Texte remanié de: thèse--Sc. phys.--Paris, 1968. / Extrait du "Journal de chimie physique" T. 65, 1968, n° 6, pp. 1129-1140 . Conservé sous la cote : [4° V. 25892 (134)].

Bacteria have adapted to CAMP insult in many ways, this study has focused on two resistance mechanism for CAMPs, firstly the putatative potassium proton antiporter RosB has been shown not to efflux potassium with treatment of polymyxin B. The mechanism of resistance of RosB in Yersinia enterococcus was proposed to be a lowering of internal pH from a potassium efflux and a proton influx. The RosB homologue from Vibrio paraheamolyticus is able to efflux potassium with electrophile treatment, but unlike the potassium proton antiporter KefKC this potassium transport is not associated with CAMP resistance. The lack of resistance is likely to be due to an absence of intracellular pH regulation seen with the Vibrio RosB. The RosB homologue from E. coli YbaL has been shown to increase resistance to the electrophile NEM in high potassium media, but YbaL does not transport potassium when NEM is present. This suggests that YbaL is transporting another ion. The mechanism of ion transport for RosB is based on the sodium antiporter NhaA and NapA, this is due to similarities in the ion selection motif. There are differences between the Vibrio and Yersina homologue which would suggest that the Yersinia homologue is not transporting potassium. This second CAMP resistance mechanism studied was the ABC transporter Sap, with the focus of work done on the periplasmic substrate binding protein SapA. SapA binds the peptide within the periplasm and delivers it to the membrane domain for uptake in to the cell. It was not possible to detect any peptide binding to the SapA homologues from Klebsiella pneumonia or E. coli. Finally CAMPs purification was attempted under taken through Ni-NTA and chitin chromatography to produce human antimicrobial peptides. It was possible to 12 produce the human antimicrobial peptide HBD2 with thioredoxin fusion complex via Ni-NTA chromatography.

The polarographic method has been described, and an attempt made to describe the difficulty of the simultaneous deposition of sodium and potassium. Various methods have been examined, of which precipitation of potassium with magnesium dipicrylaminate seems the most promising. The quantitative results were unsatisfactory, and possible sources of error are discussed. The method, while very convenient, rapid and labour-saving, is not sufficiently standardised to be trustworthy.

As global technologies and civilisation have advanced, the utilization of diverse mineral products has increased, resulting in the progressive depletion of high-grade mineral deposits. Consequently, metal production has to rely more on the use of lower-grade or complex ores, as well as metal extraction from mining and industrial wastes. Certain substances, such as phosphorous (P) and potassium (K), contained within the iron ore have a detrimental effect on the smelting process during steel manufacturing, resulting in the international steel making companies charging penalties when purchasing iron ore concentrates containing high concentrations of P and K. It has, therefore, become necessary to develop an economically viable and environmentally friendly process to reduce the high P and K concentrations contained in the iron ore concentrate of the Sishen Iron Ore Mine, resulting in the minimizing of the penalties charged by the steel making companies. During this study no microbial bioleaching candidates could be isolated from the aquatic environment in order to develop an economical process to remove the P and K from the iron ore concentrate. The most likely candidate for the removal of P and K from the iron ore concentrate would seem to be Acidithiobacillus ferrooxidans that was isolated from the iron ore concentrate, however, this bacterium produces sulphuric acid, which is undesired in the iron ore industry due its corrosive properties. Furthermore, the P and K contained in the iron ore is in a non-sulphidic phase, and therefore, conventional bioleaching processes are not viable for their removal from the ore. Metals in certain nonsulphide minerals, such as the iron ore concentrate of the Sishen Iron Ore Mine may be solubilised by a process of complexation using microbially produced inorganic or organic acids. Chemical leaching of the iron ore concentrate using citric acid proved to be more efficient than “heap leaching”, as more P and K was removed from the iron ore concentrate, as well as in a shorter time frame. The results of the chemical leaching suggested that a 1M citric acid leaching solution be used at 60°C for 5 days for the chemical leaching process, as the most P and K is removed from the iron ore concentrate using these leaching conditions. The possibility to use A. niger as a bioleaching microorganism was also investigated, due to its ability to produce organic acids such as citric acid, which has the ability to remove P and K from the iron ore concentrate by chemical leaching. Compared to chemical leaching, which requires high concentrations of citric acid and/or high leaching temperatures, bioleaching using A. niger offers a more economical method with similar efficiency for the removal of P and K from the iron ore concentrate of the Sishen Iron Ore Mine. The most economically viable process for the removal of P and K from the iron ore concentrate, although not as efficient as chemical leaching using citric acid at high temperature, proved to be the bioleaching process using A. niger with a bioleaching pulp density of 33% at 30°C for 10 days. This is the first report of the use of A.niger for the use in any bioleaching process. / Thesis (PhD)--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted

Voltage clamp fluorometry (VCF) was first developed in the mid 1990s by Isacoff and his colleagues. In this approach fluorophores are attached to substituted cysteine residues that are engineered by site-directed mutagenesis. Changes in the dielectric environment of the fluorophore report local transitions that are associated with electrically-related and electrically-silent transitions. VCF provides a powerful technique to observe real time reports of ion channel gating conformations. It has proven to be a useful technique because it adds insight that is not available using other techniques. X-ray crystallography studies give a predominantly static picture of the channel, while patch clamping of channels gives information only about residues that effect ionic current flow. Similarly, gating current provides insight only about residues that are charged and move across the membrane electric field. In this thesis we examined the structural rearrangements of the Shaker channel and the effect of 4-AP on channel gating. We also examined for the first time the structural rearrangements of the Kv1.5 gating and the how the channel responds to depolarization pulses. This work is instrumental in the examination of the potassium channel gating. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

The mechanism of oxidation of Potassium iodide by Chlorine and Fluorine gas has been studied using powdered KI, pressed pellets and single crystals (pressed pellets only in the case of Fluorine). The electrical conductivity of a KI pellet has also been determined as a function of temperature. The major part of the experimental work concerns changes in D.C. electrical conductivity during reaction. The main conclusions are as follows: (a) The room temperature conductivity of KI is always higher than that obtained by extrapolating the impurity-range, and the activation energy below about 92° C. is very small; this is tentatively attributed to a space-charge effect. (b) In the KI/CI₂ reaction, the products are invariably KCl and I₂ in various forms (including V-Centres), although poly-halides are thermodynamically more stable. Thus the reduction of Chlorine occurs in a manner which does not allow reorganization to ICI₂-. (c) In pressed pellets, the conductivity always increases at the start of oxidation, but the enhanced conductivity may be ionic or electronic in different circumstances, and the initial increase may be followed by several alternative processes which are structure-sensitive. There is an inverse correlation between initial conductance and reactivity which is interpreted in terms of competition between (i) trapping of positive holes at isolated cation vacancies and (ii) nucleation of solid Iodine at grain boundaries. (d) Unpressed powders show no increase in conductance during reaction; this is attributed to preferential oxidation of bound surface states. / Science, Faculty of / Chemistry, Department of / Graduate

The welfare of mankind is intimately bound up with the welfare of soils and plants as all of man's food comes, in the, first instance, from plants. Much research has been done to increase yields but little is known of the nutrient values of plants. Since little is known about potassium's effect on the nutrient value of plants, and because carrots have a high Vitamin A precursor content and radishes have a higher Vitamin C content, the author decided to determine what level of potash fertilization should be applied for optimum nutrient value in carrots and radishes. His decisions were, that while the addition of potash to land containing sufficient readily available potassium appears to tend to reduce yields, it does increase the mineral content of the produce. It also increases the total sugar up to a point after which it inhibits the carbohydrate formation. The author also found that additional potassium has no effect on the nitrogen content and, while it has no significant effect on the Vitamin A content it does have a very definite upward trend to produce more with the increases of potassium applied. The addition of potash increases the trend to produce more Vitamin C to the extent that high and very high levels of potassium applications become significant. The author found that correlation exists between the application of potassium and the protective nutrient value in plants. / Land and Food Systems, Faculty of / Graduate

The auxin-like properties of potassium naphthenates (KNap), and the effect of these compounds on indoleacetic acid (IAA) biosynthesis and degradation were examined. Chapter I. The auxin-like properties of KNap. Cucumber seeds were treated with 1000 ppm KNap and a significant (at the 0.05 level) inhibition of root growth (91%) , compared with control seedlings was obtained. The effects of KNap and indolebutyric acid on the initiation of roots by stem cuttings of Phaseolus vulgaris L. were examined. The treatments with 10 and 100 ppm of both compounds significantly stimulated root initiation. Root initiation of azalea stem cuttings was significantly augmented by 10, 100, and 1000 ppm KNap. The elongation of dark-grown Alaska pea stem segments was stimulated by 1.0 ppm KNap (279% over the control). Surprisingly, this stimulation did not differ significantly from that caused by 0.1 ppm IAA (339% over the control). KNap at 100 and 1000 ppm, applied to the distal end of debladed petioles, did not affect abscission. The times required for 50% abscission of petioles treated with 10 and 1000 ppm cyclohexanecarboxylic acid were significantly greater than that for abscission of control petioles, but not from that required by petioles treated with 100 ppm naphthaleneacetic acid. Chapter II. The effect of KNap on IAA biosynthesis and degradation. When the seeds of Phaseolus vulgaris L. were soaked for 12 hours in a solution of 100 ppm KNap immediately prior to sowing, there was a significant increase (140% over control plants) in the content of IAA in the apical 5-8 cm of the stems of 14-day-old plants. The immersion of the root systems of 13-day-old dark-grown bean plants in a solution of 100 ppm KNap for 24 hours resulted in a significant stimulation (4% over the control) of the activity of the IAA oxidase system. The evidence presented is interpreted as supporting the view that KNap has some auxin-like properties. The validity of this interpretation is discussed. / Science, Faculty of / Botany, Department of / Graduate

The electrical conductivity of pure KI and CdI₂-doped KI has been studied in the temperature range 200 to 23°C. Two regions A and B (corresponding to different activation energy of conductivity) are identified. The region A can be given a conventional interpretation in terms of migration of cation vacancies in the bulk, their concentration being determined by impurities. U (the energy for migration of cation vacancies) amounts to 0.96 ± 0.02 eV. Observed activation energies higher than this value are accounted for by association and precipitation effects. Association energy of cation vacancies with impurities (0.48 eV. for Cd⁺₂) and heat of solution (0.25 eV. for CdI₂) obtained here are comparable with known values for other alkali halides. Region B found in this work represents unusual behaviour and has not previously been observed in any alkali halides. The activation energy of conductivity is considerably less than the energy needed for the migration of cation vacancies in the bulk. The activation energy E(formula omitted) (for region B) is about 0.57 eV. in a single crystal and 0.38 eV. in a pure KI pellet. Such low activation energies cannot be given a similar interpretation as for region A. It is suggested that the cation vacancies are in regions of unusually high mobility such as dislocations and grain boundaries. This effect may arise partly from a lower activation energy for motion of vacancies in these regions and partly from a vacancy concentration in these regions which increases with decreasing temperature, under the control of "space- charge" effects. The value 0.57 eV. appears to refer to isolated dislocations or low angle boundaries, while the value of 0.38 eV. refers to large angle intercrystalline boundaries in a pellet. A strong piece of evidence for this suggestion comes from the conductivity runs on single crystals. In an untreated single crystal, just as in pure pellets, two regions A and B are identified but region B disappears in crystals annealed overnight and reappears in a mechanically strained crystal. Moreover, region A remains almost undisturbed in each case. This means that the conduction process in region B is governed by dislocations and grain boundaries whereas region A is governed by motion of cation vacancies in the bulk. / Science, Faculty of / Chemistry, Department of / Graduate

The purposes of this thesis are to examine ages of the Nelson batholith and its satellites because of the wide range of biotite model ages previously published in the literature, and to test hornblende and pyroxene further for their application in K⁴⁰ - Ar⁴⁰ dating as reliable minerals. K⁴⁰ - Ar⁴⁰ model ages obtained on biotite, hornblende and clinopyroxene from the present study indicate with certainty that the various phases of the Nelson batholith were emplaced during a short span of time, centered around 156 m.y. corresponding to the Upper-Middle Jurassic boundary of the Kulp’s time scale. At least a period of hydrothermal alteration has occurred in this area since that time. It is evident that these phases cannot be distinguished on the basis of their K⁴⁰ - Ar⁴⁰ model ages. It is also evident that hornblende gives reliable model ages. Clinopyroxene contains significant excess of radiogenic argon and should not be used for K⁴⁰ - Ar⁴⁰ dating. Biotite may occasionally contain excess of radiogenic argon, particularly under high temperature and high argon pressure environmental conditions. Analytical techniques used and descriptions of the samples analyzed are given as appendixes. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate