Acinetobacter sp. Y1的氨氮去除性能及其关键酶活性

【目的】研究Acinetobacter sp.Y1的氨氮(NH_4~+-N)去除性能及其关键酶的提取与酶活性。【方法】以柠檬酸钠为碳源,硫酸铵为氮源,研究菌株Y1的NH_4~+-N去除性能;采用正交实验优化超声波破碎法提取粗酶的条件,SDS-PAGE分析比较渗透压休克法和超声波破碎法获得的粗酶;检测关键酶——羟胺氧化还原酶(HAO)、亚硝酸盐还原酶(NIR)、硝酸盐还原酶(NAR)的酶活性。【结果】24 h内菌株Y1的菌密度(OD600)可达1.280,对NH_4~+-N、总氮(TN)和COD的降解率分别达到98%、94%和92%,硝化过程中羟胺、亚硝酸盐氮、硝酸盐氮不积累,反硝化产生N2;超声波破碎法提取粗酶的最佳工作条件为:破碎功率50 W,工作与间歇时间分别为4 s和7 s,OD600为1.250,总工作时间20 min,关键酶HAO、NIR和NAR的比活力分别为0.011、0.002和0.018 U/mg;渗透压休克法得到的HAO比活力是0.067 U/mg。【结论】Acinetobacter sp.Y1能同时高效去除NH_4~+-N、TN和COD。优化超声波破碎法提取粗酶的条件,检测到HAO、NIR和NAR的酶活性,且渗透压休克法比超声波破碎法更适合用来提取HAO。     

Contrasting nitrogen uptake by diatom and Phaeocystis-dominated phytoplankton assemblages in the North Sea

This paper documents ambient concentrations of nutrients in the Belgian coastal waters of the North Sea during the spring of 1996 and 1997. The paper elaborates the differences of uptake rates of oxidised nitrogen (NO₃⁻) and reduced nitrogen (NH₄ and urea) by Phaeocystis and diatoms. The nitrogen concentrations were dominated by NO₃⁻ with a maximum concentration of 30 μM (January 1997) and 40 μM (March 1996). In 1996, Phaeocystis dominated the spring biomass with a maximum of 521 μg C l⁻¹, while maximum diatom biomass was 174 μg C l⁻¹. In 1997, the maximum Phaeocystis spring biomass was 1600 μg C l⁻¹ and diatom maximum biomass was below 100 μg C l⁻¹. A maximum bacteria biomass of about 55 μg C l⁻¹ was observed in mid-May 1996. The maximum nitrogen uptake rates were recorded during spring and were dominated by NO₃⁻ (0.005 h⁻¹ in 1996 and 0.032 h⁻¹ in 1997). Maximum specific NH₄ uptake rates were between 0.005 h⁻¹ in May 1996 and 0.006 h⁻¹ in April 1997. The NO₃⁻ uptake rates displayed exponential decrease versus increasing ambient reduced nitrogen concentrations (ammonium and urea), whereas the reduced nitrogen uptake increased but never compensated the decreased nitrate uptake. The NH₄ uptake kinetics of diatoms displayed lower v_max compared to Phaeocystis. Consequently, Phaeocystis showed ability to increase their NH₄ uptake capacity when more NH₄ became available while diatoms failed to do so, after ammonium had exceeded their saturation concentration (>1 μM). Although reduced nitrogen has a negative effect on the uptake of NO₃⁻, Phaeocystis have more advantage than diatoms on the uptake of ammonium. This might be contributing to the biomass domination shown by Phaeocystis over extended periods in spring.     

不同形态氮素对专用型小麦花后氮代谢关键酶活性及籽粒蛋白质含量的影响

采用盆栽方法研究了氮素形态对不同专用型小麦开花后氮素同化关键酶活性及籽粒蛋白质含量的影响。结果表明:不同专用型小麦氮素同化关键酶硝酸还原酶、谷氨酰胺合成酶和谷氨酸合酶对氮素形态的反应不同。强筋小麦豫麦34施用酰胺态氮对旗叶硝酸还原酶和谷氨酰胺合成酶活性、籽粒谷氨酰胺合成酶和谷氨酸合酶活性具有明显的促进作用,最终籽粒蛋白质含量较高;中筋小麦豫麦4 9在施用铵态氮时,3种氮素同化关键酶活性均有较大增强,籽粒蛋白质含量最高;弱筋小麦豫麦5 0硝酸还原酶活性以铵态氮处理最高,而籽粒和旗叶谷氨酰胺合成酶和谷氨酸合酶活性在酰胺态氮处理下明显增强,酰胺态氮对籽粒中蛋白质含量的增加具有明显的促进作用。相关性分析表明,籽粒蛋白质含量与旗叶GS活性和籽粒GOGAT活性呈显著或极显著正相关,与旗叶NR活性和GS活性、籽粒GOGAT活性相关性不显著     

Arsenic exposure alters activity behaviour of key nitrogen assimilatory enzymes in growing rice plants

Rice seedlings when grown in sand cultures for 5–20 days under 25 and 50 M As₂O₃ in the medium showed a marked decline in growth when compared to controls. Increased absorption of arsenic from the medium, against the concentration gradient was observed. Greater localization of absorbed arsenic was noted in roots than in shoots. Rice plants grown for 20 days with 50 mol l^–1 arsenic in the medium accumulated upto 370 mol arsenic kg^–1 dry weight in roots. Increasing levels of As₂O₃ in situ caused a marked decline in the activities of the nitrate assimilatory enzymes nitrate reductase (NR), nitrite reductase (NiR) and glutamine synthetase (GS), whereas an increase in the activities of alanine and aspartate aminotransferases was observed. The activities of aminating (NADH-GDH) and deaminating (NAD⁺-GDH) glutamate dehydrogenases increased at moderately toxic level (25 M) of As₂O₃ whereas a higher As level of 50 M was inhibitory to the enzymes. Addition of 1 M proline in the reaction medium caused significant restoration in As-led loss of NR and GS activities. NR and GS extracted from arsenic exposed seedlings showed higher K _m values compared to the enzymes extracted from control-grown seedlings, whereas GDHs extracted from As-stressed seedlings showed a decrease in K _m. Results suggest that inhibition in the activities of N assimilatory enzymes accompanied with decreased affinity of the enzymes towards their substrates would eventually lead to a marked suppression of N assimilation and impaired growth of rice seedlings in As polluted environment.     

Nitrate reductase activity and nitrogen compounds in xylem exudate of Juglans nigra seedlings: relation to nitrogen source and supply

Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms is limited. We fertilized 1-year-old, half-sib black walnut (Juglans nigra L.) seedlings with ammonium (NH₄ ⁺) [as (NH₄)₂SO₄], nitrate (NO₃ ⁻) (as NaNO₃), or a mixed N source (NH₄NO₃) at 0, 800, or 1,600 mg N plant⁻¹ season⁻¹. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed. Specific leaf NRA was higher in NO₃ ⁻-fed and NH₄NO₃-fed plants compared to observed responses in NH₄ ⁺-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO₃ ⁻-fed than in NH₄ ⁺-fed plants. Exogenous NO₃ ⁻ was assimilated in roots or stored, so no difference was observed in NO₃ ⁻ levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over NO₃ ⁻ or NH₄ ⁺ alone, suggesting NH₄NO₃ is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms.     

Foliar and fine root nitrate reductase activity in seedlings of four forest tree species in relation to nitrogen availability

Summary Seedlings of red maple, white pine, pitch pine and red pine were fertilized with nutrient solutions containing 4 levels of nitrate or ammonium additions. These levels corresponded to approximately 0.5, 1, 2 and 4 times normal availability of nitrogen in northeastern forests. Nitrate reductase (NR) activity was assayed in roots and leaves. Red maples treated with nitrate showed much higher leaf activities and higher ratios of leaf NR activity to root NR activity than any other species. Ammonium additions to red maple and white pine appeared to inhibit NR activity in leaves. With high nitrate additions, NR activity was induced in roots and leaves of pine species, but activity in roots remained much higher than in leaves.     

Potassium induces positive changes in nitrogen metabolism and antioxidant system of oat (Avena sativa L cultivar Kent)

Potassium is actively involved in many functions such as enzyme activation, osmotic adjustment and uptake of deleterious ions like Na. Present report analyses the effectivity of different potassium salts on growth and certain components of nitrogen metabolism and antioxidant system in oat and their possible role in amelioration of water stress. Potassium induced enhancement in the activities of nitrate reductase and aminotransferases was evident indicating a positive role of potassium in nitrogen metabolism. Potassium supplementation enhanced activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) and contents of total phenols and tannins, probably strengthening both the enzymatic as well as non enzymatic antioxidant system. Free amino acids, proline and free sugars also exhibited the same trend in treated plants ensuring better plant growth.     

Detection of genes for membrane-bound nitrate reductase in nitrate-respiring bacteria and in community DNA

A nested PCR primed by four degenerate oligonucleotides was developed for the specific amplification of sequences from the narG gene encoding the membrane-bound nitrate reductase. This approach was used to amplify fragments of the narG gene from five Pseudomonas species previously shown to be able to express the membrane-bound nitrate reductase and from community DNA extracted from a freshwater sediment. Amino acid sequences encoded by the narG fragments were compared to one another, and to the corresponding regions of related enzymes. This comparison indicates that the amplification protocols are specific for their intended targets. Sequences amplified from community DNA were tightly clustered, which may indicate a degree of homogeneity in the sediment community. The PCR primers and amplification protocols described will be useful in future studies of nitrate respiring populations.     

Specific sodium dependence of a nitrate reductase in a marine bacterium

Abstract The two key enzymes of denitrification, the nitrate and nitrate reductases, were studied in a marine organism, Pseudomonas nautica , strain 617. Both enzymes were grown under anaerobic conditions with either nitrate or nitrous oxide as electron acceptor. The effect of sodium on these enzymes was studied. Only sodium activated the membranous and purified nitrate reductase, and none of the salts affected nitrite reductase.     

Nitrate,nitrate reduction and organic nitrogen in plants from different ecological and taxonomic groups of Central Europe

Summary 48 plant species of the families Asteraceae, Chenopodiaceae, Ericaceae, Fabaceae, Lamiaceae, Polygonaceae and Urticaceae were investigated in 14 natural habitats of Central Europe having different nitrate supplies, with respect to their nitrate content, nitrate reductase activity (NRA) and organic nitrogen content. Plants that were flowering were selected where possible for analysis. The plants were subdivided into flowers, laminae, petioles+shoot axes and below-ground organs. Each organ was analyzed separately. Differences among species were found for the three variables investigated. Apart from the Fabaceae, which had particularly high concentrations of organic N, these differences reflect mainly the ecological behaviour, i.e. high nitrate and organic N contents and NRA values per g dry weight were found in species on sites rich in nitrate, and vice versa. Nitrate content, NRA and organic N content were correlated with nitrogen figures of Central European vascular plants defined by Ellenberg (1979). By use of regression equations this correlation was tested with species from other systematic groups. Some species were attributed with calculated N figures for the first time.     

Carbon and nitrogen metabolism in the seagrass, Zostera marina L.: Environmental control of enzymes involved in carbon allocation and nitrogen assimilation

This study experimentally examined influences of environmental variables on the activities of key enzymes involved in carbon and nitrogen metabolism of the submersed marine angiosperm, Zostera marina L. Nitrate reductase activity in leaf tissue was correlated with both water-column nitrate concentrations and leaf sucrose levels. Under elevated nitrate, shoot nitrate reductase activity increased in both light and dark periods if carbohydrate reserves were available. When water-column nitrate was low, glutamine synthetase activity in leaf tissue increased with environmental ammonium. In contrast, glutamine synthetase activity in belowground tissues was statistically related to both nitrate and temperature. At the optimal growth temperature for this species (ca. 25 °C), increased water-column nitrate promoted an increase in glutamine synthetase activity of belowground tissues. As temperatures diverged from the optimum, this nitrate effect on glutamine synthetase was no longer evident. Activities of both sucrose synthase and sucrose-P synthase were directly correlated with temperature. Sucrose-P synthase activity also was correlated with salinity, and sucrose synthase activity was statistically related to tissue ammonium. Overall, the enzymatic responses that were observed indicate a tight coupling between carbon and nitrogen metabolism that is strongly influenced by prevailing environmental conditions, especially temperature, salinity, and environmental nutrient levels.     

Nitrification and nitrogen accumulation in the early stages of primary succession on Mt. Fuji

The relationship between nitrification potential and nitrogen accumulation was studied in an early successional sere on Mt. Fuji. Soil organic nitrogen accumulated with the invasion ofPolygonum cuspidatum and successively withMiscanthus oligostachyus and other species. Laboratory incubation experiments showed a higher nitrification potential at theM. oligostachyus state. The numbers of nitrifying bacteria increased with the progress of succession. No significant difference in nitrate reductase activity was found between pioneer and succeeding species. The soil solution at theM. oligostachyus stage contained a lower level of nitrate than rainwater, while that of the bare ground and theP. cuspidatum stage contained a higher nitrate level than rainwater. It was concluded that the high nitrate levels in the soil solution of the bare ground and theP. cuspidatum stage were due to lower nitrate-absorbing activity, leading to loss of nitrogen with precipitation, while the lower nitrate levels at theM. oligostachyus stage when higher nitrification activity occurred were due to higher nitrate-absorbing activity, preventing net loss of nitrogen from the ecosystem.     

Molecular analysis of inorganic nitrogen assimilation in yeasts

Assimilation of nitrate and various other inorganic nitrogen compounds by different yeasts was investigated. Nitrate, nitrite, hydroxylamine, hydrazine, ammonium sulphate, urea and L-asparagine were tested as sole sources of nitrogen for the growth of Candida albicans, C. pelliculosa, Debaryomyces hansenii, Saccharomyces cerevisiae, C. tropicalis, and C. utilis. Ammonium sulphate and L-asparagine supported the growth of all the yeasts tested except D. hansenii while hydroxylamine and hydrazine failed to support the growth of any. Nitrate and nitrite were assimilated only by C. utilis. Nitrate utilization by C. utilis was also accompanied by the enzymatic activities of NAD(P)H: nitrate oxidoreductase (EC 1.6.6.2) and NAD(P)H: nitrite oxidoreductase (EC 1.6.6.4), but not reduced methyl viologen-or FAD-nitrate oxidoreductases (EC 1.7.99.4). It is demonstrated here that nitrate and nitrite reductase activities are responsible for the ability of C. utilis to assimilate primary nitrogen.     

Effects of NaCl on the nitrogen metabolism of the halophyteArthrocnemum fruticosum (L.) Moq., grown in a greenhouse

Summary Arthrocnemum fruticosum (L.)Moq., a halophyte from the shore of the Dead Sea in Jordan was grown in a greenhouse with nutrient solution supplemented with various concentrations of NaCl. It was shown that with increasing salinity the plants became more succulent, mainly due to an accumulation of sodium and water. Sodium was taken up into the roots in equal amounts to chloride, but in the shoots far more sodium than chloride was found, suggesting a control of these ions either in the excretion into the xylem, or in the uptake by the shoot out of the xylem. Ammonium and nitrate in the plants decreased with time on nutrient solution more or less independently of the salt concentration. However, more nitrate appeared again in the plants when they started flowering. After an initial period of adaptation the nitrate reductase activityin vivo was not inhibited by a salinity of up to 2%, but at higher NaCl concentrations a shift of nitrate reductase activity occurred from the roots to the shoots. This was consistent with earlier observations in the field. In the vegetative phase of the plants the nitrate reductase in the roots was influenced by the soil water potential, but in the shoot it was mainly dependent on the supply of nitrate from the roots. High NaCl concentrations delayed flower initiation. During flowering the nitrate reductase was involved in the re-allocation of nitrogenous compounds from the roots to the developing flowers, and it became effectively independent from salinity.     

The spatial distribution of different phytoplankton functional groups in a Mediterranean reservoir

A new high-resolution spectrofluorimetric probe and an automatic water-quality monitoring station (AWQMS) have been used to record seasonal variations in the spatial distribution of three functional groups of phytoplankton in a Mediterranean water-supply reservoir. In comparison with classical methods, the combined use of these innovative techniques enables development of faster and less laborious spatial distribution surveys, thus favouring higher-frequency and spatially more detailed measurements, and, consequently, a better understanding of phytoplankton dynamics. The results show that the observed variations can be explained by the interaction between the buoyancy properties of the phytoplankton and the mixing characteristics of the reservoir. During the winter, when the lake was isothermal and the phytoplankton was dominated by diatoms, there was no significant spatial variation. In the spring, when the phytoplankton was dominated by chlorophytes there was also very little variation but some motile species formed patches when the wind speed was low. The most pronounced non-uniform distributions of phytoplankton were observed during the summer when the phytoplankton community was dominated by positively buoyant cyanobacteria. Then there was a very strong link between the vertical and horizontal gradients which were also related to the prevailing meteorological conditions.     

模拟酸雨及其酸化土壤对小麦幼苗体内可溶性糖和含氮量的影响

以小麦为试材,采用盆栽方法研究了模拟酸雨及其酸化土壤对小麦幼苗体内可溶性糖和含N量的影响.结果表明,pH值为5.6、4.5、3.5、3.0和2.5的系列模拟酸雨引起了土壤酸化和盐基流失.当模拟酸雨的pH值由5.6下降到2.5时,被淋溶土壤的pH值由.0下降到3.41,土壤中交换性盐基总量从56.5下降到41.1mmol·kg^-1.将小麦幼苗栽培在该系列酸化土壤上,并分别用5种不同pH值的模拟酸雨喷淋地上器官,导致小麦幼苗体内的可溶性糖含量、含N量迅速下降,某些生理活动降低.其中,模拟酸雨喷淋对小麦幼苗茎叶可溶性糖含量、含N量、叶绿素含量以及光合速率的影响大于酸化土壤对其产生的影响.而酸化土壤对小麦幼苗根系中可溶性糖含量、含N量、硝酸还原酶(NR)和谷氨酸合成酶(GOGAT)活性的影响大于模拟酸雨喷淋的影响.pH≤3.0的高强度酸雨以及由其产生的酸化土壤(T₄、T₅土壤)对小麦幼苗的碳素代谢和氮素代谢具有明显的抑制作用.     

Structural and functional analysis of denitrification genes in Pseudomonas stutzeri A1501

Denitrification is the process by which nitrates are converted to nitrogen gas under the action of microor-ganism, and in a bioenergetics viewpoint, a kind of respiration of bacteria in anoxia condition. In such a process, nitrogen in oxidation state replaces oxygen as the terminal electron acceptor in cell membrane, gen-erates potential gradient with the action of a series of oxidoreductase, and finally converts nitrate into nitro-gen[1]. Denitrification is widely present in nature, and resea…