Ammonia toxicity: from head to toe?

Ammonia is diffused and transported across all plasma membranes. This entails that hyperammonemia leads to an increase in ammonia in all organs and tissues. It is known that the toxic ramifications of ammonia primarily touch the brain and cause neurological impairment. However, the deleterious effects of ammonia are not specific to the brain, as the direct effect of increased ammonia (change in pH, membrane potential, metabolism) can occur in any type of cell. Therefore, in the setting of chronic liver disease where multi-organ dysfunction is common, the role of ammonia, only as neurotoxin, is challenged. This review provides insights and evidence that increased ammonia can disturb many organ and cell types and hence lead to dysfunction

Estuarine Nitrifiers: New Players, Patterns and Processes

Ever since the first descriptions of ammonia-oxidizing Bacteria by Winogradsky in the late 1800s, the metabolic capability of aerobic ammonia oxidation has been restricted to a phylogenetically narrow group of bacteria. However, the recent discovery of ammonia-oxidizing Archaea has forced microbiologists and ecologists to re-evaluate long-held paradigms and the role of niche partitioning between bacterial and archaeal ammonia oxidizers. Much of the current research has been conducted in open ocean or terrestrial systems, where community patterns of archaeal and bacterial ammonia oxidizers are highly congruent. Studies of archaeal and bacterial ammonia oxidizers in estuarine systems, however, present a very different picture, with highly variable patterns of archaeal and bacterial ammonia oxidizer abundances. Although salinity is often identified as an important factor regulating abundance, distribution, and diversity of both archaeal and bacterial ammonia oxidizers, the data suggest that the variability in the observed patterns is likely not due to a simple salinity effect. Here we review current knowledge of ammonia oxidizers in estuaries and propose that because of their steep physico-chemical gradients, estuaries may serve as important natural laboratories in which to investigate the relationships between archaeal and bacterial ammonia oxidizers

Ammonia removal in anaerobic digestion by biogas stripping: an evaluation of process alternatives using a first order rate model based on experimental findings

The feasibility of biogas stripping to remove ammonia in the anaerobic digestion of source segregated food waste was investigated. It was found in batch experiments that ammonia could be removed from digestate and that the removal followed 1st order kinetics with respect to total ammonia nitrogen concentration. Increasing temperature, biogas flow rate and initial pH all increased removal rates. Using kinetic data gathered in these experiments allowed the integration of ammonia stripping with an anaerobic digestion plant to be modelled for different configurations. Four scenarios were identified: post digestion, in situ, side-stream and pre-digestion ammonia removal relating to where in the process the ammonia stripping was performed. The modelling showed that in situ ammonia removal may be best able to reduce in-digester ammonia concentrations over a wide range of organic loading rates whereas pre-digestion showed most promise in terms of application due to the flexibility to control each part of the process separately. Further experimental work is required into these scenarios to confirm their viability

Ornithine-catalyzed urea formation in liver homogenate

Heretofore attempts to obtain synthesis of urea from ammonia (and carbon dioxide) in cell-free extracts have been unsuccessful. We have found the reaction to proceed in guinea pig liver homogenate. The following is the reaction mixture which has given the highest yields obtained so far: L-ornithine (0.00075 M), ammonia (0.0025 M), L-glutamate (0.01 M), oxalacetate (0.005 M), ATP (0.00025 M), and 0.33 gm. of homogenized liver in a final volume of 3.5 ml. The following are typical increases in urea over the blank observed in 1 hour, in micrograms: ornithine + ammonia 0, glutamate + oxalacetate 0, glutamate + oxalacetate + ornithine 49, glutamate + oxalacetate + ammonia 105, glutamate + oxalacetate + ornithine + ammonia 317, glutamate + ocalacetate + ornithine + ammonia (without ATP) 150

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-

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

A Simple Graphene NH₃ Gas Sensor via Laser Direct Writing.

Ammonia gas sensors are very essential in many industries and everyday life. However, their complicated fabrication process, severe environmental fabrication requirements and desorption of residual ammonia molecules result in high cost and hinder their market acceptance. Here, laser direct writing is used to fabricate three parallel porous 3D graphene lines on a polyimide (PI) tape to simply construct an ammonia gas sensor. The middle one works as an ammonia sensing element and the other two on both sides work as heaters to improve the desorption performance of the sensing element to ammonia gas molecules. The graphene lines were characterized by scanning electron microscopy and Raman spectroscopy. The response and recovery time of the sensor without heating are 214 s and 222 s with a sensitivity of 0.087% ppm-1 for sensing 75 ppm ammonia gas, respectively. The experimental results prove that under the optimized heating temperature of about 70 °C the heaters successfully help implement complete desorption of residual NH₃ showing a good sensitivity and cyclic stability

Recent progress towards the electrosynthesis of ammonia from sustainable resources

Ammonia (NH3) is a key commodity chemical of vital importance for fertilisers. It is made on an industrial scale via the Haber Bosch process, which requires significant infrastructure to be in place such that ammonia is generally made in large, centralized facilities. If ammonia could be produced under less demanding conditions, then there would be the potential for smaller devices to be used to generate ammonia in a decentralized manner for local consumption. Electrochemistry has been proposed as an enabling technology for this purpose as it is relatively simple to scale electrolytic devices to meet almost any level of demand. Moreover, it is possible to envisage electrosynthetic cells where water could be oxidised to produce protons and electrons at the anode which could then be used to reduce and protonate nitrogen to give ammonia at the cathode. If this nitrogen were sourced from the air, then the only required infrastructure for this process would be supplies of water, air and electricity, the latter of which could be provided by renewables. Hence an electrosynthetic cell for ammonia production could allow NH3 to be generated sustainably in small, low-cost devices requiring only minimal facilities. In this review, we describe recent progress towards such electrosynthetic ammonia production devices, summarizing also some of the seminal literature in the field. Comparison is made between the various different approaches that have been taken, and the key remaining challenges in the electrosynthesis of ammonia are highlighted

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%