Elevated Ammonia Concentrations Research Articles

Aquaculture and Aeromonas hydrophila: a complex interplay of environmental factors and virulence

AbstractAquaculture faces significant challenges due to bacterial pathogens like Aeromonas hydrophila, which can severely impact production and fish health. Understanding the relationship between environmental factors, host susceptibility, and bacterial virulence is crucial for effectively managing and mitigating the risks associated with A. hydrophila in aquaculture systems. A. hydrophila, found ubiquitously in aquatic environments, possesses various virulence factors that enhance its pathogenicity. These factors are closely linked to environmental conditions, such as temperature and pH, which play pivotal roles in bacterial growth, survival, and pathogenic potential. Fluctuations in temperature and pH significantly influence A. hydrophila’s metabolic activity and growth rate, thereby modulating its virulence and overall pathogenicity. Ammonia, a byproduct of aquatic organism metabolism and organic matter decomposition, can accumulate to toxic levels in aquaculture settings, compromising fish health and immune function. Elevated ammonia concentrations worsen A. hydrophila infections by compromising host immunity and creating favorable conditions for bacterial proliferation. Oxygen concentration, host signals, and diet formulation are significantly impacting the susceptibility of aquatic organisms to infection. These factors are the most crucial in shaping the ecology, physiology, and pathogenicity of A. hydrophila in aquaculture. There is limited information on how these environmental factors modulate the virulence genes of such important fish pathogens. The knowledge of A. hydrophila virulence and its interplay with environmental factors paves the way for developing strategies to prevent and control diseases in aquaculture.

The protein nutritional status affects hope of patients in the terminal phase of cancer

Progressive destruction of the patient’s body in the terminal phase of cancer intensifies the breakdown of muscle tissue proteins, producing neurotoxic ammonia and urea. These metabolites negatively affect the brain function and are more difficult to remove from the cancer-ravaged body than from better-nourished patients. Developing cachexia impairs the functioning of all body organs, including the excretory function of the kidneys, including the removal of neurotoxic metabolites. Elevated concentrations of ammonia and urea in the brain leads to cerebral dysfunction involving a spectrum of neuropsychiatric and neurological symptoms. This may negatively affect the perception of patient’s existential situation, and the experience of hope. Improving the protein nutritional status of patients in the terminal phase of cancer may decrease the muscle tissue breakdown, improve the functioning of internal organs and the efficiency of removing neurotoxic metabolites from the body. According to this, we hypothesize that the hope of patients in the terminal phase of cancer may significantly depend on their protein nutritional status. Patients less malnourished with protein experience greater hope and cope better with their existential situation than those more malnourished. We propose a clinical trial to investigate the relation between protein nutritional status and hope experience in patients in the terminal phase of cancer. The verification of this hypothesis may contribute to better and more holistic patients’ care, both professional and non-professional, which may improve the quality of their life in the last days.

Assessment of a sustainable multigeneration system integrating supercritical CO2 Brayton cycle and LNG regasification: Thermodynamic and exergoeconomic evaluation

This study proposes a cost-effective multigeneration system that integrates a supercritical carbon dioxide (sCO2) power cycle with a liquefied natural gas (LNG) regasification process. The system aims to deliver electricity, cooling, heating, and hydrogen simultaneously. Utilizing the temperature difference between the sCO2 cycle and the LNG thermal sink, an ammonia-water-based absorption refrigeration cycle (ARC) recovers waste heat from the sCO2 power cycle, producing cooling. The elevated ammonia concentration at the ARC's condenser outlet is leveraged by a heat pump system for heating production. Concurrently, cold energy from LNG is used to recover latent heat from the condenser and heat rejected from the sCO2 power cycle, providing inputs for additional electrical power through an NG turbine. The system incorporates a PEM electrolyzer (PEME) for hydrogen production. A comprehensive examination, including energy, exergy, and exergoeconomic analyses, evaluates system performance. A sensitivity analysis illustrates the impacts of key parameters. In the baseline scenario, the system achieves energy and exergy efficiencies of 62.79% and 54.89%, with a low product unit cost of 11.35 ($/GJ). The system demonstrates substantial net power output (259.184 MW), cooling capacity (88.938 MW), heating capacity (2.839 MW), and hydrogen production (391.68 kg/h). This robust performance, coupled with cost-effectiveness, positions the proposed system as a versatile and impactful solution for sustainable and environmentally friendly energy applications.

Ammonium Removal in Wastewater Treatments by Adsorbent Geopolymer Material with Granite Wastes: Full-Scale Validation

Elevated ammonium (NH4+) concentrations in untreated waterways contribute to eutrophication and dissolved oxygen depletion. Geopolymer (GP) materials are introduced as sustainable, straightforward operation and low-cost option for pollutant adsorption through ion exchange mechanism. In the present study, a porous metakaolin-based geopolymer with granite waste additions was synthetized, characterised and validated as adsorbent material for NH4+ pollution in water. At this point, treatments to reduce GP alkalis leaching were also considered to comply with the water discharge regulations. The adsorption mechanism was analysed by Redlich-Peterson isotherm model concluding that NH4+ was disposed on the GP surface as a monolayer with strong physical-chemical attraction between molecules. Kinetics of the process followed the Weber-Morris rate equation being the intraparticle diffusion the limiting process. Continuous experiments at lab-scale suggested a maximum removal of 97% during the first hours and an adsorption capacity (q) of 25.24 mg/g. Additionally, as a main novelty of the work, the GP was validated in a full-scale pilot plant monitoring pH, electrical conductivity and NH4+ concentration. The obtained data revealed that the GP is high selective in a real wastewater stream and removed 81% of NH4+, higher adsorption values than those reported for natural and some synthetic zeolites.

Tropical bloom-forming mesoalgae Cladophoropsis sp. and Laurencia sp.-responses to ammonium enrichment and a simulated heatwave.

Algal blooms are increasing worldwide, driven by elevated nutrient inputs. However, it is still unknown how tropical benthic algae will respond to heatwaves, which are expected to be more frequent under global warming. In the present study, a multifactorial experiment was carried out to investigate the potential synergistic effects of increased ammonium inputs (25 μM, control at 2.5 μM) and a heatwave (31°C, control at 25°C) on the growth and physiology (e.g., ammonium uptake, nutrient assimilation, photosynthetic performance, and pigment concentrations) of two bloom-forming algal species, Cladophoropsis sp. and Laurencia sp. Both algae positively responded to elevated ammonium concentrations with higher growth and chlorophyll a and lutein concentrations. Increased temperature was generally a less important driver, interacting with elevated ammonium by decreasing the algaes'%N content and N:P ratios. Interestingly, this stress response was not captured by the photosynthetic yield (Fv/Fm) nor by the carbon assimilation (%C), which increased for both algae at higher temperatures. The negative effects of higher temperature were, however, buffered by nutrient inputs, showing an antagonistic response in the combined treatment for the concentration of VAZ (violaxanthin, antheraxanthin, zeaxanthin) and thalli growth. Ammonium uptake was initially higher for Cladophoropsis sp. and increased for Laurencia sp. over experimental time, showing an acclimation capacity even in a short time interval. This experiment shows that both algae benefited from increased ammonium pulses and were able to overcome the otherwise detrimental stress of increasingly emerging temperature anomalies, which provide them a strong competitive advantage and might support their further expansions in tropical marine systems.

Pore-water nutrient concentrations variability under different oxygen regimes: A case study in Elefsis Bay, Greece

Anthropogenic pressures considerably affect coastal areas, increasing nitrogen and phosphorous loads that lead to eutrophication. Eutrophication sometimes results in hypoxic and/or anoxic conditions near the bottom water. Dissolved oxygen (DO) concentrations influence redox-sensitive nutrients, which can alter the benthic flux of nutrients. We retrieved sediment cores from two sites in the eastern and western parts of Elefsis Bay, a semi-enclosed area of the Eastern Mediterranean, Greece, during winter and summer. In the western part, seasonally hypoxic or anoxic conditions occurred. We analysed pore-water samples under normoxic, hypoxic and anoxic bottom water conditions to study the pore-water nutrient concentrations variability under different oxygen regimes. Ex situ incubation experiments were conducted at the site experiencing oxygen deficiency by manipulating the DO concentrations. The pore-water nutrient concentrations showed higher variability at the site experiencing oxygen deficiency. Notably, elevated ammonium concentrations were observed in the pore water during anoxic conditions, in the 2–20-cm sediment layer. However, the benthic fluxes of ammonium and phosphate at the 0–2-cm sediment layer were comparable under hypoxic and anoxic conditions. The results of the incubation experiments demonstrate a direct decrease in nitrate concentrations as the DO concentrations diminished in the overlying water. The incubations after re-oxygenating the overlying water show that phosphate was more efficiently scavenged when anoxic conditions prevailed in the bottom water. The incubation experiments indicate the rapid response of the seafloor to oxygen availability, particularly concerning processes that influence nitrate and phosphate concentrations. These observations highlight the dynamic nature of nutrient cycling in shallow, seasonally anoxic environments, such as Elefsis Bay, and emphasise the sensitivity of the seafloor ecosystem to changes in bottom water oxygen availability.

Bio-chemical treatment of landfill leachates with high load of organic and nitrogen compounds

This research encompassed an 8-month investigation to evaluate the biological treatment of complex landfill leachates. The primary objectives were the removal of organic and nitrogen compounds, as well as the mitigation of H2S and VOC emissions. Biological treatment was conducted within a sequencing batch reactor (SBR), incorporating aerobic, anaerobic, and anoxic stages. The results indicate that biological treatment is indeed effective in eliminating biodegradable organic matter, with an average removal rate of 84.5% for BOD5, 42.7% for COD, and 40.9% for TOC. Nonetheless, it is imperative to integrate supplementary processes to enhance organic removal. It is worth noting that biological nitrification proved inadequate for sufficiently reducing elevated ammonia concentrations, achieving only a 23.2% reduction. In controlled laboratory conditions, the utilization of chemical precipitation, employing either MgO+H3PO4 or MgCl2.6 H2O+Na2HPO4.7 H2O in an equimolar ratio of Mg:NH4:PO4, exhibited substantial ammonia removal rates of 76.8 ± 6.4% and 80.7 ± 4.5%, respectively. Additionally, the incorporation of an anoxic stage in reactor operation demonstrated its effectiveness in achieving proficient denitrification, with an 80% removal rate for nitrates present in the raw leachates. These findings underscore the potential for optimizing the efficiency of biological leachate treatment processes through strategic modifications and the integration of additional treatment steps.

Oxidation of Ammonia in Fish Ponds to Nitrates Using Free and Immobilized Nitrifying Bacteria

In fish farming, ammonia stands out as detrimental toxicant, with the potential to significantly impede growth and even lead to fish mortality. The adverse effects of ammonia exposure in aquatic environments primarily stem from elevated concentrations of unionized ammonium (NH3), which can readily permeate gill membranes. This study aimed at assessing the capability of free and mobilized forms of nitrifying bacteria in converting ammonia to nitrates. Nitrifying bacteria were isolated from water samples, resulting in the identification of two Pseudomonas species and two Bacillus species. The Bacillus sp., designated with the isolate code, B4 which exhibited the ability to convert ammonia to both nitrite and nitrate while demonstrating resilience to high ammonia concentrations. When Pseudomonas sp. (C4) and Bacillus sp. (B4) were utilized, the total ammonia concentration was reduced from 2 mg/L to 1.4 mg/L and 1.3 mg/L, respectively. Moreover, the immobilized forms of Pseudomonas sp. C4 and Bacillus sp. B4 achieved a more substantial reduction (75%), lowering the total ammonia concentration from 2 mg/L to 0.5 mg/L within 5-days period. Both nitrifying bacteria not only exhibited ammonia removal capabilities but also demonstrated their proficiency in transforming ammonia into nitrate. Immobilization proved effective in enhancing microbial tolerance to high ammonia concentrations, ultimately leading to improved water quality and the preservation of aquatic animal health.

Decoding Microbial Responses to Ammonia Shock Loads in Biogas Reactors through Metagenomics and Metatranscriptomics.

The presence of elevated ammonia levels is widely recognized as a significant contributor to process inhibition in biogas production, posing a common challenge for biogas plant operators. The present study employed a combination of biochemical, genome-centric metagenomic and metatranscriptomic data to investigate the response of the biogas microbiome to two shock loads induced by single pulses of elevated ammonia concentrations (i.e., 1.5 g NH4+/LR and 5 g NH4+/LR). The analysis revealed a microbial community of high complexity consisting of 364 Metagenome Assembled Genomes (MAGs). The hydrogenotrophic pathway was the primary route for methane production during the entire experiment, confirming its efficiency even at high ammonia concentrations. Additionally, metatranscriptomic analysis uncovered a metabolic shift in the methanogens Methanothrix sp. MA6 and Methanosarcina flavescens MX5, which switched their metabolism from the acetoclastic to the CO2 reduction route during the second shock. Furthermore, multiple genes associated with mechanisms for maintaining osmotic balance in the cell were upregulated, emphasizing the critical role of osmoprotection in the rapid response to the presence of ammonia. Finally, this study offers insights into the transcriptional response of an anaerobic digestion community, specifically focusing on the mechanisms involved in recovering from ammonia-induced stress.

Impaired enzymatic antioxidant defense in erythrocytes of rats with ammonia-induced encephalopathy: role NMDA receptors

Hepatic encephalopathy (HE), a medical term that deals with a neuropsychiatric disorder seen in patients with severe hepatic dysfunction, has been known for more than a century, however, pathogenetic mechanisms underlying cerebral dysfunction during conditions of liver disease are still not entirely understood. There is a consensus that an accumulation of ammonia in brain as a result of impaired detoxification capacity of the liver or the appearance of a portosystemic shunt is a primary cause of HE. Current evidence suggests that ammonia toxicity is mediated by hyperactivation of glutamate receptors, mainly N-methyl-D-aspartate receptors (NMDA-R) and affects many processes of aerobic metabolism that provides energy for a myriad of specific functions and viability of nerve cells. Recent reports on the presence of functional NMDA receptors in erythrocytes and deviations from normal ranges in many blood test parameters that was indicative of impaired hemodynamics and reduced carrying capacity for oxygen in erythrocytes in most patients with HE implicate the relationship between “erythrocyte damage” and cerebral dysfunction. In order to understand how, during hyperammonemia, disturbances in energy metabolism in brain that needs a constant supply of a high level of oxygen in the blood lead to encephalopathy, it is necessary to reveal ammonia-induced disorders in energy metabolism and antioxidant defense system of erythrocytes and explore the potential role of ammonia in reduced brain oxygenation. To detect the said missing link, the activities of erythrocyte antioxidant enzymes and concentrations of GSH, GSSG and H2O2 were measured in animals with hyperammonemia by using MK-801, a powerful noncompetitive NMDA receptor antagonist. It was found that the accumulation of ammonia in the blood of animals with hyperammonemia occurs within rat erythrocytes in large amounts and makes these cells which do not contain enzymes for the removal of ammonia, more susceptible to a prooxidant environment of ammonia created during oxidative stress that was completely or partially inhibited with the help of MK-801. Data obtained provide a support to identification of extra risk factors in cognitive disorders and in the prediction of unfavorable outcome with hypoperfusion in patients with elevated concentrations of ammonia in the blood.

Groundwater nutrient loading into the northern Indian River lagoon: measurements and modeling

The Indian River Lagoon System (IRLS) has been impacted by the surrounding development, leading to excessive nutrient loads that have resulted in frequent and prolonged phytoplankton blooms in the northern reaches. Our study focused on estimating terrestrial groundwater discharge (TGD) and associated nutrient loads by combining field measurements and hydrogeologic modeling at four transects: Eau Gallie (EGT), River Walk (RWT), Banana River (BRT), and Mosquito Lagoon (MLT) across the IRLS. Multiple monitoring stations were installed to collect groundwater and surface water levels, salinity, and nutrient concentrations during 2014-2015. Samples were analyzed for dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP). Numerical modeling was accomplished using SEAWAT to simulate TGD rates, whereas nutrient loads were calculated by multiplying simulated TGD by measured concentrations. TGD rates and nutrient loads were also estimated specifically for the “near-shore zone” along each transect. The effect of recharge from underlying Hawthorn Formation was also evaluated by incorporating estimated recharge rates into the models. Porewater and lagoon water samples showed that ammonium predominated over (NO2+NO3) and PO4 at all sites, resulting in DIN/DIP ratio surpassing the Redfield ratio. Low nitrite/nitrate, coupled with elevated ammonium concentrations at RWT, BRT, and MLT, may be attributed to biogeochemical transformations catalyzed by mangroves and wetlands. Simulated TGD showed mild temporal but significant spatial variation, especially between EGT and RWT compared to BRT and MLT. The highest average TGD of 0.73 and 0.77 m3/d.m occurred at RWT and EGT, respectively, whereas the lowest rates were predicted at BRT and MLT. The highest estimated average DIN loads of 507 and 428 g/yr.m were received at EGT and RWT, respectively, whereas MLT and BRT exhibited lower loads. The DIP loads were remarkably lower than the DIN loads and were significantly different in space and time between sites. Elevated DIN combined with reduced DIP resulted in DIN/DIP exceeding the Redfield ratio, thereby encouraging the blooming of harmful algae. Although the majority of seepage occurs through the near-shore zone, small amounts are received along the entire transect at all sites. The Hawthorn Formation does not contribute significant recharge to the aquifer at the transect locations.

Understanding photochemical adaptations of microalgal ammonium extremophiles to elevated ammonium concentrations in abattoir anaerobic digestate

Identifying microalgal species with outstanding environmental resistance to NH4+ toxicity is critical to developing effective algal-based anaerobic effluent treatment. This is the case for two microalgal NH4+ extremophiles, Chlorella sp. MUR269 and Scenedesmus sp. MUR270 well suited to treat high nitrogen digestates. However, their exact tolerance mechanisms to high NH4+ conditions still need to be understood. A chlorophyll fluorescence approach based on high-throughput pulse amplitude-modulated fluorimetry was used to understand the photochemical adaptations of these species under increasing NH4+ concentrations (0, 100, 200 mgNL−1) derived from abattoir anaerobic digestate. Both species tolerated 200 mgN-NH4+L−1 in the digestate by exhibiting different photochemical mechanisms. Chlorella decreased its PSII primary photochemistry efficiency (Fq′/FM′) and maximum electron transport (rETRmax) immediately after exposure to the treatment conditions. In contrast, Scenedesmus maintained unaltered Fq′/FM′ regardless of NH4+-N concentration, while rETRmax was significantly reduced to a level of Chlorella at 200 mgNL−1. Energy transduction parameters showed Chlorella increased the size of its reaction centre antennae to capture more photons, which increased the trapping flux ratio and maintained efficient dissipation of excess energy. Conversely, Scenedesmus displayed reductions in the absorbed, trapped and dissipated energy fluxes, though its transported flux for photochemical energy production was similar to Chlorella sp. The energetic communication and connectivity between Chlorella PSII units went up by 47 % and 40 % when the NH4+-N level increased from 50 to 100 and N200 mgL−1, respectively, while Scenedesmus exhibited a dose-dependent decrease in the connectivity between its PSII components. The photosynthetic performance index revealed that the overall energetic flux processing efficiency by Scenedesmus was 86 % (50 mgNL−1), 73 % (100 mgNL−1) and 91 % (200 mgNL−1) higher than Chlorella sp. Thus, the two chlorophytes maintained their overall photochemical capacity by simple, economic biological mechanisms involving adjustments of antenna size and energetic communications between PSII neighbour units.

Impaired Enzymatic Antioxidant Defense in Erythrocytes of Rats with Ammonia-Induced Encephalopathy: Role of NMDA Receptors.

Hepatic encephalopathy (HE), a neuropsychiatric disorder developing in patients with severe hepatic dysfunction, has been known for more than a century. However, pathogenetic mechanisms of cerebral dysfunction associated with liver disease are still poorly understood. There is a consensus that the primary cause of HE is accumulation of ammonia in the brain as a result of impaired liver detoxification capacity or the portosystemic shunt. Current evidence suggests that ammonia toxicity is mediated by hyperactivation of glutamate receptors, mainly N-methyl-D-aspartate receptors (NMDARs), and affects brain aerobic metabolism, which provides energy for multiple specific functions and neuronal viability. Recent reports on the presence of functional NMDARs in erythrocytes and the data on the deviations of blood parameters from their normal ranges indicate impaired hemodynamics and reduced oxygen-carrying capacity of erythrocytes in most patients with HE, thus suggesting a relationship between erythrocyte damage and cerebral dysfunction. In order to understand how hyperammonemia (HA)-induced disturbances in the energy metabolism in the brain (which needs a constant supply of large amounts of oxygen in the blood) lead to encephalopathy, it is necessary to reveal ammonia-induced impairments in the energy metabolism and antioxidant defense system of erythrocytes and to explore a potential role of ammonia in reduced brain oxygenation. To identify the said missing link, the activities of antioxidant enzymes and concentrations of reduced glutathione (GSH), oxidized glutathione (GSSG), and H2O2 were measured in the erythrocytes of rats with HA that were injected with the noncompetitive NMDAR antagonist MK-801. We found that in rats with HA, ammonia was accumulated in erythrocytes (cells lacking ammonia removal enzymes), which made them more susceptible to the prooxidant environment created during oxidative stress. This effect was completely or partially inhibited by MK-801. The data obtained might help to identify the risk factors in cognitive disorders and facilitate prediction of unfavorable outcomes of hypoperfusion in patients with a blood elevated ammonia concentration.

The effects of acutely elevated ammonia concentrations on haemolymph parameters in the Mediterranean mussel, Mytilus galloprovincialis

In aquaculture systems, ammonia nitrogen is a major component of waste products arising from the metabolism of cultured organisms and can significantly affect the quality of the rearing environment. The purpose of the current study was to determine modulation of the haemocyte population and selected haemolymph biochemical parameters of the Mediterranean mussel Mytilus galloprovincialis (Lamarck, 1919) exposed to acutely elevated ammonia concentrations.In order to investigate the extent and dynamics of an expected reduction of physiological fitness and survival rate of cultured mussels the stress-on-stress test was conducted combining ammonia and air exposure. The latter test illustrated the extent of reduced mussel physiological fitness and survival rate upon 72 h exposure to 10 and 30 mM NH4Cl in experimental tanks followed by additional exposure to air. Mussels cultured for up to 48 h in experimental tanks comprising 5, 10 and 30 mM NH4Cl, revealed dose and time dependent increase in haemolymph enzyme lactate dehydrogenase levels, urea, and uric acid metabolite levels, as well as the corresponding redistribution in haemocyte population profiles, indicating an inherent response of this organism to ammonia. Finally, a significant negative linear correlation between the mussel hyalinocytes subpopulation and the mean urea levels was observed. The obtained result suggests a possible function of basophilic and acidophilic granulocyte subpopulations in ammonia metabolism leading to urea synthesis by means of surplus ammonium ions are sequestered and extracted from the body. Therefore, defined modulation of the mussel haemocyte population structure may serve as an accurate bioindicator of mussels exposure to acutely elevated ammonia concentrations in environmental and aquaculture biomonitoring studies.

Case report: therapeutic monitoring of vancomycin in an acute liver failure patient with anuria under high-flow continuous hemodiafiltration

BackgroundHigh-flow continuous hemodiafiltration (HF-CHDF) combines diffusive and convective solute removal and is employed for artificial liver adjuvant therapy. However, there is no report on dosage planning of vancomycin (VCM) in patients with acute liver failure under HF-CHDF.Case presentationA 20-year-old woman (154 cm tall, weighing 50 kg) was transferred to the intensive care unit (ICU) with acute liver failure associated with autoimmune liver disease. On the following day, HF-CHDF was started due to elevated plasma ammonia concentration. On ICU day 8, VCM was started for suspected pneumonia and meningitis (30 mg/kg loading dose, then 20 mg/kg every 12 hrs). However, on ICU day 10, VCM blood concentration was under the limit of detection (< 3.0 μg/mL) and the patient developed anuria. The VCM dose was increased to 20 mg/kg every 6 hrs. Calculation with a one-compartment model using the HF-CHDF blood flow rate as a surrogate for VCM clearance, together with hematocrit and protein binding ratio, predicted a trough VCM blood concentration of 15 μg/mL. The observed concentration was about 12 μg/mL. The difference may represent non-HF-CHDF clearance. Finally, living donor liver transplantation was performed.ConclusionWe report an acute liver failure patient with anuria under HF-CHDF in whom VCM administration failed to produce an effective blood concentration, likely due to HF-CHDF-enhanced clearance. VCM dosage adjustment proved successful, and was confirmed by calculation using a one-compartment model.

Effects of elevated atmospheric ammonia concentration on photosynthetic characteristics and grain yield in wheat under different nitrogen rates.

To evaluate the effects of nitrogen (N) application rates on the growth, photosynthetic traits and yield of winter wheat under elevated atmospheric ammonia (NH3) concentrations could provide guidance for N management under high NH3 environment. We conducted a split-plot experiment for two consecutive years (2020-2021 and 2021-2022) with top-open chambers. The treatments included two NH3 concentrations [elevated ambient NH3 concentration at 0.30-0.60 mg·m-3 (EAM) and air NH3 concentration at 0.01-0.03 mg·m-3 (AM)] and two N application rates [recommended N dose (+N) and no N application (-N)]. We analyzed the effects of aforementioned treatments on net photosynthetic rate (Pn), stomatal conductance (gs), chlorophyll content (SPAD value), plant height, and grain yield. The results showed that averaged across the two years, EAM significantly increased Pn, gs, and SPAD values at the jointing and booting stages at the -N level by 24.6%, 16.3%, 21.9% and 20.9%, 37.1%, 5.7%, respectively, compared with AM. However, EAM significantly decreased Pn, gs, and SPAD values at jointing and booting stages at +N level by 10.8%, 5.9%, 3.6% and 6.8%, 18.9%, 9.3%, respectively, over AM treatment. There was a significant effect of NH3 treatment, N application rates and their interaction on plant height and grain yield. Compared with AM, EAM increased the average plant height and grain yield by 4.5% and 32.1% at -N level and decreased by 1.1% and 8.5% at +N level, respectively. In a nutshell, the eleva-ted ambient NH3 concentration had positive effect on photosynthetic characteristics, plant height, and grain yield under ambient N condition, but a inhibitory effect under N application.

Bifidobacterium longum subsp. infantis utilizes human milk urea to recycle nitrogen within the infant gut microbiome

ABSTRACT Human milk guides the structure and function of microbial commensal communities that colonize the nursing infant gut. Indigestible molecules dissolved in human milk establish a microbiome often dominated by bifidobacteria capable of utilizing these substrates. Interestingly, urea accounts for ~15% of total human milk nitrogen, representing a potential reservoir for microbiota that may be salvaged for critical metabolic operations during lactation and neonatal development. Accordingly, B. infantis strains are competent for urea nitrogen utilization, constituting a previously hypothetical phenotype in commensal bacteria hosted by humans. Urease gene expression, downstream nitrogen metabolic pathways, and enzymatic activity are induced during urea utilization to yield elevated ammonia concentrations. Moreover, biosynthetic networks relevant to infant nutrition and development are transcriptionally responsive to urea utilization including branched chain and other essential amino acids. Importantly, isotopically labeled urea nitrogen is broadly distributed throughout the expressed B. infantis proteome. This incisively demonstrates that the previously inaccessible urea nitrogen is incorporated into microbial products available for infant host utilization. In aggregate, B. infantis possesses the requisite phenotypic foundation to participate in human milk urea nitrogen recycling within its infant host and thus may be a key contributor to nitrogen homeostasis early in life.

NH3 concentrations below the current critical level affect the epiphytic macrolichen communities – Evidence from a Northern European City

Acidophytic, oligotrophic lichens on tree trunks are widely considered to be the most sensitive biota to elevated concentrations of atmospheric ammonia (NH3). We studied the relationships between measured NH3 concentrations and the composition of macrolichen communities on the acidic bark of Pinus sylvestris and Quercus robur and the base-rich bark of Acer platanoides and Ulmus glabra at ten roadside and ten non-roadside sites in Helsinki, Finland. NH3 and nitrogen dioxide (NO2) concentrations were higher at the roadside than non-roadside sites indicating traffic as the main source of NH3 and nitrogen oxides (NOx). The diversity of oligotrophs on Quercus was lower at the roadside than non-roadside sites, while that of eutrophs was higher. The abundance and presence of oligotrophic acidophytes (e.g., Hypogymnia physodes) decreased with increasing NH3 concentration (2-year means = 0.15–1.03 μg m−3) especially on Q. robur, while those of eutrophic/nitrophilous species (e.g., Melanohalea exasperatula, Physcia tenella) increased. The abundance of some nitrophytes seemed to depend only on bark pH, i.e., their abundances were highest on Ulmus, which had the highest average bark pH. Overall, the results of lichen bioindicator studies may depend on tree species (bark pH) and lichen species used in calculating indices describing the air quality impact. Nevertheless, Quercus is recommended to be used to study the impact of NH3 alone and in combination with NOx on lichen communities, because the responses of both oligotrophic acidophytes and eutrophic species can already be observed at NH3 concentrations below the current critical level.

Ammonia and nutritional therapy in the critically ill: when to worry, when to test and how to treat?

Hyperammonaemia is almost always develops in patients with severe liver failure and this remains the commonest cause of elevated ammonia concentrations in the ICU. Nonhepatic hyperammonaemia in ICU presents diagnostic and management challenges for treating clinicians. Nutritional and metabolic factors play an important role in the cause and management of these complex disorders. Nonhepatic hyperammonaemia causes such as drugs, infection and inborn errors of metabolism may be unfamiliar to clinicians and risk being overlooked. Although cirrhotic patients may tolerate marked elevations in ammonia, other causes of acute severe hyperammonaemia may result in fatal cerebral oedema. Any coma of unclear cause should prompt urgent measurement of ammonia and severe elevations warrant immediate protective measures as well as treatments such as renal replacement therapy to avoid life-threatening neurological injury. The current review explores important clinical considerations, the approach to testing and key treatment principles that may prevent progressive neurological damage and improve outcomes for patients with hyperammonaemia, especially from nonhepatic causes.

Inhibitory mechanisms on dry anaerobic digestion: Ammonia, hydrogen and propionic acid relationship

Inhibitory pathways in dry anaerobic digestion are still understudied and current knowledge on wet processes cannot be easily transferred. This study forced instability in pilot-scale digesters by operating at short retention times (40 and 33 days) in order to understand inhibition pathways over long term operation (145 days). The first sign of inhibition at elevated total ammonia concentrations (8 g/l) was a headspace hydrogen level over the thermodynamic limit for propionic degradation, causing propionic accumulation. The combined inhibitory effect of propionic and ammonia accumulation resulted in further increased hydrogen partial pressures and n-butyric accumulation. The relative abundance of Methanosarcina increased while that of Methanoculleus decreased as digestion deteriorated. It was hypothesized that high ammonia, total solids and organic loading rate inhibited syntrophic acetate oxidisers, increasing their doubling time and resulting in its wash out, which in turn inhibited hydrogenotrophic methanogenesis and shifted the predominant methanogenic pathway towards acetoclastic methanogenesis at free ammonia over 1.5 g/l. C/N increases to 25 and 29 reduced inhibitors accumulation but did not avoid inhibition or the washout of syntrophic acetate oxidising bacteria.