Descripción: The extent and seasonality of nutrient limitation of Posidonia oceanica (L.) Delile in the Costa Brava littoral (NW Mediterranean) in 5 meadows was investigated by means of repeated nutrient additions along a year cycle. Nutrient additions had a modest effect on leaf growth. The response to fertilization varied considerably among meadows, with those meadows consistently maintaining low (300 μM dissolved inorganic nitrogen and 9 μM soluble reactive phosphorus) dissolved inorganic nutrient concentrations in sediment pore waters showing the greatest response to fertilization. The seasonality of the growth response to fertilization was consistent with calculated nutrient deficiencies, which were greatest in late spring and summer. Nutrient deficiency was alleviated in the fall, partially due to reduced growth, but also to nutrient reclamation from old leaves, which represented 20% and 18% of the annual nitrogen and phosphorus incorporation, respectively. The relative deficiency of nitrogen and phosphorus differed among sites, with the highest response found in P-deficient meadows. Nutrient limitation of P. oceanica meadows was greatest in late spring and summer, but differed greatly in magnitude and nature (nitrogen vs phosphorus) depending on local nutrient regimes.

Descripción: In plant sexual reproduction, water and solute movement are tightly regulated, suggesting the involvement of aquaporins. We previously identified TIP5;1 and TIP1;3 as the only Arabidopsis aquaporin genes that are selectively and highly expressed in mature pollen, and showed that they can transport both water and urea when expressed in Xenopus oocytes. Here, we show that TIP5;1 has unusual characteristics, as its water transport activity is regulated by pH. Analysis of the water transport activity of a mutant version of TIP5;1 (TIP5;1-H131A) and amino acid alignment with other plant aquaporins regulated by pH suggested that a conserved motif is involved in pH sensing. GFP-TIP5;1 is located in the mitochondria of pollen tubes. The single mutants tip1;3 and tip5;1, as well as the tip1;3 tip5;1 double mutant, are fertile, but all mutants had shorter than normal pollen tubes when germinated in vitro in the absence of exogenous nitrogen. Thus, we propose that TIP5;1 and TIP1;3 are involved in nitrogen recycling in pollen tubes of Arabidopsis thaliana. © 2010 The Authors. The Plant Journal © 2010 Blackwell Publishing Ltd.

Descripción: The Saccharomyces cerevisiae UGA4 gene, which encodes the γ-aminobutyric acid (GABA) and δ-aminolaevulinic acid (ALA) permease, is well known to be regulated by the nitrogen source. Its expression levels are low in the presence of a rich nitrogen source but are higher when a poor nitrogen source is used. In addition, GABA can induce UGA4 expression when cells are grown with proline but not when they are grown with ammonium. Although vast amounts of evidence have been gathered about UGA4 regulation by nitrogen, little is known about its regulation by the carbon source. Using glucose and acetate as rich and poor carbon source respectively, this work aimed to shed light on hitherto unclear aspects of the regulation of this gene. In poor nitrogen conditions, cells grown with acetate were found to have higher UGA4 basal expression levels than those grown with glucose, and did not show UGA4 induction in response to GABA. Analysis of the expression and subcellular localization of the transcription factors that regulate UGA4 as well as partial deletions and site-directed mutations of the UGA4 promoter region suggested that there are two parallel pathways that act in regulating this gene by the carbon source. Furthermore, the results demonstrate the existence of a new factor operating in UGA4 regulation. © 2007 SGM.

Descripción: Dielectronic recombination data for nitrogen-like ions forming oxygen-like ions has been calculated as part of the assembly of a level-resolved dielectronic recombination database necessary for the modelling of dynamic finite-density plasmas (Badnell et al. 2003). Dielectronic recombination rate coefficients for a selection of ions from O+ to Xe47+ are presented and the results discussed.

Descripción: Sinorhizobium meliloti is a symbiotic nitrogen-fixing bacterium that elicits nodule formation on roots of alfalfa plants. S. meliloti produces two exopolysaccharides (EPSs), termed EPS I and EPS II, that are both able to promote symbiosis. EPS I and EPS II are secreted in two major fractions that reflect differing degrees of subunit polymerization, designated high- and low-molecularweight fractions. We reported previously that EPSs are crucial for autoaggregation and biofilm formation in S. meliloti reference strains and isogenic mutants. However, the previous observations were obtained by use of "domesticated" laboratory strains, with mutations resulting from successive passages under unnatural conditions, as has been documented for reference strain Rm1021. In the present study, we analyzed the autoaggregation and biofilm formation abilities of native S. meliloti strains isolated from root nodules of alfalfa plants grown in four regions of Argentina. 16S rRNA gene analysis of all the native isolates revealed a high degree of identity with reference S. meliloti strains. PCR analysis of the expR gene of all the isolates showed that, as in the case of reference strain Rm8530, this gene is not interrupted by an insertion sequence (IS) element. A positive correlation was found between autoaggregation and biofilm formation abilities in these rhizobia, indicating that both processes depend on the same physical adhesive forces. Extracellular complementation experiments using mutants of the native strains showed that autoaggregation was dependent on EPS II production. Our results indicate that a functional EPS II synthetic pathway and its proper regulation are essential for cell-cell interactions and surface attachment of S. meliloti. © 2012, American Society for Microbiology.

Descripción: A recombinant E. coli strain (K24K) was constructed and evaluated For poly(3-hydroxybutyrate) (PHB) production from whey and corn steep liquor as main carbon and nitrogen sources. This strain bears the pha biosynthetic genes from Azotobacter sp. strain FA8 expressed from a T5 promoter under the control of the lactose operator. K24K does not produce the lactose repressor, ensuring constitutive expression of genes involved in lactose transport and utilization. PHB was efficiently produced by the recombinant strain grown aerobically in fed-batch cultures in a laboratory scale bioreactor on a semisynthetic medium supplemented with the agroindustrial by-products. After 24 h, cells accumulated PHB to 72.9% of their cell dry weight, reaching a volumetric productivity of 2.13 g PHB per liter per hour. Physical analysis of PHB recovered from the recombinants showed that its molecular weight was similar to that of PHB produced by Azotobacter sp. strain FA8 and higher than that of the polymer from Cupriavidus necator and that its glass transition temperature was approximately 20°C higher than those of PHBs from the natural producer strains. Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Descripción: Nitrogen 14 quadrupole coupling constants for H2CN+ and HCN are predicted via ab initio self-consistent-field and configuration interaction theory. Effects of electron correlation, basis set completeness, and geometrical structure on the predicted electric field gradients are analyzed. The quadrupole coupling constant obtained for H2CN+ is one order of magnitude less than in HCN, providing an explanation for the experimental fact that the fine structure of the microwave spectrum of H 2CN+ has not been resolved. This research also allows a reliable prediction of the nuclear quadrupole moment of 14N, namely Q(14N)=2.00×10-26 cm2. © 1986 American Institute of Physics.

Descripción: Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non-transferred arc torch with a rod-type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min -1. A flat ion saturation region was found in the current-voltage curve of the probe. The ion saturation current to a cylindrical probe in a high-pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processes inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 × 10 22 m -3, were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying-type plasma jets characterized by electron temperatures in the range 9000-14 000 K. © 2012 American Institute of Physics.

Descripción: The characteristic geometry of a pulsed capillary discharge (PCD), a narrow open end tube with a large aspect ratio, establishes natural conditions for the generation of plasma jets, that propagate in the neutral background gas surrounding the capillary. We have investigated the plasma jet emission in a PCD, with electron beam assisted on-axis initiation. A local storage capacitor, coaxial with the capillary assembly, is pulse charged up to a maximum of -11 kV, which results in an initial ∼ 10 ns, ∼ 2 kA current pulse. The discharge is operated in Argon and Nitrogen, in a continuous pulsing mode, at frequencies between 5 to 20 Hz, and in a pressure range between 300 to 1100 Torr. A fast Langmuir probe, placed at the anode side, close to the capillary exit, is used to measure the characteristic electron temperature (Te) and electron density (Ne) of the plasma jets. Results obtained in Nitrogen at 10 Hz indicate that Te is in the 10 to 60 eV range with Ne of the order of 1014 (cm-3). Significant changes in the probe floating potential are observed for a fixed operating pressure when the pulsing frequency is varied, which can be ascribed to the presence of metastables in the gas fed into the capillary, which result from the interaction of the plasma jet with the plenum gas, at the cathode side. The presence of metastables reduces the energy cost involved in the capillary plasma production, which results in a pulsing frequency dependence of the plasma parameters. © 2006 American Institute of Physics.

Descripción: A psychrotolerant marine bacterial strain, designated JUB59 T, was isolated from Antarctic surface seawater and classified as a new species of the genus Bizionia. Here, we present the first draft genome sequence for this genus, which suggests interesting features such as UV resistance, hydrolytic exoenzymes, and nitrogen metabolism. © 2011, American Society for Microbiology.

Descripción: The yeast Yarrowia lipolytica accumulates oils and is able to produce extracellular lipases when growing in different carbon sources including glycerol, the principal by-product of the biodiesel industry. In this study, biomass production of a novel mutant strain of Y. lipolytica was statistically optimized by Response Surface Methodology in media containing biodiesel-derived glycerol as main carbon source. This strain exhibited distinctive morphological and fatty acid profile characteristics, and showed an increased extracellular lipase activity. An organic source of nitrogen and the addition of 1.0 g/l olive oil were necessary for significant lipase production. Plackett-Burman and Central Composite Statistical Designs were employed for screening and optimization of fermentation in shaken flasks cultures, and the maximum values obtained were 16.1 g/l for biomass and 12.2 Units/ml for lipase, respectively. Optimized batch bioprocess was thereafter scaled in aerated bioreactors and the values reached for lipase specific activity after 95 % of the glycerol had been consumed, were three-fold higher than those obtained in shaken flasks cultures. A sustainable bioprocess to obtain biomass and extracellular lipase activity was attained by maximizing the use of the by-products of biodiesel industry.

Descripción: 17O chemical shifts are found to be highly sensitive probes in the study of keto-enol tautomeric equilibria due to the strong sensitivity of these shifts to the coordination of the oxygen atom. The large shielding effect observed, both experimentally and theoretically, for the carbonyl oxygen atom in 2-pyridone suggests that the carbonyl π-electronic system is undergoing a strong conjugation with the formal C3=C4 double bond and/or the nitrogen lone pair. A Cl or NH2 substitution at position 6 of the pyridine ring shifts the tautomeric equilibrium toward the 2-hydroxypyridine form, while a CH3 substitution results in the keto form being predominant, as is the case in the parent compound. © 1992 American Chemical Society.

Descripción: The chemical synthesis of nitrogen-doped titanium dioxide (N-TiO 2) is explored in an attempt to understand the mechanisms of doping. Urea is used as precursor in a sol gel synthesis of N-TiO 2. Chemical and structural changes during thermal treatment of the precursors were followed by several techniques. The effect of doping on band gap, morphology, and microstructure was also determined. The byproducts produced during firing correspond to those obtained during urea thermal decomposition. Polynitrogenated colored compounds produced at temperatures below 400°C may act as sensitizer. Incorporation of N in the TiO 2 structure is possible at higher temperatures. Degradation experiments of salicylic acid under UVA and visible light (γ≥400 nm) in the presence of TiO 2 or N-TiO 2 indicate that doping decreases the activity under UVA light, while stable byproducts are produced under visible light. © 2011 Matias Factorovich et al.

Descripción: Nitrogen compounds like urea and melamine are known to be commonly used for milk adulteration resulting in undesired intoxication; a well-known example is the Chinese episode occurred in 2008. The development of a rapid, reliable and economic test is of relevance in order to improve adulterated milk identification. Cyclic voltammetry studies using an Au working electrode were performed on adulterated and non-adulterated milk samples from different independent manufacturers. Voltammetric data and their first derivative were subjected to functional principal component analysis (f-PCA) and correctly classified by the KNN classifier. The adulterated and non-adulterated milk samples showed significant differences. Best results of prediction were obtained with first derivative data. Detection limits in milk samples adulterated with 1% of its total nitrogen derived from melamine or urea were as low as 85.0 mg·L-1 and 121.4 mg·L-1, respectively. We present this method as a fast and robust screening method for milk adulteration analysis and prevention of food intoxication. © 2012 by the authors; licensee MDPI, Basel, Switzerland.

Descripción: Nocardia globerula strain 432 was able to synthesize triacylglycerols (TAG) during cultivation on 2,6,10,14-tetramethyl pentadecane (pristane) under nitrogen-limiting conditions. Within these cells, 4,8,12-trimethyl tridecanoic acid was the major fatty acid detected. Fatty acids with an odd number of carbon atoms and minor amounts of even-numbered fatty acids were also observed. Experiments carried out with acrylic acid, an inhibitor of β-oxidation, suggested that odd-numbered fatty acids such as C15:0, C17:0 and 10-methyl C17:0 were synthesized de novo using propionyl-CoA, the β-oxidation product, as precursor. Although N. globerula 432 incorporated mainly straight chain fatty acids into TAG, the branched fatty acid 4,8,12-trimethyl tridecanoic acid also appeared, to some extent, in the acylglycerols. The importance of TAG biosynthesis by pristane-grown cells of N. globerula strain 432 is discussed. © 2001 Federation of European Microbiological Societies.

Descripción: The rise in the world demand for food poses a challenge to our ability to sustain soil fertility and sustainability. The increasing use of no-till agriculture, adopted in many areas of the world as an alternative to conventional farming, may contribute to reduce the erosion of soils and the increase in the soil carbon pool. However, the advantages of no-till agriculture are jeopardized when its use is linked to the expansion of crop monoculture. The aim of this study was to survey bacterial communities to find indicators of soil quality related to contrasting agriculture management in soils under no-till farming. Four sites in production agriculture, with different soil properties, situated across a west-east transect in the most productive region in the Argentinean pampas, were taken as the basis for replication. Working definitions of Good no-till Agricultural Practices (GAP) and Poor no-till Agricultural Practices (PAP) were adopted for two distinct scenarios in terms of crop rotation, fertilization, agrochemicals use and pest control. Non-cultivated soils nearby the agricultural sites were taken as additional control treatments. Tag-encoded pyrosequencing was used to deeply sample the 16S rRNA gene from bacteria residing in soils corresponding to the three treatments at the four locations. Although bacterial communities as a whole appeared to be structured chiefly by a marked biogeographic provincialism, the distribution of a few taxa was shaped as well by environmental conditions related to agricultural management practices. A statistically supported approach was used to define candidates for management-indicator organisms, subsequently validated using quantitative PCR. We suggest that the ratio between the normalized abundance of a selected group of bacteria within the GP1 group of the phylum Acidobacteria and the genus Rubellimicrobium of the Alphaproteobacteria may serve as a potential management-indicator to discriminate between sustainable vs. non-sustainable agricultural practices in the Pampa region. © 2012 Figuerola et al.

Descripción: Rhizobium leguminosarum is a soil bacterium that infects root hairs and induces the formation of nitrogen-fixing nodules on leguminous plants. Light, oxygen, and voltage (LOV)-domain proteins are bluelight receptors found in higher plants and many algae, fungi, and bacteria. The genome of R. leguminosarum bv. viciae 3841, a peanodulating endosymbiont, encodes a sensor histidine kinase containing a LOV domain at the N-terminal end (R-LOV-HK). R-LOV-HK has a typical LOV domain absorption spectrum with broad bands in the blue and UV-A regions and shows a truncated photocycle. Here we show that the R-LOV-HK protein regulates attachment to an abiotic surface and production of flagellar proteins and exopolysaccharide in response to light. Also, illumination of bacterial cultures before inoculation of pea roots increases the number of nodules per plant and the number of intranodular bacteroids. The effects of light on nodulation are dependent on a functional lov gene. The results presented in this work suggest that light, sensed by R-LOV-HK, is an important environmental factor that controls adaptive responses and the symbiotic efficiency of R. leguminosarum.

Descripción: Changes in biomass and elemental composition (dry mass, W; carbon, C; nitrogen, N; hydrogen, H) were studied in the laboratory during complete larval and early juvenile development of the southern stone crab Paralomis granulosa (Jacquinot). At 6 ± 0.5°C; total larval development from hatching to metamorphosis lasted ca. 56 d, comprising 2 demersal zoeal stages and a benthic megalopa, with mean stage durations of 5, 11 and 45 d, respectively. All larval stages of P. granulosa are lecithotrophic, and first feeding and growth were consistently observed immediately after metamorphosis to the first juvenile crab stage. Regardless of presence or absence of food, W, C, N, and H decreased throughout larval development. Also the C:N mass ratio decreased significantly, from 7.2 at hatching to 4.2 at metamorphosis, indicating that a large initial lipid store remaining from the egg yolk was gradually utilised as an internal energy source. In total, about 68% of the initial quantities of C and H present at hatching, and 44% of N were lost during non-feeding larval development to metamorphosis. Approximately 10% of the initially present C, N and H were lost with larval exuviae, half of which was lost in the megalopa stage alone. Hence, metabolic biomass degradation accounted for losses of ca. 59% in C and H, but for only 33% in N, Most of the losses in C and H reflected metabolic energy consumption (primarily lipid degradation), while ca. 1/4 of the losses in N and 2/3 of those in W were due to larval exuviation. Complete larval lecithotrophy is based on an enhanced maternal energy investment per offspring, and on energy-saving mechanisms such as low larval locomotory activity and low exuvial losses. These traits are interpreted as bioenergetic adaptations to food-limited conditions in subantarctic regions, where a pronounced seasonality limits the period of primary production.

Descripción: The three transition-metal complexes, (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (perchlorato-κO)copper(II), [Cu(ClO4)2(C18H40N4)], (I), (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (nitrato-κO)zinc(II), [Zn(NO3)2(C18H40N4)], (II), and aqua chlorido (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetraazacyclo tetra decane-κ4 N)copper(II) chloride, [CuCl(C18H40N4)(H2O)]Cl, (III), are described. The mol ecules display a very similarly distorted 4+2 octa hedral environment for the cation [located at an inversion centre in (I) and (II)], defined by the macrocycle N4 group in the equatorial sites and two further ligands in trans-axial positions [two O-ClO3 ligands in (I), two O-NO2 ligands in (II) and one chloride and one aqua ligand in (III)]. The most significant difference in mol ecular shape resides in these axial ligands, the effect of which on the intra- and inter molecular hydrogen bonding is discussed. In the case of (I), all strong hydrogen-bond donors are saturated in intra molecular inter actions, while weak inter molecular C - H⋯O contacts result in a three-dimensional network. In (II) and (III), instead, there are N - H and O - H donors left over for inter molecular inter actions, giving rise to the formation of strongly linked but weakly inter acting chains. © 2013 International Union of Crystallography.