Photoproduction Of Ammonia Research Articles

Factor influencing photoproduction of ammonia from dinitrogen byNostoc muscorum

Effective photoproduction of ammonia from dinitrogen has been achieved in a system consisting of a cell suspension of cyanobacteriumNostoc treated with a low concentration ofl-methionine sulfoximine (MSX). As a result of inactivation of cellular glutamate-ammonia ligase by MSX, growth was prevented, the rate of nitrogenase activity increased and about 90% of ammonia resulting from dinitrogen fixation was exported and accumulated in the ambient medium. The rate of NH4+ production was found to be regulated by different factors such as light-dark cycle, cell density, depth of culture and air bubbling. Ammonia production was stimulated by (i) a culture density corresponding to 1.5 μg chlorophyll a per mL, (ii) a depth of 10 mm, and (iii) continuous illumination for 24 h. The nitrogenase activity was found to be enhanced in the experimental sets where ammonia production was maximal.

Plasma-sprayed semiconductor electrodes: photoelectrochemical characterization and ammonia photoproduction by substoichiometric tungsten oxides

Two substoichiometric tungsten oxide coatings have been obtained by plasma spray of WO{sub 3} powder on Ti substrates. The films are 40 {plus minus} 20 {mu}m thick and are yellow (WO{sub 2.99}) or dark blue (WO{sub 2.97}). WO{sub 2.99} coatings show a highly textured surface with a specific area 27.9 times the geometrical one. X-ray diffraction pattern reveals that their structure is a mixture of monoclinic and triclinic phases. The yellow films have been characterized photoelectrochemically in regenerative cells by using O{sub 2}/H{sub 2}O redox at pH 2.0. Under anodic polarization of 1.5 V (SCE) their quantum yield is between 10% and 20% in the wavelength range comprised between 270 and 430 nm with an indirect bandgap of 2.55 eV and a flatband potential of {minus}0.1 V. WO{sub 2.99} films have been tested for NH{sub 3} photoproduction.

Effects of three pesticides on MSX-induced ammonia photoproduction by the cyanobacterium Nostoc linckia

Three pesticides (2,4-D, basalin, aldrin) inhibited l-methionine- dl-sulfoximine (MSX)-induced photoproduction of ammonia by the nitrogen-fixing cyanobacterium Nostoc linckia. Combinations of pesticides and MSX were inhibitory except at low concentrations (100 and 500 μg/ml) of 2,4-D which stimulated NH 4 + production. Similar results were obtained when pesticides were added 6 hr after the addition of MSX, but the inhibition was weaker. When MSX was added to the culture 6 hr after the addition of pesticides, the pesticides stimulated NH 4 + photoproduction. Similar results were obtained on nitrogenase activity of the organism.

Sustained photoproduction of ammonia from nitrate or nitrite by permeabilized cells of the cyanobacterium Phormidium laminosum

The addition of micromolar amounts of the glutamate analogue l-methionine- d, l-sulphoximine (MSX) to cell suspensions of the filamentous non N 2-fixing cyanobacterium Phormidium laminosum rapidly caused the complete inhibition of glutamine synthetase activity and prevented cell growth. Such MSX-treated cells were able to photoproduce ammonia from nitrate or nitrite at about 2.3 μmol (mg chlorophyll) −1 h −1. This value could be significantly increased after cell permeabilization by repeated freeze—thaw (F/T) cycles or by storing cells frozen at −20 °C for several days. Photoproduction of ammonia showed an optimum pH value of 8.5 and was saturated by 10 mM nitrate or nitrite. However, the ratio ammonia released/nitrate disappearance was higher at low nitrate concentrations. Although free F/T cells showed higher initial rates of ammonia production, when such cells were immobilized in calcium alginate beads and packed into a continuous flow reactor they photoproduced ammonia for 100 h at a maximal rate of about 10 μmol (mg chlorophyll) −1 h −1.

Factors affecting the photoproduction of ammonia from dinitrogen and water by the cyanobacterium Anabaena sp. strain ATCC 33047

Synthesis of ammonia from dinitrogen and water by suspensions of Anabaena sp. Strain ATCC 33047 treated with the glutamine synthetase inhibitor L-methionine-D,L-sulfoximine is strictly dependent on light. Under otherwise optimal conditions, the yield of ammonia production is influenced by irradiance, as well as by the density, depth, and turbulence of the cell suspension. The interaction among these factors seems to determine the actual amount of light available to each single cell or filament in the suspension for the photoproduction process. Under convenient illumination, the limiting factor in the synthesis of ammonia seems to be the cellular nitrogenase activity level, but under limiting light conditions the limiting factor could, however, be the assimilatory power required for nitrogen fixation. Photosynthetic ammonia production from atmospheric nitrogen and water can operate with an efficiency of ca. 10% of its theoretical maximum, representing a remarkable process for the conversion of light energy into chemical energy.

Ammonia photoproduction by immobilized Cyanospira rippkae

Ammonia photoproduction by immobilized Cyanospira rippkae

Ammonia photoproduction byCyanospira rippkae cells ‘entrapped’ in dialysis tube

The photoproduction of ammonia by cells of the heterocystous cyanobacteriumCyanospira rippkae in the presence of the glutamine synthetase inhibitor, L-methionine D,L-sulfoximine (MSX), was investigated. The time course of changes in protein, pigment and carbohydrate concentrations and the C2H2-reducing activity of nitrogenase in MSX treated and untreated filament suspensions was also determined. The results show that nearly 40 h after MSX addition the cells are able to recover from the nitrogen starvation induced by the inhibitor by themselves, without the removal of MSX or the addition of nitrogenous compounds. Biliproteins, mobilized as a consequence of MSX addition, seem to play a key role in the process of cell recovery. These findings were exploited in a semicontinuous ammonia producing process with cells ‘immobilized’ in a dialysis tube photobioreactor.

Ammonia and hydrogen production by immobilized cyanobacteria

Heterocystous cyanobacteria Anabaena azollae (symbiotic) and Mastigocladus laminosus (thermophilic) were immobilized in polyvinyl or polyurethane foams and in alginate. Following immobilization there was a progressive colonization of the matrices when incubated under light in suitable growth media. Scanning electron microscopy studies of polyvinyl and polyurethane foam immobilized cells showed the development of a filamentous mucilage connected to the surface of the matrix. Immobilization led to an increase and/or to a stabilization of the rate of H 2 photoproduction. This increase occurred mainly via hydrogenase-mediated production. Immobilization also stabilized nitrogenase activity and increased initial rates of nitrogen fixation by both species of cyanobacteria. Photoproduction of ammonia was monitored in the presence of l-methionine- d,l-sulfoximine, an inhibitor of glutamine synthetase activity. High yields of ammonia production, up to 400 μmol and 100 μmol mg chlorophyll −1 per 24 h, were obtained in batch reactors from polyvinyl foam immobilized A. azollae and M. laminosus, respectively, whereas control free-living cultures produced less than 10 μmol ammonia under the same conditions. A similar yield increase was observed when the membrane permeability of alginate-immobilized A. azollae was increased by an acetone pretreatment. This suggests that the increase in ammonia production on immobilization in polyvinyl foam is at least partly related to changes in membrane permeability induced by the immobilization process itself as a consequence of cell-matrix interactions.

Photoproduction of ammonia by immobilized heterocystic cyanobacteria. Effect of nitrite and anaerobiosis

Anabaena cylindrica was immobilized in calcium alginate beads and was placed in a batch reactor in the presence of a glutamine synthetase inhibitor (methionine sulfoximide). Ammonia was released in the medium during two days with a rate of 0.35 μ moles h−1mgChl−1. Addition of nitrite to the medium increased the ammonia production as cells used the nitrite reductase pathway to form ammonia. When reactors were placed in anaerobiosis by N2 bubbling, ammonia production was sustained several days and the total ammonia formed was about two fold higher than in aerobiosis. Long term effects of MSX, nitrite and anaerobiosis are discussed.

Sustained Photoproduction of Ammonia from Dinitrogen and Water by the Nitrogen-Fixing Cyanobacterium Anabaena sp. Strain ATCC 33047

Conditions have been developed that lengthen the time during which photosynthetic dinitrogen fixation by filaments of the cyanobacterium Anabaena sp. strain ATCC 33047 proceeds freely, whereas the subsequent conversion of ammonia into organic nitrogen remains blocked, with the resulting ammonia released to the outer medium. When l-methionine-dl-sulfoximine was added every 20 h, maximal rates of ammonia production (25 to 30 mumol/mg of chlorophyll per h) were maintained for about 50 h. After this time, ammonia production ceased due to a deficiency of glutamine and other nitrogenous compounds in the filaments, conditions which finally led to cell lysis. The effective ammonia production period could be further extended to about 7 days by adding a small amount of glutamine at the end of a 40-h production period or by allowing the cells to recover for 8 h in the absence of l-methionine-dl-sulfoximine after every 40-h period in the presence of the inhibitor. A more prolonged steady production of ammonia, lasting for longer than 2 weeks, was achieved by alternating treatments with the glutamine synthetase inhibitors l-methionine-dl-sulfoximine and phosphinothricin, provided that 8-h recovery periods in the absence of either compound were also alternated throughout. The biochemically manipulated cyanobacterial filaments thus represent a system that is relatively stable with time for the conversion of light energy into chemical energy, with the net generation of a valuable fuel and fertilizer through the photoreduction of dinitrogen to ammonia.

Optimization of Conditions for Photoproduction of Ammonia from Nitrate by Anacystis nidulans

The effect of several relevant environmental factors influencing the photoproduction of ammonia from nitrate by Anacystis nidulans cells treated with the glutamine synthetase inhibitor l-methionine-dl-sulfoximine has been investigated. The optimal ratio between l-methionine-dl-sulfoximine concentration (micro-molar) and cell density (micrograms of chlorophyll per milliliter) was around 1, the process taking place at maximal rate at a temperature of about 40 degrees C, within the pH range of 7 to 10. Ammonia production was stimulated by CO(2) or bicarbonate and was not affected by the accumulation of ammonia in the medium up to concentrations of 30 mM. The rate of ammonia production was found to be determined by the interaction of at least four factors, namely, irradiance and the density, depth, and turbulence of the cell suspension. Ammonia photoproduction from nitrate and water represents an interesting process for the conversion of light energy into chemical energy, which can operate at high efficiency, around 30% of its theoretical maximum.

Sustained Photoproduction of Ammonia from Nitrate by Anacystis nidulans

Conditions that lengthen the time during which l-methionine-dl-sulfoximine (MSX) promotes excretion of ammonia produced by photosynthetic nitrate reduction in Anacystis nidulans have been sought. If MSX was added every 24 h, maximal rates of ammonia production were maintained for 3 days. After this time, ammonia production ceased due to a specific deficiency of glutamine in the cells, which finally led to cell lysis. The effective ammonia production period could be further extended either by adding a low amount of glutamine at the end of the 3-day period or by allowing the cells to recover for 8 h in the absence of MSX after every 48-h period in the presence of inhibitor. In this way, a steady production of ammonia lasting for at least 10 days was achieved. The MSX-treated cyanobacterial cells thus represent a system relatively stable with time for the conversion of light energy into chemical energy through the photoreduction of nitrate to ammonia.

Photoproduction of ammonia from nitrate by Anacystis nidulans cells

The addition of some glutamate analogs to illuminated cell suspensions of the cyanobacterium Anacystic nidulans in nitrate-containing medium promoted the release of significant amounts of ammonia. Best results were obtained with micromolar concentrations of the glutamine synthetase inactivator l-methionine- dl-sulfoximine (MSX). Inactivation of cellular glutamine synthetase by MSX was followed by prevention of cell growth and by a significant increase in the rates of uptake and reduction of nitrate. Between 85 and 90% of the ammonia resulting from the photosynthetic reduction of nitrate by the cells was found to accumulate in the outer medium. High rates of ammonia production (25–30 μmol per mg chlorophyll per h) were sustained for longer than 24 h, without interferences of the accumulated ammonia on the process. The MSX-treated cells actively producing ammonia did not appear to suffer of a general nitrogen deficiency, but they rather exhibited a specific deficiency in glutamine and abnormally high levels of carbohydrates. The results indicate the feasibility of using whole cyanobacterial cells for the photoproduction of significant amounts of ammonia from nitrate at the expense of light energy, in a simple version of photobiological energy transduction and storage.

Conversion of solar energy to chemical energy by photoassisted processes—II. Influence of the iron content on the activity of doped titanium dioxide catalysts for ammonia photoproduction

One of the new approaches of the energy problems concerning the chemical processes is the use of energy sources not yet exploited. The possibility of using in situ the products of water photodecomposition over oxide catalysts has recently received more attention. This paper reports the results of a study devoted to the ammonia photoproduction from nitrogen and water over catalysts made up of titanium and iron oxides supported on γ-alumina. A fluidized bed laboratory reactor, with radial irradiation by a high pressure mercury lamp, was used for the experiments at 120°C and atmospheric pressure. The main result is that ammonia was produced in all the experiments. A reaction mechanism has been proposed in which the photogeneration of electron-hole pairs and their separation have been considered to be the determining steps of the overall reaction with respect to the photoassisted ammonia synthesis.

277 - Photoproduction of ammonia and hydrogen peroxide

Conversion of solar energy into suitable redox energy by photosynthetic systems capable of using water as the electron donor is at the present time of great interest and significance. There are, in principle, two different kinds of redox pairs whose reduction may be coupled with the photooxidation of water to molecular oxygen : those which have potential levels similar to the hydrogen electrode and must accept electrons at the reducing side of photosystem I, and those which have positive potentials and can interact at the reducing side of photosystem II. The second group includes the couples ammonia—nitrate and hydrogen peroxide—oxygen, which exhibit standard redox potentials equal or higher than +0.3 V. Both can steadily operate in vivo and in vitro under aerobic conditions and do not have an ATP requirement.

Photoproduction of ammonia and hydrogen peroxide

Conversion of solar energy into suitable redox energy by photosyntetic systems capable of using water as the electron donor is at the present time of great interest and significance. There are, in principle, two different kinds of redox pairs whose reduction may be coupled with the photooxidation of water to molecular oxygen: those which have potential levels similar to the hydrogen electrode and must accept electrons at the reducing side of photosystem I , and those which have positive potentials and can interact at the reducing side of photosystem II . The second group includes the couples ammonia-nitrate and hydrogen peroxide-oxygen, which exhibit standard redox potentials equal or higher than +0.3V. Both can steadily operate in vivo and in vitro under aerobic conditions and do not have an ATP requirement.