Presence Of Nitrogen Sources Research Articles

Carotenoid accumulation in aerial microalga Coelastrella rubescens KGU-H009 in light- and nitrogen-stress conditions

Some natural carotenoids remain unexplored in terms of their function because they occur only in trace amounts, or their stereochemistry is unclear. It is expected that scientists will discover new physiological activities that have a positive impact on human heath by analysis of such carotenoids. The purpose of this study was to analyze the carotenoids synthesized by the novel aerial microalga Coelastrella rubescens KGU–H009, and the dynamics of their accumulation. Cultivation experiments were conducted for 7 days at 25 °C, combining different light conditions with the presence or absence of nitrate ions. Short-term (2-h) cultivation was also performed, and tests were conducted with the addition of the inhibitor of photosynthesis 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU). Strain KGU-H009 exhibited its highest carotenoid content (34.5 mg g−1) in the presence of nitrogen sources and strong light. Upon nitrogen source depletion, the content of zeaxanthin and β-carotene decreased, while the content of astaxanthin and adonixanthin increased. Strain KGU-H009 exhibited reversible control of the xanthophyll cycle to adapt to changes in light intensity, but the xanthophyll cycle was inhibited by the addition of DCMU. Strain KGU-H009 demonstrated the ability to synthesize carotenoids involved in both light harvesting and photoprotection, suggesting its adaptability to environmental change.

Fission Yeast TORC2 Signaling Pathway Ensures Cell Proliferation under Glucose-Limited, Nitrogen-Replete Conditions.

Target of rapamycin (TOR) kinases form two distinct complexes, TORC1 and TORC2, which are evolutionarily conserved among eukaryotes. These complexes control intracellular biochemical processes in response to changes in extracellular nutrient conditions. Previous studies using the fission yeast, Schizosaccharomyces pombe, showed that the TORC2 signaling pathway, which is essential for cell proliferation under glucose-limited conditions, ensures cell-surface localization of a high-affinity hexose transporter, Ght5, by downregulating its endocytosis. The TORC2 signaling pathway retains Ght5 on the cell surface, depending on the presence of nitrogen sources in medium. Ght5 is transported to vacuoles upon nitrogen starvation. In this review, we discuss the molecular mechanisms underlying this regulation to cope with nutritional stress, a response which may be conserved from yeasts to mammals.

Nitrate-inducible NIGT1 proteins modulate phosphate uptake and starvation signalling via transcriptional regulation of SPX genes.

Nitrogen and phosphorus are two major soil nutrients required for plant growth. Because requirements of both these elements are interdependent, acquisition of one must be balanced with that of the other. However, the mechanism underlying this balanced acquisition remains unclear. Here, we show by in vivo luciferase imaging that the presence of nitrogen sources is a pre-requisite for strong activation of phosphate starvation responses. In addition, we also show that nitrate rather than ammonium is a potent modulator of phosphate starvation-induced gene expression. Furthermore, protoplast-based transient expression assay and chromatin immunoprecipitation assay demonstrate that NIGT1 GARP-type transcriptional repressors, which are encoded by nitrate-inducible genes, directly bind to and repress the promoters of genes encoding SPX proteins. Consistent with the role of SPX proteins in the suppression of the PHR1 transcriptional activator, the master regulator for phosphate starvation responses, nitrate-dependent enhancement of phosphate starvation responses, such as accumulation of anthocyanin and promotion of root hair growth and phosphate uptake, was less evident in the nigt1.1-nigt1.4 quadruple mutant. Consistently, NIGT1 overexpression alleviated the reduction in phosphate uptake under phosphate-replete conditions. We further reveal the intricate feedback regulations involving PHR1, NIGT1, and SPX family proteins in the phosphate starvation signalling network. Importantly, results of mutant protoplast-based assays and in planta analysis using NIGT1 overexpression in the spx1 spx2 double mutant indicated that the NIGT1-SPX-PHR cascade mediates nitrogen status-responsive regulation of phosphate uptake and starvation signalling. These findings uncover the mechanism underlying the balanced acquisition of nitrogen and phosphorus.

Dye-sensitized solar cell (DSSC) coated with energy down shift layer of nitrogen-doped carbon quantum dots (N-CQDs) for enhanced current density and stability

Utilizing ultraviolet light by using Energy Down Shift (EDS) of quantum dots is a recent approach to efficiently utilize a broader spectrum of light, for energy harvesting. Other than higher efficiency, EDS is highly promising for increasing the stability of Dye-Sensitized Solar cells (DSSC); as it decreases the UV degradation of the cell. Previously, heavy metals-based (Cadmium etc) quantum dots are used for the purpose, which are not only toxic but also have less stability and have complicated synthesis methods. To overcome these issues, a thin coating of green emissive Nitrogen-doped Carbon Quantum Dots (N-CQDs) on DSSC, as a stable and efficient EDS layer is proposed here. N-CQDs were synthesized by a scalable, green and facile one-pot hydrothermal pyrolysis of citric acid in presence of nitrogen source, with a production yield of 65%, and quantum yield of 70%. The readily dispersible and highly stable colloid of N-CQDs was coated on the device, and with an optimized thickness, the power conversion efficiency was increased by 10%. This increase was further confirmed by external quantum efficiency (EQE) test, i.e. N-CQDs coated device showed EQE enhancement majorly in the UV spectrum and enhanced stability in UV light was recorded. The transmittance of FTO-glass was increased due to EDS and it also has an antireflection effect, which intern produces a small increase in EQE in the visible spectrum.

CuI catalyzed sulfamidation of arylboronic acid using TsNBr2 at room temperature

An expeditious protocol for amidation arylboronic acid has been developed using TsNBr2 as the nitrogen source in presence of a CuI as catalyst. Various arylboronic acids could be transformed into corresponding N-arylsulfonamide derivatives within a very short time using CuI as catalyst in presence of DBU at room temperature.

Co-synthesis of atomic Fe and few-layer graphene towards superior ORR electrocatalyst

Large-scale synthesis of either single-metal atom catalyst or graphene from graphite direct exfoliation at high yield is quite challenging. Here we demonstrated a scalable electrochemical approach to synthesize few-layer graphene flakes and isolated Fe atoms at the same time. It was found that graphite could be expanded in FeCl4--based ionic liquid at a low potential of 2V. Fe isolated onto graphene resulted from electrochemical reactions of FeCl4--based intercalates. After annealing at the presence of nitrogen source, atomic Fe isolation was kept and coordinated with nitrogen. The paintable atomic layer material exhibited superior oxygen reduction reaction performance to Pt/C. The catalytic activity could be enhanced 30 times per gram and 100 times per metal atom, if Fe-Nx/graphene was compared with Pt/C (20wt.% Pt) on the basis of metal content.

Facile Synthetic Route to a Nitrogen‐doped Titanium Oxide with Enhanced Photoelectrochemical Property via Proton Beam Irradiation

A layered titanate with a light harvesting property only in a UV region was irradiated with a proton beam in the presence of nitrogen source like ammonium cation, in order to modify its band gap from UV to visible region. According to X‐ray diffraction and X‐ray absorption spectroscopy results, a protonic titanate maintains its lamellar structure even after proton beam bombardment, showing that the crystal structure of layered titanate was preserved even after the ammonium adsorption and successive proton beam irradiation for nitrogen doping. However, UV–vis and X‐ray photoelectron spectra clearly show that the proton beam irradiation could provide enough energy to introduce ~0.5 at. % of nitrogen atoms into the titanium oxide for absorbing not only UV but also visible light. Photocurrent measurement clearly reveals that the nitrogen‐doped titanium oxide via the proton beam treatment shows highly enhanced photocurrent in comparison with that of the bare titanium oxide, suggesting that the proton beam irradiation could be a potential method for band gap engineering of a wide variety of semiconducting materials.

Nitrogen Source Pretreatment of Ragi Straw for Fermentable Sugar Production using Bacillus Pumilus

Biochemical conversion of lingo cellulosic biomass to ethanol provides a sustainable energy production system. Ragi straw is a fast growing domestic feedstock for Bio-ethanol production. In the present study ragi straw (Eleusine coracana L) was supplemented with different nitrogen Source prior to enzymatic hydrolysis by Bacillus pumilus isolated from marine sources process to produce fermentable sugars using different concentrations of the nitrogen source in the range of 0.5%, 1.0%, 1.5 % and 2.0%.The presence of nitrogen sources had an impact on the growth of the organism and supported enzymatic hydrolysis to degrade complex sugars to simple sugars, which could be further used for Bio-ethanol production. Ammonium nitrate proved to be the best nitrogen source at 0.5% concentration to support enzymatic hydrolysis of ragi straw which could be utilized for ethanol production as ragi straw is abundantly available.

Genetic analysis of the sam mutations, which induce sexual development with no requirement for nutritional starvation in fission yeast.

The cAMP pathway and the Ras pathway are the two major pathways to sexual development in the fission yeast Schizosaccharomyces pombe. To understand the cAMP pathway or the related pathway, we analyzed mutants that display a phenotype similar to cyr1-, that is, hyper-sporulation. Nine mutants termed sam (sporulation abnormal mutant), which are highly inclined to sexual development despite the presence of nitrogen sources, were partially characterized. Cyclic AMP was detected in all nine sam mutant cells, and over-expression of the adenylyl cyclase gene (cyr1) failed to suppress the hyper-sporulation phenotype of these sam mutants, suggesting that none of the sam mutants were likely to be allelic to cyr1. Epistatic tests of sam mutants showed that they were divided into two dominant and seven recessive mutants. Dominants were able to make spores in sam/sam+ heterodiploid cells upon abundant nutrients. Both two dominant mutants bypassed the inability to make spores in ras1 deficient diploid cells, suppressed the deficiency to execute sporulation in byr2 deficient diploid cells, but failed to suppress the byr1 deficiency. Two dominant mutations seem not to occur within the byr2 gene.

Reversibility characteristics of glucose-induced trehalase activation associated with the breaking of dormancy in yeast ascospores.

The breaking of dormancy in yeast ascospores by addition of glucose is associated with a sudden tenfold increase in the activity of trehalase. The rapid activation of trehalase is followed by a slower inactivation process which is greatly retarded in the presence of nitrogen sources and cycloheximide. When glucose is washed away from the spores after some time and the spores resuspended in glucose-free medium, the trehalase activity decreases sharply. Subsequent addition of new glucose partially reactivates the enzyme. The extent of reactivation decreases further with each subsequent activation/inactivation step. Changing the duration of the inactivation periods has no effect on this diminution of the reversibility. However, prolonging the duration of the activation step speeds up the loss of reversibility. On the other hand, addition of a nitrogen source or cycloheximide completely prevents the loss of reversibility. The results of the reversibility studies are in agreement with the phosphorylation mechanism which has been proposed for the underlying molecular process of trehalase activation. Apparently, they are also in agreement with proteolytic breakdown being responsible for the inactivation of trehalase after its initial activation. However, the effect of cycloheximide and nitrogen sources, at least in ascospores, does not appear to be due to inhibition or repression of protease synthesis, respectively, since the addition in the presence of glucose of a nitrogen source after trehalase inactivation immediately reactivates the enzyme completely.

Influence of Nitrogen Sources on Glycogen Metabolism in Saccharomyces carlsbergensis

Summary: Storage of glycogen in yeast (Saccharomyces carlsbergensis) cells was strongly suppressed by the presence of nitrogen sources. Peptone initiated glycogen breakdown within minutes. This effect could not be duplicated with ammonium ions alone nor with single amino acids or mixtures of a few amino acids, but it could be duplicated by the addition of all the amino acids in the molar ratios found in casein. If fewer amino acids were supplied, glycogen was initially synthesized but then depleted after 30–60 min at 28 °C, the time being shorter for more easily utilized amino acids. In the presence of glucose, dinitrophenol (10-4 m) slowed down or inhibited glycogen synthesis, but it did not initiate glycogen breakdown in the absence of glucose. Energy charge and the concentrations of adenylates and UDP-glucose were not significantly different in the presence and absence of peptone; pyruvate accumulated under the former condition. No turnover of glycogen was observed during glycogen synthesis, pointing to an effective regulation of glycogen metabolism via an unknown mechanism.

Preliminary studies on the mechanism of biological action of ultraviolet irradiation and metabolic recovery phenomenon

On the basis of experimental evidence, the action of ultraviolet irradiation on bacteria should be interpreted in terms of degrees of biological injury rather than in terms of an “all alive or all dead cell.” The injury measured in terms of alterations produced within metabolic and synthetic processes of the cell may depend on many factors, such as radiation dose, bacterial concentration, genetic background, and metabolic conditions. The ultraviolet effect on bacterial metabolism and synthesis was measured in terms of O 2 uptake or CO 2 release in aerobic and anaerobic conditions. Data can be summarized as follows: 1. 1. O 2 uptake in the presence of nitrogen source seems to be most affected and in the presence of glucose least affected. 2. 2. In the presence of metabolites belonging to the tricarboxylic acid cycle, O 2 uptake is usually suppressed, but in the presence of some metabolites an increase takes place; the decrease and increase of O 2 uptake varies among various metabolites. 3. 3. Respiration or adaptive synthesis in terms of O 2 uptake in the presence of a galactose is generally suppressed but occasionally is increased depending on a variety of experimental factors. 4. 4. There is no relation between cellular ability for adaptive synthesis for galactose and metabolic recovery. 5. 5. In relative terms, anaerobic metabolism and synthesis are affected more than aerobic, but the effects appear in general similar. 6. 6. Occasionally a metabolite can become, after irradiation injury, toxic or inhibitory to bacterial metabolism. 7. 7. Metabolites exhibit a certain degree of specificity in influencing the adaptive synthesis for galactose. The over-all effect of ultraviolet on a cell may be represented by a concept of multiple pattern injury in which the cyclic processes seem to occupy one of the most vulnerable positions. The significance of these findings is discussed in the section concerning the general background of metabolic recovery.