Nitrogenase: A nucleotide-dependent molecular switch

In the simplest terms, the biological nitrogen cycle is the reduction of atmospheric dinitrogen (N2) to ammonia with the subsequent reoxidation ammonia to dinitrogen (1). At the reduction level of ammonia, nitrogen incorporated into precursors for biological macromolecules such as proteins and nucleic acids. Reoxidation of ammonia to dinitrogen ("denitrification") by a variety of microbes (by way of nitrite and other oxidation levels of nitrogen) leads to the depletion of the "fixed," biologically usable, nitrogen pool. Besides the relatively small contribution from commercial ammonical fertilizer production, replenishing of the nitrogen pool falls mainly to a limited number of physiologically diverse microbes (e.g. eubacteria and archaebacteria; free-living and symbiotic; aerobic and anaerobic) that contain the nitrogenase enzyme system

Evaluation of a spacecraft nitrogen generator

An experiment was completed to demonstrate that low ammonia concentrations in the product nitrogen stream are possible using the staging concept. Mixtures of nitrogen, hydrogen and ammonia were fed into a temperature controlled packed bed ammonia dissociator. An ammonia concentration of 1.03% in the feed stream was reduced to less than 50 ppm at temperatures greater than or equal to 777K. The actual inlet ammonia concentration to the final nitrogen generation module ammonia dissociation stage was only 0.09%

Recycling of phosphorus and ammonia nitrogen from digestate

Digestate from biogas plants, formed by dewatering anaerobically stabilized sludge, is characteristic of high concentrations of phosphates and ammonia nitrogen suitable for further use. Phosphorus is an element widely used to produce fertilizers, and because of its continually shortening natural supplies, recycling of phosphorus is gaining on significance. Both phosphorus and nitrogen are important elements and their presence affect the quality of water resources. Both elements can contribute to eutrophication. At the same time, both phosphorus and ammonia nitrogen, are important elements for agricultural production, and therefore greater demands are being made on the effort to connect sewage treatment processes and the process of recycling of these nutrients. A suitable product of phosphorus and ammonia nitrogen are phosphates in the form of a structurally-poorly soluble precipitate of magnesium ammonium phosphate (struvite). This form of slowly decomposing fertilizer is distinguished by its fertilizing abilities. Compared to direct use of digestate as a fertilizer, struvite is more stable and can gradually release ammonia nitrogen for a long time without unnecessary losses. In the reported experiments, the precipitation efficiency of the recycling of ammonia nitrogen and phosphorus from the digestate liqour (liquid discharge from digestate) was, at a stoichiometric ratio of Mg2+: NH4+: PO43- (3.2: 1: 0.8) and a stirring time of 15 minutes, 87 % for ammonia nitrogen ions

Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration

Partitioning of elemental nitrogen in star-forming regions is not well constrained. Most nitrogen is expected to be partitioned among atomic nitrogen, molecular nitrogen (N2), and icy N-bearing molecules, such as ammonia (NH3) and N2. Atomic nitrogen is not directly observable in the cold gas. In this paper, we propose an indirect way to constrain the amount of atomic nitrogen in the cold gas of star-forming clouds, via deuteration in ammonia ice, the [ND2H/NH2D]/[NH2D/NH3] ratio. Using gas-ice astrochemical simulations, we show that if atomic nitrogen remains as the primary reservoir of nitrogen during cold ice formation stages, the [ND2H/NH2D]/[NH2D/NH3] ratio is close to the statistical value of 1/3 and lower than unity, whereas if atomic nitrogen is largely converted into N-bearing molecules, the ratio should be larger than unity. Observability of ammonia isotopologues in the inner hot regions around low-mass protostars, where ammonia ice has sublimated, is also discussed. We conclude that the [ND2H/NH2D]/[NH2D/NH3] ratio can be quantified using a combination of VLA and ALMA observations with reasonable integration times, at least toward IRAS 16293-2422 where high molecular column densities are expected.Comment: Accepted for publication in MNRAS, 12 pages, 9 figures, 1 Tabl

Glutamate biosynthesis in Bacillus azotofixans. 15N NMR and enzymatic studies

Pathways of ammonia assimilation into glutamic acid in Bacillus azotofixans, a recently characterized nitrogen-fixing species of Bacillus, were investigated through observation by NMR spectroscopy of in vivo incorporation of 15N into glutamine and glutamic acid in the absence and presence of inhibitors of ammonia-assimilating enzymes, in combination with measurements of the specific activities of glutamate dehydrogenase, glutamine synthetase, glutamate synthase, and alanine dehydrogenase. In ammonia-grown cells, both the glutamine synthetase/glutamate synthase and the glutamate dehydrogenase pathways contribute to the assimilation of ammonia into glutamic acid. In nitrate-grown and nitrogen-fixing cells, the glutamine synthetase/glutamate synthase pathway was found to be predominant. NADPH-dependent glutamate dehydrogenase activity was detectable at low levels only in ammonia-grown and glutamate-grown cells. Thus, B. azotofixans differs from Bacillus polymyxa and Bacillus macerans, but resembles other N2-fixing prokaryotes studied previously, as to the pathway of ammonia assimilation during ammonia limitation. Implications of the results for an emerging pattern of ammonia assimilation by alternative pathways among nitrogen-fixing prokaryotes are discussed, as well as the utility of 15N NMR for measuring in vivo glutamate synthase activity in the cell

Nitrogen efficiency of dairy cattle : from protein evaluation to ammonia emission

Diet optimization contributes considerably to increased nitrogen efficiency of dairy cattle, resulting in reduced nitrogen losses. This thesis focuses on three themes: the potential advances in protein evaluation systems for ruminants, the relationship between dairy cow diet and ammonia emission and the opportunities to monitor ammonia emission from dairy cow barns by application of milk urea content as a practical indicator. Overall, the present work shows that farm management can be aimed at increased nitrogen efficiency of dairy cattle and reduced ammonia emission without compromising other sustainability objectives such as the integral ecological footprint, animal health and farm profitability. </p

Antipollution system to remove nitrogen dioxide gas

Gas phase reaction system using anhydrous ammonia removes nitrogen dioxide. System consists of ammonia injection and mixing section, reaction section /reactor/, and scrubber section. All sections are contained in system ducting

Preprototype nitrogen supply subsystem development

A nitrogen supply subsystem based on the dissociation of hydrazine into a mixture of hydrogen and nitrogen is developed. The latter is separated to provide makeup nitrogen to control the composition of spacecraft atmospheres. Specific hardware developments resulted in the design and fabrication of a nominal 3.6 kg/d nitrogen generation module. The design integrates a hydrazine catalytic dissociator, three ammonia dissociation stages and four hydrogen separation stages into a 33 kg, 14 cu dm module. A technique was devised to alternate the ammonia dissociation and hydrogen separation stages to give high nitrogen purity in the end product stream. Tests show the product stream to contain less than 0.5 percent hydrogen and 10 parts per million ammonia. The design and development of a test stand for the nitrogen generation module and a series of tests which verified its operation and performance capability are described

NITROGEN DYNAMICS IN THE RUMEN AND ABOMASUM OF SHEEP DETERMINED WITH 15 N-LABELLED AMMONIA OR 15 N-LABELLED DUCKWEED

An experiment was carried out to investigate the dynamics of nitrogen (N) in the rumen and abomasum of rumen and abomasum-cannulated sheep using 15 N dilution techniques. The 15 N tracer was administered into the rumen as 15 N-ammonia or 15 N-labelled duckweed and the transfer of the 15 N label to various N pools was followed. Flow of digesta from the rumen into the abomasum was ascertained by double marker technique with cobalt and acid insoluble ash as liquid digesta and particle digesta marker, respectively. Results showed that the average of rumen water volume was 4.5 l ± SEM 0.57 and the mean water flow through the abomasum (8.6 ± 0.45 l/d) was higher than outflow from the rumen (7.4 ± 0.55 l/d). Nitrogen intake tended to be higher, but total-N passing the abomasum tended to be lower when the sheep were infused by 15 N-ammonia than when they were ingesting 15 N-duckweed. The ammonia concentration in abomasal digesta was about 93 mg N/kg and non ammonia N (NAN) was about 1.58 g N/kg. The rates of flow of total-N as ammonia-N and as NAN did not differ (P>0.05) between animals or diets, with means (± SEM) of 57.7 ± 0.96 and 964 ± 2.13 mmol/d (or 0.81 and 13.5 g N/d), respectively. About 34-59% of the dietary N was removed from the rumen as ammonia (absorbed and in digesta). The enrichments of rumen ammonia N appeared to have reached plateau values after about 10 h of 15 N-ammonia infusion. The percentage of bacterial-N derived from ammonia-N (from the period of 15 N-ammonia infusion) was 53.63 % (ratio of plateau enrichments) and thus 37.47% of bacterial-N was derived from NAN sources in the rumen. The total 15 N flow through the abomasum was higher (P<0.001) when 5 N duckweed was given rather than 15 N-ammonia (2.40 0.02 mmol/d). The 15 N in NAN flowing to the abomasum (mmol/d) was also significantly higher (P<0.001) when 15 N-duckweed was given rather than 15 N ammonia, with means of 0.00, respectively. The flow of 15 N in ammonia, on the other hand, was lower (P<0.01) when sheep ingested 15 N-duckweed than when they were infused with 15 N-ammonia (0.09  0.00v. 0.13  0.09  mmol/d).Damry 1 Keywords : Nitrogen Dynamics, Rumen, Ammonia-N, Bacterial-