Enhancement of Nitrogen Dioxide-Induced Lipid Peroxidation and Dna Strand Breaking by Cysteine and Glutathione

Nitrogen dioxide less than 100 ppm in air induced lipid peroxidation of liposome composed of l-palmitoyl-2-arachidonylphosphatidylcholine as assessed by thiobarbituric acid reactivity. The nitrogen dioxide-induced lipid peroxidation was enhanced by cysteine, glutathione and bovine serum albumin. While the activity of nitrogen dioxide in air to induce single strand breaks of supercoiled plasmid DNA was low, the breaking was remarkably enhanced by cysteine, glutathione and bovine serum albumin. ESR spin trapping using 5,5-dimethyl-1-pyrroline N-oxide showed that certain strong oxidant(s) were generated by interaction of nitrogen dioxide and cysteine. The spin trapping using 3,5-dibromo-4-nitrosobenzene-sulfonate suggested that sulfur-containing radicals were generated by interaction of nitrogen dioxide and cysteine or glutathione. Hence, certain sulfur-containing radicals generated by the interaction which could effectively induce lipid peroxidation and DNA strand breaks.     

Enumeration of denitrifying microbial populations in turf

Summary Denitrifer populations of a silt and silt loam soil under a Kentucky bluegrass turf were enumerated using the most probable number (MPN) procedure. The influence of soil texture, soil depth, soil moisture, and additions of nitrate fertilizer on denitrifier populations were determined. Saturated soil conditions increased denitrifier populations 87-fold in the silt soil and 121-fold in the silt loam soil. Denitrifier populations did not differ significantly between soil depths and additions of fertilizer nitrate did not influence populations.     

Response of lentil to VA Mycorrhizal inoculation and plant available P levels of unsterile soils

Summary Responses of lentil in unsterile soils at low, medium and high levels of plant available soil P toGlomus fasciculatum inoculation were evaluated. It was observed that growth, dry matter accumulation, nodulation, and nitrogen fixation were considerably improved in VAM inoculated plants over uninoculated control at low and medium levels of plant available soil P.     

Soil and plant tests for available sulfur in wetland rice soils

Summary Soil tests, plant performance, and plant tissue analyses were used to study the availability of sulfur to wetland rice in 30 Philippine soils. The critical concentrations of available sulfur by the calcium phosphate, lithium chloride, ammonium acetate, and hydrochloric acid extractions were 9, 25, 30, and 5 mg/kg, respectively. The critical total sulfur limits were 0.11% in the shoot at maximum tillering 0.055% in the straw at maturity, and 0.065% in the grain. The critical N:S ratio was 15 in the shoot at maximum tillering, 14 in the straw at maturity, and 26 in the grain. The critical sulfate-sulfur limit was 150 mg/kg in the shoot at maximum tillering and 100 mg/kg in the straw at maturity. The critical sulfate-sulfur/total sulfur percentage ratio was 15% in the shoot at maximum tillering and the straw at maturity. Plant performance, judged by appearance and yield of dry matter, straw, and grain, was generally poorer in the sulfur deficient soils than in the other soils. Although the calcium phosphate and ammonium acetate methods gave a better correlation between plant performance and available sulfur than the others, all four methods separated sulfur-deficient soils from non-deficient ones. The hydrochloric acid method merits further study because it is simple and versatile.     

Stable isotope-based statistical tools as ecological indicator of pollution sources in Mediterranean transitional water ecosystems

N-stable isotope analysis of macroalgae has become a popular method for the monitoring of nitrogen pollution in aquatic ecosystems. Basing on changes in their δ¹⁵N, macroalgae have been successfully used as biological traps to intercept nitrogen inputs. As different nitrogen sources differ in their isotopic signature, this technique provides useful information on the origin of pollutants and their extension in the water body. However, isotopic fractionation potentially resulting from microbial nitrogen processing, and indirect isotopic variations due to effects of physicochemical conditions on algal nutrient uptake and metabolism, may affect anthropogenic N isotopic values during transportation and assimilation. This in turn can affect the observed isotopic signature in the algal tissue, inducing isotopic variations not related to the origin of assimilated nitrogen, representing a “background noise” in isotope-based water pollution studies.In this study, we focused on three neighbouring coastal lakes (Caprolace, Fogliano and Sabaudia lakes) located south of Rome (Italy). Lakes were characterized by differences in terms of anthropogenic pressure (i.e. urbanization, cultivated crops, livestock grazing) and potential “background noise” levels (i.e. nutrient concentration, pH, microbial concentration). Our aim was to assess nitrogen isotopic variations in fragments of Ulva lactuca specimens after 48 h of submersion to identify and locate the origins of nitrogen pollutants affecting each lake. δ¹⁵N were obtained for replicated specimens of U. lactuca spatially distributed to cover the entire surface of each lake, previously collected from a benchmark, unpolluted site. In order to reduce the environmental background noise on isotopic observations, a Bayesian hierarchical model relating isotopic variation to environmental covariates and random spatial effects was used to describe and understand the distribution of isotopic signals in each lake.Our procedure (i) allowed to remove background noise and confounding effects from the observed isotopic signals; (ii) allowed to detect “hidden” pollution sources that would not be detected when not accounting for the confounding effect of environmental background noise; (iii) produced maps of the three lakes providing a clear representation of the isotopic signal variation even where background noise was high. Maps were useful to locate nitrogen pollution sources, identify the origin of the dissolved nitrogen and quantify the extent of pollutants, showing localized organic pollution impacting Sabaudia and Fogliano, but not Caprolace. This method provided a clear characterization of both intra- and inter-lake anthropogenic pressure gradients, representing a powerful approach to the ecological indication and nitrogen pollution management in complex systems, as transitional waterbodies are.     

Metabolic engineering of a diazotrophic bacterium improves ammonium release and biofertilization of plants and microalgae

The biological nitrogen fixation carried out by some Bacteria and Archaea is one of the most attractive alternatives to synthetic nitrogen fertilizers. However, with the exception of the symbiotic rhizobia-legumes system, progress towards a more extensive realization of this goal has been slow. In this study we manipulated the endogenous regulation of both nitrogen fixation and assimilation in the aerobic bacterium Azotobacter vinelandii. Substituting an exogenously inducible promoter for the native promoter of glutamine synthetase produced conditional lethal mutant strains unable to grow diazotrophically in the absence of the inducer. This mutant phenotype could be reverted in a double mutant strain bearing a deletion in the nifL gene that resulted in constitutive expression of nif genes and increased production of ammonium. Under GS non-inducing conditions both the single and the double mutant strains consistently released very high levels of ammonium (>20 mM) into the growth medium. The double mutant strain grew and excreted high levels of ammonium under a wider range of concentrations of the inducer than the single mutant strain. Induced mutant cells could be loaded with glutamine synthetase at different levels, which resulted in different patterns of extracellular ammonium accumulation afterwards. Inoculation of the engineered bacteria into a microalgal culture in the absence of sources of C and N other than N₂ and CO₂ from the air, resulted in a strong proliferation of microalgae that was suppressed upon addition of the inducer. Both single and double mutant strains also promoted growth of cucumber plants in the absence of added N-fertilizer, while this property was only marginal in the parental strain. This study provides a simple synthetic genetic circuit that might inspire engineering of optimized inoculants that efficiently channel N₂ from the air into crops.     

Nitrogen Oxyanion-dependent Dissociation of a Two-component Complex That Regulates Bacterial Nitrate Assimilation

Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression.     

Nutritional interaction in an alga-barnacle association

Nitrogen is the major growth-limiting nutrient for marine algae. One potential source of nitrogen for marine algae is ammonium released by invertebrates. Many mid-intertidal reefs in northeastern New Zealand are dominated by a close association between the honeycomb barnacle Chamaesipho columna and an encusting brown alga Pseudolithoderma sp. Growth of Pseudolithoderma was enhanced in the presence of live C. columna, which released ammonium at a greater rate than the maximum rate of ammonium uptake by Pseudolithoderma. Algal tissue on barnacle tests had a lower C:N ratio than tissue located more than 2 cm from the nearest barnacle, suggesting the barnacle is an important source of nitrogen for the alga. The role of nutrient exchange in determining ecological patterns of species in marine communities is discussed.     

P-31 in-vivo NMR investigation on the function of polyphosphates as phosphate-and energysource during the regreening of the green alga Chlorella fusca

The green alga Chlorella fusca accumulates polyphosphates under conditions of nitrogen starvation while deassembling the photosynthetic apparatus. The polyphosphate content of cells regreening after resupply with nitrate under different culture conditions was investigated by P-31 in-vivo NMR spectroscopy. Neither phosphate deficiency nor anaerobiosis during the first hours of regreening inhibited the recovery of the cells. Polyphosphates were degraded during regeening. Differences in the amount of polyphosphates of phosphate supplied and deficient cells occurred only after more then 8 h. After 16 h phosphate deficient cells had still 75% of the polyphosphate content of phosphate suppled cells. In cells kept under anaerobic conditions polyphosphate degradation was much higher than in oxygen supplied cells. After 8 h they contained less than 50% of the polyphosphate content of oxygen supplied cells. These data suggest that polyphosphates serve as obligatory phosphate source during regreening and may be used as an energy source.Non standard abbreviations EDTA Ethylene diamine tetraacetic acid - FID Free induction decay - MOPSO 3-(N-morpholine)-2-hydroxy-propanesulfonic acid - NMR Nuclear magnetic resonance - PP Polyphosphates - PP₄ central phosphate groups of polyphosphates