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Results for “nitrogen uptake efficiency”

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PubMed1990

Recent advances in rumen microbial ecology and metabolism: potential impact on nutrient output.

Feedstuffs consumed by ruminants are all initially exposed to fermentative activity in the rumen prior to gastric and intestinal digestion. The extent and type of transformation of feedstuffs thus determines the productive performance of the host. Research on rumen microbial ecology and metabolism is essentially a study of the interactions between the host, microorganisms present, substrates available, and end products of digestion. Furthermore, the interactions of the normal microbial flora with the host can be manipulated to improve the efficiency of nutrient utilization in ruminant animals. Three important areas of ruminal fermentation will be reviewed, N metabolism, fiber degradation, and biotransformation of toxic compounds. The extent of protein degradation and the rate of uptake of resultant peptides and ammonia are extremely important factors in determining the efficiency of N utilization by rumen bacteria and, therefore, the relative amounts of microbial or bypass protein available to the host. Strategies aimed at identifying and characterizing rate-limiting enzymes of cellulolytic bacteria are essential in elucidating mechanisms involved in ruminal fiber degradation. Results obtained with ruminococci will be described. The detoxification of phytotoxins by passage through the gastrointestinal tract of ruminants is a process deserving special attention and several examples will be presented. Opportunities for manipulation of rumen fermentation are good. However, successful manipulation and full exploitation depend on a through understanding of the mechanisms involved.

Animal Feed↗

PubMed1990

The role of amino acids in the energy generating pathways of Litomosoides carinii.

The filarial parasite Litomosoides carinii was able to survive for longer than 15 h in basic filarial medium (BFM) containing either glutamine or alanine as a sole substrate. The filariids were more motile in BFM containing glucose, but even higher motility was recorded in media containing both glucose and glutamine. Incubations under aerobic conditions showed that radiolabelled glutamine was metabolised primarily to CO2. In addition, small amounts of lactate and acetate were excreted in almost equimolar quantities. Incubations where both glutamine and glucose were present demonstrated that the glutamine carbon utilised by the parasite could be completely recovered in the above three end products. The glutamine nitrogen could be recovered in the additional excretory products, alanine and ammonia. The glutamine-dependent viability of L. carinii was affected by known inhibitors of the mitochondrial respiratory chain. Glucose utilisation, and the production of CO2 from this substrate, were greatly stimulated by the presence of glutamine in the external medium. Various carbon balance studies, in conjunction with enzymatic analyses, suggest that in L. carinii, glutamine provides an input of carbon into the tricarboxylic acid (TCA) cycle, probably at the level of alpha-ketoglutarate. This increased availability of Krebs cycle intermediates will stimulate the rate of pyruvate oxidation via acetyl-CoA and the TCA cycle, and thus increase the rate of carbon flux through glycolysis. The energetic advantage associated with the utilisation of the glucose/glutamine substrate couple may explain the worm's enhanced motor activity compared to incubations with glucose as the sole energy source. Alanine was found to be degraded by the filariid to equivalent amounts of lactate, acetate and CO2, indicating a relatively low energetic efficiency. There was no detectable uptake of glutamate. A variety of other amino acids tested were neither metabolised nor able to maintain worm viability in vitro.

Acetates↗

PubMed1995

Increased intestinal amino-acid retention from the addition of carbohydrates to a meal.

Carbohydrates, added to a protein meal, are known to enhance the efficiency of dietary protein utilisation. However, the respective roles of the gut and liver in relation to this enhanced efficiency are not known. Therefore, we studied amino-acid, ammonia, urea, glucose and lactate fluxes for 6 h across the portal drained viscera and liver in conscious, multi-catheterised pigs of approximately 25 kg body weight after receiving a protein meal with added carbohydrates, a pure protein meal or a control meal. Additional carbohydrate caused a net glucose efflux in the portal drained viscera and increased arterial blood insulin levels. The appearance of amino-acids in the portal blood declined by some 30%, in spite of the dietary true amino-acid digestibility being approximately 95%. Liver uptake of most amino-acids was lower and there was a lower liver urea production. Finally, there was a smaller postprandial increase in the arterial blood concentration for most of the amino-acids. The results of this study suggest that inclusion of maltodextrin in the diet increases the net retention of meal-derived amino-acids in the portal drained viscera. The lower urea production and liver amino-acid uptake suggest a lower nitrogen loss. The gut could be an important site for nitrogen retention induced by the addition of carbohydrates to a protein meal.

Journal Article↗

PubMed1985

The interaction between radiation and complexes of cis-Pt(II) and Rh(II): studies at the molecular and cellular level.

A range of Rh(II) carboxylates and cis-Pt(II) complexes have been examined for their ability to increase the radiation sensitivity of aerobic and hypoxic V79 cells in vitro. The transition metal complexes sensitize in both air and nitrogen, with the greater effect generally occurring in nitrogen. The cis-Pt(II) complexes only show small levels of sensitization with dose modification factors (DMFs) of no more than 1.2. In contrast, the Rh(II) complexes can give DMFs of 2.0. Radiation chemical experiments show the transition metal complexes to have substantially lower redox potentials than metronidazole and, in addition, neither type of complex undergoes electron transfer reaction or adduct formation on interaction with radicals derived from DNA bases. Thus, the inorganic complexes do not operate by mechanisms similar to those occurring with electron affinic or stable free radical sensitizers. The increase in radiation sensitivity for cells treated with the Rh(II) carboxylates, but not the cis-Pt(II) complexes, is attributed to the ability of the Rh compounds to deplete intracellular thiols. Further, the efficiency of sensitization by the Rh(II) complexes and their ability to interact with cellular thiols depends upon the nature of the carboxylate ligand and follows the order butyrate greater than propionate greater than acetate greater than methoxyacetate. The differences between the carboxylates may be due to differences in drug uptake. A combination of the Rh(II) complexes with misonidazole given to hypoxic cells irradiated in vitro gives an additive response. However, it was not possible to demonstrate a similar effect in tumours in mice given the combination of Rh(II) methoxyacetate and the misonidazole analogue RSU 1070.

Animals↗

PubMed1999

High-affinity transport of choline-O-sulfate and its use as a compatible solute in Bacillus subtilis.

We report here that the naturally occurring choline ester choline-O-sulfate serves as an effective compatible solute for Bacillus subtilis, and we have identified a high-affinity ATP-binding cassette (ABC) transport system responsible for its uptake. The osmoprotective effect of this trimethylammonium compound closely matches that of the potent and widely employed osmoprotectant glycine betaine. Growth experiments with a set of B. subtilis strains carrying defined mutations in the glycine betaine uptake systems OpuA, OpuC, and OpuD and in the high-affinity choline transporter OpuB revealed that choline-O-sulfate was specifically acquired from the environment via OpuC. Competition experiments demonstrated that choline-O-sulfate functioned as an effective competitive inhibitor for OpuC-mediated glycine betaine uptake, with a Ki of approximately 4 microM. Uptake studies with [1, 2-dimethyl-14C]choline-O-sulfate showed that its transport was stimulated by high osmolality, and kinetic analysis revealed that OpuC has high affinity for choline-O-sulfate, with a Km value of 4 +/- 1 microM and a maximum rate of transport (Vmax) of 54 +/- 3 nmol/min. mg of protein in cells grown in minimal medium with 0.4 M NaCl. Growth studies utilizing a B. subtilis mutant defective in the choline to glycine betaine synthesis pathway and natural abundance 13C nuclear magnetic resonance spectroscopy of whole-cell extracts from the wild-type strain demonstrated that choline-O-sulfate was accumulated in the cytoplasm and was not hydrolyzed to choline by B. subtilis. In contrast, the osmoprotective effect of acetylcholine for B. subtilis is dependent on its biotransformation into glycine betaine. Choline-O-sulfate was not used as the sole carbon, nitrogen, or sulfur source, and our findings thus characterize this choline ester as an effective compatible solute and metabolically inert stress compound for B. subtilis. OpuC mediates the efficient transport not only of glycine betaine and choline-O-sulfate but also of carnitine, crotonobetaine, and gamma-butyrobetaine (R. Kappes and E. Bremer, Microbiology 144:83-90, 1998). Thus, our data underscore its crucial role in the acquisition of a variety of osmoprotectants from the environment by B. subtilis.

Journal Article↗

PubMed2004

Gene transfer with three amphiphilic glycol chitosans--the degree of polymerisation is the main controller of transfection efficiency.

A number of studies have examined the possibility of delivering genes for the treatment of genetic diseases using various polymers and lipids. We have previously demonstrated the gene transfer ability of amphiphilic polymers (a soluble amine polymer covalently bound to lipid pendant groups). In the current communication we explore the gene transfer activity of amphiphilic glycol chitosans. Glycol chitosan was acid depolymerised to give polymers of various molecular weights. Palmitoyl or hexadecyl and in some cases additional N-methyl quaternary ammonium groups were attached to the polymers. DNA binding was studied by measuring the reduced fluorescence of ethidium bromide and the polyplex particle size and zeta potential. Biological characterisation of the polyplexes involved haemolysis, cytotoxicity and gene transfer assays. For the 22 polymers tested, DNA binding was optimum at a nitrogen to phosphate ratio of 2:1 and above. Polyplexes were 200-500 nm in diameter with a neutral or positive zeta potential. The haemolytic activity of the N-methyl polymers was studied and no haemolysis was detected up to a concentration of 10 mg ml-1. Cytotoxicity studies showed that the biocompatibility of glycol chitosan was adversely affected by a combination of a palmitoyl group and depolymerisation and that biocompatibility was subsequently restored with the introduction of N-methyl groups. In vitro transfection efficiency superior to the cationic lipid formulation N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl sulphate (DOTAP) was seen with depolymerised glycol chitosan in the A431 cell line only and with the depolymerised N-methyl quaternary ammonium amphiphilic derivatives in both the A431 and A549 cell lines. Degree of polymerisation (DP) was the most important controller of transfection efficiency and transfection resided within polymers with a DP of 73-171. High DP polymers diminished DNA-cell association, the first step in the cellular gene transfer process, thus apparently diminishing cell uptake. In vivo transfection with the N-methyl quaternary ammonium amphiphile was best at a DP of 86 and this glycol chitosan amphiphile gave superior liver and heart gene expression levels when compared to both Exgen 500 (linear polyethylenimine) and Superfect (a polyamidoamine dendrimer).

Animals↗

PubMed2006

Comparative studies on Ureide Permeases in Arabidopsis thaliana and analysis of two alternative splice variants of AtUPS5.

The recovery of free purine and pyrimidine bases and their degradation products represent alternative pathways in plant cells either to synthesize nucleotides (salvage pathways) by low energy consumption or to reuse organic nitrogen. Such recycling of metabolites often requires their uptake into the cell by specialized transport systems residing in the plasma membrane. In plants, it has been suggested that several protein families are involved in this process, but only a few transporters have so far been characterized. In this work, gene expression, substrate specificities, and transport mechanisms of members of the Ureide Permease family in Arabidopsis (AtUPS) were analyzed and compared. Promoter-GUS studies indicated that the members of the family have distinct and partially overlapping expression patterns with regard to developmental stages or tissue specific localization. In addition, two alternative splice variants of AtUPS5, a novel member of the transporter family, were identified and investigated. The abundance of both alternative mRNAs varied in different organs, while the relative amounts were comparable. AtUPS5l (longer isoform) shares similar structural prediction with AtUPS1 and AtUPS2. In contrast, AtUPS5s (shorter isoform) lacks two transmembrane domains as structural consequence of the additional splice event. When expressed in yeast, AtUPS5l mediates cellular import of cyclic purine degradation products and pyrimidines similarly to AtUPS1 and AtUPS2, but differences in transport efficiencies were observed. AtUPS5s, however, could not be shown to mediate uptake of these compounds into yeast cells and might therefore be defective or have a different function.

Alternative Splicing↗

PubMed1998

Spectroscopic and biochemical characterisation of self-aggregates formed by antitumor drugs of the camptothecin family: their possible role in the unique mode of drug action.

We describe the effect strongly influencing the biological activity of some camptothecin (CPT) drugs, the inhibitors of DNA topoisomerase I (topo I), namely, the formation of J-type aggregates in an aqueous buffer solution. These aggregates were built up under certain dilution conditions of the stock DMSO solutions of 20-S-camptothecin (20(S)CPT), 10,11-methylenedioxy-CPT (10,11-CPT) and 7-ethyl-10-hydroxy-CPT (SN38). The aggregates were found to be stereospecific, not being detectable for the 20(R)-stereoisomer of CPT. They were formed by the stacking interaction between quinoline rings of CPT chromophores with the inverse position of the nitrogen atoms. The aggregates were stable at acidic and neutral pHs, but dissociated at basic pHs. Self-aggregation prevented hydrolysis of the lactone ring at neutral pHs, thus preserving the drugs in a biologically active form. Addition of BSA did not induce either disaggregation or hydrolysis of the lactone ring, whereas the monomeric form of the drugs was shown to undergo rapid conversion to an inactive carboxylate form in the presence of human serum albumin [5]. The drugs did not form the aggregates in the presence of topo I. Moreover, rapid dissociation of the aggregates was observed if a self-aggregated drug solution was added to topo I alone or to the DNA-topo I cleavage assay. Neither DNA alone nor oligonucleotides derived from the sequences of the CPT-enhanced or topo I-induced cleavage sites in SV40 plasmid DNA induces changes in the aggregation state of the drugs. These observations are indicative of interaction between the aggregates and topo I. The aggregates were found to penetrate within the cells with much higher efficiency than a monomeric form of the drugs. Cellular uptake of aggregated and nonaggregated species correlated well with cytotoxic effects produced by the drug. In this manner, CPT's self-aggregation should be regarded as a favourable phenomenon producing species with a more stable biologically active structure of the lactone ring and exhibiting enhanced cellular uptake levels relative to the monomeric forms of medications.

Antineoplastic Agents, Phytogenic↗

PubMed2001

Differential regulation of the NO3- and NH4+ transporter genes AtNrt2.1 and AtAmt1.1 in Arabidopsis: relation with long-distance and local controls by N status of the plant.

Regulation of root N uptake by whole-plant signalling of N status was investigated at the molecular level in Arabidopsis thaliana plants through expression analysis of AtNrt2.1 and AtAmt1.1. These two genes encode starvation-induced high-affinity NO3- and NH4+ transporters, respectively. Split-root experiments indicate that AtNrt2.1 expression is controlled by shoot-to-root signals of N demand. Together with 15NO3- influx, the steady-state transcript level of this gene is increased in NO3--fed roots in response to N deprivation of another portion of the root system. Thus AtNrt2.1 is the first identified molecular target of the long-distance signalling informing the roots of the whole plant's N status. In contrast, AtAmt1.1 expression is predominantly dependent on the local N status of the roots, as it is mostly stimulated in the portion of the root system directly experiencing N starvation. The same behaviour was found for NH4+ influx, suggesting that the NH4+ uptake system is much less efficient than the NO3- uptake system, to compensate for a spatial restriction of N availability. Other major differences were found between the regulations of AtNrt2.1 and AtAmt1.1 expression. AtNrt2.1 is strongly upregulated by moderate level of N limitation, while AtAmt1.1 transcript level is markedly increased only under severe N deficiency. Unlike AtNrt2.1, AtAmt1.1 expression is not stimulated in a nitrate reductase-deficient mutant after transfer to NO3- as sole N source, indicating that NO3- per se acts as a signal repressing transcription of AtAmt1.1. These results reveal two fundamentally different types of mechanism involved in the feedback regulation of root N acquisition by the N status of the plant.

Anion Transport Proteins↗

PubMed2001

Uptake of 15N by macrophytes in subsurface-flow wetlands treating domestic wastewater.

Constructed subsurface-flow wetlands are becoming more common for on-site treatment of domestic wastewater to provide secondary quality effluent. Macrophytes are generally added to wetlands to increase treatment efficiency but their role in reducing N content is controversial. Our investigation utilized two subsurface-flow wetlands to determine the efficiency of different macrophytes in uptake of 15N labeled ammonium sulfate. Macrophytes in Wetland 1 recovered 35% of the added N in their shoots but only 5% of the added N was recovered in the shoots and roots in Wetland 2. A major difference for the two wetlands was N and hydraulic loadings. Wetland 1 received 7.5 Kg N ha(-1)d(-1) and Wetland 2 received 16.9 Kg N ha(-1)d(-1). Retention time for Wetland 1 based on pore volumes was 2.9 d and for Wetland 2 it was 1.2 d. The retardation factor for NH4+ was approximately 2.5 for both wetlands and the breakthrough curves indicated lack of plug flow. The importance of macrophytes in taking up NH4 appeared to dependent on N and hydraulic loadings.

Ecosystem↗

PubMed2000

Nickel availability and hupSL activation by heterologous regulators limit symbiotic expression of the Rhizobium leguminosarum bv. viciae hydrogenase system in Hup(-) rhizobia.

A limited number of Rhizobium and Bradyrhizobium strains possess a hydrogen uptake (Hup) system that recycles the hydrogen released from the nitrogen fixation process in legume nodules. To extend this ability to rhizobia that nodulate agronomically important crops, we investigated factors that affect the expression of a cosmid-borne Hup system from Rhizobium leguminosarum bv. viciae UPM791 in R. leguminosarum bv. viciae, Rhizobium etli, Mesorhizobium loti, and Sinorhizobium meliloti Hup(-) strains. After cosmid pAL618 carrying the entire hup system of strain UPM791 was introduced, all recipient strains acquired the ability to oxidize H(2) in symbioses with their hosts, although the levels of hydrogenase activity were found to be strain and species dependent. The levels of hydrogenase activity were correlated with the levels of nickel-dependent processing of the hydrogenase structural polypeptides and with transcription of structural genes. Expression of the NifA-dependent hupSL promoter varied depending on the genetic background, while the hyp operon, which is controlled by the FnrN transcriptional regulator, was expressed at similar levels in all recipient strains. With the exception of the R. etli-bean symbiosis, the availability of nickel to bacteroids strongly affected hydrogenase processing and activity in the systems tested. Our results indicate that efficient transcriptional activation by heterologous regulators and processing of the hydrogenase as a function of the availability of nickel to the bacteroid are relevant factors that affect hydrogenase expression in heterologous rhizobia.

Gene Expression Regulation, Bacterial↗

PubMed2006

Treatment of landfill leachate by irrigation and interaction with landfill gas.

The treatment efficiency of landfill leachate irrigation and the effect of landfill gas addition were investigated in a vegetated compost/gravel substrate by monitoring soil moisture content, drainage water volume and quality in a two years lysimeter experiment. Landfill leachate irrigation exceeding 350 mm increased soil moisture and drainage volumes owing to the deterioration of the vegetation resulting from high sodium chloride inputs. Even so sodium chloride was lost in between the irrigation periods, the total reduction of the landfill leachate volume by irrigation decreased from 71% in the first year to 38% in the second year. Landfill gas addition also increased drainage volumes, but was less pronounced. Twenty-two percent of magnesium was retained under landfill leachate irrigation, while decreasing pH values, redox potential and high initial concentrations in the substrate released calcium, iron and potassium. Ninety-eight percent of ammonium was removed by irrigation, but 44% of the applied ammonium was leached as nitrate after oxidation took place due to a decreased uptake after the vegetation deteriorated. Landfill gas fumigation influenced landfill leachate treatment by decreasing the redox potential and the pH and increasing the drainage water content, which improved the retention of total nitrogen and sulfate, but increased the release of iron, calcium and magnesium. To conclude, landfill leachate irrigation is a valuable treatment option to minimize leachate quantities and remove ammonium independent from the presence of landfill gas if salt accumulation is avoided.

Drainage, Sanitary↗

PubMed1997

Pathway for uptake and degradation of X-prolyl tripeptides in Streptococcus mutans VA-29R and Streptococcus sanguis ATCC 10556.

The growth of Streptococcus mutans and Streptococcus sanguis in the oral environment requires that these micro-organisms be able to degrade salivary proteins and to assimilate the resulting peptides as an amino nitrogen source. Our research is aimed at the definition of the proteolytic enzyme systems in these oral streptococci which allow them to utilize such substrates. In the present work, the nature of the hydrolytic activity expressed by S. mutans VA-29R and S. sanguis ATCC 10556 against X-Pro4-nitroanilide and X-Pro-Y tripeptide substrates was investigated. This activity was predominantly associated with a cytoplasmic dipeptidyl peptidase which preferentially catalyzes the release of an N-terminal dipeptide from substrates in which proline is the penultimate residue. These streptococci also possess a second cytoplasmic peptidase, pepD, which catalyzes the hydrolysis of X-Pro dipeptides. We found that Gly-Pro-Ala or Ala-Pro-Gly were transported into the bacterial cells only when an energy source such as glucose was present. Peptide uptake was time-dependent, and selective exodus of peptide-derived amino acids from the bacterial cells occurred during peptide uptake. Results from these studies provide evidence that S. mutans VA-29R and S. sanguis ATCC 10556 possess a pathway for the complete degradation of X-Pro tripeptides. Transport of the peptides into cells prior to hydrolysis provides an efficient way by which all amino acids of a peptide may be obtained at an energy expense equivalent to that associated with the transport of just one amino acid. In light of the abundance of proline in salivary polypeptides, this degradative pathway could be an important component in the proteolytic pathway for salivary polypeptide utilization in these oral streptococci.

Aminopeptidases↗

PubMedDate not supplied

Maximal parenteral glucose oxidation in hypermetabolic young children: a stable isotope study.

BACKGROUND: During periods in which nutrition support of critically ill young children must be parenteral, glucose infusions are administered at up to 10 or more mg.kg-1.min-1 to meet predicted energy needs. However, data in adults suggest that such high glucose loads exceed the ability to oxidize glucose in the hormonal milieu that characterizes critical illness. The purpose of this study was to determine if these high glucose loads are oxidized by critically ill young children. METHODS: Ten young children with serious burns were enrolled in a stable isotope study of glucose metabolism. These five boys and five girls were an average age of 5.2 years (range, 1 to 11 years), weight of 18.4 kg (range, 10 to 31 kg) and burn size of 51.6% of the body surface (range, 35% to 86%). During clinically required episodes of parenteral nutrition support, we used the [13C6]glucose tracer to assess the efficacy of glucose oxidation at both 5 and 8 mg.kg-1.min-1. Serum glucose was recorded and indirect calorimetry was performed. RESULTS: The fraction of exogenous glucose oxidation fell from 59% +/- 5% to 47% +/- 5% (p < .05). Although there was a significantly increased level of total glucose oxidation (3.2 to 3.8 mg.kg-1.min-1), this increment (29% +/- 9%) was accompanied by a significant decrease in the efficiency of energy production, because the bulk of the additional glucose above 5 mg.kg-1.min-1 was not being oxidized. Plasma glucose concentration did not change (145 +/- 4 vs 137 +/- 4 mg/dL, p < .01) and whole-body expired gas respiratory quotients remained consistent with a mixed fuel oxidation, implying that there exists an increased rate of exogenous glucose uptake by tissues in nonoxidative pathways. CONCLUSIONS: Maximum glucose oxidation in severely burned children occurs at intakes approximating 5 mg.kg-1.min-1. Exogenous glucose in excess of this amount enters nonoxidative pathways and is unlikely to improve energy balance. Clinical markers such as serum glucose levels or expired respiratory quotient may not detect inefficient glucose utilization.

Acute Disease↗

PubMed2006

Expression profiles of 10,422 genes at early stage of low nitrogen stress in rice assayed using a cDNA microarray.

Development of crop varieties with high nitrogen use efficiency (NUE) is imperative for sustainable agriculture. Understanding how plant genes respond to low N stress is essential for formulating approaches to manipulating genes for improving NUE. In this study we analyzed the expression profiles of an indica rice cultivar Minghui 63 at seedling stage at 20 min, 1 and 2 h after low N stress with the normal N as the control, using a microarray of 11,494 rice ESTs representing 10,422 unique genes. While no significant difference was detected in the leaf tissue, a total of 471 ESTs were detected as responsive to low N stress in the root tissue with 115 ESTs showing up-regulation and 358 ESTs showing down-regulation. The analysis of expression profiles after low N stress identified following patterns: (1) the genes involved in photosynthesis and energy metabolism were down-regulated rapidly; (2) many of the genes involved in early responses to biotic and abiotic stresses were up-regulated while many other stress responsive genes were down-regulated; (3) regulatory genes including transcription factors and ones involved in signal transduction were both up- and down-regulated; and (4) the genes known to be involved in N uptake and assimilation showed little response to the low N stress. The challenges for future studies are to characterize the functional roles of the low N stress responsive genes in N metabolisms, including the large number of genes presently with unknown functions.

Gene Expression Profiling↗

PubMed2003

Suitability of macrophytes for nutrient removal from surface flow constructed wetlands receiving secondary treated sewage effluent in Queensland, Australia.

From a botanical perspective the major difference between waste stabilisation ponds and wetlands is the dominance of algae or floating plants in the former and emergent plants in the latter. Algae, floating and submerged plants remove nutrients directly from the water column whereas emergent species remove nutrients from the sediment. Water depth is a crucial factor in determining which plant types will become established. Surface flow constructed wetlands offer the greatest potential to grow a wide variety of different types of macrophytes. In assessing the suitability of plant species for nutrient removal, consideration must be given not only to nutrient uptake for growth but also storage of nutrients as plant biomass. A survey of macrophytes in 15 surface flow constructed wetlands treating secondary effluent was conducted in Queensland; 63 native species and 14 introduced species were found. Emergent species have been able to tolerate deeper water than in their natural environment and permanent waterlogging. All species grew well in the higher nutrient enriched wastewater. Submerged, floating leaved-attached and free floating species had the highest tissue nutrient content, followed by aquatic creepers. All these species remove nutrients from the water column. Emergent species had lower nutrient content but a greater biomass and were therefore able to store more nutrients per unit area of wetland. In order to maximise the efficiency of constructed wetlands for nutrient removal, a range of species should be used. Native species should be selected in preference to introduced/exotic species.

Biodegradation, Environmental↗

PubMed1975

Energetics of Bacillus stearothermophilus growth: molar growth yield and temperature effects on growth efficiency.

The major growth yield of a prototrophic strain of Bacillus stearothermophilus under aerobic conditions on salts medium containing ammonium nitrate as the nitrogen source and glucose or succinate as the carbon source was maximal at the lowest growth temperature employed and decreased steadily as the temperature was raised. The temperature optima for growth yield and for growth rate were thus different. The molar growth yield values of the thermophile, especially at the lower growth temperatures, were similar to those reported for aerobically grown mesophilic bacteria, both on glucose and on succinate. At the higher growth temperatures, a lower proportion of glucose carbon was incorporated into cells and a correspondingly greater proportion was left incompletely utilized in the medium, mostly as acetate. This suggests a greater inefficiency in the coordination of the nonoxidative and oxidative phases of glucose metabolism at the gigher temperatures. Another factor causing a decreased cell yield at higher temperatures was possibly an uncoupling of energy production from respiration. The rates of respiration by intact cells of the thermophile on glucose and on succinate followed the Arrhenius relationship from 55 C to 20 C, which is some 20 C below the minimal growth temperature of the organism. The Arrhenius constant was 17.1 kcal/mol for glucose oxidation and 13.5 kcal/mol for succinate oxidation. These results are comparable to those reported for some mesophiles, and they suggest that the inability of the thermophile to grow at temperatures below about 41 C is not due to an abnormally high temperature coefficient for the uptake and oxidation of the carbon source.

Acetates↗

PubMed2001

[Effect of NPK and B supply levels on boron uptake and biological properties of different genotypic oilseed rape].

Pot experiment was conducted to study the boron absorption by oilseed rape(Brassica napus), the mechanism of its resistance to boron deficiency, and the effect of boron deficiency on its biological properties under different NPK supply levels. The results indicated that under boron deficiency, increasing NPK supply aggravated boron deficiency symptoms, which led to the decrease of leaf area and its growth rate and nitrate reductase activity(NRA) and the increase of chlorophyll(a + b) content at seedling stage, and the decrease of the number of productive branches and pods of each plant and seed yield at maturity. It was suggested that the ratio of boron concentration in youngest open leaves(YOL) to youngest mature leaves(YML) at seedling stage could be an index to judge the boron mobility in plants of different genotypic oilseed rape. Boron mobility and its utilization efficiency were one of the important nutritional mechanisms responsible for the difference in response of different genotypic oilseed rapes to boron deficiency.

Boron↗