Ammonium Uptake Rates Research Articles

Seasonal Effects of Influent Ammonia Oxidizing Bacteria of Municipal Wastewater Treatment Plants on Activated Sludge System

The specific ammonia uptake rates (SAUR) and ammonia oxidizing bacteria (AOB) community of influent sewage and activated sludge in the 2nd wastewater treatment plant (WWTP) of Xi'an without the primary settling tank were analyzed over multiple years to explore the seasonal effects of the influent AOB on the activated sludge systems. During the experiment, the SAUR of the raw sewage and activated sludge were 0.48-3.02 mg·(g·h)-1 and 0.68-2.25 mg·(g·h)-1, respectively. Meanwhile, the correlation analysis indicated that the monthly SAUR of the raw sewage was highly correlated with that of the activated sludge of the following month (r=0.862,P<0.05), which indicated that influent nitrifiers had a significant effect on the nitrification performance of activated sludge. Considering that the estimated AOB seeding intensities based on the ammonia oxidizing activity were 0.21-0.92 g·(g·d)-1, the nitrifier immigration from the raw sewage should added to the design of WWTP and the activated sludge modeling. Moreover, the qPCR results revealed that the AOB abundance of activated sludge in winter decreased but remained at 1010 cells·g-1, indicating that the immigration of influent nitrifiers could partially compensate for the reduction of the AOB abundance in the activated sludge caused by decreasing temperatures. Finally, the Illumina MiSeq sequencing demonstrated that the shared dominant AOB between the raw sewage and activated sludge were Nitrosomonas sp. Nm58, Nitrosomonas sp. JL21, and bacterium CYCU-0253. These findings can provide theoretical support for the design and operation of a WWTP.

Stable partial nitrification at low temperature via selective inactivation of enzymes by intermittent thermal treatment of thickened sludge

• Thermal treatment (35 °C/2 days) could expand the difference between SAUR and SNUR. • A stable NAR of 90.18 ± 5.74% was rapidly achieved in the long-term experiment. • NOR selective inactivation is the main reason for nitrite accumulation. • Cold-adapted Nitrotoga is the dominant NOB throughout the experiment. • A novel method of intermittent thickened sludge thermal treatment is proposed. Achieving stable nitrite accumulation at low temperature continues to be a challenging problem in partial nitrification (PN). This study proposes a strategy to achieve stable PN of thickened sludge at low temperatures through selective inactivation of enzymes by intermittent thermal treatment. This method was verified using a sequencing batch reactor (SBR) operated at 9 ± 1 °C in full nitrification mode. After thermally treating the activated sludge at 35 °C for 2 days, which was the optimal condition for selective inactivation of enzymes determined by batch tests, an average nitrite accumulation rate (NAR) of 90.18 ± 5.74% was rapidly achieved and the SBR was stably operated at 9 ± 1 °C for 80 days. This was consistent with a significant decrease of the specific nitrite uptake rate (SNUR), but no a reduction, or even an increase, of the specific ammonia uptake rate (SAUR). Also, there was no remarkable change in the nitrifying bacterial community except for a slight increase in both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). In addition, after thermal treatment at 35 °C for 2 days, the nitrite oxidoreductase (NOR) activity was significantly decreased, while those of ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) showed an increasing trend. Thus, the achievement of stable PN at low temperatures with this strategy may be due to the selective inactivation of NOR, rather than NOB washout.

Responses of microbial structures, functions and metabolic pathways for nitrogen removal to different hydraulic retention times in anaerobic side-stream reactor coupled membrane bioreactors

Synchronous sludge reduction and nitrogen removal have attracted increasing attention, while the underlying mechanisms of diverse nitrogen metabolism within the complicated processes remain unclear. Four anoxic/oxic membrane bioreactors, three of which were upgraded by anaerobic side-stream reactors (ASSR) and carriers (APSSR-MBRs), were operated to determine effects of hydraulic retention time of ASSRs. APSSR-MBRs achieved more significant nitrogen removal and higher nitrate uptake rate because of more denitrifying bacteria and the supernumerary release of secondary substrates. Ammonia uptake rate showed the diverse Nitrospira preceded over anaerobic decay and sulfide inhibition in the ASSR, and made the reactor exhibit higher nitrification capacity. Metagenomic analysis indicated that APSSR-MBRs showed higher abundances of genes related to nitrogen consumption processes, and higher abundances on the carriers, confirming their pivotal roles in nitrogen metabolism. This study provided novel perspectives to build a bridge between process model and nitrogen metabolism in the sludge reduction system..

Improving Nitrogen Use Efficiency Through Overexpression of Alanine Aminotransferase in Rice, Wheat, and Barley.

Nitrogen is an essential nutrient for plants, but crop plants are inefficient in the acquisition and utilization of applied nitrogen. This often results in producers over applying nitrogen fertilizers, which can negatively impact the environment. The development of crop plants with more efficient nitrogen usage is, therefore, an important research goal in achieving greater agricultural sustainability. We utilized genetically modified rice lines over-expressing a barley alanine aminotransferase (HvAlaAT) to help characterize pathways which lead to more efficient use of nitrogen. Under the control of a stress-inducible promoter OsAnt1, OsAnt1:HvAlaAT lines have increased above-ground biomass with little change to both nitrate and ammonium uptake rates. Based on metabolic profiles, carbon metabolites, particularly those involved in glycolysis and the tricarboxylic acid (TCA) cycle, were significantly altered in roots of OsAnt1:HvAlaAT lines, suggesting higher metabolic turnover. Moreover, transcriptomic data revealed that genes involved in glycolysis and TCA cycle were upregulated. These observations suggest that higher activity of these two processes could result in higher energy production, driving higher nitrogen assimilation, consequently increasing biomass production. Other potential mechanisms contributing to a nitrogen-use efficient phenotype include involvements of phytohormonal responses and an alteration in secondary metabolism. We also conducted basic growth studies to evaluate the effect of the OsAnt1:HvAlaAT transgene in barley and wheat, which the transgenic crop plants increased seed production under controlled environmental conditions. This study provides comprehensive profiling of genetic and metabolic responses to the over-expression of AlaAT and unravels several components and pathways which contribute to its nitrogen-use efficient phenotype.

Effect of Three Pesticides Used in Salmon Farming on Ammonium Uptake in Central-Southern and Northern Patagonia, Chile

Chile is the second largest global producer of farmed salmon. The growth of salmon production has not been free of environmental challenges, such as the increasing use of pesticides to control the parasitic load of the sea lice Caligus rogercresseyi. The lack of the specificity of pesticides can potentially affect non-target organisms, as well as the structure and functioning of aquatic ecosystems. The aim of this study, was to understand the effect of pesticides on natural microbial communities to the addition of the anti-lice pesticide azamethiphos, deltamethrin and emamectin benzoate, and their potential impact in ammonium uptake rates in the coast off central-southern Chile and Northern Patagonia. The addition of pesticides on natural microbial communities resulted in a rapid response in ammonium uptake, which was significant for the single use of pesticide, azamethiphos and emamectin benzoate, as well as the combination, azamethiphos, deltamethrin and emamectin benzoate. In northern Patagonia, azamethiphos addition produced a 53% decrease in photoautotrophic uptake. However, an increase, although variable, was observed in chemoautotrophic uptake. Emamectin benzoate produced a 36 to 77% decrease in chemo and photoautotrophic ammonium uptake, respectively. The combined use of pesticides, also produced up to 42% decrease in both photo and chemoautotrophic assimilation. We conclude that the use of pesticides in salmon farming produces diverse responses at the microbial level, stimulating and/or inhibiting microbial communities with subsequent impact on nitrogen budgets. Further studies are necessary to understand the impact of pesticides in the ecology of central-southern and northern Patagonia, Chile.

Competition for nitrogen between the seaweed Caulerpa prolifera and the seagrass Cymodocea nodosa

The rhizophytic seaweed Caulerpa prolifera has been expanding rapidly in the Ria Formosa lagoon, southern Portugal, taking over deeper unvegetated areas and mixing with the native seagrass Cymodocea nodosa in shallower areas. In the Ria Formosa lagoon, belowground ammonium uptake from the sediment represents the main source of nitrogen for the 2 macrophytes, except during the ammonium pulses from the sediment to the water column that are incorporated through aboveground plant parts. We examined the competition for inorganic and organic nitrogen between C. prolifera and C. nodosa through a series of 15N-ammonium and 15N-amino acid surge uptake experiments combining single-species and mixed incubations at a range of nutrient concentrations. Our results showed that C. prolifera is generally faster than C. nodosa in the acquisition of ammonium and amino acids by both above- and belowground parts, and that the uptake rates of ammonium and amino acids of one species were not affected by the presence of the other species. The exception was the amino acid uptake through the rhizoids of C. prolifera, which was slightly enhanced in the presence of C. nodosa. In this situation, the aboveground ammonium uptake becomes the main contributor to the nitrogen budget of C. nodosa but not to that of C. prolifera. When ammonium pulses are considered, C. nodosa is more competitive for nitrogen than C. prolifera. In this case, the leaf uptake of ammonium is the largest contributor to the total nitrogen (ammonium plus amino acids) budget of the seagrass. Our results showed that the different nutritional strategies of the 2 macrophytes allow their coexistence in the Ria Formosa lagoon.

Stepwise treatment of undiluted raw piggery wastewater, using three microalgal species adapted to high ammonia

A high ammonia concentration and chemical oxygen demand (COD) in piggery wastewater force it to be diluted before conventional microalgal treatment to reduce ammonia toxicity. Incomplete treatment of ammonia and COD in piggery wastewater may cause eutrophication, resulting in algal blooms. This study tried to treat raw piggery wastewater without dilution, using three strains of microalgae (Chlorella sorokiniana, Coelastrella sp. and Acutodesmus nygaardii) that outcompeted other algae under heterotrophic, mixotrophic, and autotrophic conditions, respectively, through adaptive evolution at high ammonia concentration. The three stepwise processes were designed to remove (1) small particles, COD, and phosphorus in the 1st heterotrophic C. sorokiniana cultivation, (2) ammonia and COD in the 2nd mixotrophic Coelastrella sp. cultivation, and (3) the remaining ammonia in the 3rd photoautotrophic A. nygaardii cultivation. To enhance ammonia uptake rate, each algal species were inoculated after 2-day nitrogen starvation. When the N-starved three species were inoculated at each step sequentially at 7 g/L for 2 days, the final phosphorus, COD, and ammonia removal efficiencies were 100% (16.4–0 mg/L), 92% (6820–545 mg/L), 90% (850–81 mg/L) and turbidity (99%) after total 6 days.

Adaptability of Nitrifying Biofilm Systems to Low Temperature: MBBR and IFAS

The long-term effects of a decreasing temperature on the nitrification performance, biofilm characteristics, and nitrifier community in a moving-bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS) system were investigated at various temperatures (20, 15, and 10℃) to explore the adaptability of nitrifying biofilm systems to low temperatures. During the experiment, the extracellular polymeric substances (EPS) in the biofilms increased with decreasing temperature, which resulted in an increased biofilm mass and thickness. As there was only a biofilm phase in the MBBR to remove ammonia, the part of the carriers in the MBBR at 10℃ became plugged, which partially led to a deterioration in the effluent water quality. This indicated that the IFAS system was more adaptable to low temperatures than was the MBBR. Meanwhile, the results for the nitrifier activities showed that, although the nitrification contribution rate of the suspended phase in the IFAS system always dominated during the experiment, that of the fixed phase with regards to the ammonia uptake rate (AUR) gradually increased from 30.72% at 20℃ to 39.85% at 10℃. This indicated that the biofilm played an enhanced role in nitrification in the IFAS system. Moreover, the qPCR results revealed that the nitrifier copies of the number of biofilms increased slightly with decreased temperature, and coincided with an increase in biomass, which partially compensated for the decreased nitrification activity. These findings provide a theoretical basis for the application of the biofilm systems to wastewater treatment.

Seasonal Nitrogen Uptake Dynamics and Harmful Algal Blooms in the York River, Virginia

During a 2-year study of planktonic nitrogen (N) nutrition, temporal variability of (1) ambient nutrient concentrations; (2) uptake rates of ammonium (NH4+), nitrate (NO3−), nitrite (NO2−), urea, and amino acids (AA) in three size fractions (> GF/F, > 5 μm, and 5–0.2 μm); (3) NH4+ regeneration and NO3− regeneration (nitrification); and (4) an unexpected bloom of Alexandrium monilatum were examined. Dissolved organic N (DON) was the most abundant form of fixed N. High concentrations of NH4+ and NO2− were detected during the late summer and fall, reaching maximums of 9.9 and 7.6 μmol N L−1, respectively. The highest uptake rates were for NH4+ at all stations, size fractions, and seasons sampled and ranged from 34 to 80% of total absolute N uptake. The magnitude of uptake rates in the > GF/F fraction generally followed the pattern of NH4+ > NO3− > urea > AA > NO2− with some exceptions when urea uptake rates were higher than NO3−. Rates of NH4+ regeneration and nitrification often exceeded uptake rates, indicating autochthonous pathways for nutrient loading. Exceptionally high dinoflagellate biomass was found in late summer and corresponded with harmful algal blooms. Kinetic curves measured during an A. monilatum bloom showed high Vmax (33.7 ± 2.7 × 10−3 h−1) and high Ks (7.3 μmol N L−1) for NH4+ suggesting that it can rapidly utilize high concentrations when available but may be outcompeted by other phytoplankton when concentrations of NH4+ are low. However, A. monilatum demonstrated that it is capable of using a diverse suite of N substrates, giving it a potential competitive advantage under diverse nutrient conditions.

Root nitrogen acquisition strategy of trees and understory species in a subtropical pine plantation in southern China

Nitrogen (N) is considered as a major factor that limits plant growth and metabolism, and absorptive roots play a critical role in plant resource acquisition. However, little is known about the roles of mycorrhizal colonization, and morphological and architectural traits of absorptive roots in N uptake rates. We examined the uptake rates for ammonium ( $${\text{NH}}_{4}^{ + }$$ ), nitrate ( $${\text{NO}}_{3}^{ - }$$ ) and glycine using a 15N isotope tracer technique and measured mycorrhizal colonization rates and functional traits (morphology, architecture and chemistry) of absorptive roots in a subtropical plantation during the growing season. Results showed that trees, shrubs and herbs all preferred to take up $${\text{NH}}_{4}^{ + }$$ over $${\text{NO}}_{3}^{ - }$$ and glycine, likely due to the dominant available N form in native soils. Species coexisting in the subtropical plantation did not show chemical niche differentiation, but there was a temporal niche separation in N acquisition across plant species. Absorptive roots with higher mycorrhizal colonization rates exhibited higher N uptake rates than those with lower colonization. In May, morphological traits (diameter and root tissue density) seemed playing important roles in N acquisition on that the absorptive roots with larger diameter and shorter specific root length (SRL) showed higher uptake rates for $${\text{NH}}_{4}^{ + }$$ , $${\text{NO}}_{3}^{ - }$$ , and glycine than those with smaller diameter and longer SRL. While in August, the architectural traits of root branching might be essential to enhance nutrient absorption on that the absorptive roots with intensive branching exhibited higher N uptake rates than those with less branching. Our findings suggested that plant species may evolve effective N acquisition strategies integrated mycorrhizal symbiosis, and root morphological and architectural traits over a temporal scale to acclimate to the changing environments.

Study on the uptake of dissolved nitrogen by Oocystis borgei in prawn (Litopenaeus vannamei) aquaculture ponds and establishment of uptake model

The increase of ammonia nitrogen, nitrite, nitrate, urea, and other dissolved nitrogen in prawn pond often causes eutrophication of water body and prawn poisoning, which brings great harm to aquaculture. Microalgae are the main biological factors in prawn pond, which can effectively utilize dissolved nitrogen. The goal of this study was to evaluate the effects of the forms and concentrations of various dissolved nitrogen on the uptake rate (ρ) by Oocystis borgei, and establish the relationship model between ammonia nitrogen uptake rate and key environmental factors using 15N isotope labeling technique. Temperature (A), light intensity (B), salinity (C), pH (D), and algal concentration (E) were the factors used to construct an empirical model. Study results showed that nitrogen concentrations had a significant effect on the uptake rates of ammonium, nitrate, nitrite, and urea (P 0.05), which demonstrated the high fitting degree of simulation equation. This study provides valuable insight into the removal of dissolved nitrogen in a controllable prawn farming mode such as high-elevation ponds by O. borgei.

High Nitrogen and Phosphorous Acquisition by Belowground Parts of Caulerpa prolifera (Chlorophyta) Contribute to the Species' Rapid Spread in Ria Formosa Lagoon, Southern Portugal.

Despite worldwide proliferation of the genus Caulerpa and subsequent effects on benthic communities, little is known about the nutritional physiology of the Caulerpales. Here, we investigated the uptake rates of ammonium, nitrate, amino acids,and phosphate through the fronds and rhizoids+stolon, the internal translocation of nitrogen, and developed a nitrogen budget for the rapidly spreading Caulerpa prolifera in Ria Formosa lagoon, southern Portugal. Caulerpaprolifera acquired nutrients by both aboveground and belowground parts at similar rates, except nitrate, for which fronds showed 2-fold higher uptake rates. Ammonium was the preferential nitrogen source (81% of the total nitrogen acquisition), and amino acids, which accounted for a significant fraction of total N acquisition (19%), were taken up at faster rates than nitrate. Basipetal translocation of 15 N incorporated as ammonium was nearly 3-fold higher than acropetal translocation, whereas 15 N translocation as nitrate and amino acids was smaller but equal in either direction. The estimated total nitrogen acquisition by C.prolifera was 689 μmol · m-2 ·h-1 , whereas the total nitrogen requirement for growth was 672μmol·m-2 ·h-1 . The uptake of ammonium and amino acids by belowground parts accounted for the larger fraction of the total nitrogen acquisition of C.prolifera and is sufficient to satisfy the species nitrogen requirements for growth. This may be one reason explaining the fast spreading of the seaweed in the bare sediments of Ria Formosa where it does not have any macrophyte competitors and the concentration of nutrients is high.

Epilithic algae from an urban river preferentially use ammonium over nitrate

Epilithon is a taxonomically diverse assemblage of aquatic organisms which grow on rocks; this biological compartment is involved in several reactions that contribute to the dynamics of dissolved organic nitrogen in water. Using ceramic tiles colonized in an urban river, this experimental study assessed the relative importance of ammonium uptake by inhibiting nitrification blocking ammonium oxidation with acetylene, as well it tested the hypothesis that epilithon preferentially assimilated ammonium over nitrate. In our experiments, ammonium uptake by epilithon accounted for 46% – 100 % of the ammonium decrease in the water column, whereas nitrate uptake accounted for 0% – 11% of the nitrate decrease. Ammonium uptake rates ranged from 197 to 519 μmol m-2 h-1, while nitrate uptake rates were from 47 to 85 μmol N-NO3- m-2 h-1. The rate of preferential assimilation (RPI) was between 1.15 and 1.26, indicating preference for ammonium over nitrate. The results of this research provide valuable information regarding the relative contribution of algal uptake relative to nitrification in epilithon from an urban river.

Using path analysis to determine interacting effects of biotic and abiotic factors on patch-scale biogeochemical rates in a prairie stream

Biogeochemical rates within streams vary with ecosystem properties including the distribution of fishes. While many studies investigate the singular effect of fishes on ecosystem components, there is a limited understanding of how fish presence interacts with other ecosystem properties to affect ecosystem structure and function. Here, we used path analyses to elucidate direct and indirect effects of fish presence, and other ecosystem properties on ecosystem respiration (ER), gross primary production (GPP), and ammonium uptake. Experimental responses of fish removal on patch scale (300 cm2) benthic rates of ER, GPP, and ammonium uptake were measured at two sites in a prairie stream. The effect of fish was determined by comparing substrata from field exclosures with fish absent to substrata exposed to fish. Total path model-explained variance was greatest for ER (R2 = 0.55) and least for ammonium uptake (R2 = 0.36) and GPP (R2 = 0.34). Fish decreased algal biomass and directly increased all biogeochemical rates. The relative importance of the different abiotic ecosystem properties varied by process; however, FBOM and substrata size were important for most rates. This study provides evidence for predominantly direct effects of fish on both stream structure and function in a prairie stream. Our results emphasize that interactions between biotic and abiotic factors should be considered when determining drivers of biogeochemical activity. We suggest that simple linear food webs that consist of top–down or bottom–up control are not always sufficient to describe animal effects on ecosystem rates.

On the Estimation of Zooplankton-Mediated Active Fluxes in Oxygen Minimum Zone Regions

In the Peruvian upwelling system, the mesopelagic oxygen minimum zone (OMZ) is the main vertically structuring feature of the pelagic habitat. Several zooplankton and nekton species undertake diel vertical migrations (DVMs) into anoxic depths. It has been argued that these migrations contribute substantially to the oxygen consumption as well as excretion of dissolved compounds (in particular ammonium) in subsurface waters. However, metabolic suppression as a response to low ambient oxygen partial pressure ($pO_2$) has not been accounted for in these estimates. Here, we present estimates of zooplankton- and nekton-mediated oxygen consumption and ammonium release based on vertically stratified net hauls (day/night, upper 1000m). Samples were scanned, followed by image analysis and size-/taxon-specific estimation of metabolic rates of all identified organisms as a function of their biomass as well as ambient temperature and $pO_2$. The main crustacean migrants were euphausiids (mainly \textit{E. mucronata}) on offshore stations and the commercially exploited squat lobster \textit{Pleuroncodes monodon} on the upper shelf, where it often undertakes migration to the seafloor during the day. Correction for metabolic suppression results in a substantial reduction of both respiration and ammonium excretion within the OMZ core. Ignoring this mechanism leads to tenfold higher estimate of DVM-mediated active export of carbon by respiration to below 100 m depth at deep-water stations. The DVM-mediated release of ammonium by euphausiids into the 200 to 400 m depth layer ranges between $0$ and $36.81 \mu mol NH_4 m^{-2} d^{-1}$, which is insufficient to balance published estimates of ammonium uptake rates due to anammox. It seems critical to account for the modulation of zooplankton metabolic activity at low oxygen in order to correctly represent the contribution of migrating species to the biological pump.

Treatment of aqueous wastes by means of Thermophilic Aerobic Membrane Reactor (TAMR) and nanofiltration (NF): process auditing of a full-scale plant.

This work focuses on the Thermophilic Aerobic Membrane Reactor (TAMR) process. The research was carried out on a full-scale facility where, all along a 12-year period, daily monitoring and process audit tests were conducted for the process analysis and optimization. The plant treated-light and high-strength aqueous wastes and two different configurations were adopted: (1) thermophilic biological reactor + ultrafiltration (TAMR) and (2) TAMR + nanofiltration (TAMR + NF). In the latter case, the average chemical oxygen demand removal yield was equal to 89% and an effective denitrification (nitrogen oxides removal equal to 96%) was achieved by reducing the dissolved oxygen concentration in the bioreactor. Low specific sludge production was observed. Poor sludge settling properties were measured by a lab-scale settling test; respirometric tests (nitrogen uptake rate and ammonia uptake rate) showed the presence of denitrification and the inhibition of nitrification. Hydrodynamic tests revealed the presence of a significant dead space, thus showing room for improving the overall process performance. Finally, the rheological properties of the sludge were measured as a function of the biomass concentration, pH, temperature, and aeration scheme.

P: 33 In Vivo Longitudinal 1H MRS Study of Hippocampal, Cereberal and Striatal Metabolic Changes in the Adult Brain Using an Animal Model of Chronic Hepatic Encephalopathy

BACKGROUND: Chronic hepatic encephalopathy (CHE) is a severe complication of chronic liver disease (CLD) characterized by cognitive and motor deficits. The diseased liver fails to metabolize toxins from the blood (ammonium, bilirubin etc.) which accumulate in the blood and brain.1 There is evidence that ammonium uptake rate differs among the brain regions.2 Since the CHE patients present various symptoms with different severity, the susceptibility to CHE and the mechanisms causing the damage may depend on the brain region. The aim of this study was to investigate, for the first time, potential metabolic differences between hippocampus, cerebellum and striatum as key brain regions implicated in manifestation of CHE. METHODS: Hippocampus (n = 7), cerebellum (n = 8) and striatum (n = 4) of adult male Wistar rats were scanned longitudinally using in-vivo 1H-MRS (SPECIAL sequence-TE = 2.8 ms,3 quantification with LCModel) at 9.4T before (week 0) and after bile duct ligation (BDL-CHE model4). Scans and blood tests were performed every two-weeks till week 8. RESULTS: All BDL rats showed an increase in plasma bilirubin and blood ammonia validating the presence of CLD. Increase in brain Glutamine (Gln) was observed for all brain regions being the most pronounced in cerebellum (+134%-week 8) (Figure 1c). Furthermore, this increase showed a strong correlation with blood ammonia for all three brain regions (Figure 1b). The main brain organic osmolytes (Inositol, Taurine, Creatine and total-Choline) displayed a similar decreasing trend in concentration as a response to Gln increase (osmoregulation) for both hippocampus and cerebellum, always having a stronger change for cerebellum. Interestingly, despite the smallest Gln increase, striatum showed more pronounced decrease in concentration of osmolytes than hippocampus (Figure 1d,e). Also, trend towards a decrease in NAA and PE was observed uniquely for striatum (data not shown). A tendency of increase in Lactate was observed being the strongest for cerebellum (+84%-cerebellum, +8%-hippocampus, +5%-striatum) indicating a possible energy metabolism perturbation (Figure 1f). Brain regions displayed different antioxidant response with a decrease in Ascorbate being stronger in cerebellum (data not shown). CONCLUSIONS: This is the first study showing in-vivo longitudinal analysis of neurometabolism in three different brain regions in a model of CHE. Hippocampus and cerebellum displayed similar trends in metabolite changes during the course of disease, while the changes were much more pronounced in cerebellum. Striatum showed differences in metabolic response when compared to the other brain regions. Clinical relevance of these findings remain to be determined. We conclude that different brain regions are differentially susceptible to the metabolic consequences of CLD, a field which warrants further study.

Different strategies of nitrogen acquisition in two tropical seagrasses under nitrogen enrichment.

Tropical marine seagrasses live in environments with low nutrient concentrations. However, as land development intensifies along tropical coastlines, the marine environment in which these organisms grow is becoming more nutrient-rich. Nitrogen (N) uptake, assimilation, translocation and storage under a diversity of N sources in enriched conditions were investigated in two tropical seagrass species, Cymodocea serrulata and Thalassia hemprichii, from an oligotrophic marine environment. Both seagrasses were able to take up different inorganic and organic N sources through their above- and belowground tissues when enriched with high N concentrations. The uptake rates of T.hemprichii were generally higher than C.serrulata in leaves and rhizome, whereas root uptake was systematically higher in C.serrulata. Acropetal and basipetal translocation was observed in both species. Reduction and assimilation of N, measured in terms of their nitrate reductase and glutamine synthetase activity, were correlated with nitrate and ammonium uptake rates, respectively. Cymodocea serrulata showed a tendency to immediately use the available N, whereas T.hemprichii allocated more N in assimilation and storage investment. The responses of these seagrasses to N-enrichment demonstrate their ability to adapt to over-enrichment by varying N sources in the first step of the eutrophication process.

Channelizing Streams for Agricultural Drainage Impairs their Nutrient Removal Capacity.

In agricultural basins, fluvial ecosystems can work as filters when retaining the nutrient excess from agricultural activities, mitigating the impacts downstream. In frequently flooded areas, like the Pampas Region of Argentina, natural streams are being channelized to reduce flood frequency and intensity, thus increasing land suitability for crop production, but the impact of these interventions on nutrient removal capacity by streams is unknown. To evaluate the effects of channelizing streams on the assimilation rate of nitrate, ammonia, and phosphorus, nutrient addition experiments were performed in streams of the southern Pampas under three different conditions: (i) channelized reaches without (C.A. Mey.) Palla (reeds), (ii) unchannelized reaches without reeds, and (iii) unchannelized reaches with reeds. Assimilation rates were estimated by applying the one-dimensional transport with inflow and storage (OTIS) model, which considers the solute transport with lateral flow and storage. Nitrate and ammonia uptake rates were higher in unchannelized than in channelized stream reaches, and a higher nitrate assimilation rate was found in the presence of reeds, indicating an important role of this macrophyte in the nitrate uptake. In the case of phosphorous, uptake rates were higher in unchannelized reaches with reeds than in the channelized reaches. These results suggest that channelizing first-order streams in agricultural landscapes of the Argentine Pampas may significantly reduce the ability of streams to mitigate nutrients loss to continental and marine water sinks.

Fba-Based Prediction of Biomass and Ethanol Concentration Time Profiles in Saccharomyces cerevisiae Fed-Bath Cultures

Abstract A Flux Balance Analysis (FBA)-based dynamical model is proposed for predicting biomass and ethanol concentration time profiles in Saccharomyces cerevisiae fed-batch cultures, with glucose and ammonium uptake rates as inputs. It is based on a metabolic network compiling the necessary internal fluxes for reproducing respiratory as well as respiro-fermentative metabolisms. While the objective cost function classically accounts for biomass growth maximization, additional linear constraints are used to reproduce overflow metabolism phenomena. New conditional equality constraints are introduced in the FBA linear programs to account for variable biomass composition (based on protein mass fraction identification with or without ammonium feeding). The proposed FBA-based model contains only 7 parameters which are estimated with the experimental data. A two-step procedure for separately solving the FBA linear programs and the macroscopic mass balance ODEs significantly lowers the computational load for parameter identification. Direct and leave-one-out cross-validation results are provided.