No description available.

This study was undertaken to investigate denitrification and nitrous oxide production in sediments and the key environmental factors influencing these within selected river systems of the LOIS (Land-Ocean Interaction Study) area in North-East England and southern Scotland. Seasonal and spatial trends were evident in both environmental and denitrification data measured monthly for 1.5 years along the Swale-Ouse system from source to tidal limits. Denitrification, measured in sediment cores using acetylene inhibition and expressed by unit area of sediment, increased with distance from source down to freshwater tidal limits. Results from a supplementary survey of the freshwater tidal reaches of the Yorkshire Ouse showed a decrease from the tidal limits. Denitrification activity showed a spring (March to May) peak, particularly in the lowland sites. The highest rate (883±134 µmol N m(^-2) h(^-1)) was measured on the River Wiske, a highly eutrophic lowland tributary to the Swale. A high degree of colinearity was evident between environmental variables, although a significant relationship between denitrification, nitrate and temperature was found through multiple regression. For comparison, measurements were made in the less populated Tweed river system. The seasonal and spatial trends evident in both the environmental and denitrification data from the River Tweed, under a more limited sampling programme, were generally consistent with those observed in the Swale-Ouse system. An intensive field investigation of 50 river sites showed that both potential denitrification rate and N(_2)O production in sediment slurries were positively correlated with nitrate water concentration, sediment water content and percentage of fine (<100 µm) sediment particles. An experimental study investigating the kinetic parameters for denitrification, found that sediment cores taken along the Swale-Ouse exhibited a saturation type curve with added nitrate. Apparent affinity and estimates of apparent maximum velocity for mixed populations of denitrifying bacteria showed an increase on moving downstream and were highest on the Wiske.

No description available.

No description available.

The mobility of trace metals and radionuclides released into aquatic and terrestrial environments by mining, industrial processes, and municipal waste disposal practices is an area that deserves significant scientific, public health, and regulatory attention. Indirect microbial interaction offers one potential mechanism for immobilizing these contaminants. For example, many metals, such as uranium and chromium, are less soluble once bound as iron oxide precipitates, thus inhibiting the spread of soluble heavy metals and radionuclides within groundwater and halting them from contaminating additional areas. Microbial iron oxidation is known to contribute to the immobilization of heavy metals and radionuclides in contaminated sites. A safe, cost-effective decontamination method for these materials is the association of radionuclides with iron oxides formed via microbial pathways, thus precipitating them out of solution and providing a promising technique for in situ bioremediation. Nitrate-dependent iron-oxidizing bacteria have been shown to play an important role in the retention of soluble uranium by forming iron oxides that absorb onto soluble U(VI) particles, rendering them immobile as U(VI)-iron oxides. Dechloromonas aromatica strain RCB is a β-proteobacterium that has been cultured and extensively studied in our laboratory and is capable of reducing perchlorate and anaerobically oxidizing benzene, humic acids, and ferrous iron. In addition, a newly-isolated β-proteobacterium, Diaphorobacter sp. strain TPSY, is of interest due to its ability to anaerobically oxidize humic acids, uranium, and ferrous iron. Thus, these two strains have enormous bioremediative potential and are prime candidates for in situ bioremediation. Microarray analysis was used to identify genes induced under iron-oxidizing conditions and RNA dot blotting was used to confirm mRNA expression in D. aromatica. As a follow-up, RNA arbitrarily primed (RAP)-PCR, a method used to randomly reverse-transcribe RNA into cDNA, was also used to identify expression that might not have been observed in the microarray. Genes that were identified from both microarray and RAP-PCR experiments include several hypothetical proteins, lipoproteins, and transmembrane proteins located in major operons, as well as genes annotated as signal transduction enzymes, c-type cytochromes, and proteins involved in chemotaxis, flagellar, and pilus development. Suicide vectors were used to create deletion mutations targeting the genes of interest. Additionally, transposon mutagenesis was used in Diaphorobacter sp. TPSY to identify any potential iron-oxidizing mutants. Out of seven TPSY mutants deficient in iron oxidation, four were identified as genes that encode an inner membrane protein, a signal transduction protein, a putative lipoprotein downstream of a cytochrome c, and a regulatory DNA-binding protein. Mutants were confirmed for their inability to oxidize iron by measuring Fe(II) concentrations over time with a ferrozine assay. The identification of genes involved in microbial anaerobic nitrate-dependent iron oxidation will prove to be a valuable asset when designing and assessing bioremediative strategies.

Humic substances (HS) are the humified portions of totally decomposed soil organic matter that are ubiquitous in nature. Although these substances have been studied for more than 200 years, neither their metabolic capabilities nor a specific chemical structure has yet to be determined. HS have been studied as a carbon source in many environments where they are degraded; however, previous studies have shown that some microorganisms are capable of utilizing humic substances as electron acceptors and electron donors in anaerobic respiration. Even though there have been humic-reducing and humic-oxidizing microorganisms isolated and studied in recent years, the mechanism of humics metabolism and its interaction in the natural environment are not well understood. However, it is known that the continuous change in the redox state of HS is important to the cycling of iron, stability of nitrogen and carbon, and the mobility and bioavailability of inorganic and organic environmental pollutants. In this study, microbial communities were examined to evaluate the community dynamics of nitrate-dependent HS-oxidizing populations and to provide a snapshot of the phylogenetic diversity of these microorganisms. Column studies were performed using nitrate as the sole electron acceptor and the following as the electron donors in different columns: reduced humic acids, oxidized humic acids, and acetate as the control. Liquid buffered media was added to a separate column to serve as an additional control. Polymerase chain reactions of the 16S rRNA genes using DNA from the column studies were performed and analyzed by constructing 16S rDNA clone libraries and by performing denaturing gradient gel electrophoresis (DGGE). Clones from the library have been sequenced and analyzed to paint a phylogenetic picture of the microbial community under the various conditions. Results indicate that the majority of the clones were assigned to four well-characterized divisions, the Acidobacteria, the Bacteroidetes, the Firmicutes, and the Proteobacteria. Additional findings suggest that members related to Bacteroidetes are involved in some sort of HS cycling in the environment or may be excellent electron scavengers enabling them to outcompete other microorganisms and that members of Proteobacteria may be the dominant HS-oxidizing microorganisms in natural environments. An additional aspect of this project hypothesizes that specific genes are differentially expressed when HS-oxidizing bacteria are growing on reduced HS as compared to acetate or in the presence of oxidized HS. To test this hypothesis, the global gene expression profile of Acidovorax ebreus strain TPSY was assessed using microarray analysis. This method led to the identification of several genes potentially involved in nitrate-dependent HS oxidization and a proposed model for this respiratory process in strain TPSY. The final section in this project was designed to assess in-service teachers' perceived levels of familiarity with and interest in learning more about selected microbiology concepts and their actual understanding of the selected microbiology concepts. Sixty-two in-service elementary, middle, and high school teachers from several school districts across southern Illinois completed a three-part instrument that included additional open-ended questions to gain more information about the teachers' conceptual understanding. The results of this study suggest that teachers who hold a teaching certification specific for teaching life science have taken more life science courses and scored significantly higher on the familiarity and conceptual knowledge sections of this study. The current research explores what is currently known about humic substances, specifically humics as an electron donor, analyzes the community structure in a humics oxidizing environment, identifies genes that are induced under nitrate-reducing, HS-oxidizing conditions, and evaluates the importance of microbiology to biological scientific literacy in today's society.

Conservation practices are needed to reduce nitrate loss across the Midwest. Different riparian wetland designs have been investigated, but the physical, chemical and biological processes controlling nutrient cycling in restored oxbows are not well understood. A restored oxbow’s influence on nutrient cycling was investigated by studying the hydrogeology and water quality at a recently reconstructed oxbow site adjacent to Morgan Creek in Linn County, Iowa. Over a one-year period, the lentic oxbow’s nitrate loading was found to be dominated by flood pulses. Nitrate concentrations in the stream ranged from 7.38 – 12.95 mg l-1, concentrations were consistently low in the oxbow ranging from < 0.10 – 5.35 mg l-1, and the lowest nitrate concentrations were detected in the groundwater ranging from 0.10 to 3.4 mg l-1. Following a spring flood event, an in-situ sensor measured the nitrate concentration in the oxbow. Nitrate retention efficiency was estimated to be 0.30 g N m-2 d-1 or a 74.2% reduction efficiency. The observed nitrate reduction was compared to a first order denitrification model. The observed nitrate reduction measured in the oxbow followed a linear decay rather than an exponential decay suggested by first order kinetics.

Green ammonia production has been an important topic that is being researched during the last decades due to the increasing demand and to cut down CO2 emissions. One of the promising pathways to achieve green chemical energy synthesis is the Photoelectrochemical (PEC) approach. To realize low-cost and scalable green ammonia production, the direct integration of solar photovoltaic modules and catalysts as a Photovoltaic-Electrochemical (PV-EC) system is highly suitable. In this study, Molybdenum Carbide(Mo2C) decorated with different metal nanoparticles (Pt, Pd, Ru) is being investigated as a potential nitrate reduction (NO3RR) to ammonia. Here various metal-decorated M o2C was successfully synthesized by the chemical reduction method. The metal-decorated M o2C is characterized by Transmission Electron Microscopy(TEM), Raman Spectroscopy, and X-ray diffraction(XRD) analysis and confirmed the formation. Initially, electrocatalytic NO3RR was carried out, and Pt decorated Mo2C was found to demonstrate high Faradic efficiency and NH3 of 30% and 4400 μg/h/cm2. Next, PV-EC was carried out, and a stable solar-powered NO3RR was carried out with Pt-M o2C and Si PV module. The proposed system delivers a yield of 600 ug/h/cm2 and a Faradic Efficiency of 7% .

Mycobacterium avium is human and animal opportunistic pathogen responsible for disseminated disease in immunocompromised patients. Mycobacteria have a capacity to adapt to the environmental conditions by inducing enzyme activities and altering their metabolism. M. avium A5 cells were grown in a defined minimal medium (Nitrogen Test Medium) with glutamine, nitrite, nitrate, or ammonia as sole nitrogen source at a concentration of 2 mM at 370C aerobically. The strain grew well on all the nitrogen sources except nitrite. It grew slowly on nitrite with a generation time of 6 days and cultures were not viable after 4 weeks of storage. These data confirm that M. avium can utilize a single nitrogen source in a defined minimal medium as documented by McCarthy (1987). M. avium genome has been sequenced and contains genes sharing sequence similarities to respiratory nitrate reductase and dissimilatory nitrite reductases. Because, M. avium can use nitrate or nitrite as sole nitrogen source for growth (McCarthy, 1987), it must have assimilatory nitrate- and nitrite-reductases. Nitrate- and nitrite-reductase activities of M. avium cells growing aerobically or undergoing anaerobic shift in the presence of ammonia, nitrate or ammonia and nitrate in combination were measured. M. avium produced nitrate- as well as nitrite-reductase activity. Nitrite- and nitrate-reductases used either NADH or NADPH as an electron donor. Nitrite reductase activity was greater than nitrate reductase activity. This observation supports the rapid reduction of nitrite and slow reduction of nitrate in M. avium as documented by McCarthy (1987) and explained why M. avium gives a negative result by the standard nitrate reductase test. In addition to assimilatory enzyme activity, M. avium A5 also produced dissimilatory nitrate- and nitrite-reductase activities. / Master of Science

Les technologies de traitement physico-chimique et biologique des eaux usées ne permettent pas un traitement efficace de l’azote puisque 40% est encore rejeté en rivière. La thèse porte sur le développement de nouveaux matériaux d’électrode pour la conversion des polluants azotés (nitrates, urée) en produits valorisables (NH3, H2) ou inertes (N2). Le travail consiste à synthétiser des matériaux composites constitués de nanoparticules mono ou bimétalliques jouant le rôle de catalyseurs, dispersées dans des carbones de grande surface spécifique. La forme ultra-divisée permet d’augmenter les surfaces actives et ainsi réduire les quantités de métal. Ces produits sont caractérisés par Microscopie Electronique à Balayage et en Transmission, par analyses ICP et DRX pour décrire leur morphologie, composition et structure. Des études électrochimiques analytiques sont ensuite réalisées à l’aide d’une MicroÉlectrode à Cavité afin de déterminer l’activité électro-catalytique des matériaux et accéder à des aspects mécanistiques. La première partie de la thèse a concerné l’électro-réduction des nitrates. Des composites Cu-Rh/C et Cu-Ni/C avec différentes compositions ont été synthétisés par une méthode chimique consistant à imprégner le carbone par des sels métalliques puis à les réduire par NaBH4 en présence d’un surfactant (CTAB). Les particules présentent des tailles d’environ 2 nm de diamètre. Ces bimétalliques présentent des courants plus élevés que ceux obtenus avec des particules monométalliques. En particulier, dans le cas du système Cu-Rh, il a été mis en évidence un comportement « bi-fonctionnel » où le cuivre réduit les nitrates en nitrites et le rhodium les nitrites en ammoniaque. Des matériaux composites ont ensuite été synthétisés dans les mêmes conditions mais en utilisant un carbone greffé afin de contrôler la dispersion et l’ancrage des nanoparticules. Pour cela, les carbones sont préalablement greffés par des groupements aryle avec substituant puis décorés des nanoparticules métalliques. Le but est de déterminer les conditions de greffage optimales conduisant aux réactivités les plus élevées en contrôlant l’épaisseur des films organiques greffés et la nature du substituant (-SH, -NH2, -COOH). La seconde partie de la thèse a concerné l’électro-oxydation de l’urée. Cette réaction est généralement effectuée sur des matériaux à base de nickel et, d’après la littérature, l’ajout d’un co-élément permet de modifier les propriétés électrochimiques (potentiel, intensité). Une étude sur des composites bimétalliques Ni100-xMx / C avec M = Co, Rh, Mn, Fe (selon la méthode déjà décrite ci-dessus) a été conduite pour déterminer le rôle de différents co-éléments. Le rhodium est apparu comme l’élément apportant la meilleure intensité et la meilleure stabilité. Une étude plus complète a alors été réalisée avec la synthèse de composites Ni100-xRhx / C avec différentes compositions par réduction des ions métalliques sous Ar/H2 dans un four à température modérée (500°C). L'oxydation électrochimique de l'urée est significativement améliorée par l'ajout de rhodium qui induit une forte diminution de la taille des nanoparticules (de 15 nm pour le nickel et à 2 nm le rhodium). Ce travail de thèse a montré l’intérêt d’utiliser des catalyseurs bimétalliques dispersés dans des matrices carbonées pour le traitement de polluants azotés. Elle confirme par ailleurs que la Microélectrode à Cavité est un outil performant pour l’étude des poudres grâce à la bonne résolution des signaux électrochimiques. La perspective la plus intéressante de ce travail est de poursuivre l’étude de l’électrocatalyse de l’urée sur les Ni-M/C pour pouvoir dépolluer l’urine tout en produisant à faible coût de l’hydrogène comme moyen de stockage de l’électricité renouvelable. Il a permis d’initier des collaborations avec d’autres laboratoires et un industriel de l’assainissement des eaux en vue de traiter de l’urine collectée à la source / Physico-chemical and biological wastewater treatment technologies do not allow efficient nitrogen treatment since 40% is still discharged into rivers. The thesis concerns the development of new electrode materials for the conversion of nitrogenous pollutants (nitrates, urea) into recoverable (NH3, H2) or inert products (N2). The work consists in synthesizing composite materials made of mono or bimetallic nanoparticles acting as catalysts, dispersed in large surface area carbons. The ultra-divided shape increases the active surface and thus reduces the amount of metal. These products are characterized by Scanning and Transmission Electron Microscopy, ICP and DRX analysis to describe their morphology, composition and structure. Electrochemical analytical studies are then carried out using a Cavity MicroElectrode to determine the electro-catalytic activity of the materials and access mechanistic aspects.The first part of the thesis concerned the electro-reduction of nitrates. Cu-Rh/C and Cu-Ni/C composites with different compositions were synthesized by a chemical method consisting of impregnating the carbon with metal salts and then reducing them with NaBH4 in the presence of a surfactant (CTAB). The particles are approximately 2 nm in diameter. These bimetals have higher currents than those obtained with monometallic particles. In particular, in the case of the Cu-Rh system, a "bi-functional" behavior has been demonstrated where copper reduces nitrates to nitrites and rhodium reduces nitrites to ammonia. Composite materials were then synthesized under the same conditions by using grafted carbon to control the dispersion and anchoring of nanoparticles. For this, the carbons are previously grafted by aryl groups with a substituent and then decorated with metal nanoparticles. The aim is to determine the optimal grafting conditions leading to the highest reactivity by controlling the thickness of the grafted organic films and the nature of the substituent (-SH, -NH2, -COOH). The second part of the thesis concerned the electro-oxidation of urea. This reaction is generally carried out on nickel-based materials and, according to the literature, the addition of a co-element makes it possible to modify the electrochemical properties (potential, intensity). A study on bimetallic composites Ni100-xMx / C with M = Co, Rh, Mn, Fe (according to the method described above) was conducted to determine the role of the different co-elements. Rhodium appeared as the element providing the best intensity and the best stability. A more complete study was then carried out by synthesizing Ni100-xRhx / C composites with different compositions through the reduction of metal ions under Ar/H2 in a furnace at moderate temperature (500°C). The electrochemical oxidation of urea is significantly improved by the addition of rhodium which induces a strong decrease in the nanoparticle size (from 15 nm for nickel to 2 nm for rhodium). This thesis work has shown the interest of using bimetallic catalysts dispersed in carbon matrices for the treatment of nitrogenous pollutants. It also confirms that the Cavity Microelectrode is a powerful tool for the study of powders thanks to the good resolution of electrochemical signals.The most interesting perspective of this work is to continue the study of urea electrocatalysis on Ni-M/C to be able to depollute urine while producing hydrogen at low cost for chemical storage of renewable electricity. It has enabled collaborations to be initiated with other laboratories and a water purification industrial company to treat urine collected separately