939 resultados para Fe3 immobilized
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Localizado na poro centro-oeste do Estado de Minas Gerais, o Quadriltero Ferrfero abrange uma rea de aproximadamente 7.000 km. Desde o sculo XVII, a regio conhecida como uma provncia aurfera e ferrfera, sendo por essa razo uma das regies mais bem estudadas do Brasil no contexto geolgico. A regio de topografia muito acidentada, onde predominam solos pouco evoludos pedogeneticamente, com destaque para Cambissolos Hplicos, Neossolos Litlicos e Neossolos Regolticos. Em menor proporo e em rampas de colvio (relevo suave ondulado), ocorrem Latossolos Vermelhos muito ricos em Fe, anteriormente denominados Latossolos Ferrferos. Neste trabalho, foram realizados estudos para caracterizar fsica, qumica e mineralogicamente amostras de nove perfis de Latossolos Vermelhos frricos e perfrricos, desenvolvidos de itabirito e rochas afins no Quadriltero Ferrfero, com os objetivos de melhor entender sua gnese e avaliar critrios taxonmicos que permitam sua diferenciao no SiBCS, em nveis categricos mais baixos. Os elevados valores de densidade de partculas so peculiares nesses solos e, ao lado da estrutura forte, muito pequena e granular, so fatores que contribuem para subestimar os teores de argila e superestimar os de silte, resultando em relao silte/argila maior do que aquela proposta pelo SiBCS para os Latossolos. A variao dos teores de SiO2, Fe2O3, Al2O3, TiO2, MnO, P2O5 e de alguns elementos-trao aponta para a diversidade na composio qumica do itabirito ou, ainda, provvel mistura com rochas filticas da regio. Os valores das relaes Fe2O3/TiO2 (no molecular) e TiO2/Fe2O3 (molecular) revelaram-se diferentes daqueles sugeridos na literatura para separao de Latossolos Vermelhos desenvolvidos de itabirito daqueles de rochas mficas. As fraes areia, silte e argila apresentaram grande variao na atrao magntica, com as duas primeiras fraes evidenciando maior magnetizao, em razo da presena de magnetita. Os valores de substituio isomrfica de Fe por Al variaram 0,07 a 0,11 e 0,09 a 0,38 mol mol-1 nas estruturas da hematita e magnetita, respectivamente.
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Hidrxidos duplos lamelares (HDL) so intercaladores potenciais aninicos. Com o objetivo de obter fertilizantes de liberao lenta de nitrato, foram sintetizados HDL com a frmula geral [M2+1-xM3+x(OH)2]x-(NO3)x.yH2O, em que M2+ = Mg2+ e M3+ = Al3+ e, ou, Fe3+, utilizando-se o mtodo de coprecipitao a pH alcalino constante. Medidas de difrao de raios-X evidenciaram que a cristalinidade aumenta com o acrscimo do valor de pH e da razo molar M2+/M3+. As medidas de FTIR apresentaram bandas caractersticas de nitrato livre no espao interlamelar, alm de pequena contaminao de ons carbonato. Medidas de TGA/DTA possibilitaram a confirmao das composies e dos teores de ons de nitrato intercalados. As curvas de liberao de nitrato demonstraram dois comportamentos de liberao complementar, um inicial rpido (A) e um lento gradativo (D), sendo, este ltimo, relacionado orientao planar do on nitrato intercalado. Os materiais sintetizados e investigados neste trabalho apontaram grande potencial para serem utilizados como matrizes para fertilizantes de liberao lenta de nitrato.
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Non crystalline (nc) EuIG and DyIG have been prepared by dcsputtering. Mssbauer data on 57Fe, 151Eu and 161Dy reveal sharp magnetic transitions at 62 K and 70 K for nc EuIG and DyIG, respectively. The 57Fe hyperfine (hf) spectra consist of three superpositioned patterns for Fe3+ in tetrahedral and octahedral and for Fe2+ in tetrahedral oxygen coordination. The saturation hf fields at 4.2 K are reduced compared to the values of the corresponding crystalline materials. The induced hf field at 151Eu is only 1/8 of that for crystalline EuIG
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The distribution of Sn4+ cations within the five crystallographic sites of the magnetoplumbite (M) like compound BaFe122xCoxSnxO19 has been analyzed using singlecrystal xraydiffraction data. The species Fe3+ and Co2+ cannot be distinguished using x rays because of their very similar atomic numbers; however, the calculation of the apparent valencies for the different sites allows an insight into the Co2+ cation segregation. The use of previous data from neutron powder diffraction allows a precise picture of the cation distribution, which indicates a pronounced site selectivity for both Sn4+ and Co2+ cations. The Sn4+ cations prefer the 4f2 sites and to a much lower extent the 12k sites, while they do not enter the octahedral 2a sites at all. Co2+ cations are distributed among tetrahedral and octahedral sites displaying a clear preference for the tetrahedral 4f1 sites. Magnetic measurements indicate that the compound still exhibits uniaxial anisotropy with the easy direction parallel to the c axis. Nevertheless, the magnetic structure shows a considerable degree of noncolinearity. A strong reduction of the magnetic anisotropy regarding that of the undoped compound is also detected.
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We report here on the magnetic properties of compounds of composition Fe1xCrxSbO4 and Fe1xGaxSbO4. The introduction of paramagnetic Cr3+ and diamagnetic Ga3+ into the rutilerelated iron antimonate lattice does not destroy the antisite atomic ordering which exists in iron antimonate of composition FeSbO4. The initial slope of the Curie temperature dependence on x is similar in both series, indicating that Fe3+Cr3+ interactions are very small. The magnetic susceptibility measurements recorded from the compounds of composition Fe1xCrxSbO4, x<0.4, and Fe0.9Ga0.1SbO4 show them to behave as spin glasses at low temperatures. The inhibition of compounds of the type Fe1xCrxSbO4, x>0.4, and Fe1xGaxSbO4, x>0.1 to undergo a spinglass transition above 4.2 K is associated with a dilution effect.
Hydrogen isotope fractionations between amphiboles, micas, and fluids in alkaline igneous intrusions
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RSUM DE LA THSE Les teneurs des amphiboles en lments majeurs et en isotopes stables ont t analyses dans plusieurs complexes igns alcalins et hyperalcalins, dans le but de dterminer l'importance des variations de composition des minraux pour le fractionnement isotopique de l'hydrogne dans un systme naturel minral-magma-fluide. Cette tude se concentre principalement sur les synites nphliniques de complexes intrusifs alcalins bien connus mais chimie variable, dont les amphiboles, ainsi que d'autres silicates hydrats tels que micas et eudialytes, lorsque cela tait possible, ont t spars. L'intrt principal s'est port sur le complexe alcalin d'Ilmaussaq de la Province du Gardar, au Sud du Groenland. Dans une optique de comparaison, nous avons collect et analys d'autres chantillons provenant du complexe de Tugtutq (Sud Groenland), des complexes de Khibina et Lovozero (Pninsule de Kola, Russie), du Mont St-Hilaire et du Mont Royal (Canada) et de 6 autres du nord-ouest de la Namibie (Cape Cross, Okenyenya, Messum, Etaneno, Kalkfeld,et Okorusu). Les compositions isotopiques de l'hydrogne des amphiboles des ces diffrentes zones prsentent de grandes variations (-227 -700/00), ce qui est atypique pour des magmas d'origine mantellique. Les valeurs comprises entre -80 et -400/00 indiquent une provenance du manteau. Ces larges variations de compositions ainsi que l'extrme appauvrissement en isotope lourd de l'hydrogne (D), en comparaison avec d'autres roches ignes, semblent tre propres.aux roches alcalines et hyperalcalines de ce type, ce qui indiquerait un processus commun. Les diffrents complexes alcalins choisis prsentent un large intervalle de composition chimique des amphiboles. La caractrisation des amphiboles par microscopie lectronique et par spectroscopie Mssbauer contribuent observer le contrle du Fe sur le fractionnement des isotopes de l'hydrogne. En effet, cela a mis en vidence un contrle du Fe sur le fractionnement et mme, dans le cas du complexe hyperalcalin d'Ilmaussaq, une relation entre le rapport Fei3+/FeT et les variations du rapport D/H. Les complexes tudis diffrent de par leur index agpatique (Na+K/Al) et galement de par leur contenu en fer. Les plus hautes valeurs en Fe (27-35 wt%) et en lments alcalins dans les amphiboles, ainsi que les teneurs de D/H les plus basses et leur grande variation, sont celles du complexe d'Ilmaussaq. Les amphiboles de la Pninsule de Kola et du Canada sont similaires, mais toutefois moins appauvries en D. En ce qui concerne les amphiboles des complexes du NO de la Namibie, elles prsentent des compositions isotopiques de l'hydrogne magmatiques normales (-73 -100 0/00), contiennent moins de Fe (15-17 wt%) et sont fortement enrichies en Ca et moins en Na. Dans ce cas, l'alcalinit est moins importante en comparaison des autres complexes tudis. En dehors des teneurs en lments alcalins des amphiboles, l'alcalinit des fluides s'avre galement un facteur important, ce qui est cohrent avec certaines suggestions partir de systmes exprimentaux. Afin de mieux contraindre ce facteur, des expriences d'changes hydrothermaux entre les amphiboles et les fluides de salinit diffrente ont t effectues en simulant des conditions naturelles. L'approximation d'amphiboles naturelles de complexes igns alcalins, couple aux expriences d'change, aide prciser les facteurs contrlant le fractionnement des isotopes de l'hydrogne dans les roches alcalines. Les valeurs extrmement basses de 3D des amphiboles de ces complexes alcalins peuvent tre dues une combinaison de diffrents facteurs, telles qu'une haute alcalinit, une haute teneur en Fe et une faible profondeur d'intrusion. Les grandes variations ainsi que les faibles valeurs de SD des amphiboles tudies peuvent rsulter d'un processus magmatique interne et il est peu probable que de l'eau mtorique soit implique et/ou que le dgazage magmatique ait jou un rle. THESIS ABSTRACT Major element and stable isotope compositions of amphiboles were analyzed from a number of alkaline and peralkaline igneous complexes in order to determine the importance of compositional variations in minerals to hydrogen isotope fractionations in natural mineral-melt-fluid systems. The thesis mainly focuses on nepheline syenites of well-studied, but chemically variable alkaline intrusive rocks, from which amphiboles and, if possible, other hydrous silicates such as micas and eudialytes were separated. The system of primary interest was the alkaline Ilmaussaq Complex of the Gardar Province of South Greenland. For the purpose of comparison additional samples were collected and examined from the Tugtutq Complex (South Greenland), the Khibina and Lovozero Complexes (Kola Peninsular, Russia), Mount St-Hilaire and Mount Royal (Canada) and six further complexes from NW Namibia (Cape Cross, Okenyenya, Messum, Etaneno, Kalkfeld, and Okorusu). The hydrogen isotope compositions of amphiboles from the localities studied differ greatly, which is atypical for amphiboles from mantle, range between - 227 and - 700/00 (latter compatible with a simple mantle origin). As this wide range in compositions and the extreme depletion in the heavy hydrogen isotope (D) content relative to other igneous rocks appear to be unique to alkaline to peralkaline rocks of this type, a common process is indicated. The different alkaline complexes chosen cover a wide range of amphibole chemical compositions. Detailed chemical characterization of amphiboles by electron microprobe and Mssbauer spectroscopy analyses helped to constrain the control of Fe on the H-isotope fractionations. Complete characterization of the chemical compositions of the amphiboles support Fe-control on fractionations and at least for the peralkaline Ilmaussaq complex a relationship between Fe3+/FeT ratios and variations in D/H. The studied complexes differ in their agpaitic index (Na+K/Al) and also in their Fe-content. The most iron (27-35 wt. %) and alkaline element rich amphiboles, with the lowermost D/H ratio, as well with very wide range, are the ones from Ilmaussaq complex. Similar, but less D depleted amphiboles are from the Kola Peninsula and the Canadian localities. The complexes described from NW Namibia have amphiboles with normal magmatic hydrogen isotope composition (-730/00 to -1000/00), and have less Fe-content (15-17 wt. %), and are more Ca-and less Na-rich. In this case alkalinity is not that important in comparison to the other studied complexes. Beside the alkaline element contents in the amphiboles, the alkalinity of the fluids has been found to be an important factor, in conjunction with earlier suggestions from experimental systems. To further constrain this factor, hydrothermal exchange experiments between amphiboles and fluids of different salinity simulating natural conditions were performed. The approach of examining natural amphiboles from alkaline igneous complexes in parallel to performing exchange experiments - helped to further constrain the factors controlling the H-isotope fractionations in alkaline rocks. The observed changes between the hydrogen and oxygen isotope compositions of amphiboles and fluids before and after the experiments suggest that another phase was produced during the experiments, which influenced the final hydrogen isotope composition of the system. This presumably hydrous phase has also influenced the Fe3 +/Fe2+ ratio of the amphiboles, which became more oxidized. The extremely low SD values of amphiboles in these alkaline complexes may be due to a combination of different factors such as high alkalinity, high Fe-content, and shallow intrusion depths. This wide range and the low SD values of the amphiboles studied might be a result of internal, magmatic processes and it is unlikely that meteoric water was involved and/or magmatic degassing played an important role. RSUM DE LA THSE (pour le grand public) Fractionnement isotopique de l'hydrogne entre amphiboles, micas et fluides dans des intrusions alcalines Zsfia Wczek Directeur de thse, Prof. Torsten W. Vennemann Institut de Minralogie et Gochimie, Universit de Lausanne Les roches alcalines et celles qui leurs sont associes sont des sources importantes de nombreux minraux et minerais, tels l'apatite, le niobium, le diamant et autres pierres prcieuses. Cette tude se concentre sur des complexes alcalins localiss dans le sud du Groenland, au Canada, dans la pninsule de Kola en Russie et au nord-ouest de la Namibie. Ces complexes sont composs de roches ayant cristallis partir de magmas et de fluides trs enrichis en alcalins. Cet enrichissement permet la prcipitation de minraux inhabituels riches en potassium et/ou sodium, telles les amphiboles sodiques, galement enrichies en fer. Les amphiboles tudies ont des compositions calciques, sodi-calciques et sodiques, qui refltent leurs diffrents environnements de formation. Des tudes prcdentes ont rvl une large gamme de rapports isotopiques de l'hydrogne dans les amphiboles de roches hyperalcalines, dont certains extrmement bas. Cette variation importante est trs intrigante, sachant que des valeurs entre -40 et -800/00 correspondent des silicates igns hydrats et non altrs, alors que des valeurs descendant jusqu'a -1500/00 ncessiteraient une altration par de l'eau mtorique et/ou une contamination par les roches environnantes ou des sdiments riches en matire organique. Dans l cas prcis du complexe d'Ilmaussaq (sud du Groenland), aucune de ces explications n'a pu tre dmontre et des valeurs encore plus faibles ont t trouves. Le complexe d'Ilmaussaq prsente des valeurs de rapport isotopique de l'hydrogne entre -227 et -500/00 dans les amphiboles. Une origine mantellique permet d'expliquer les valeurs leves, mais d'autres processus doivent entrer en jeu pour engendrer les valeurs les plus ngatives. C'est l'identification de ces processus que nous nous sommes attachs dans ce travail. Les grandes variations observes dans les teneurs en fer et dans le rapport Fe3+/FeT des roches et des minraux de ces complexes sont corrles avec d'autres paramtres chimiques, tels que la composition isotopique de l'hydrogne dans les amphiboles. Nous avons ds lors abord les questions suivantes: quelle est la relation entre la teneur en fer des amphiboles et leur composition isotopique? Que nous apprennent les changements de la teneur en fer et les changements dans le rapport Fe3+/FeT sur les processus ptrologiques dans ces roches? Pour rpondre ces questions, nous avons analys les compositions isotopiques de l'oxygne et de l'hydrogne dans les amphiboles et d'autres silicates hydrats. La composition chimique et le rapport Fe3+/FeT des amphiboles ont galement t dtermins. Des expriences hydrothermales simulant des conditions naturelles ont t entreprises afin de mieux comprendre les processus de fractionnement isotopiques dans ces systmes trs alcalins. Nos conclusions sont les suivantes: (1) Les valeurs extrmement faibles ainsi que les larges variations des rapports isotopiques de l'hydrogne des amphiboles de ces complexes alcalins sont dues une combinaison de facteurs tels que la forte alcalinit, la haute teneur en fer et la profondeur trs faible de l'intrusion. (2) Ces valeurs sont probablement le rsultat de processus magmatiques internes. (3) Il est peu probable que les eaux mtoriques et/ou le dgazage magmatique aient jou un rle lors de la formation de ces amphiboles. (4) Certaines corrlations, en accord avec les tudes prcdentes, ont pu tre trouves au niveau des concentrations en fer. (5) Dans le cas du complexe d'Ilmaussaq exclusivement, une relation a t trouve entre le rapport Fe3+/FeT et la composition isotopique de l'hydrogne des amphiboles.
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When massively expressed in bacteria, recombinant proteins often tend to misfold and accumulate as soluble and insoluble nonfunctional aggregates. A general strategy to improve the native folding of recombinant proteins is to increase the cellular concentration of viscous organic compounds, termed osmolytes, or of molecular chaperones that can prevent aggregation and can actively scavenge and convert aggregates into natively refoldable species. In this study, metal affinity purification (immobilized metal ion affinity chromatography [IMAC]), confirmed by resistance to trypsin digestion, was used to distinguish soluble aggregates from soluble nativelike proteins. Salt-induced accumulation of osmolytes during induced protein synthesis significantly improved IMAC yields of folding-recalcitrant proteins. Yet, the highest yields were obtained with cells coexpressing plasmid-encoded molecular chaperones DnaK-DnaJ-GrpE, ClpB, GroEL-GroES, and IbpA/B. Addition of the membrane fluidizer heat shock-inducer benzyl alcohol (BA) to the bacterial medium resulted in similar high yields as with plasmid-mediated chaperone coexpression. Our results suggest that simple BA-mediated induction of endogenous chaperones can substitute for the more demanding approach of chaperone coexpression. Combined strategies of osmolyte-induced native folding with heat-, BA-, or plasmid-induced chaperone coexpression can be thought to optimize yields of natively folded recombinant proteins in bacteria, for research and biotechnological purposes.
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Microbial mats are complex but stable, multi-layered and multi-functional biofilms, which are the most frequent bacterial formations in nature. The functional strategies and physiological versatility of the bacterial populations growing in microbial mats allow bacteria to resist changing conditions within their environment. One of these strategies is the accumulation of carbon- and energy-rich polymers that permit the recovery of metabolic activities when favorable conditions are restored. In the present study, we systematically screened microbial mats for bacteria able to accumulate large amounts of the ester carbon polymers polyhydroxyalkanoates (PHA). Several of these strains were isolated from Ebro Delta microbial mats and their ability to accumulate PHA up to 40-60 % of their dry weight was confirmed. According to two identification approaches (16S rRNA and ropD genes), these strains were identified as Halomonas alkaliphila (MAT-7, -13, -16), H. neptunia (MAT-17), and H. venusta (MAT-28). To determine the mode of growth yielding maximum PHA accumulation, these three different species were cultured in an artificial biofilm in which the cells were immobilized on alginate beads. PHA accumulation by cells that had detached from the biofilm was compared with that of their planktonic counterparts. Experiments in different culture media showed that PHA accumulation, measured as the relative fluorescence intensity after 48 h of incubation at 30 C, was higher in immobilized than in planktonic cells, with the exception of cells growing in 5 % NaCl, in which PHA accumulation was drastically lower in both. Therefore, for obtaining high PHA concentrations, the use of immobilized cells may be a good alternative to the PHA accumulation by bacteria growing in the classical, planktonic mode. From the ecological point of view, increased PHA accumulation in detached cells from biofilms would be a natural strategy to improve bacterial dispersion capacity and, consequently, to increase survival in stressed environments.
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Microbial mats are complex but stable, multi-layered and multi-functional biofilms, which are the most frequent bacterial formations in nature. The functional strategies and physiological versatility of the bacterial populations growing in microbial mats allow bacteria to resist changing conditions within their environment. One of these strategies is the accumulation of carbon- and energy-rich polymers that permit the recovery of metabolic activities when favorable conditions are restored. In the present study, we systematically screened microbial mats for bacteria able to accumulate large amounts of the ester carbon polymers polyhydroxyalkanoates (PHA). Several of these strains were isolated from Ebro Delta microbial mats and their ability to accumulate PHA up to 40-60 % of their dry weight was confirmed. According to two identification approaches (16S rRNA and ropD genes), these strains were identified as Halomonas alkaliphila (MAT-7, -13, -16), H. neptunia (MAT-17), and H. venusta (MAT-28). To determine the mode of growth yielding maximum PHA accumulation, these three different species were cultured in an artificial biofilm in which the cells were immobilized on alginate beads. PHA accumulation by cells that had detached from the biofilm was compared with that of their planktonic counterparts. Experiments in different culture media showed that PHA accumulation, measured as the relative fluorescence intensity after 48 h of incubation at 30 C, was higher in immobilized than in planktonic cells, with the exception of cells growing in 5 % NaCl, in which PHA accumulation was drastically lower in both. Therefore, for obtaining high PHA concentrations, the use of immobilized cells may be a good alternative to the PHA accumulation by bacteria growing in the classical, planktonic mode. From the ecological point of view, increased PHA accumulation in detached cells from biofilms would be a natural strategy to improve bacterial dispersion capacity and, consequently, to increase survival in stressed environments.
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We present a new lab-on-a-chip system for electrophysiological measurements on Xenopus oocytes. Xenopus oocytes are widely used host cells in the field of pharmacological studies and drug development. We developed a novel non-invasive technique using immobilized non-devitellinized cells that replaces the traditional "two-electrode voltage-clamp" (TEVC) method. In particular, rapid fluidic exchange was implemented on-chip to allow recording of fast kinetic events of exogenous ion channels expressed in the cell membrane. Reducing fluidic exchange times of extracellular reagent solutions is a great challenge with these large millimetre-sized cells. Fluidic switching is obtained by shifting the laminar flow interface in a perfusion channel under the cell by means of integrated poly-dimethylsiloxane (PDMS) microvalves. Reagent solution exchange times down to 20 ms have been achieved. An on-chip purging system allows to perform complex pharmacological protocols, making the system suitable for screening of ion channel ligand libraries. The performance of the integrated rapid fluidic exchange system was demonstrated by investigating the self-inhibition of human epithelial sodium channels (ENaC). Our results show that the response time of this ion channel to a specific reactant is about an order of magnitude faster than could be estimated with the traditional TEVC technique.
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Oxalic and oxamic acids are the ultimate and more persistent by-products of the degradation of N-aromatics by electrochemical advanced oxidation processes (EAOPs). In this paper, the kinetics and oxidative paths of these acids have been studied for several EAOPs using a boron-doped diamond (BDD) anode and a stainless steel or an air-diffusion cathode. Anodic oxidation (AO-BDD) in the presence of Fe2+ (AO-BDD-Fe2+) and under UVA irradiation (AO-BDD-Fe2+-UVA), along with electro-Fenton (EF-BDD), was tested. The oxidation of both acids and their iron complexes on BDD was clarified by cyclic voltammetry. AO-BDD allowed the overall mineralization of oxalic acid, but oxamic acid was removed much more slowly. Each acid underwent a similar decay in AO-BDD-Fe2+ and EFBDD, as expected if its iron complexes were not attacked by hydroxyl radicals in the bulk. The faster and total mineralization of both acids was achieved in AO-BDD-Fe2+-UVA due to the high photoactivity of their Fe(III) complexes that were continuously regenerated by oxidation of their Fe(II) complexes. Oxamic acid always released a larger proportion of NH4 + than NO3- ion, as well as volatile NOx species. Both acids were independently oxidized at the anode in AO-BDD, but in AO-BDD-Fe2+-UVA oxamic acid was more slowlydegraded as its content decreased, without significant effect on oxalic acid decay. The increase in current density enhanced the oxidation power of the latter method, with loss of efficiency. High Fe2+ contents inhibited the oxidation of Fe(II) complexes by the competitive oxidation of Fe2+ to Fe3+. Low current densities and Fe2+ contents are preferable to remove more efficiently these acids by the most potent AO-BDD-Fe2+-UVA method.
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Genetically constructed microbial biosensors for measuring organic pollutants are mostly applied in aqueous samples. Unfortunately, the detection limit of most biosensors is insufficient to detect pollutants at low but environmentally relevant concentrations. However, organic pollutants with low levels of water solubility often have significant gas-water partitioning coefficients, which in principle makes it possible to measure such compounds in the gas rather than the aqueous phase. Here we describe the first use of a microbial biosensor for measuring organic pollutants directly in the gas phase. For this purpose, we reconstructed a bioluminescent Pseudomonas putida naphthalene biosensor strain to carry the NAH7 plasmid and a chromosomally inserted gene fusion between the sal promoter and the luxAB genes. Specific calibration studies were performed with suspended and filter-immobilized biosensor cells, in aqueous solution and in the gas phase. Gas phase measurements with filter-immobilized biosensor cells in closed flasks, with a naphthalene-contaminated aqueous phase, showed that the biosensor cells can measure naphthalene effectively. The biosensor cells on the filter responded with increasing light output proportional to the naphthalene concentration added to the water phase, even though only a small proportion of the naphthalene was present in the gas phase. In fact, the biosensor cells could concentrate a larger proportion of naphthalene through the gas phase than in the aqueous suspension, probably due to faster transport of naphthalene to the cells in the gas phase. This led to a 10-fold lower detectable aqueous naphthalene concentration (50 nM instead of 0.5 micro M). Thus, the use of bacterial biosensors for measuring organic pollutants in the gas phase is a valid method for increasing the sensitivity of these valuable biological devices.
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Soil pollution with hexachlorocyclohexane (HCH) has caused serious environmental problems. Here we describe the targeted degradation of all HCH isomers by applying the aerobic bacterium Sphingobium indicum B90A. In particular, we examined possibilities for large-scale cultivation of strain B90A, tested immobilization, storage and inoculation procedures, and determined the survival and HCH-degradation activity of inoculated cells in soil. Optimal growth of strain B90A was achieved in glucose-containing mineral medium and up to 65% culturability could be maintained after 60 days storage at 30 degrees C by mixing cells with sterile dry corncob powder. B90A biomass produced in water supplemented with sugarcane molasses and immobilized on corncob powder retained 15-20% culturability after 30 days storage at 30 degrees C, whereas full culturability was maintained when cells were stored frozen at -20 degrees C. On the contrary, cells stored on corncob degraded gamma-HCH faster than those that had been stored frozen, with between 15 and 85% of gamma-HCH disappearance in microcosms within 20 h at 30 degrees C. Soil microcosm tests at 25 degrees C confirmed complete mineralization of [(14)C]-gamma-HCH by corncob-immobilized strain B90A. Experiments conducted in small pits and at an HCH-contaminated agricultural site resulted in between 85 and 95% HCH degradation by strain B90A applied via corncob, depending on the type of HCH isomer and even at residual HCH concentrations. Up to 20% of the inoculated B90A cells survived under field conditions after 8 days and could be traced among other soil microorganisms by a combination of natural antibiotic resistance properties, unique pigmentation and PCR amplification of the linA genes. Neither the addition of corncob nor of corncob immobilized B90A did measurably change the microbial community structure as determined by T-RFLP analysis. Overall, these results indicate that on-site aerobic bioremediation of HCH exploiting the biodegradation activity of S. indicum B90A cells stored on corncob powder is a promising technology.
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This project was undertaken jointly with a project supported by the Iowa Corn Promotion Board. Together the projects aimed at producing the organic acids, propionic acid and acetic acid, by fermentation. The impacts were to provide agriculturally-based alternatives to production of these acids, currently produced mainly as petrochemicals. The potentially high-demand use for acetic acid is as the "acetate" in Calcium Magnesium Acetate (CMA), the non-corrosive road deicer. Fermentation was, however, far from being an economically acceptable alternative. Gains were made in this work toward making this a feasible route. These advances included (1) development of a variant strain of propionibacteria capable of producing higher concentrations of acids; (2) comparison of conditions for several ways of cultivating free cells and establishment of the relative benefits of each; (3) achievement of the highest productivity in fermentations using immobilized cells; (4) identification of corn steep liquor as a lower cost substrate for the fermentation; (5) application of a membrane extraction system for acid recovery and reduction of product inhibition; and (6) initial use of more detailed economic analysis of process alternatives to guide in the identification of where the greatest payback potential is for future research. At this point, the fermentation route to these acids using the propionibacteria is technically feasible, but economically unfeasible. Future work with integration of the above process improvements can be expected to lead to further gains in economics. However, such work can not be expected to make CMA a less expensive deicer than common road salt.
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Microbial mats are complex but stable, multi-layered and multi-functional biofilms, which are the most frequent bacterial formations in nature. The functional strategies and physiological versatility of the bacterial populations growing in microbial mats allow bacteria to resist changing conditions within their environment. One of these strategies is the accumulation of carbon- and energy-rich polymers that permit the recovery of metabolic activities when favorable conditions are restored. In the present study, we systematically screened microbial mats for bacteria able to accumulate large amounts of the ester carbon polymers polyhydroxyalkanoates (PHA). Several of these strains were isolated from Ebro Delta microbial mats and their ability to accumulate PHA up to 40-60 % of their dry weight was confirmed. According to two identification approaches (16S rRNA and ropD genes), these strains were identified as Halomonas alkaliphila (MAT-7, -13, -16), H. neptunia (MAT-17), and H. venusta (MAT-28). To determine the mode of growth yielding maximum PHA accumulation, these three different species were cultured in an artificial biofilm in which the cells were immobilized on alginate beads. PHA accumulation by cells that had detached from the biofilm was compared with that of their planktonic counterparts. Experiments in different culture media showed that PHA accumulation, measured as the relative fluorescence intensity after 48 h of incubation at 30 C, was higher in immobilized than in planktonic cells, with the exception of cells growing in 5 % NaCl, in which PHA accumulation was drastically lower in both. Therefore, for obtaining high PHA concentrations, the use of immobilized cells may be a good alternative to the PHA accumulation by bacteria growing in the classical, planktonic mode. From the ecological point of view, increased PHA accumulation in detached cells from biofilms would be a natural strategy to improve bacterial dispersion capacity and, consequently, to increase survival in stressed environments.
