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1.
The biodegradation potential of an innovative enclosed tubular biofilm photobioreactor inoculated with a Chlorella sorokiniana strain and an acclimated activated sludge consortium was evaluated under continuous illumination and increasing pretreated (centrifuged) swine slurry loading rates. This photobioreactor configuration provided simultaneous and efficient carbon, nitrogen, and phosphorous treatment in a single-stage process at sustained nitrogen and phosphorous removals efficiencies ranging from 94% to 100% and 70–90%, respectively. Maximum total organic carbon (TOC), NH4 +, and PO4 3− removal rates of 80 ± 5 g C mr −3 day−1, 89 ± 5 g N mr −3 day−1, and 13 ± 3 g P mr −3 day−1, respectively, were recorded at the highest swine slurry loadings (TOC of 1,247 ± 62 mg L−1, N–NH4 + of 656 ± 37 mg L−1, P–PO4 3+ of 117 ± 19 mg L−1, and 7 days of hydraulic retention time). The unusual substrates diffusional pathways established within the phototrophic biofilm (photosynthetic O2 and TOC/NH4 + diffusing from opposite sides of the biofilm) allowed both the occurrence of a simultaneous denitrification/nitrification process at the highest swine slurry loading rate and the protection of microalgae from any potential inhibitory effect mediated by the combination of high pH and high NH3 concentrations. In addition, this biofilm-based photobioreactor supported efficient biomass retention (>92% of the biomass generated during the pretreated swine slurry biodegradation).  相似文献   

2.
Zu-Hua Yin  John A. Raven 《Planta》1998,205(4):574-580
The impacts of various nitrogen sources, i.e. NO 3, NH4 + or NH4NO3 in combination with gaseous NH3, on nitrogen-, carbon- and water-use efficiency and 13C discrimination (δ13C) by plants of the C3 species Triticum aestivum L. (wheat) and the C4 species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m−3 of N supplied as NO 3, NH4 + or NH4NO3 for 21 and 18 d, respectively, and thereafter exposed to gaseous NH3 at 320 μg · m−3 or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH4NO3-N > NO 3-N > NH4 +-N and NO 3-N > NH4NO3-N > NH4 +-N, respectively. Fumigation with NH3 decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use efficiency (WUE) values in the decreasing order of NH4 +-N > NO 3-N≈NH4NO3-N in non-fumigated T. aestivum, while fumigation with NH3 increased the WUE of NO 3-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ13C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH4 +-grown plants of T. aestivum and Z. mays than in those supplied with NH4NO3 or NO 3. Regardless of the N-form supplied to the roots of the plant species, exposure to NH3 caused more-positive δ13C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant variations in δ13C values in plants of T. aestivum and Z. mays. These differences in δ13C values are in the direction expected from differences in WUE values over long or short growth periods and with differences in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net C acquisition, as a function of N-source. Received: 12 September 1997 / Accepted: 13 January 1998  相似文献   

3.
Burhenne N  Tischner R 《Planta》2000,211(3):440-445
 A method is presented to isolate mutants of Chlorella sorokiniana with defects in NO3 metabolism. Three nitrite-reductase (NIR; E.C.1.7.7.1)-deficient mutants were obtained from 500 pinpoint-colony-forming clones. The final screening was performed using NO3 , NO2 or NH+ 4 as N-source. The mutants isolated absorb NO3 with rates close to those measured for the wild type and they excrete NO2 into the medium. The ratio between NO3 uptake and NO2 excretion was 1:1. The sensitivity of NO3 uptake to NH+ 4 was reduced in the mutant strains as it was in the N-starved wild type of Chlorella. Nitrate reductase (NR; EC 1.6.6.1) expression and NR activity were slightly reduced compared to the wild type due to feedback regulation in the mutant strains. No NIR protein was found in the three mutants. However, NIR activity was obtained (50% of the wild-type) for one mutant strain. The NIR-deficient mutants and the already available NR-deficient mutants will be promising tools for investigations of the nitrate assimilation pathway on the molecular level and for studies searching for signaling of C and N metabolism by inorganic N-compounds. Received: 8 October 1999 / Accepted: 25 January 2000  相似文献   

4.
Sampling spatial and temporal variation in soil nitrogen availability   总被引:18,自引:0,他引:18  
There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+ 4) and nitrate (NO 3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH+ 4 and NO 3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+ 4 and NO 3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+ 4 and NO 3 concentrations decreased with the age of the dune. Soil NO 3 concentration showed strong spatial structure, but soil NH+ 4 concentration was not spatially structured. Plant-available NH+ 4 and NO 3 showed relatively little spatial structure: only NO 3 availability in the second sampling period had significant patch structure. Spatial maps of NH+ 4 and NO 3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO 3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO 3 concentrations, providing some evidence that patches of plant-available NO 3 may reappear at the same spatial locations at irregular points in time. Received: 20 February 1998 / Accepted: 23 November 1998  相似文献   

5.
Controlled cultivation of marine macroalgal biomass such as Ulva species, notably Ulva lactuca, is currently studied for production of biofuels or functional food ingredients. In a eutrophic environment, this macrophyte is exposed to varying types of nutrient supply, including different and fluctuating levels of nitrogen sources. Our understanding of the influences of this varying condition on the uptake and growth responses of U. lactuca is limited. In this present work, we examined the growth response of U. lactuca exposed to different sources of nitrogen (NH4+; NO3; and the combination NH4NO3) by using photo-scanning technology for monitoring the growth kinetics of U. lactuca. The images revealed differential increases of the surface area of U. lactuca disks with time in response to different N-nutrient enrichments. The results showed a favorable growth response to ammonium as the nitrogen source. The NH4Cl and NaNO3 rich media (50 μM of N) accelerated U. lactuca growth to a maximum specific growth rate of 16.4 ± 0.18% day−1 and 9.4 ± 0.72% day−1, respectively. The highest biomass production rate obtained was 22.5 ± 0.24 mg DW m−2·day−1. The presence of ammonium apparently discriminated the nitrate uptake by U. lactuca when exposed to NH4NO3. Apart from showing the significant differential growth response of U. lactuca to different nitrogen sources, the work exhibits the applicability of a photo-scanning approach for acquiring precise quantitative growth data for U. lactuca as exemplified by assessment of the growth response to two different N-sources.  相似文献   

6.
Supplying both N forms (NH4 ++NO3 ) to the maize (Zea mays L.) plant can optimize productivity by enhancing reproductive development. However, the physiological factors responsible for this enhancement have not been elucidated, and may include the supply of cytokinin, a growth-regulating substance. Therefore, field and gravel hydroponic studies were conducted to examine the effect of N form (NH4 ++NO3 versus predominantly NO3 ) and exogenous cytokinin treatment (six foliar applications of 22 μM 6-benzylaminopurine (BAP) during vegetative growth versus untreated) on productivity and yield of maize. For untreated plants, NH4 ++NO3 nutrition increased grain yield by 11% and whole shoot N content by 6% compared with predominantly NO3 . Cytokinin application to NO3 -grown field plants increased grain yield to that of NH4 ++NO3 -grown plants, which was the result of enhanced dry matter partitioning to the grain and decreased kernel abortion. Likewise, hydroponically grown maize supplied with NH4 ++NO3 doubled anthesis earshoot weight, and enhanced the partitioning of dry matter to the shoot. NH4 ++NO3 nutrition also increased earshoot N content by 200%, and whole shoot N accumulation by 25%. During vegetative growth, NH4 ++NO3 plants had higher concentrations of endogenous cytokinins zeatin and zeatin riboside in root tips than NO3 -grown plants. Based on these data, we suggest that the enhanced earshoot and grain production of plants supplied with NH4 ++NO3 may be partly associated with an increased endogenous cytokinin supply.  相似文献   

7.
The activities of antioxidative enzymes and contents of proline and total phenolics were assayed in roots of two maize (Zea mays L.) genotypes grown in a medium containing nitrate (NO3 ) or both nitrogen forms, nitrate and ammonium (NH4 +/NO3 ). An increase in the activities of class III peroxidases (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), ascorbate oxidase (AO) and proline content, and decrease in phenolic content were observed in NH4 +/NO3 in comparison with NO3 grown plants. When polyethylene glycol (PEG) was added to both nitrogen treatments, the content of total phenolics and proline was increased, especially in NH4 +/NO3 treatment. The PEG treatment decreased enzyme activities in NH4 +/NO3 grown plants, but in NO3 grown plants activities of POD and SOD were increased, opposite to decreased APX and AO. Isoelectric focusing demonstrated increased activities of acidic POD isoforms in PEG treated NO3 grown plants, and lower activities of both, acidic and basic isoforms in NH4 +/NO3 grown plants.  相似文献   

8.
Fluctuating salinities at different sites on the German salt-polluted rivers Werra and Weser were compared with extracellular ion levels of specimens of Gammarus tigrinus (Sexton; Amphipoda, Crustacea), collected at the same sites. G. tigrinus regulated haemolymph concentrations of inorganic anions (Cl, SO2− 4, PO3− 4) and cations (Na+, K+, Mg2+, Ca2+) during fluctuations of salt pollution in the upper Weser. This capacity to regulate varying levels of salt pollution in the upper Weser, correlated well with the distribution of the brackish amphipods in this river ecosystem. G. tigrinus tolerated periods of Na+ and Cl stress (>380 mmol l−1) without compensating these maxima by regulating extracellular Na+ and Cl. However, during such bursts of Na+ and Cl stress in Werra and Weser, the ability to regulate extracellular [K+] at river water K+ stress of ≥6.0 mmol l−1 may explain why this brackish species has been more successful in these rivers than its competitors like Gammarus pulex. The present investigation demonstrates that the water salinity affects the [NO 3] in the haemolymph of G. tigrinus. With increasing hypo-osmotic stress the animals accumulate increasing amounts of NO 3. A simultaneous increase in stream water [NO 3] causes an additional accumulation of NO 3 in the haemolymph. The high extent of accumulation indicates that active ion transport systems may be involved. The accumulation of NO 3 in the haemolymph has low physiological consequences to G. tigrinus, but when hypo-osmotically stressed under anoxic conditions, nitrite formed by the reduction of nitrate may have an adverse affect on the metabolism of G. tigrinus. Accepted: 4 October 1999  相似文献   

9.
The kinetics of NH4 + and NO3 uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the Vmax of NH4 + uptake was higher than that of NO3 uptake. The Km of NH4 + uptake and Km of NO3 uptake differed not significantly. When both NH4 + and NO3 were present, the Vmax for NH4 + uptake became slightly higher, and the Km for NH4 + uptake remained in the same order. Under these conditions the NO3 uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH4 + occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}  相似文献   

10.
The mechanism of transbranchial excretion of total ammonia of brackish-water acclimated shore crabs, Carcinus maenas was examined using isolated, perfused gills. Applying physiological gradients of NH4Cl (100–200 μmol · l−1) directed from the haemolymph space to the bath showed that the efflux of total ammonia consisted of two components. The saturable component (excretion of NH4 +) greatly exceeded the linear component (diffusion of NH3). When an outwardly directed gradient (200 μmol · l−1) was applied, total ammonia in the perfusate was reduced by more than 50% during a single passage of saline through the gill. Effluxes of ammonia along the gradient were sensitive to basolateral dinitrophenol, ouabain, and Cs+ and to apical amiloride. Acetazolamide (1 mmol · l−1 basolateral) or Cl-free conditions had no substantial effects on ammonia flux, which was thus independent of both carbonic anhydrase mediated pH regulation and osmoregulatory NaCl uptake. When an inwardly directed gradient (200 μmol · l−1) was employed, influx rates were about 10-fold smaller and unaffected by basolateral ouabain (5 mmol · l−1) or dinitrophenol (0.5 mmol · l−1). Under symmetrical conditions (100 μmol · l−1 NH4Cl on both sides) ammonia was actively excreted against the gradient of total ammonia, which increased strongly during the experiment and against the gradient of the partial pressure of NH3. The active excretion rate was reduced to 7% of controls by basolateral dinitrophenol (0.5 mmol · l−1), to 44% by basolateral ouabain (5 mmol · l−1), to 46% by Na+-free conditions and to 42% by basolateral Cs+ (10 mmol · l−1), indicating basolateral membrane transport of NH4 + via the Na+/K+-ATPase and K+-channels and a second active, apically located, Na+ independent transport mechanism of NH4 +. Anterior gills, which are less capable of active ion uptake than posterior gills, exhibited even increased rates of active excretion of ammonia. We conclude that, under physiological conditions, branchial excretion of ammonia is a directed process with a high degree of effectiveness. It even allows active extrusion against an inwardly directed gradient, if necessary. Accepted: 11 March 1998  相似文献   

11.
The effects of macronutrients (NO3 , NH4 + and PO4 3−) on cell growth and triterpenoids production inCentella asiatica cell suspension cultures were analyzed using the Box-Behnken response surface model experimental design. In screening and optimization experiments, PO4 3− as a single factor significantly influenced cell growth where increasing the phosphate level from 0.1 to 2.4 or 2.6 mM, elevated cell growth from 3.9 to 14–16 g/L. The optimum values predicted from the response surface model are 5.05 mM NH4 +, 15.0 mM NO3 and 2.6 mM PO4 3−, yielding 16.0 g/L cell dry weight with 99% fitness to the experimental data. While the NH4 +-NO3 interaction influenced cell growth positively in the optimization experiment, NH4 + and NO3 as single factors; and interactions of NO3 -PO4 3−, NH4 +-PO4 3− and NH4 +-NO3 were all negative in the screening experiment. Cell growth and the final pH level were positively affected by PO4 3−, but negatively affected by NH4 + and NH4 +-PO4 3− interactions. The different effects of factors and their interactions on cell growth and final pH are influenced by a broad or narrow range of macronutrient concentrations. The productions of triterpenoids however were lower than 4 mg/g cell dry weight.  相似文献   

12.
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.  相似文献   

13.
14.
Spatial variability of soil total nitrogen (N), available N (KCl extractable NH4+ and NO3), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province, southwestern China in June and August 2000. In a study area of 90 × 105 m2, three soil samples were collected from each 5 × 5 m2 plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification were measured by in situ core incubation and the rates were estimated based on the difference of NH4+ and NO3 contents between the two sampling dates. Total N, NH4+, and NO3 were all spatially structured with different semivariogram ranges (from high to low: NH4+, NO3, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH4+ was the dominant soil inorganic N form in the system. Both NH4+ and NO3 affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification as indicated by greatly increased soil NO3 content. High spatial auto-correlations (>0.7) were found between available N and NH4+, available N and NO3 on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation between NH4+ and NO3 were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values, particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold for detection in this study.  相似文献   

15.
Nitrite (NO2 ) is an intermediate in a variety of soil N cycling processes. However, NO2 dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3 , NH4 + and NO2 . Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of functional links between (1) NH4 + oxidation, the main process for NO2 production (nitritation), and NO2 reduction, and (2) oxidation of soil organic N, the dominant NO3 production process in this soil, and dissimilatory NO3 reduction to NH4 + (DNRA). The production of NH4 + via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the rate of DNRA was several magnitudes higher than the rate of other NO3 reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic conditions of this Nothofagus ecosystem.  相似文献   

16.
Withania somnifera is an important medicinal plant that contains withanolides and withaferins, both bioactive compounds. We have tested the effects of macroelements and nitrogen source in W. somnifera cell suspension cultures with the aim of optimizing the production of biomass and withanolide A. The effects of the macroelements NH4NO3, KNO3, CaCl2, MgSO4 and KH2PO4 at concentrations of 0.0, 0.5, 1.0, 1.5 and 2.0× strength and of the nitrogen source [NH4 +/NO3 (mM/mM) ratio of: 0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20, and 14.38/37.60 (mM)] in Murashige and Skoog medium were tested for biomass and withanolide A production. The highest accumulation of biomass [147.81 g l−1 fresh weight (FW) and 14.02 g l−1 (dry weight (DW)] was recorded in the medium containing a 0.5× concentration of NH4NO3, and the highest production of withanolide A content was recorded in the medium with 2.0× KNO3 (4.36 mg g−1 DW). The NH4 +/NO3 ratio also influenced cell growth and withanolide A production, with both parameters being larger when the NO3 concentration was higher than that of NH4 +. Maximum biomass growth (110.45 g l−1 FW and 9.29 g l−1 DW) was achieved at an NH4 +/NO3 ratio of 7.19/18.80, while withanolide A production was greatest (3.96 mg g−1 DW) when the NH4 +/NO3 ratio was 14.38/37.60 mM.  相似文献   

17.
Physiology, regulation and biochemical aspects of the nitrogen assimilation are well known in Prokarya or Eukarya but they are poorly described in Archaea domain. The haloarchaeon Haloferax mediterranei can use different nitrogen inorganic sources (NO3, NO2 or NH4+) for growth. Different approaches were considered to study the effect of NH4+ on nitrogen assimilation in Hfx. mediterranei cells grown in KNO3 medium. The NH4+ addition to KNO3 medium caused a decrease of assimilatory nitrate (Nas) and nitrite reductases (NiR) activities. Similar effects were observed when nitrate-growing cells were transferred to NH4+ media. Both activities increased when NH4+ was removed from culture, showing that the negative effect of NH4+ on this pathway is reversible. These results suggest that ammonium causes the inhibition of the assimilatory nitrate pathway, while nitrate exerts a positive effect. This pattern has been confirmed by RT-PCR. In the presence of both NO3 and NH4+, NH4+ was preferentially consumed, but NO3 uptake was not completely inhibited by NH4+ at prolonged time scale. The addition of MSX to NH4+ or NO3 cultures results in an increase of Nas and NiR activities, suggesting that NH4+ assimilation, rather than NH4+ per se, has a negative effect on assimilatory nitrate reduction in Hfx. mediterranei. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

18.
Batch cultures of the green microalga Chlorella vulgaris and cyanobacterium Planktothrix isothrix and their corresponding co-cultures were grown in municipal wastewater in order to study their growth as well as the nitrogen (NH4–N) and phosphorus (PO43−–P) removal. The cultures were grown under two irradiances of 20 and 60 μmol photons m−2 s−1 in shaken and unshaken conditions. The co-culture of unshaken Chlorella and Planktothrix showed the greatest growth under both irradiances. The monoalgal Planktotrix cultures showed better growth when unshaken than when shaken, whereas Chlorella cultures grew better when mixed, but only at the higher irradiance. The highest percentage of nitrogen removal (up to 80%) was attained by the unshaken co-cultures of Chlorella and Planktothrix. The amount of nitrogen recycled in the biomass reached up to 85% of that removed. Shaken monoalgal cultures of Chlorella showed phosphorus removal under both irradiances. They completely removed the initial phosphorus concentration (7.47 ± 0.17 mg L−1) within 96 and 48 h under 20 and 60 μmol photons m−2 s−1, respectively.  相似文献   

19.
Nitrous oxide (N2O), a greenhouse gas, is emitted during autotrophic and heterotrophic ammonia oxidation. This emission may result from either coupling to aerobic denitrification, or it may be formed in the oxidation of hydroxylamine (NH2OH) to nitrite (NO2 ). Therefore, the N2O production during NH2OH oxidation was studied with Alcaligenes faecalis strain TUD. Continuous cultures of A. faecalis showed increased N2O production when supplemented with increasing NH2OH concentrations. 15N-labeling experiments showed that this N2O production was not due to aerobic denitrification of NO2 . Addition of 15N-labeled NH2OH indicated that N2O was a direct by-product of NH2OH oxidation, which was subsequently reduced to N2. These observations are sustained by the fact that NO2 production was low (0.23 mM maximum) and did not increase significantly with increasing NH2OH concentration in the feed. The NH2OH-oxidizing capacity increased with increasing NH2OH concentrations. The apparent V max and K m were 31 nmol min−1 mg dry weight−1 and 1.5 mM respectively. The culture did not increase its growth yield and was not able to use NH2OH as the sole N source. A non-haem hydroxylamine oxidoreductase was partially purified from A. faecalis strain TUD. The enzyme could only use K3Fe(CN)6 as an electron acceptor and reacted with antibodies raised against the hydroxylamine oxidoreductase of Thiosphaera pantotropha. Received: 1 September 1998 / Received revision: 5 November 1998 / Accepted: 7 November 1998  相似文献   

20.
Humans have increased the availability of nutrients including nitrogen and phosphorus worldwide; therefore, understanding how microbes process nutrients is critical for environmental conservation. We examined nutrient limitation of biofilms colonizing inorganic (fritted glass) and organic (cellulose sponge) substrata in spring, summer, and autumn in three streams in Michigan, USA. Biofilms were enriched with nitrate (NO3 ), phosphate (PO4 3−), ammonium (NH4 +), NO3  + PO4 3−, NH4 + + PO4 3−, or none (control). We quantified biofilm structure and function as chlorophyll a (i.e., primary producer biomass) and community respiration on all substrata. In one stream, we characterized bacterial and fungal communities on cellulose in autumn using clone library sequencing and denaturing gradient gel electrophoresis to determine if community structure was linked to nutrient limitation status. Despite oligotrophic conditions, primary producer biomass was infrequently nutrient limited. In contrast, respiration on organic substrata was frequently limited by N + P combinations. We found no difference between biofilm response to NH4 + versus NO3 enrichment, although the response to both N-species was positively related to water column PO4 3− concentrations and temperature. Molecular analysis for fungal community composition suggested no relationship to nutrient limitation, but the dominant members of the bacterial community on cellulose were different on NO3 , PO43, and NO3  + PO4 3− treatments relative to control, NH4 +, and NH4 + + PO4 3− treatments, which matched patterns for biofilm respiration rates from each treatment. Our results show discrete patterns of nutrient limitation dependent upon substratum type and season, and imply changes in bacterial community structure and function may be linked following nutrient enrichment in streams.  相似文献   

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