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At least 487 records · Page 27Linked to original sources
PubMed2006

Regulation of glutamine and glutamate metabolism by GlnR and GlnA in Streptococcus pneumoniae.

Several genes involved in nitrogen metabolism are known to contribute to the virulence of pathogenic bacteria. Here, we studied the function of the nitrogen regulatory protein GlnR in the Gram-positive human pathogen Streptococcus pneumoniae. We demonstrate that GlnR mediates transcriptional repression of genes involved in glutamine synthesis and uptake (glnA and glnPQ), glutamate synthesis (gdhA), and the gene encoding the pentose phosphate pathway enzyme Zwf, which forms an operon with glnPQ. Moreover, the expression of gdhA is also repressed by the pleiotropic regulator CodY. The GlnR-dependent regulation occurs through a conserved operator sequence and is responsive to the concentration of glutamate, glutamine, and ammonium in the growth medium. By means of in vitro binding studies and transcriptional analyses, we show that the regulatory function of GlnR is dependent on GlnA. Mutants of glnA and glnP displayed significantly reduced adhesion to Detroit 562 human pharyngeal epithelial cells, suggesting a role for these genes in the colonization of the host by S. pneumoniae. Thus, our results provide a thorough insight into the regulation of glutamine and glutamate metabolism of S. pneumoniae mediated by both GlnR and GlnA.

Base Sequence↗
PubMed2001

The Rhizobium GstI protein reduces the NH4+ assimilation capacity of Rhizobium leguminosarum.

We show that the protein encoded by the glutamine synthetase translational inhibitor (gstI) gene reduces the NH4+ assimilation capacity of Rhizobium leguminosarum. In this organism, gstI expression is regulated by the ntr system, including the PII protein, as a function of the nitrogen (N) status of the cells. The GstI protein, when expressed from an inducible promoter, inhibits glutamine synthetase II (glnII) expression under all N conditions tested. The induction of gstI affects the growth of a glutamine synthetase I (glnA-) strain and a single amino acid substitution (W48D) results in the complete loss of GstI function. During symbiosis, gstI is expressed in young differentiating symbiosomes (SBs) but not in differentiated N2-fixing SBs. In young SBs, the PII protein modulates the transcription of NtrC-regulated genes such as gstI and glnII. The evidence presented herein strengthens the idea that the endocytosis of bacteria inside the cytoplasm of the host cells is a key step in the regulation of NH4+ metabolism.

Bacterial Proteins↗
PubMed2002

Overexpression of cytosolic glutamine synthetase. Relation to nitrogen, light, and photorespiration.

In plants, ammonium released during photorespiration exceeds primary nitrogen assimilation by as much as 10-fold. Analysis of photorespiratory mutants indicates that photorespiratory ammonium released in mitochondria is reassimilated in the chloroplast by a chloroplastic isoenzyme of glutamine synthetase (GS2), the predominant GS isoform in leaves of Solanaceous species including tobacco (Nicotiana tabacum). By contrast, cytosolic GS1 is expressed in the vasculature of several species including tobacco. Here, we report the effects on growth and photorespiration of overexpressing a cytosolic GS1 isoenzyme in leaf mesophyll cells of tobacco. The plants, which ectopically overexpress cytosolic GS1 in leaves, display a light-dependent improved growth phenotype under nitrogen-limiting and nitrogen-non-limiting conditions. Improved growth was evidenced by increases in fresh weight, dry weight, and leaf soluble protein. Because the improved growth phenotype was dependent on light, this suggested that the ectopic expression of cytosolic GS1 in leaves may act via photosynthetic/photorespiratory process. The ectopic overexpression of cytosolic GS1 in tobacco leaves resulted in a 6- to 7-fold decrease in levels of free ammonium in leaves. Thus, the overexpression of cytosolic GS1 in leaf mesophyll cells seems to provide an alternate route to chloroplastic GS2 for the assimilation of photorespiratory ammonium. The cytosolic GS1 transgenic plants also exhibit an increase in the CO(2) photorespiratory burst and an increase in levels of photorespiratory intermediates, suggesting changes in photorespiration. Because the GS1 transgenic plants have an unaltered CO(2) compensation point, this may reflect an accompanying increase in photosynthetic capacity. Together, these results provide new insights into the possible mechanisms responsible for the improved growth phenotype of cytosolic GS1 overexpressing plants. Our studies provide further support for the notion that the ectopic overexpression of genes for cytosolic GS1 can potentially be used to affect increases in nitrogen use efficiency in transgenic crop plants.

Carbon Dioxide↗
PubMed2006

Tobacco isoenzyme 1 of NAD(H)-dependent glutamate dehydrogenase catabolizes glutamate in vivo.

Glutamate (Glu) dehydrogenase (GDH, EC 1.4.1.2-1.4.1.4) catalyzes in vitro the reversible amination of 2-oxoglutarate to Glu. The in vivo direction(s) of the GDH reaction in higher plants and hence the role(s) of this enzyme is unclear, a situation confounded by the existence of isoenzymes comprised totally of either GDH beta- (isoenzyme 1) or alpha- (isoenzyme 7) subunits, as well as another five alpha-beta isoenzyme permutations. To clarify the in vivo direction of the reaction catalyzed by GDH isoenzyme 1, [(15)N]Glu was supplied to roots of two independent transgenic tobacco (Nicotiana tabacum) lines with increased isoenzyme 1 levels (S4-H and S49-H). The [(15)N]ammonium (NH(4)(+)) accumulation rate in these lines was elevated approximately 65% compared with a null segregant control line, indicating that isoenzyme 1 catabolizes Glu in roots. Leaf glutamine synthetase (GS) was inhibited with a GS-specific herbicide to quantify any contribution by GDH toward photorespiratory NH(4)(+) reassimilation. Transgenic line S49-H did not show enhanced resistance to the herbicide, indicating that the large pool of isoenzyme 1 in S49-H leaves was unable to compensate for GS and suggesting that isoenzyme 1 does not assimilate NH(4)(+) in vivo.

Glutamate Dehydrogenase (NADP+)↗
PubMed1999

Nitrogen regulation in Corynebacterium glutamicum: isolation of genes involved and biochemical characterization of corresponding proteins.

The regulation of nitrogen assimilation was investigated in the Gram-positive actinomycete Corynebacterium glutamicum. Biochemical studies and site-directed mutagenesis revealed that glutamine synthetase activity is regulated via adenylylation in this organism. The genes encoding the central signal transduction protein PH (glnB) and the primary nitrogen sensor uridylyltransferase (glnD) were isolated and sequenced. Additionally, genes putatively involved in the degradation of ornithine (ocd) and sarcosine (soxA), ammonium uptake (amtP) and protein secretion (ftsY, srp) were identified in C. glutamicum. Based on these observations, the mechanism of N regulation in C. glutamicum is similar to that of the Gram-negative Escherichia coli. As deduced from data base searches, the described regulation may also hold true for the important pathogen Mycobacterium glutamicum.

Bacterial Proteins↗
PubMed2004

Application of real-time PCR to study effects of ammonium on population size of ammonia-oxidizing bacteria in soil.

Ammonium oxidation by autotrophic ammonia-oxidizing bacteria (AOB) is a key process in agricultural and natural ecosystems and has a large global impact. In the past, the ecology and physiology of AOB were not well understood because these organisms are notoriously difficult to culture. Recent applications of molecular techniques have advanced our knowledge of AOB, but the necessity of using PCR-based techniques has made quantitative measurements difficult. A quantitative real-time PCR assay targeting part of the ammonia-monooxygenase gene (amoA) was developed to estimate AOB population size in soil. This assay has a detection limit of 1.3 x 10(5) cells/g of dry soil. The effect of the ammonium concentration on AOB population density was measured in soil microcosms by applying 0, 1.5, or 7.5 mM ammonium sulfate. AOB population size and ammonium and nitrate concentrations were monitored for 28 days after (NH4)2SO4 application. AOB populations in amended treatments increased from an initial density of approximately 4 x 10(6) cells/g of dry soil to peak values (day 7) of 35 x 10(6) and 66 x 10(6) cells/g of dry soil in the 1.5 and 7.5 mM treatments, respectively. The population size of total bacteria (quantified by real-time PCR with a universal bacterial probe) remained between 0.7 x 10(9) and 2.2 x 10(9) cells/g of soil, regardless of the ammonia concentration. A fertilization experiment was conducted in a tomato field plot to test whether the changes in AOB density observed in microcosms could also be detected in the field. AOB population size increased from 8.9 x 10(6) to 38.0 x 10(6) cells/g of soil by day 39. Generation times were 28 and 52 h in the 1.5 and 7.5 mM treatments, respectively, in the microcosm experiment and 373 h in the ammonium treatment in the field study. Estimated oxidation rates per cell ranged initially from 0.5 to 25.0 fmol of NH4+ h(-1) cell(-1) and decreased with time in both microcosms and the field. Growth yields were 5.6 x 10(6), 17.5 x 10(6), and 1.7 x 10(6) cells/mol of NH4+ in the 1.5 and 7.5 mM microcosm treatments and the field study, respectively. In a second field experiment, AOB population size was significantly greater in annually fertilized versus unfertilized soil, even though the last ammonium application occurred 8 months prior to measurement, suggesting a long-term effect of ammonium fertilization on AOB population size.

Ammonia↗
PubMed1977

The cellular role of nitrogen in the biosynthesis of alkaloids by submerged culture of Claviceps purpurea (Fr.) Tul.

Asparagine was a superior nitrogen source for clavine-alkaloid production in Claviceps purpurea. Its transport into the cell excedded the cell's biosynthetic need for this amino acid. Asparagine entered the cell without degradation. This disturbed the relative pool sizes of various amino acids resulting in a change in the genetically determined ratio at which amino acids were utilized for protein synthesis. Overproduction of alkaloids (4500 mug.ml-1) may be associated with increased availability of tryptophan because of the enhanced assimilation of asparagine-derived ammonia via glutamine synthetase (EC 6.3.1.2). However, ammonium salts in the fermentation broth led to a depression of the alkaloid yield. Partial replacement of the ammonium salt by aspartic acid elevated alkaloid production.

Amino Acids↗
PubMed1990

Pathways for apical and basolateral membrane NH3 and NH4+ movement in rat proximal tubule.

To examine the mechanism of preferential luminal ammonia secretion in the proximal tubule the apical and basolateral membrane pathways for NH3 and NH4+ movement were studied in the in vivo microperfused rat proximal tubule. Na and Cl were absent from all perfusates. Changes in pHi in response to rapid addition of NH3-NH4+ to either the luminal or peritubular perfusates were measured microfluorimetrically and expressed as the H(+)-equivalent flux (JeqH in pmol.mm-1.min-1). After ammonia addition ([NH3] 0.3 mM; [NH4+] 14.7 mM) to the luminal or peritubular fluids, pHi increased, and JeqH = 1,713 +/- 181 and 1,040 +/- 132 pmol.mm-1.min-1, respectively. To determine whether the above difference was due to NH3- or NH4(+)-driven fluxes, the effect of a fivefold greater [NH4+] ([NH3] 0.3 mM; [NH4+] 74.5 mM) on JeqH was examined. With luminal addition of a fivefold greater [NH4+], JeqH increased to 3,299 +/- 292 pmol.mm-1.min-1, demonstrating a pathway for NH4(+)-driven H+ efflux. One millimolar luminal amiloride inhibited JeqH in response to luminal NH3-NH4+ addition, suggesting that the amiloride-sensitive Na(+)-H+ antiporter mediates the NH4(+)-driven H+ efflux. JeqH was unaffected by addition of a fivefold greater [NH4+] to the peritubular perfusate, demonstrating the absence of an NH4(+)-driven H+ flux on the basolateral membrane. From these data, the calculated NH3 permeabilities were 6.2 +/- 1.3 and 7.0 +/- 0.9 X 10(-2) cm/s for the apical and basolateral membranes, respectively (NS). We conclude that apical and basolateral membrane NH3 permeabilities are similar and large. The apical membrane can also transport NH4+ on the amiloride-sensitive Na(+)-H+ antiporter.

Amiloride↗
PubMed1994

Dissociation of ammoniagenic enzyme adaptation in rat S1 proximal tubules and ammonium excretion response.

We measured ammonium production rates, phosphate-dependent glutaminase (PDG) activity, and glutamate dehydrogenase (GDH) activity in microdissected S1 proximal tubules of rats to investigate the role of adaptations of PDG activity and GDH activity in response to a step increase in acid intake. In vivo ammonium excretion increased much more rapidly than did single-tubule ammonium production in vitro or ammoniagenic enzyme activities measured in microdissected tubules, manifesting an 85-fold increase in the first 24 h. In vitro ammonium production rates in microdissected tubules rose only twofold in the first 24 h, fourfold by day 2, and fivefold by day 4 of acid loading. The adaptation of PDG activity paralleled the increase in single-tubule ammoniagenic capacity measured in vitro. GDH activity, on the other hand, did not change significantly even after 4 days of acid loading. From these observations, we conclude that 1) the adaptation of in vitro ammoniagenic capacity in S1 proximal tubules is temporally associated with an adaptation in PDG activity and not GDH activity, and 2) a major portion of the increased ammonium excretion seen in the first 24 h is due to factors other than an adaptive increase in ammoniagenic enzyme activity.

Adaptation, Physiological↗
PubMed2003

Effects of cerium on nitrogen metabolism of peach plantlet in vitro.

The effect of CeCl3 on the rooting and nitrogen metabolism of the peach plantlet in vitro was studied when the CeCl3 was added to the rooted medium. The results showed that the rooting rate and the fresh weight of roots could be increased and the length of root could be enlarged, and the activities of nitrate reductase, glutamine synthetase, glutamate dehydrogenase in the roots were increased significantly, the transformation of NO(3-) to NH(4+) and protein were promoted, and the nitrogen metabolism was accelerated when the plantlets grew in the optimum rooted medium that contained the concentration 0.3 micromol/L Ce(3+).

Cerium↗
PubMed2003

[Effect of enhanced ammonium nutrition on photosynthesis and nitrate reductase and glutamine synthetase activities of winter wheat].

A controlled hydroponics experiment was conducted to investigate the effects of three NH4+/NO3- ratios (0/100, 50/50 and 100/0) on the photosynthesis and the key nitrogen metabolism enzymes of three wheat cultivars with different sensitivity to enhanced ammonium nutrition (EAN). Compared with NO3- alone, EAN significantly increased the leaf chlorophyll content, net photosynthetic rate, and soluble sugar content. It also significantly increased the soluble protein content in leaves and roots and the nitrate reductase activity in leaves, but had no significant effect on Glutamine synthetase (GS) activity. EAN increased the soluble sugar content in leaves, and correspondingly, enhanced the net photosynthetic rate and maintained a higher soluble sugar/protein in leaves and roots, which was favorable to the nitrogen assimilation and plant growth.

Chlorophyll↗
PubMed2003

Feedback regulation of the ammonium transporter gene family AMT1 by glutamine in rice.

The three members of the rice OsAMT1 gene family of ammonium transporters show distinct expression patterns; constitutive and ammonium-promoted expression in shoots and roots for OsAMT1;1; root-specific and ammonium-inducible expression for OsAMT1;2; root-specific and nitrogen-repressible expression for OsAMT1;3 [Sonoda et al. (2003), Plant Cell Physiol. 44: 726]. To clarify the feedback mechanisms, and to identify regulatory factors of the OsAMT1 genes, the accumulation of the three mRNAs and its dependence on endogenous nitrogen compounds (as quantified by capillary electrophoresis) was studied. Ammonium application to roots following a period of nitrogen starvation induced accumulation of OsAMT1;1 and OsAMT1;2 mRNA, but a decrease of OsAMT1;3 mRNA levels. The expression patterns of the three genes showed good correlation (positive in OsAMT1;1 and OsAMT1;2, negative in OsAMT1;3) with the root tissue contents of glutamine but not of ammonium. The ammonium effects on OsAMT1 expression were prevented by methionine sulfoximine, an inhibitor of glutamine synthetase. Moreover, glutamine had the same effect on transcriptional regulation of OsAMT1 genes as ammonium, indicating that glutamine rather than ammonium controls the expression of ammonium transporter genes in rice. These results imply that rice possesses unique mechanisms of adaptation to variable nitrogen sources in the soil.

Cation Transport Proteins↗
PubMed2002

Effect of operating conditions on the separation of ammonium and nitrate ions with nanofiltration and reverse osmosis membranes.

This paper presents the pilot scale membrane separation studies on the Elmali Lake raw water in Istanbul, which is highly polluted by discharging of sewage waters. Low pressure nanofiltration (NF) and reverse osmosis (LPRO) membranes having the surface area of 2 m2 have been used during the experimental runs. Experiments were conducted at different pressures, temperature and pH ranges. Feed flow rate was about 300 L/h. As a result, flux values increased linearly with increasing pressure. Ammonia and nitrate ion rejections also increased with increasing pressure and characteristics of rejection were similar for the both types of membranes. Permeate flux value increased proportionally with the temperature. The temperature changing has also influenced the rejection rate of ammonia and nitrate ions. Both ammonia and nitrate ion rejections at neutral pH values were very high. Therefore, neutral pH value is suitable for TFC-S and TFC-HR membranes to remove ammonia and nitrate ions.

Filtration↗
PubMed2005

Bacterial community shift along a subsurface geothermal water stream in a Japanese gold mine.

Change of bacterial community occurring along a hot water stream in the Hishikari gold mine, Japan, was investigated by applying a combination of various culture-independent techniques. The stream, which is derived from a subsurface anaerobic aquifer containing plentiful CO2, CH4, H2, and NH4+, emerges in a mine tunnel 320 m below the surface providing nutrients for a lush microbial community that extends to a distance of approximately 7 m in the absence of sunlight-irradiation. Over this distance, the temperature decreases from 69 degrees C to 55 degrees C, and the oxidation-reduction potential increases from -130 mV to +59 mV. In the hot upper reaches of the stream, the dominant phylotypes were: 1) a deeply branching lineage of thermophilic methane-oxidizing gamma-Proteobacteria, and 2) a thermophilic hydrogen- and sulfur-oxidizing Sulfurihydrogenibium sp. In contrast, the prevailing phylotypes in the middle and lower parts of the stream were closely related to ammonia-oxidizing Nitrosomonas and nitrite-oxidizing Nitrospira spp.. Changes in the microbial metabolic potential estimated by competitive PCR analysis of genes encoding the enzymes, particulate methane monooxygenase (pmoA), ammonia monooxygenase (amoA), and putative nitrite oxidoreductase (norB), also substantiated the community shift indicated by 16S rRNA gene analysis. The diversity of putative norB lineages was assessed for the first time in the hot water environment. Estimation of dominant phylotypes by whole-cell fluorescent in situ hybridization and changes in inorganic nitrogen compounds such as decreasing ammonium and increasing nitrite and nitrate in the mat-interstitial water along the stream were consistent with the observed transition of the bacterial community structure in the stream.

Ammonia↗
PubMed1996

Nitrogen metabolism in actinorhizal nodules of Alnus glutinosa: expression of glutamine synthetase and acetylornithine transaminase.

Two nodule cDNA clones representing genes involved in Alnus glutinosa nitrogen metabolism were analysed. ag11 encoded glutamine synthetase (GS), the enzyme responsible for ammonium assimilation, while ag118 encoded acetylornithine transaminase (AOTA), an enzyme involved in the biosynthesis of citrulline, the nitrogen transport form in Alnus. GS mRNA was found at highest levels in root nodules, where it was present in the infected cells as well as in the cells of the pericycle of the vascular system. AOTA transcripts were found at high levels in nodules, confined to the infected cells, suggesting that in nodules of A. glutinosa, citrulline biosynthesis takes place mainly in the infected cells.

Actinomycetales↗