This thesis describes phytochemical studies on Buxus macowanii, a medicinal plant collected from South Africa and the fungal transformation of glycyrrhetinic acid (71), a triterpenoid found in Glycyrrhiza plants. The crude methanolic extract of B. macowanii was active in the acetylcholinesterase inhibition assay (IC50 = 30 μg/mL). Chemical investigation of its alkaline dichloromethane extract afforded five novel triterpenoidal alkaloids, 31-hydroxybuxatrienone (56), macowanioxazine (57), 16α-hydroxyma- cowanitriene (58), macowanitriene (59), and macowamine (60), along with two known Buxus bases, Nb-demethylpapillotrienine (61) and moenjodaramine (62). Compounds 56, 57, and 61 exhibited different level of AChE inhibitory activities with compound 56 being significantly active (IC50 = 8.0 μM). Glycyrrhetinic acid (71) was incubated with Curvularia lunata (ATCC 12017) for ten days to afford one metabolite which was characterized by NMR spectral data as known biotransformed product, 3-oxo-glycyrrhetinic acid (85). This metabolite was previously obtained through biotransformation of 71 by using other fungi.