Nitrogen Source Research Articles

Facile synthesis of N-doped graphene quantum dots as a fluorescent sensor for Cr(vi) and folic acid detection.

The development of stable fluorescent sensors for toxic pollutants and drugs is meaningful to the environment and public health. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were facially synthesized by a one-step hydrothermal method using soluble starch and l-arginine as carbon and nitrogen sources in pure water at 190 °C for 4 h. The as-synthesized N-GQDs were well characterized and displayed blue fluorescence emission at 445 nm with excellent pH stability, salt tolerance, thermostability, photobleaching resistance and reproducibility. Moreover, N-GQDs could serve as an "on-off" sensor for selective detection of Cr(vi) and folic acid with low detection limit (0.80 and 2.1 μM), good linear correlation over wide linear range (0-50 μM and 0-200 μM) as well as short response time (<10 s). The practical applications of N-GQDs for Cr(vi) and folic acid detection in actual samples were further investigated and showed acceptable recoveries (92-105%) with relative standard deviations less than 5%. These results indicated that this N-GQDs-based sensor could be a potential alternative for Cr(vi) and folic acid detection in the fields of environmental monitoring and drug analysis.

Study on Lipid and Pigment Contents of Microalgae Cultivated in Water from Litopenaeus vannamei Shrimp Farm

This study aimed to cultivate microalgae in water from Litopenaeus vannamei shrimp farm to be used as supplement for shrimp. The study focused on its growth, lipid and pigment contents and effects of urea addition as nitrogen source and scale-up of microalgae cultivation. Microalga Chlorella sp. SHP isolated from shrimp farm showed higher pigment content and antioxidant activity than other two isolated strains. Chlorella sp. SHP grew best in effluent from treatment pond compared to water from reservoir pond and shrimp pond. The addition of urea at 2 g/L and the scale up in 50 L microalgae cultivation pond gave the maximum biomass of 0.19±0.03 g/L, the lipid content of 44.96±2.79%, and the contents of chlorophyll ab and carotenoids of 11.65 mg/g and 5.45 mg/g, respectively. The antioxidant activity based on radical scavenging activity of 1 g microalgal biomass was 66.71±0.02%. The findings from this study could be an alternative for producing microalgae with high lipid and pigment contents, and further utilization as low-cost supplements for shrimp cultivation.

Comparative Transcriptomic Analysis on the Effect of Sesamol on the Two-Stages Fermentation of Aurantiochytrium sp. for Enhancing DHA Accumulation.

Aurantiochytrium is a well-known long-chain polyunsaturated fatty acids (PUFAs) producer, especially docosahexaenoic acid (DHA). In order to reduce the cost or improve the productivity of DHA, many researchers are focusing on exploring the high-yield strain, reducing production costs, changing culture conditions, and other measures. In this study, DHA production was improved by a two-stage fermentation. In the first stage, efficient and cheap soybean powder was used instead of conventional peptone, and the optimization of fermentation conditions (optimal fermentation conditions: temperature 28.7 °C, salinity 10.7‱, nitrogen source concentration 1.01 g/L, and two-nitrogen ratio of yeast extract to soybean powder 2:1) based on response surface methodology resulted in a 1.68-fold increase in biomass concentration. In the second stage, the addition of 2.5 mM sesamol increased the production of fatty acid and DHA by 93.49% and 98.22%, respectively, as compared to the optimal culture condition with unadded sesamol. Transcriptome analyses revealed that the addition of sesamol resulted in the upregulation of some genes related to fatty acid synthesis and antioxidant enzymes in Aurantiochytrium. This research provides a low-cost and effective culture method for the commercial production of DHA by Aurantiochytrium sp.

Conditional Optimization of Single Cell Protein Production from Crude Oil by &amp;lt;i&amp;gt;Pseudomonas aeruginosa&amp;lt;/i&amp;gt;

The study was carried out to investigate the possible biodegradation of crude oil as a carbon by the bacterium &amp;lt;i&amp;gt;Pseudomonas aeruginosa&amp;lt;/i&amp;gt; isolated from marine environment (Ras El-Menkar- Benghazi- Libya) using basal yeast extract protease peptone-3 (BYP) enriched medium. The isolated bacterium was identified and characterized according to its cultural condition and microbial biochemical properties. Different experiments were developed throughout this study to stimulate bacterial growth and production of single cell protein (SCP). The results show that the optimal concentration of crude oil as a carbon source for the highest bacterial growth (1.14g/l), and production of SCP (0.65g/l; 57.02% of the biomass dry weight) was 1%. This was required to utilize up to 50.6% of oil as a carbon source. As to the nitrogen source, the optimal concentration of ammonium chloride was 0.1%, in which the bacterial growth and SCP production increased to 1.23 g/l and 0.67 g/l respectively. The stimulating effects of organic and inorganic factors on the bacterial growth and SCP production was also tested. Addition of inorganic nutrients such as potassium phosphate (0.05%), magnesium sulphate (0.01%), and organic nutrient in the form of yeast extract (0.1%) to the fermentation medium slightly promoted the bacterial growth which reflected positively on SCP production and the percentage of the consumed crude oil, (&amp;gt;57%) at final pH value of 8.0. The obtained results indicated that the isolated&amp;lt;i&amp;gt; Pseudomonas aeruginosa&amp;lt;/i&amp;gt; posses the ability to utilize the crude oil and use it as a carbon for bacterial growth and production of SCP.

Novel design of Sn4P3@NxC electrodes and their electrochemical properties

Tin phosphide (SnxPy) is recognized as one of the most promising anode materials for lithium-ion batteries due to its exceptionally high theoretical capacity. However, its application is hampered by significant volume expansion during charge-discharge cycles and inferior electrical conductivity. Proper structural design plays a pivotal role in addressing these challenges, paving the way for high-performance anode materials. This study introduces a nitrogen-doped carbon-coated Sn4P3 nanosphere with a core-shell structure, employing dopamine as the nitrogen source. This innovative approach, utilizing template removal and solid-phase phosphorization, results in both the core and shell acting as active materials, thereby enhancing the volumetric energy density of the electrode. The internal voids within the shell layer mitigate volume expansion during charge-discharge cycles, while the presence of the nitrogen-doped carbon layer maintains the material's stability throughout cycling and improves its electrical conductivity. Electrochemical performance tests confirm this material's outstanding energy storage capability, with an initial Coulombic efficiency reaching up to 73.6 %. Furthermore, it maintains a stable capacity of 585 mAh g−1 after 1200 cycles at a current density of 2 A g−1. This research offers a design paradigm for developing novel energy storage materials.

Growth of complete ammonia oxidizers on guanidine

Guanidine is a chemically stable nitrogen compound that is excreted in human urine and is widely used in manufacturing of plastics, as a flame retardant and as a component of propellants, and is well known as a protein denaturant in biochemistry1–3. Guanidine occurs widely in nature and is used by several microorganisms as a nitrogen source, but microorganisms growing on guanidine as the only substrate have not yet been identified. Here we show that the complete ammonia oxidizer (comammox) Nitrospira inopinata and probably most other comammox microorganisms can grow on guanidine as the sole source of energy, reductant and nitrogen. Proteomics, enzyme kinetics and the crystal structure of a N. inopinata guanidinase homologue demonstrated that it is a bona fide guanidinase. Incubation experiments with comammox-containing agricultural soil and wastewater treatment plant microbiomes suggested that guanidine serves as substrate for nitrification in the environment. The identification of guanidine as a growth substrate for comammox shows an unexpected niche of these globally important nitrifiers and offers opportunities for their isolation.

Modeling Bibb Lettuce Nitrogen Uptake and Biomass Productivity in Vertical Hydroponic Agriculture

Global fertilizer production and mismanagement significantly contribute to many harmful environmental impacts, revealing the need for a greater understanding of crop growth and nutrient uptake, which can be used to optimize fertilizer management. This study experimentally adapts first-principles microbial modeling techniques to the hydroponic cultivation of Bibb lettuce (Lactuca sativa) under nitrogen-limited conditions. Monod and Michaelis–Menten’s approaches are applied to predict biomass productivity and nutrient uptake and to evaluate the feasibility of reclaimed wastewater as a nutrient source of nitrogen. Experimental and modeling results reveal significantly different kinetic saturation constants (Ks = 1.331 and Km = 17.887 mg L−1) and a corresponding cell yield strongly dependent on nutrient concentration, producing visually and compositionally distinct tissue between treatments receiving ≤26.2 and ≥41.7 mgN L−1. The resulting Monod model overestimates dry mass predictions during low nutrient conditions, and the collective results support the development of a dynamic Monod curve that is temporally dependent during the plants’ lifecycle. Despite this shortcoming, these results support the feasibility of reclaiming nitrogen from wastewater in hydroponic agriculture, expecting to produce lesser biomass lettuce exhibiting healthy tissue. Furthermore, this study provides a mathematical foundation for agricultural simulations and nutrient management.

Urea-modified hazelnut shell biochar (N-HSB) for efficient Cr(VI) removal: Performance and mechanism insights

Composite with a high specific surface area of 224.62 m2 g−1 was prepared by adding urea as a nitrogen source to hazelnut shell biochar (HSB). Nitrogen doping significantly enhanced the ability of biochar for Cr(VI) elimination, achieving twice the removal efficiency of unmodified biochar. The impacts of varying the pH and initial concentrations on Cr(VI) removal by urea-modified biochar (N-HSB) were investigated. The Cr(VI) removal by N-HSB was better described by intra particle diffusion model and pseudo-second order kinetic model under optimal conditions. Furthermore, XPS, FTIR, SEM, and BET analyses were used to verify the pivotal roles of oxygen- and nitrogen-containing functional groups. Electrostatic attraction, redox reaction, and complexation constituted the principal mechanisms facilitating Cr(VI) elimination by N-HSB. This study demonstrated that the modification of biochar with urea as a nitrogen source represented a promising strategy for enhancing the removal capacity of biochar for Cr(VI) in aqueous environments.

Novel Approaches to Mortierella alpina Identification and Arachidonic Acid Production Optimization.

Arachidonic acid (ARA) is an integral constituent of cell structures and is instrumental for the nervous, muscular, and immune systems' functions. The sore need for this nutrient may be fulfilled via production based on the fungus Mortierella alpina. The identity of the M. alpina culture obtained from Assiut University, Egypt, was confirmed based on internal transcribed spacer DNA barcoding and elongation enzyme RNA sequencing. Liquid media glucose and peptone as carbon and nitrogen sources, respectively, and diverse micronutritional factors were adjusted for optimal biomass and ARA production. Shake flask cultivation at 25 °C for 7 days produced around 0.570 g of ARA per liter of culture. M. alpina treatment using mutagen 5-fluorouracil and octyl gallate-supplemented glucose-yeast-agar screening plates and shake-flask incubation at 25 °C, then at 20 °C, followed by aging at 10 °C, led to >3 g ARA/liter culture, a yield considered suitable for potential commercial production.

Photocatalytic Synthesis of Glycine from Methanol and Nitrate.

Photocatalytic utilization of methanol and nitrate as carbon and nitrogen sources for the direct synthesis of amino acids could provide a sustainable way for the valorization of green "liquid sunlight" and nitrate waste. In this study, we developed an efficient photochemical method to synthesize glycine directly from methanol and nitrate, which cascades the C-C coupling to form glycol, nitrate reduction to NH3, and finally C-N coupling to generate glycine. Interestingly, the involved photocatalytic tandem reactions show a synergistic effect, in which the presence of nitrate is the dominant factor to enable the overall reaction and reach high synthetic efficiency. Ba2+-TiO2 nanoparticles are confirmed as a feasible and efficient catalyst system for the photosynthesis of glycine with a remarkable glycine photosynthesis rate of 870 μmol gcat-1 h-1 under optimal conditions. This work establishes a novel catalytic system for amino acid synthesis from methanol and nitrate under mild conditions. These results also allow us to further suppose the formation pathways of amino acids on the primitive earth, as an extension to proposals based on the Miller-Urey experiments.

Different Nitrogen Consumption Patterns in Low Temperature Fermentations in the Wine Yeast Saccharomyces cerevisiae.

Nowadays, the wine industry carries out fermentations at low temperatures because this oenological practice clearly improves the aromatic complexity of the final wines. In addition, nitrogen content of the must also influences the quality of the wine. In this study, we carried out a phenotypic and fermentative analysis of two industrial wine Saccharomyces cerevisiae strains (P5 and P24) at 15 and 28 °C and three nitrogen concentrations (60, 140 and 300 mg N/L) in synthetic must. Our results show that both parameters, temperature and nitrogen, are interrelated and clearly determine the competitiveness of the wine strains and their ability to adapt at low temperatures. The best adapted strain at low temperatures decreased its competitiveness at lower nitrogen concentrations. In addition, our results show that it is not only the quantity of nitrogen transported that is important but also the quality of the nitrogen source used for wine yeast adaptation at low temperatures. The presence of some amino acids, such as arginine, branched chain amino acids, and some aromatic amino acids can improve the growth and fermentation activity of wine yeasts at low temperatures. These results allow us to better understand the basis of wine yeast adaptation to fermentation conditions, providing important information for winemakers to help them select the most appropriate yeast strain, thus reducing the economic costs associated with long and sluggish fermentations. The correlation between some amino acids and better yeast fermentation performance could be used in the future to design inactive dry yeast enriched in some of these amino acids, which could be added as a nutritional supplement during low temperature fermentations.

Optimizing Chlorella vulgaris Cultivation to Enhance Biomass and Lutein Production.

Lutein is widely used in medicine, health care, and food processing due to its antioxidant effects; however, it is difficult for the traditional extraction of lutein using marigolds to meet the increasing market demand for lutein. To achieve high-efficiency lutein production, we investigated the effects of different conditions on the biomass accumulation and lutein yield of Chlorella vulgaris. The optimized cultivation conditions include mixotrophic cultivation using sodium nitrate as a nitrogen source, maintaining a total-organic-carbon-to-total-nitrogen ratio of 12:1, a total-nitrogen-to-total-phosphorus ratio of 10:1, and lighting duration of 24 h. The results of the study indicated that under these specific conditions, Chlorella vulgaris attained a final biomass concentration, biomass productivity, and growth yield of 6.08 g·L-1, 1.00 g·L-1·d-1, and 1.67 g biomass/g TOC, respectively. Additionally, the concentrations of total chlorophyll, carotenoid, lutein, and protein reached 139.20 mg·L-1, 31.87 mg·L-1, 15.02 mg·L-1, and 2.17 g·L-1, respectively, and the content of lutein reached 2.47 mg·g-1. This study supplies a theoretical basis for the industrial application of lutein production using Chlorella vulgaris.

Modulating N doping in cobalt-derived catalyst from zeolitic imidazolate frameworks for high performance zinc-air batteries

In this work, the N-content was varied using ammonium hydroxide (A), urea (U), and melamine (M) impregnated in a zeolitic imidazolate framework (ZIF-67) with a Co to Zn ratio of 7:93. The N-doped ZIF-derived carbon materials and the reference ZIF Co 7:93 underwent pyrolysis under identical conditions, yielding C-ZIF, CA-ZIF, CU-ZIF, and CM-ZIF. Different nitrogen sources mainly affected the surface area and graphitic-N content, yielding up to three times the N-content of the reference. All materials presented ORR onset potentials near 0.9 V and E10mA cm−2 near 1.6 V for the OER. However, CM-ZIF enabled rechargeability at different current densities, with a round-trip efficiency of 68.8 % at 5 mA cm−2, decreasing only to 54 % at 15 mA cm−2.

Carbon type and quantity regulate soil free-living nitrogen fixation through restructuring diazotrophic community

Free-living nitrogen fixation (FLNF) is a ubiquitous and significant source of new nitrogen in ecosystems. This process requires a substantial amount of energy, and as a result, the input of labile carbon to soils may enhance FLNF. Here, we aim to explore the precise influence of different types and quantities of carbon on FLNF. We conducted experiments where sugars, carboxylic acids, and amino acids (common labile carbon inputs via root exudates) were added to cropland and forest soils. We monitored the changes in FLNF rate and diazotrophic community in response to these additions. Our findings revealed that sugars and carboxylic acids significantly stimulated FLNF rate, with an increase of up to three orders of magnitude, while amino acids either restricted FLNF or had no effect. When a mixture of sugars and carboxylic acids was added, the stimulation of FLNF was not observed until a threshold quantity of carbon was reached, indicating competition between diazotrophs and other microbes. Furthermore, the enhanced FLNF rate following carbon addition was attributable to shifts in diazotrophic community composition (e.g., increased abundance of Paenibacillus, a genus frequently used as biofertilizers), rather than to changes in the overall abundance of diazotrophs (reflected by nifH gene copy number). Our findings highlight the significant role of carbon type and quantity in regulating soil FLNF, partly through restructuring the diazotrophic community. The results have implications for predicting the response of rhizosphere FLNF to shifts in root exudation under environmental changes and can contribute to the application of diazotrophic biofertilizers in sustainable agriculture.

Yeast9: a consensus genome-scale metabolic model for S. cerevisiae curated by the community

Genome-scale metabolic models (GEMs) can facilitate metabolism-focused multi-omics integrative analysis. Since Yeast8, the yeast-GEM of Saccharomyces cerevisiae, published in 2019, has been continuously updated by the community. This has increased the quality and scope of the model, culminating now in Yeast9. To evaluate its predictive performance, we generated 163 condition-specific GEMs constrained by single-cell transcriptomics from osmotic pressure or reference conditions. Comparative flux analysis showed that yeast adapting to high osmotic pressure benefits from upregulating fluxes through central carbon metabolism. Furthermore, combining Yeast9 with proteomics revealed metabolic rewiring underlying its preference for nitrogen sources. Lastly, we created strain-specific GEMs (ssGEMs) constrained by transcriptomics for 1229 mutant strains. Well able to predict the strains’ growth rates, fluxomics from those large-scale ssGEMs outperformed transcriptomics in predicting functional categories for all studied genes in machine learning models. Based on those findings we anticipate that Yeast9 will continue to empower systems biology studies of yeast metabolism.

Alternative Oxidase Alleviates Mitochondrial Oxidative Stress during Limited Nitrate Reduction in Arabidopsis thaliana.

The conversion of nitrate to ammonium, i.e., nitrate reduction, is a major consumer of reductants in plants. Previous studies have reported that the mitochondrial alternative oxidase (AOX) is upregulated under limited nitrate reduction conditions, including no/low nitrate or when ammonium is the sole nitrogen (N) source. Electron transfer from ubiquinone to AOX bypasses the proton-pumping complexes III and IV, thereby consuming reductants efficiently. Thus, upregulated AOX under limited nitrate reduction may dissipate excessive reductants and thereby attenuate oxidative stress. Nevertheless, so far there is no firm evidence for this hypothesis due to the lack of experimental systems to analyze the direct relationship between nitrate reduction and AOX. We therefore developed a novel culturing system for A. thaliana that manipulates shoot activities of nitrate reduction and AOX separately without causing N starvation, ammonium toxicity, or lack of nitrate signal. Using shoots processed with this system, we examined genome-wide gene expression and growth to better understand the relationship between AOX and nitrate reduction. The results showed that, only when nitrate reduction was limited, AOX deficiency significantly upregulated genes involved in mitochondrial oxidative stress, reductant shuttles, and non-phosphorylating bypasses of the respiratory chain, and inhibited growth. Thus, we conclude that AOX alleviates mitochondrial oxidative stress and sustains plant growth under limited nitrate reduction.

Microcystis abundance is predictable through ambient bacterial communities: A data-oriented approach

The number of cyanobacterial harmful algal blooms (cyanoHABs) has increased, leading to the widespread development of prediction models for cyanoHABs. Although bacteria interact closely with cyanobacteria and directly affect cyanoHABs occurrence, related modeling studies have rarely utilized microbial community data compared to environmental data such as water quality. In this study, we built a machine learning model, the multilayer perceptron (MLP), for the prediction of Microcystis dynamics using both bacterial community and weekly water quality data from the Daechung Reservoir and Nakdong River, South Korea. The modeling performance, indicated by the R2 value, improved to 0.97 in the model combining bacterial community data with environmental factors, compared to 0.78 in the model using only environmental factors. This underscores the importance of microbial communities in cyanoHABs prediction. Through the post-hoc analysis of the MLP models, we revealed that nitrogen sources played a more critical role than phosphorus sources in Microcystis blooms, whereas the bacterial amplicon sequence variants did not have significant differences in their contribution to each other. Similar to the MLP model results, bacterial data also had higher predictability in multiple linear regression (MLR) than environmental data. In both the MLP and MLR models, Microscillaceae showed the strongest association with Microcystis. This modeling approach provides a better understanding of the interactions between bacteria and cyanoHABs, facilitating the development of more accurate and reliable models for cyanoHABs prediction using ambient bacterial data.

Efficient utilization of winter nitrogen sources by soil microorganisms and plants in a temperate grassland

In seasonal snow-covered regions, the soil microbial community remains highly active, enabling nitrogen (N) mineralization processes to occur even during the winter. Therefore, winter N accumulation is likely to be a primary N source for plant growth in the subsequent spring. However, the availability of winter N resources (i.e., ammonium and nitrate N) to soil microorganisms and plants in temperate grasslands remains unclear. Here, we applied 15NH4Cl and K15NO3 tracers before autumn-winter freezing, and then investigated the retention of both 15N tracers in soil microorganisms and different plants during the winter and spring period in a typical steppe. The results showed that approximately 33 % and 27 % of 15NH4Cl and K15NO3 tracers were immobilized by soil microorganisms, while little had been uptake by plants during winter. In the subsequent spring, soil retained 32 % and 34 %, microorganisms immobilized 5.1 % and 5.2 %, plant acquired 40 % and 28 % of the 15NH4Cl and K15NO3 tracers, respectively. At a temporal scale, perennial bunch grasses first acquired 15N in the winter-spring transition, followed by perennial rhizome grasses and forbs in early spring, while legumes utilized little 15N. In contrast, the 15N absorption capacity of perennial rhizome grasses and perennial forbs was similar to that of bunch grasses. Additionally, only dominant bunch grasses showed a preference for ammonium N over nitrate N, while other plant species did not exhibit a clear preference for different forms of N. Our results suggest that the temporal differentiation of N utilization between plants and microorganisms enhances the availability of winter N sources. Importantly, the differences among plant species in the timing and quantity of winter N resource utilization contribute to species coexistence in temperate grasslands. This study highlights the crucial role of winter N accumulation as a primary N source for plant growth in temperate grasslands. Understanding the availability of winter N sources for plant and microbial growth is essential for predicting plant community dynamics and species coexistence in these ecosystems.

NRT2.1 mediates the reciprocal regulation of nitrate and NO/SNO in seedling leaves of Fraxinus mandshurica and Betula platyphylla

Nitric oxide (NO) and S-nitrosothiol (SNO) are signal molecules and the products of nitrogen metabolism. Nitrate (NO3−) is the main nitrogen source, and nitrate transporters (NRTs) are responsible for NO3− absorption or transport. However, the interactive effect between NO3−/NRT and NO/SNO in tree plants remains ambiguous. In the present study, 25 mmol L−1 NO3− and 1 mmol L−1 NO donor sodium nitroprusside (SNP) treatment that was conducted for 24 h enhanced NO/SNO and NO3− metabolism, whereas 2.5 mmol L−1 NO3− and 80 μmol L−1 N6022 (a compound that increases SNO content) treatment reduced them in seedling leaves of Fraxinus mandshurica and Betula platyphylla. Among the nine NRT family members examined, the gene expression level of NRT2.1 had a greater response to NO/SNO and NO3− treatment in the seedling leaves of F. mandshurica and B. platyphylla. Meanwhile, FmNRT2.1 mediated NO and SNO production in seedling leaves of F. mandshurica using Agrobacterium-mediated transient transformation. These findings shed light on the reciprocal regulation between NO3− and NO/SNO in seedlings of F. mandshurica and B. platyphylla, and NRT2.1 may act as a key regulatory hub.

Oxygen reduction reaction performance of Fe-N-C catalyst with dual nitrogen source

Oxygen reduction reaction performance of Fe-N-C catalyst with dual nitrogen source