An indigenous mixed culture of bacteria collected from a Wastewater Treatment Plant (Brits, North West Province, South Africa), biocatalytically reduced Cr(VI) in the presence of As(III). Both the reduced chromium (Cr(III)) and the oxidised arsenic (As(V)) readily form amorphous hydroxides that can be easily separated or precipitated from the aqueous phase as part of the treatment process. Treatment of Cr(VI) and As(III) before disposal of wastewater is critical since both compounds are known to be carcinogenic and mutagenic at very low concentrations, and acutely toxic at high concentrations. Batch experiments were conducted to evaluate the rate of Cr(VI) reduction under anaerobic condition in the presence of its co-contaminant As(III) typically found in the groundwater and mining effluent. Results showed near complete Cr(VI) reduction under initial Cr(VI) concentrations up to 70 mg/L in a batch amended with 20 mg/L As(III). However, increasing Cr(VI) concentrations up to 100 mg/L resulted in the inhibition of Cr(VI) reduction activity. Further investigation was conducted in a batch reactor amended with 70 mg/L Cr(VI) concentration at different As(III) concentrations ranging from 5-70 mg/L to evaluate the effect of varying As(III) concentration on Cr(VI) reduction efficiency. Results showed that Cr(VI) reduction efficiency increased as As(III) concentrations increased from 5-40 mg/L. However, further increase in As(III) concentration up to 50 mg/L resulted in incomplete Cr(VI) reduction and decrease in Cr(VI) reduction efficiency. These results suggest that the rate of Cr(VI) reduction depends on the redox reaction of As(III) and As(V) with Cr(VI). Moreover, the inhibitory effect observed at high Cr(VI) and As(III) concentration may also be attributed to the dual toxicity effect of Cr(VI) and As(III) on microbial cell. From the above batch kinetic studies lethal concentration of Cr(VI) and As(III) for these strains was evaluated and established. Initial evaluation of the bacteria using 16S rRNA partial sequence method showed that cells in the mixed culture comprised predominantly of the Gram-positive species: Staphylococcus sp., Enterobacter sp., and Bacillus sp. The biokinetic parameters of these strains were estimated using a non-competitive inhibition model with a computer programme for simulation of the Aquatic System “AQUASIM 2.0”. Microbial reduction of Cr(VI) in the presence of As(III) was further investigated in continuous-flow bioreactors (biofilm reactor) under varying Cr(VI) loading rates. The reactor achieved Cr(VI) removal efficiency of more than 96 % in the first three phases of continuous operation at lower Cr(VI) concentration ranging from 20-50 mg/L. However, 20 % decrease in Cr(VI) removal efficiency was observed as Cr(VI) concentration increase up to 100 mg/L. The reactor was able to recover from Cr(VI) and As(III) overloading phase after establishing the resilient nature of the microorganism. Similarly to the batch reactor studies the overall performance of the reactor also demonstrated that the presence of As(III) greatly enhance Cr(VI) reduction in a bioreactor. This was evident by near complete removal of Cr(VI) concentration up to 50 mg/L. The basic mass balance expressions on Cr(VI) along with the non-competitive inhibition model were used to estimate the biokinetic parameters in the continuous flow bioreactor system. Cr(VI) reduction efficiency along the longitudinal column was also evaluated in this study. Results showed that Cr(VI) efficiency increased as Cr(VI) concentration travels along the longitudinal column. Other important factors such as oxygen and pH during biological Cr(VI) reduction in the presence of As(III) oxidation were also evaluated. / Dissertation (MEng)--University of Pretoria, 2014. / tm2015 / Chemical Engineering / MEng / Unrestricted

Elevated levels of geogenic arsenic (As) in groundwater are regarded as the most formidable environmental crisis in the contemporary world and an estimated 30-70 million people in Bangladesh are at risk. Many of the provided options for mitigation have not been well accepted. In recent years, local drillers have been targeting As-low groundwater on the basis of the color of the sediments. A correlation between the color characteristics of the sediments and the groundwater redox conditions and thereby the risk for As mobilization has been established. It is possible to assess the relative possibility of occurrence of high As concentrations in groundwater if the color characteristics of the sediments are known. One main objective of the present study is to validate if targeting As-safe groundwater is a sustainable mitigation strategy. This has been done through monitoring groundwater from tube-wells installed in sediments with different color, depth and redox characteristics. Samples were collected yearly from a set of 17 tube-wells for the period of 2004 to 2008 in Matlab, Bangladesh. The wells were grouped into oxidized and reduced/non-oxidized wells. All of these wells tap water within a depth of 85 m from the surface. Major cations and trace elements including As were analysed by high resolution ICP-OES; and anions were measured by ion chromatography. Groundwater chemistry of the water abstracted from different sediments revealed that no major change had occurred over the period of 5 years. In reduced wells, concentration of major cations and anions varied by <10% over time, and no significant variation was observed in redox sensitive elements, such as Fe, Mn and S. There were some minor variations in the As concentrations in the wells. In the oxidized wells, except well 58, major cations, anions and redox sensitive elements varied by <5%, while the As concentrations were found quite low and stable (<5.2 μg/L). Time series trends thus suggest that the change in groundwater chemistry is insignificant over the period of 5 years from 2004 to 2008. Low As concentrations in the tubewells installed in the oxidized brownish sediments thus validate the mitigation strategy corresponding to the conceptual understanding of the groundwater system in Matlab in southeastern Bangladesh.

Las etapas de transferencia electrónica o transferencia de carga involucradas en reacciones electroquímicas juegan un papel muy importante en un gran número de procesos biológicos y bioquímicos. Hoy en día, el interés de la comunidad científica se centra en explorar y entender exhaustivamente la naturaleza biológica y química de los fenómenos bioelectroquímicos que ocurren en los seres vivos, con el objeto de mimetizarlos en el laboratorio. Los procesos bioelectrocatalíticos presentan un amplio abanico de aplicaciones dirigidas al: (i) desarrollo de biorreactores electroquímicos para la mitigación de las emisiones de gases de efecto invernadero, la eliminación de contaminantes presentes en aguas residuales y urbanas, o la síntesis de productos con alto valor añadido para la industria, (ii) el desarrollo de biopilas y biobaterías, y (iii) el desarrollo de (bio)sensores electroquímicos con fines analíticos. Sin embargo, la implantación en el mercado de dispositivos basados en procesos biocatalíticos aún se enfrenta a varios desafíos, como son la robustez, la estabilidad a largo plazo, la reproducibilidad y la rentabilidad de producción en términos de materiales y fabricación de los dispositivos electroquímicos. La motivación de esta tesis doctoral es la de enfrentarse a algunos de los desafíos con los que se encuentra hoy en día la bioelectrocatálisis, para ello esta tesis doctoral se centra, principalmente en el estudio de nuevos materiales y mejora de rutas y estrategias bioelectrocatalíticas, con la finalidad de desarrollar dispositivos electroquímicos con aplicaciones analíticas y en la obtención de productos de valor añadido. En primer lugar esta tesis doctoral recoge el estudio y desarrollo de (bio)sensores electroquímicos para la determinación de lactato, L-cisteína, peróxido de hidrógeno y pH en medios biológicos complejos, y en segundo lugar estudia la bioelectrosíntesis de ácido fórmico a través de la reducción bioelectroquímica de dióxido de carbono.

The reversible reduction of hexacyanoferrate(III) to the Fe(II) form is a well-known standard in electrochemistry. It is however reported to be highly dependent on the solvent environment.[i] This electrochemical project has aimed to examine the behaviour of ferricyanide in aprotic environment by changing the solvent to acetonitrile, a medium polar solvent with a high dielectric constant. The method used for research is cyclic voltammetry. Ferricyanide has been examined in aqueous and aprotic solvent and has been studied in comparison to ferrocene, which is a well-known chemical substance. When studying ferricyanide in acetonitrile solvent under inert conditions, a completely new voltammetric picture was drawn where the standard reduction potential in aqueous solvent of 43 mV (SCE) was dramatically lowered and a new redox reaction with a higher reduction potential seemed to be present at -97mV (Ag/Ag+) when ferricyanide went through redox process from 0 V to +1.3 V to -0.5 V and back to 0V again. When examining the redox process an EC reaction was found to be coupled to the new peak. This process was studied within the time limit for the project. Some properties of the possible chemical has been presented and the conclusions are discussed in the report. Suggestions are made for how to move forward with the research. [i] (a) Gutmann V., Gritzner G., and Danksagmuller K., Inorganica Chimica Acta, 17 1976 81; (b) Noftle R.E. and Pletcher D., Journal of Electroanalytical Chemistry, 1990 273, 293.

UCP1 is a member of the mitochondrial transmembrane anion carrier protein superfamily and is required to mediate adaptive thermogenesis in brown adipose tissue (BAT). Once activated, UCP1 uncouples mitochondrial respiration from ATP synthesis, thereby wasting the protonmotive force formed across the mitochondrial inner membrane as heat. It is hypothesized that proton leaks through UCP1 could be a molecular target to combat certain forms of obesity. Although it is well established that UCP1 is regulated by allosteric mechanisms, alternative methods such as post-translational modification still remain to be explored. The aims of the present study were to confirm the phosphorylation of UCP1 and the physiological relevance of this modification. Using isoelectric focusing, we confirmed that UCP1 displayed acidic shifts consistent with phosphorylation in BAT mitochondria isolated from cold exposed versus warm acclimated mice. A mouse model that ectopically expressed UCP1 in skeletal muscle was used to explore the link between the mitochondrial redox status and UCP1 function. Our results show that the expression of UCP1 in skeletal muscle led to decreases in body and tissues weights. In contrast, glucose uptake into skeletal muscle, food intake and energy expenditure was increased with the expression of UCP1. Finally, proton leaks through UCP1 were determined to be increased in isolated mitochondria from transgenic versus wild-type mice. Taken together these results indicate a complex interplay between mitochondrial redox status, post-translational modification and UCP1 function. Elucidation of novel mechanisms regulating UCP1 offers alternatives strategies that can be explored in order to modulate BAT thermogenesis.

Nickel enzymes have been suggested, through numerous phylogenetic studies, to have been among the very first catalytic compounds on the early Earth, possibly present in the last universal common ancestor (LUCA) or prior to the onset of life. This is because of the type of reactions catalyzed by some of these enzymes, the nature of organisms that utilize them, their distribution in the tree of life, and their key roles in what is now thought of as possibly one of the oldest carbon fixation pathways, the Wood-Ljungdahl (WL) pathway. Additionally, nickel is generally thought to have been an abundant element on the early Earth, highly soluble in what were, theoretically, euxinic (anoxic and sulfidic) ocean waters. This combined with the fact that the enzymes involved in the WL pathway have an active center configuration that resembles that of minerals found in hydrothermal vent walls, makes nickel enzymes a likely candidate to have evolved from what were proto-enzymes, responsible for the prebiotic catalysis of the first simple organic molecules prior to the origins of life, according to the so-called submarine alkaline hydrothermal vent theory, first presented by Michael J. Russell in 1993 (Russell et al. 1994). In this study, I expand the known coverage on the distribution of these enzymes by mapping them in 10,575 OTUs of microbial taxa. Using their pattern of distribution, I reconstruct their histories along the branches of a reference phylogenetic tree of the same taxa through methods of ancestral reconstruction of discrete traits. Additionally, I construct an individual gene tree for each of the enzymes in order to consolidate gene history with species history. My results showed that the redox nickel enzymes (except methyl-coenzyme M reductase) are ancestral to all prokaryotes, while non-redox enzymes are derived and with multiple origins, possibly due to lateral gene transfer events or convergent evolution. I propose that the patterns observed are a product of the drastic changes during early Earth history, namely a hypothesized “nickel famine” or the Great Oxidation Event, which acted as selective pressures.

No description available.

Despite the consensus that glutamatergic and GABAergic imbalance is likely to be involved in anesthesia or coma, there is little known about molecular mechanisms of action of gaseous anesthetics. The target article by Smythies (1999) is engagingly analytical and insightful, proposing novel and testable hypotheses for the molecular mechanisms of action of anesthetics as well as for processes that may be involved in coma. The most creative and convincing of his hypotheses concerns the crucial role of iron in maintaining neural respiration and energy production as well as its involvement in synaptic plasticity. Smythies' paper is certain to stimulate new ideas and experiments on the molecular mechanisms of anesthesia and coma.

Reactive oxygen species (ROS) generated during ischemia-reperfusion (I/R) enhance myocardial injury, but brief periods of myocardial ischemia followed by reperfusion [ischemic preconditioning (IP)] induce cardioprotection. Ischemia is reported to stimulate glucose uptake through the translocation of GLUT-4 from the intracellular vesicles to the sarcolemma. In the present study we demonstrated involvement of ROS in IP-mediated GLUT-4 translocation along with increased expression of caveolin (Cav)-3, phospho (p)-endothelial nitric oxide synthase (eNOS), p-Akt, and decreased expression of Cav-1. The rats were divided into the following groups: 1) control sham, 2) N-acetyl-L-cysteine (NAC, free radical scavenger) sham (NS), 3) I/R, 4) IP + I/R (IP), and 5) NAC + IP (IPN). IP was performed by four cycles of 4 min of ischemia and 4 min of reperfusion followed by 30 min of ischemia and 3, 24, 48 h of reperfusion, depending on the protocol. Increased mRNA expression of GLUT-4 and Cav-3 was observed after 3 h of reperfusion in the IP group compared with other groups. IP increased expression of GLUT-4, Cav-3, and p-AKT and p-eNOS compared with I/R. Coimmunoprecipitation demonstrated decreased association of Cav-1/eNOS in the IP group compared with the I/R group. Significant GLUT-4 and Cav-3 association was also observed in the IP group. This association was disrupted when NAC was used in conjunction with IP. It clearly documents a significant role of ROS signaling in Akt/eNOS/Cav-3-mediated GLUT-4 translocation and association in IP myocardium. In conclusion, we demonstrated a novel redox mechanism in IP-induced eNOS and GLUT-4 translocation and the role of caveolar paradox in making the heart euglycemic during the process of ischemia, leading to myocardial protection in a clinically relevant rat ischemic model.

Philosophiae Doctor - PhD / The depletion of fossil fuel resources such as coal and the concern of climatic change arising from the emission of greenhouse gases (GHG) and global warming [1] lead to the identification of the 'hydrogen economy' as one of the renewable energy sources and possible futuristic energy conversion solution. Sources of hydrogen as fuel such as water through electrolysis and liquid organic fuel (Hydrogen carriers) have been found as potential game-changers and received increased attention, due to its low-carbon emission.