The limits of phosphorus removal in wetlands

The phosphorus concentrations exported from wetlands are explored via data and a first order model. The graph of outlet concentration versus areal phosphorus loading is used to display these data and the model. For a given wetland, data and models show that P concentrations show an S curve response to increasing P loadings. The lower plateau is the background concentration and the upper plateau is the inlet concentration. The position of the ascending limb between the two plateaus is positioned differently for different wetlands. Phosphorus (P) removal in wetlands is often typified by a stable decreasing gradient of P concentrations from inlet to outlet, and an accompanying stable decreasing gradient in P assimilation. Limits to removal are inherent in the physical, chemical and biological processes. A lower outlet concentration limit exists because of the P cycle in the un-impacted wetland. The loading at which the outlet concentration departs from background, the lower knee in the loading curve, varies from wetland to wetland. An upper outlet concentration limit is imposed by the source concentration for extremely high inflows. The first order mass balance equation interpolates between these limits. The model gives further insights about performance within an overall envelope. The water carrying capacity of the wetland precludes flows in excess of the hydraulic conveyance capacity, thus limiting the possible P loadings to the system. Conversely, extremely low hydraulic loadings cause the wetland to be dominated by atmospheric additions and losses. The central tendency of inter-system data in the North American Database is shown to be inadequate to draw generalized conclusions about ecosystem processes in an individual wetland. The proposed one gram rule of Richardson, et al. (1997) is shown to be an over-simplification.     

Floral nectaries, nectar production dynamics and chemical composition in six ipomoea species (convolvulaceae) in relation to pollinators

BACKGROUND AND AIMS: Floral nectaries and nectar features were compared between six Argentinian Ipomoea species with differences in their pollinator guilds: I. alba, I. rubriflora, I. cairica, I. hieronymi var. hieronymi, I. indica, and I. purpurea. METHODS: Pollinators were recorded in natural populations. The morpho-anatomical study was carried out through scanning electron and light microscopy. Nectar sugars were identified via gas chromatography. Nectar production and the effect of its removal on total nectar sugar amount were determined by using sets of bagged flowers. KEY RESULTS: Hymenopterans were visitors of most species, while hummingbirds visited I. rubriflora and sphingids I. alba. All the species had a vascularized discoidal nectary surrounding the ovary base with numerous open stomata with a species-specific distribution. All nectar samples contained amino acids and sugars. Most species had sucrose-dominant nectars. Flowers lasted a few hours. Mean nectar sugar concentration throughout the lifetime of the flower ranged from 34.28 to 39.42 %, except for I. cairica (49.25 %) and I. rubriflora (25.18 %). Ipomoea alba had the highest nectar volume secreted per flower (50.12 microL), while in the other taxa it ranged from 2.42 to 12.00 microL. Nectar secretion began as soon as the flowers opened and lasted for a few hours (in I. purpurea, I. rubriflora) or it was continuous during the lifetime of the flower (in the remaining species). There was an increase of total sugar production after removals in I. cairica, I. indica and I. purpurea, whereas in I. alba and I. rubriflora removals had no effect, and in I. hieronymi there was a decrease in total sugar production. CONCLUSIONS: The chemical composition, production dynamics and removal effects of nectar could not be related to the pollinator guild of these species. Flower length was correlated with nectary size and total volume of nectar secreted, suggesting that structural constraints may play a major role in the determination of nectar traits of these species.     

Cold ethanol fractionation and heat inactivation of hepatitis a virus during manufacture of albumin from human plasma

The purpose of the present study was to examine the efficacy and mechanism of fraction IV cold ethanol fractionation and pasteurization (60°C heat treatment for 10h), involved in the manufacture of albumin from human plasma, in the removal and/or inactivation of the hepatitis A virus (HAV). Samples from the relevant stages of the production process were spiked with HAV and the amount of virus in each fraction then quantified using a 50% tissue culture infectious dose (TCID₅₀). HAV was effectively partitioned from albumin during the fraction IV cold ethanol fractionation with a log reduction factor of 3.43. Pasteurization was also found to be a robust and effective step in inactivating HAV, where the titers were reduced from an initial titer of 7.60 log TCID₅₀ to undetectable levels within 5 h of treatment. The log reduction factor achieved during pasteurization was≽4.76. Therefore, the current results indicate that the production process for albumin has sufficient HAV reducing capacity to achieve a high margin of virus safety.     

Behavior of microbial communities developed in the presence/reduced level of soluble microbial products

Soluble microbial products (SMP) are organics produced by microorganisms as they degrade substrates. The available literature does not reveal how SMP affect and regulate microbial activities. In this study, we monitored variations in pH, dissolved oxygen concentration, soluble biological and chemical oxygen demands (sBOD₅ and sCOD) as a measure of microbial activity in synthetic wastewater. Aerobic degradation tests were carried out under the following conditions: aeration, 1,500 cm³ /min; initial sBOD₅, 515±5 mg/l; initial sCOD, 859±6 mg/l; initial biomass concentration (defined as mixed liquor suspended solids), 1,200±25 mg/l; sludge retention time, 24 h; and temperature, 20±1°C. The study involved non-acclimated biomass (R0 flora), biomass developed in the presence of SMP (R1 flora), and biomass developed in reduced level of SMP (R2 flora). We also determined which of these flora produced more refractory SMP. The results showed that R2 flora utilized the synthetic feed more quickly, and produced less refractory organic matter than R0 and R1 flora. The production of more refractory organics by R0 and R1 flora shows that not all the biomass was active. R1 flora degraded the substrates irregularly, suggesting that some microbes were dependent on the metabolic products of those that could utilize the feed components. These results show that production of SMP also depends on the prior substrates and on the ability of the flora to respond to changes in substrate composition.     

Identification and comparison of aerobic and denitrifying polyphosphate-accumulating organisms

Two laboratory-scale sequencing batch reactors (SBRs) were operated for enhanced biological phosphorus removal (EBPR) in alternating anaerobic-aerobic or alternating anaerobic-anoxic modes, respectively. Polyphosphate-accumulating organisms (PAOs) were enriched in the anaerobic-aerobic SBR and denitrifying PAOs (DPAOs) were enriched in the anaerobic-aerobic SBR. Fluorescence in situ hybridization (FISH) demonstrated that the well-known PAO, "Candidatus Accumulibacter phosphatis" was abundant in both SBRs, and post-FISH chemical staining with 4,6-diamidino-2-phenylindol (DAPI) confirmed that they accumulated polyphosphate. When the anaerobic-anoxic SBR enriched for DPAOs was converted to anaerobic-aerobic operation, aerobic uptake of phosphorus by the resident microbial community occurred immediately. However, when the anaerobic-aerobic SBR enriched for PAOs was exposed to one cycle with anoxic rather than aerobic conditions, a 5-h lag period elapsed before phosphorus uptake proceeded. This anoxic phosphorus-uptake lag phase was not observed in the subsequent anaerobic-aerobic cycle. These results demonstrate that the PAOs that dominated the anaerobic-aerobic SBR biomass were the same organisms as the DPAOs enriched under anaerobic-anoxic conditions.     

Synthesis of 3-tert-butylcatechol by an engineered monooxygenase

Recombinant Escherichia coli JM101 was used for the in vivo biocatalytic synthesis of 3-tert-butyl- catechol. The bacterial strain synthesized the laboratory-evolved variant HbpA(T2) of 2-hydroxybiphenyl 3-monooxygenase (HbpA, EC 1.14.13.44) from Pseudomonas azelaica HBP1. The mutant enzyme HbpA(T2) is able to hydroxylate 2-tert-butylphenol to the corresponding catechol, a reaction that is not catalyzed by the wild-type enzyme. The biotransformation was performed in a 3-L bioreactor for 24 h. To mitigate the toxicity of the 2-tert-butylphenol starting material, we applied a limited substrate feed. Continuous in situ product removal with the hydrophobic resin Amberlite XAD-4 was used to separate the product from culture broth. In addition, binding to the resin stabilized the product, which was important because 3-tert-butylcatechol is very labile in aqueous solution. The productivity of the process was 63 mg L(-1) h(-1) so that after 24 h, 3.0 g of 3-tert-butylcatechol were isolated. Down-stream processing consisted of two steps. First, bound 2-tert-butylphenol and 3-tert-butylcatechol were eluted from Amberlite XAD-4 with methanol. Second, the two compounds were separated over neutral aluminum oxide, which selectively binds the produced catechol but not the phenol substrate. The final purity of 3-tert-butylcatechol was greater than 98%.     

Simultaneous nitrification and denitrification using stored substrate (PHB) as the electron donor in an SBR

The potential for PHB (poly-beta-hydroxybutyrate) to serve as the electron donor for effective simultaneous nitrification and denitrification (SND) was investigated in a 2-L sequencing batch reactor (SBR) using a mixed culture and acetate as the organic substrate. During the feast period (i.e., acetate present), heterotrophic respiration activity was high and nitrification was prevented due to the inability of nitrifying bacteria to compete with heterotrophs for oxygen. Once acetate was depleted the oxidation rate of PHB was up to 6 times slower than that of soluble acetate and nitrification could proceed due to the decreased competition for oxygen. The slow nature of PHB degradation meant that it was an effective substrate for SND, as it was oxidised at a similar rate to ammonium and was therefore available for SND throughout the entire aerobic period. The percentage of nitrogen removed via SND increased at lower DO concentrations during the famine period, with up to 78% SND achieved at a DO concentration of 0.5 mg L(-1). However, the increased percentage of SND at a low DO concentration was compromised by a 2-times slower rate of nitrogen removal. A moderate DO concentration of 1 mg L(-1) was optimal for both SND efficiency (61%) and rate (4.4 mmol N x Cmol x(-1) x h(-1)). Electron flux analysis showed that the period of highest SND activity occurred during the first hour of the aerobic famine period, when the specific oxygen uptake rate (SOUR) was highest. It is postulated that a high SOUR due to NH(4) (+) and PHB oxidation decreases oxygen penetration into the floc, creating larger zones for anoxic denitrification. The accumulation of nitrate towards the end of the SND period showed that SND was finally limited by the rate of denitrification. As PHB degradation was found to follow first-order kinetics (df(PHB)/dt = -0.19 x f(PHB)), higher PHB concentrations would be expected to drive SND faster by increasing the availability rate of reducing power and reducing penetration of oxygen into the floc, due to the corresponding increased SOUR. Process control techniques to accumulate higher internal PHB concentrations to improve PHB-driven SND are discussed.     

Patterns and mechanisms of selection on a family-diagnostic trait: evidence from experimental manipulation and lifetime fitness selection gradients

Plant traits that show little variation across higher taxa are often used as diagnostic traits, but the reason for the stasis of such traits remains unclear. Wild radish, Raphanus raphanistrum, exhibits tetradynamous stamens (four long and two short, producing a dimorphism in anther height within each flower), as do the vast majority of the more than 3,000 species in the Brassicaceae. Here we examine the hypothesis that selection maintains the stasis of dimorphic anther height by investigating the effects of this trait on pollen removal, seed siring success, and seed set in R. raphanistrum using both experimental and observational methods. Observational selection gradient analysis based on lifetime seed siring success provided evidence for an optimum dimorphism that was greater than zero in one of three years. In both experimentally manipulated and unmanipulated flowers, more pollen was removed in single visits from flowers with less dimorphism. There was no significant effect of anther dimorphism on female fitness (seed set). Therefore, there is some evidence to suggest that selection is maintaining anther dimorphism in wild radish, and that higher male fitness might result from restriction of single-visit pollen removal. We discuss these results in light of pollen presentation theory.     

A morpholino phenocopy of the cyclops mutation

Summary: Conditional and tissue specific gene targeting using the Cre‐loxP recombination system in combination with established ES cell techniques has become a standard for in vivo loss of function studies. In a typical flox and delete gene targeting strategy, the loxP‐neo‐loxP cassette is inserted into an intron and an additional loxP site is located in one of the homology arms so that loxP sites surround a functionally essential part of the gene. The neo cassette in usually removed by transient expression of the Cre recombinase in ES cells to avoid selection gene interference and genetic ambiquity. However, this causes a significant increase in manipulation of ES cells and often compromises ES cell pluripotency. Here we describe a method in which the floxed neo gene is removed from a knockout allele by infecting 16‐cell‐stage morulae by the recombinant Cre adenovirus. This virus provides only transient Cre expression and does not integrate into the mouse genome. Produced mosaic mice transmitted the desired allele without the neo cassette with high frequency to their offspring. This method is rapid and easy and does not require any special equipment. Moreover, because superovulated mice can be used as donors, this method does not necessitate a large number of mice. genesis 31:126–129, 2001. © 2001 Wiley‐Liss, Inc.