Absence Of Phosphate Research Articles

The Sorption Processes of U(VI) onto SiO2 in the Presence of Phosphate: from Binary Surface Species to Precipitation.

The ternary system containing aqueous U(VI), aqueous phosphate and solid SiO2 was comprehensively investigated using a batch sorption technique, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, time-resolved luminescence spectroscopy (TRLS), and surface complexation modeling (SCM). The batch sorption studies on silica gel (10 g/L) in the pH range 2.5 to 5 showed no significant increase in U(VI) uptake in the presence of phosphate at equimolar concentration of 20 μM, but significant increase in U(VI) uptake was observed for higher phosphate concentrations. In situ infrared and luminescence spectroscopic studies evidence the formation of two binary U(VI) surface species in the absence of phosphate, whereas after prolonged sorption in the presence of phosphate, the formation of a surface precipitate, most likely an autunite-like phase, is strongly suggested. From SCM, excellent fitting results were obtained exclusively considering two binary uranyl surface species and the formation of a solid uranyl phosphate phase. Ternary surface complexes were not needed to explain the data. The results of this study indicate that the sorption of U(VI) on SiO2 in the presence of inorganic phosphate initially involves binary surface-sorption species and evolves toward surface precipitation.

Importance of Protons and Specifically Adsorbing Ions on Changing Capacitance, Space Charge Potential Inside the Solid, and the Interfacial Potential at the TiO2 Aqueous Solution Interface

This paper reports on the effect of protons and specifically adsorbing ions on the capacitance in aqueous systems employing TiO2 porous thin-film electrodes. The influence of surface potential on capacitance was studied through zeta potential (ζ) measurements, open circuit potential (OCP) studies and charge-discharge testing. Both ζ and OCP varies as a function of pH and phosphate adsorption. The slopes of the OCP versus pH curve were close to but lower than the Nernstian value as often reported in the literature. The shift of OCP-OCPpztc (OCP evaluated at the Point of Zero Total Charge) with phosphate adsorption implies that the space charge (charge developed inside the solid oxide material itself) potential, varies with phosphate concentration. We show that the electrochemical capacitance increases with the deposition of TiO2 thin-films on the platinized Ti electrode that directly relates to its ζ with the lowest values in capacitance occurring near the isoelectric pH (pH (I) or pHiep), in the absence of phosphate. We also demonstrate that capacitance can be improved with phosphate adsorption over the pH range of 5 to 9 for aqueous based systems. As expected, capacitance depends on OCP, the voltage range referenced to the OCP, and the rates of adsorbing and desorbing ions. In this context, it would appear that it is easier to electro-adsorb than desorb protons in these porous oxide thin-film electrodes. Capacitance extracted from cyclic voltammetry (CV) conducted over a large voltage range from −0.5 to +0.5V resulted in a high pseudocapacitance. However, when cycled continuously (5-25 scans) pseudocapacitance decreased from 110 to 65F/g but electrical double layer (EDL) capacitance (OCP to OCP+0.1V) increased in the process, depending upon pHiep, between 100-150%. Lastly, the highest value of capacitance (encompassing both Pseudo and EDL capacitance) was 155F/g and obtained over a voltage range of 1V at a scan rate of 5mV/s for a pH of 6.

Effect of solution composition on seeded precipitation of calcium for high recovery RO of magnesium-bearing wastewater, surface water or groundwater

The accelerated seeded precipitation (ASP) of calcium salts from simulated municipal wastewater RO brines using calcium carbonate seed is compared to the much more effective but more expensive ASP using calcium phosphate seed. The aim of this study was to identify the test water compositional limitations of ASP using calcium carbonate seed, and to elucidate the chemistry responsible for the different performance of calcium carbonate and calcium phosphate as seed materials in the ASP of calcium from municipal wastewater and magnesium-bearing groundwater. The results of seeded precipitation of calcium from simulated wastewaters and groundwater using CaCO3 seed was found to only be effective in the absence of phosphate and at conditions where the driving force for MgCO3 formation was low. Seeded precipitation using CaHPO4 seed greatly outperformed CaCO3 seeded precipitation at high carbonate-high magnesium concentration conditions where inhibition was the greatest for CaCO3 seeded precipitation. SEM images of the seed particles after seeded precipitation showed CaCO3 seeds that appeared to be covered with a thin layer of precipitate. SEM images of the solid formed after CaHPO4 seeded precipitation, however, showed seed that had a thick covering of very small particles.

Secondary Mineralization of Ferrihydrite Affects Microbial Methanogenesis in Geobacter-Methanosarcina Cocultures.

The transformation of ferrihydrite to stable iron oxides over time has important consequences for biogeochemical cycling of many metals and nutrients. The response of methanogenic activity to the presence of iron oxides depends on the type of iron mineral, but the effects of changes in iron mineralogy on methanogenesis have not been characterized. To address these issues, we constructed methanogenic cocultures of Geobacter and Methanosarcina strains with different ferrihydrite mineralization pathways. In this system, secondary mineralization products from ferrihydrite are regulated by the presence or absence of phosphate. In cultures producing magnetite as the secondary mineralization product, the rates of methanogenesis from acetate and ethanol increased by 30.2% and 135.3%, respectively, compared with a control lacking ferrihydrite. Biogenic magnetite was proposed to promote direct interspecies electron transfer between Geobacter and Methanosarcina in a manner similar to that of c-type cytochrome and thus facilitate methanogenesis. Vivianite biomineralization from ferrihydrite in the presence of phosphate did not significantly influence the methanogenesis processes. The correlation between magnetite occurrence and facilitated methanogenesis was supported by increased rates of methane production from acetate and ethanol with magnetite supplementation in the defined cocultures. Our data provide a new perspective on the important role of iron biomineralization in biogeochemical cycling of carbon in diverse anaerobic environments. It has been found that microbial methanogenesis is affected by the presence of iron minerals, and their influences on methanogenesis are associated with the mineralogical properties of the iron minerals. However, how changes in iron mineralogy affect microbial methanogenesis has not been characterized. To address this issue, we constructed methanogenic cocultures of Geobacter and Methanosarcina strains with different ferrihydrite mineralization pathways. The experimental results led to two contributions, i.e., (i) the transformation of iron minerals might exert an important influence on methanogenesis under anaerobic conditions and (ii) both biogenic and chemical magnetite can accelerate syntrophic ethanol oxidization between Geobacter metallireducens and Methanosarcina barkeri This study sheds new light on the important role of iron biomineralization in the biogeochemical cycling of carbon in diverse anaerobic environments, particularly in iron-rich natural and agricultural wetland soils.

Leaching of brannerite in the ferric sulphate system. Part 3: The influence of reactive gangue minerals

Brannerite, UTi2O6, is one of the most common refractory uranium minerals and it requires aggressive leaching conditions for efficient uranium extraction. It is often associated with apatite and fluorite, which affect the leaching process by formation of iron-phosphate and iron-fluoride complexes, respectively. While the effects of these gangue minerals on uranium leaching processes are well documented, there is little to no information on these effects specific to brannerite containing ores. At the high acid concentrations required for brannerite dissolution (>25g/L H2SO4), acid soluble gangue will dissolve faster, posing a bigger problem than under milder conditions.The addition of 10g/L fluorapatite reduced the extraction of both uranium and titanium from brannerite over the full range of leaching conditions studied (25–96°C, 25–100g/L H2SO4, 2.8g/L Fe3+). Phosphate caused the formation of secondary titanium oxide on the surface of leached brannerite particles. This was not observed when leaching in the absence of phosphate. The secondary titanium oxide phase was enriched in phosphorus. The negative effects of phosphate on uranium leaching were reduced at higher acid concentrations (>50g/L H2SO4) and increased at higher temperatures (96°C). When leaching high-P refractory uranium ores, higher acid concentrations are needed for effective extraction compared with low-P uranium ores. Elevated temperatures were less effective for increasing uranium extraction, suggesting that the optimum temperature for leaching high-P refractory uranium ores is lower than the optimum temperature for leaching low-P uranium ores.Fluorite (10g/L) had a positive effect on uranium and titanium extraction. This was attributed to the formation of hydrofluoric acid during the dissolution of fluorite. Brannerite particles were heavily pitted and corroded after leaching in the presence of fluorite, with near complete dissolution occurring in 2–3h.

Formation of bromate during ferrate(VI) oxidation of bromide in water

Ferrate (VI) is traditionally recognized as a safe oxidant without production of disinfection byproducts (DBPs). However, here we detected probable carcinogenic bromate (BrO3−) during ferrate(VI) oxidation of bromide (Br−)-containing water, and evaluated the effects of pH, ferrate(VI) dose, initial Br− concentration, and co-existing anions on the BrO3− formation. BrO3− was produced at a moderately–weakly acidic pH condition and in the absence of phosphate that was commonly applied as a buffer and stabilizing agent in previous ferrate(VI) studies. At pH 5.0, the produced BrO3− was increased from 12.5 to 273.8 μg/L with the increasing initial Br− concentration from 200 to 1000 μg/L at 10 mg/L Fe(VI), corresponding to an increase in the molar conversion ([BrO3−]/initial [Br−]) from 2.3% to 10.3%, in a bicarbonate-buffered solution. As pH increased to 7.0, the BrO3− concentration gradually dropped. The BrO3− production appeared to be associated with the oxidation by high valence iron species (i.e. Fe(VI), Fe(V) and Fe(IV)). Two key intermediate products (i.e. hypobromous acid/hypobromite (HOBr/OBr−) and hydrogen peroxide (H2O2)) relevant to the bromate formation were identified. The production of HOBr, a requisite intermediate for the ensuing bromate formation, was indirectly validated through identification of bromine-containing trihalomethanes and haloacetic acids during ferrate oxidation in a natural water, though these bromo-organic DBPs produced were insignificant. Furthermore, the inhibition effects of various anions on the formation of BrO3− followed chloride < sulfate < silicate < phosphate. More H2O2 was detected at higher phosphate concentration. It could reduce HOBr to Br−, thereby inhibiting the bromate formation.

Bromide oxidation by ferrate(VI): The formation of active bromine and bromate

Ferrate (VI) (abbreviated as Fe(VI)) has long been considered as a green oxidant that does not produce any known hazardous byproducts. However, this work shows that Fe(VI) can slowly oxidize bromide forming active bromine (HOBr/OBr−) and bromate, and in natural waters total organic bromine (TOBr) can also be detected. Results showed that the highest levels of active bromine and bromate were formed at lower pHs and in the absence of phosphate. Hydrogen peroxide, which forms from the reaction of Fe(VI) and water, plays an essential role in suppressing bromate formation by reducing active bromine back to bromide. Fe(VI) decomposition products (assumed to be particulate phase Fe(III)) can catalyze the decomposition of hydrogen peroxide by Fe(VI). Phosphate had a substantial inhibiting effect on the formation of active bromine, but less so on bromate formation. The presence of the raw water matrix in natural water suppressed bromate formation. For a natural water spiked with 0.1 mg/L of bromide, the bromate and TOBr concentrations after Fe(VI) oxidation were below 3.0 and 15 μg/L, respectively. No consistent trend regarding the effect of pH or buffer ions on TOBr formation was observed due to the competition between Fe(VI), hydrogen peroxide, and natural organic matter (NOM) for reaction with active bromine. Under environmentally relevant conditions, the formation of bromate and TOBr would not be a problem for Fe(VI) application as their concentration levels are quite low.

The ploidy level of Synechocystis sp. PCC 6803 is highly variable and is influenced by growth phase and by chemical and physical external parameters.

Synechocystis sp. PCC 6803 is a cyanobacterial model strain widely used to study many biological processes and is also applied for the production of biopolymers. Recently, it was reported that two of its substrains are highly polyploid. To test whether this can be generalized to the whole strain, six substrains were selected and their ploidy levels quantified. The ploidy levels of all substrains were highly growth phase regulated and the copy number was on average about 20 at an OD750 of 0.1 and about 4 at an OD750 of 2.5. In addition to growth phase, external conditions were found to influence the ploidy level, i.e. the copy number was elevated at lower light intensity and at higher phosphate concentrations (53 and 35 copies, respectively). In the absence of external phosphate, considerable growth was observed, although growth rate and growth yield were much lower than in the presence of either orthophosphate or genomic DNA as external source of phosphate. A rapid reduction in genome copy number was observed during growth in the absence of phosphate, indicating that replication ceased and genomes were distributed to the daughter cells. During prolonged incubation of stationary-phase cultures in the absence of phosphate, the cells eventually became monoploid. Taking the data together, the ploidy level of Synechocystis sp. PCC 6803 is extremely variable and is influenced by both growth phase and physical and chemical environmental parameters.

Oxygenation properties and isoform diversity of snake hemoglobins.

Available data suggest that snake hemoglobins (Hbs) are characterized by a combination of unusual structural and functional properties relative to the Hbs of other amniote vertebrates, including oxygenation-linked tetramer-dimer dissociation. However, standardized comparative data are lacking for snake Hbs, and the Hb isoform composition of snake red blood cells has not been systematically characterized. Here we present the results of an integrated analysis of snake Hbs and the underlying α- and β-type globin genes to characterize 1) Hb isoform composition of definitive erythrocytes, and 2) the oxygenation properties of isolated isoforms as well as composite hemolysates. We used species from three families as subjects for experimental studies of Hb function: South American rattlesnake, Crotalus durissus (Viperidae); Indian python, Python molurus (Pythonidae); and yellow-bellied sea snake, Pelamis platura (Elapidae). We analyzed allosteric properties of snake Hbs in terms of the Monod-Wyman-Changeux model and Adair four-step thermodynamic model. Hbs from each of the three species exhibited high intrinsic O2 affinities, low cooperativities, small Bohr factors in the absence of phosphates, and high sensitivities to ATP. Oxygenation properties of the snake Hbs could be explained entirely by allosteric transitions in the quaternary structure of intact tetramers, suggesting that ligation-dependent dissociation of Hb tetramers into αβ-dimers is not a universal feature of snake Hbs. Surprisingly, the major Hb isoform of the South American rattlesnake is homologous to the minor HbD of other amniotes and, contrary to the pattern of Hb isoform differentiation in birds and turtles, exhibits a lower O2 affinity than the HbA isoform.

Inorganic and methylated thioarsenates pass the gastrointestinal barrier.

Arsenic forms different species that are toxic for humans. Toxicity to internal organs is, however, only relevant if the respective species passes the gastrointestinal barrier. Thioarsenates were known to be produced by gut microbiota and to be toxic to bladder and liver cells, but their intestinal transport was largely unknown. Using a Caco-2 cell model, we show here that dimethylmonothioarsenate has the highest cellular retention and intestinal transport of all methylated species. Mono- and trithioarsenate show little cellular retention like arsenate, but their intestinal transport is much higher than that of arsenate; for trithioarsenate, it is almost as high as that for arsenite. The transport of all thioarsenates increases in the absence of phosphate. With the present study, we link previous reports of thioarsenate formation and toxicity by proving their bioavailability and confirm the relevance of their consideration in As risk assessments.

Anammox endogenous metabolism during long-term starvation: Impacts of intermittent and persistent modes and phosphates

Starvation of anaerobic ammonium oxidation (anammox) bacteria can occur in underloaded bioreactors or during the storage of sludge. In this study, the impacts of intermittent and persistent resting modes and phosphates on the endogenous metabolism of anammox bacteria during long-term starvation were investigated. Batch experiments were performed to evaluate the response of anammox granules to different modes of starvation (persistent-resting and intermittent-resting cells) in the presence and absence of phosphates. The endogenous decay coefficient of anammox granules (based on the decreased biomass) over a 30-d persistent starvation period was 0.0062d−1, while the intermittent starvation by means of providing substrates every 10days accelerated the biomass decay approximately twice (0.0110d−1). Moreover, the intermittent-resting cells displayed exacerbated decreases in specific anammox activity relative to the persistent-resting cells, whereas no significant difference was observed in the heme c contents. Regardless of the physiological status of the cells, the presence of low levels of phosphates may be beneficial; however, a high level of phosphates is not recommended. Although different metabolic strategies were adopted depending on the starvation mode, anammox bacteria possessed a better survival strategy via a relatively low maintenance energy requirement to ensure their survival in nutrient-limited systems. In addition, the variations in extracellular protein-like components were indicative of different intracellular metabolic regulation mechanisms. These results provide a better understanding of the endogenous metabolism of anammox bacteria.

Roles of DgD14 in regulation of shoot branching in chrysanthemum (Dendranthema grandiflorum ‘Jinba’)

Shoot branching plays an important role in determining plant architecture. Strigolactones (SLs) negatively regulate shoot branching, and can respond to conditions of low or absent phosphate or nitrogen. The D14 gene is a probable candidate as an SL receptor in rice, petunia, and Arabidopsis. To investigate the roles of D14 in shoot branching of chrysanthemum, we isolated the D14 homolog DgD14. Functional analysis showed that DgD14 was a nuclear-localized protein, and restored the phenotype of Arabidopsis d14-1. Exogenous SL (GR24) could down-regulate DgD14 expression, but this effect could be overridden by apical auxin application. Decapitation could down-regulate DgD14 expression, but this effect could be restored by exogenous auxin. In addition, DgD14 transcripts produced rapid responses in shoot and root under conditions of phosphate absence, but only a mild variation in bud and stem with low nitrogen treatment. Indistinct reductions of P levels in shoot were observed in plants grown under low nitrogen conditions. The absence of phosphate and low levels of nitrogen negatively affected plant growth. These results demonstrate that P levels in shoot had a close relationship with phosphate, whereas nitrogen did not directly regulate DgD14 expression in shoot. Taken together, these results demonstrated that DgD14 was the functional strigolactone signaling component in chrysanthemum.

Effects of Phosphate on Secondary Mineral Formation During the Bioreduction of Akaganeite (.&amp;#946;-FeOOH): Green Rust Versus Framboidal Magnetite

The activity of microorganisms is a key component of the biogeochemical cycle of Fe in natural systems, where green rusts are often observed as products of microbially driven redox processes. To better define the factors that control green rust formation during microbial Fe(III) reduction, we examined the effects of the presence of an electron shuttle [9,10-anthraquinone-2,6-disulfonate (AQDS)] and phosphate on akaganeite (β-FeOOH) bioreduction by the iron(III)-reducing bacterium (IRB) Shewanella putrefaciens CN32. Framboidal magnetite was the principal secondary mineral formed during akaganeite bioreduction in the absence of phosphate; this is the first time framboidal magnetite has been reported as a product of microbial Fe(III) oxide reduction. Framboidal magnetite was less crystalline when formed in the presence of AQDS than without AQDS and over time was further reduced to chukanovite. Carbonate green rust was the primary secondary mineral observed from akaganeite bioreduction in the presence of phosphate, with and without AQDS; however, siderite was also observed in the presence of AQDS. This first report of green rust as a product of akaganeite bioreduction expands the range of Fe(III) oxides that can be transformed to green rust by IRB, suggesting that the reduction of Fe(III) oxides such as ferrihydrite, lepidocrocite, and akaganeite by IRB is a key process leading to the formation of green rusts in aquatic and terrestrial environments. Keywords: AQDS, akaganeite, bioreduction, chukanovite, electron shuttle, framboidal magnetite, green rust, iron(III) oxide, iron-reducing bacteria, magnetite, phosphate, Shewanella, siderite.

Effect of pH and Phosphate on Calcium Carbonate Polymorphs Precipitated at near-Freezing Temperature

The effects of pH and phosphate on the precipitation of calcium carbonate polymorphs from aqueous solution were investigated. Experiments were carried out at near-freezing temperature and two different pH conditions (pH 13.4 and 9.0). At each pH condition, solutions having different concentrations of CaCl2 and NaHCO3 were mixed to achieve Ca/CO3 ratios of 1:1 and 10:1 at different pumping rates with and without phosphate. Results showed that, at pH 13.4, only ikaite was formed, independent of pumping rate, Ca/CO3 ratio, and phosphate. At pH 9.0, the precipitate was predominantly vaterite in the absence of phosphate and ikaite in the presence of phosphate regardless of the ratio of Ca/CO3. These results indicate that at low temperatures and moderate alkaline conditions (pH 9.0), phosphate can act as a switch between ikaite and vaterite polymorphs. Contrastingly, at higher alkaline conditions (pH 13.4) phosphate is not prerequisite and the high pH in itself is enough to trigger ikaite formation over vaterite.

Effect of lysine to alanine mutations on the phosphate activation and BPTES inhibition of glutaminase

The GLS1 gene encodes a mitochondrial glutaminase that is highly expressed in brain, kidney, small intestine and many transformed cells. Recent studies have identified multiple lysine residues in glutaminase that are sites of N-acetylation. Interestingly, these sites are located within either a loop segment that regulates access of glutamine to the active site or the dimer:dimer interface that participates in the phosphate-dependent oligomerization and activation of the enzyme. These two segments also contain the binding sites for bis-2[5-phenylacetamido-1,2,4-thiadiazol-2-yl]ethylsulfide (BPTES), a highly specific and potent uncompetitive inhibitor of this glutaminase. BPTES is also the lead compound for development of novel cancer chemotherapeutic agents. To provide a preliminary assessment of the potential effects of N-acetylation, the corresponding lysine to alanine mutations were constructed in the hGACΔ1 plasmid. The wild type and mutated proteins were purified by Ni+-affinity chromatography and their phosphate activation and BPTES inhibition profiles were analyzed. Two of the alanine substitutions in the loop segment (K311A and K328A) and the one in the dimer:dimer interface (K396A) form enzymes that require greater concentrations of phosphate to produce half-maximal activation and exhibit greater sensitivity to BPTES inhibition. By contrast, the K320A mutation results in a glutaminase that exhibits near maximal activity in the absence of phosphate and is not inhibited by BPTES. Thus, lysine N-acetylation may contribute to the acute regulation of glutaminase activity in various tissues and alter the efficacy of BPTES-type inhibitors.

Transport of U(VI) through sediments amended with phosphate to induce in situ uranium immobilization

Phosphate amendments can be added to U(VI)-contaminated subsurface environments to promote in situ remediation. The primary objective of this study was to evaluate the impacts of phosphate addition on the transport of U(VI) through contaminated sediments. In batch experiments using sediments (<2 mm size fraction) from a site in Rifle, Colorado, U(VI) only weakly adsorbed due to the dominance of the aqueous speciation by Ca–U(VI)-carbonate complexes. Column experiments with these sediments were performed with flow rates that correspond to a groundwater velocity of 1.1 m/day. In the absence of phosphate, the sediments took up 1.68–1.98 μg U/g of sediments when the synthetic groundwater influent contained 4 μM U(VI). When U(VI)-free influents were then introduced with and without phosphate, substantially more uranium was retained within the column when phosphate was present in the influent. Sequential extractions of sediments from the columns revealed that uranium was uniformly distributed along the length of the columns and was primarily in forms that could be extracted by ion exchange and contact with a weak acid. Laser induced fluorescence spectroscopy (LIFS) analysis along with sequential extraction results suggest adsorption as the dominant uranium uptake mechanism. The response of dissolved uranium concentrations to stopped-flow events and the comparison of experimental data with simulations from a simple reactive transport model indicated that uranium adsorption to and desorption from the sediments was not always at local equilibrium.

Regulation of Mycobacterium tuberculosis D-3-phosphoglycerate dehydrogenase by phosphate-modulated quaternary structure dynamics and a potential role for polyphosphate in enzyme regulation.

D-3-phosphoglycerate dehydrogenase (PGDH) catalyzes the first reaction in the "phosphorylated" pathway of l-serine biosynthesis. In Mycobacterium tuberculosis, it is a type 1 enzyme (mtPGDH) in that it contains both an ACT domain and an ASB domain in addition to a catalytic domain. The published crystal structures (Protein Data Bank entries 1YGY and 3DC2) show a tartrate molecule interacting with cationic residues at the ASB-ACT domain interfaces and a serine molecule bound at the ACT domain interface. These sites have previously been shown to be involved in the mechanism of serine and substrate inhibition of catalytic activity. This investigation has revealed a mechanism of allosteric quaternary structure dynamics in mtPGDH that is modulated by physiologically relevant molecules, phosphate and polyphosphate. In the absence of phosphate and polyphosphate, the enzyme exists in equilibrium between an inactive dimer and an active tetramer that is insensitive to inhibition of catalytic activity by L-serine. Phosphate induces a conversion to an active tetramer and octamer that are sensitive to inhibition of catalytic activity by L-serine. Small polyphosphates (pyrophosphate and triphosphate) induce a conversion to an active dimer that is insensitive to L-serine inhibition. The difference in the tendency of each respective dimer to form a tetramer as well as slightly altered elution positions on size exclusion chromatography indicates that there is likely a conformational difference between the serine sensitive and insensitive states. This appears to constitute a unique mechanism in type 1 PGDHs that may be unique in pathogenic Mycobacterium species and may provide the organisms with a unique metabolic advantage.

Polyploidy in haloarchaea: advantages for growth and survival.

The investigated haloarchaeal species, Halobacterium salinarum, Haloferax mediterranei, and H. volcanii, have all been shown to be polyploid. They contain several replicons that have independent copy number regulation, and most have a higher copy number during exponential growth phase than in stationary phase. The possible evolutionary advantages of polyploidy for haloarchaea, most of which have experimental support for at least one species, are discussed. These advantages include a low mutation rate and high resistance toward X-ray irradiation and desiccation, which depend on homologous recombination. For H. volcanii, it has been shown that gene conversion operates in the absence of selection, which leads to the equalization of genome copies. On the other hand, selective forces might lead to heterozygous cells, which have been verified in the laboratory. Additional advantages of polyploidy are survival over geological times in halite deposits as well as at extreme conditions on earth and at simulated Mars conditions. Recently, it was found that H. volcanii uses genomic DNA as genetic material and as a storage polymer for phosphate. In the absence of phosphate, H. volcanii dramatically decreases its genome copy number, thereby enabling cell multiplication, but diminishing the genetic advantages of polyploidy. Stable storage of phosphate is proposed as an alternative driving force for the emergence of DNA in early evolution. Several additional potential advantages of polyploidy are discussed that have not been addressed experimentally for haloarchaea. An outlook summarizes selected current trends and possible future developments.

Influence of agglomeration of cerium oxide nanoparticles and speciation of cerium(III) on short term effects to the green algae Chlamydomonas reinhardtii

Cerium oxide nanoparticles (CeO2 NP) are increasingly used in industrial applications and may be released to the aquatic environment.The fate of CeO2 NP and effects on algae are largely unknown. In this study, the short term effects of CeO2 NP in two different agglomeration states on the green algae Chlamydomonas reinhardtii were examined. The role of dissolved cerium(III) on toxicity, its speciation and the dissolution of CeO2 NP were considered. The role of cell wall of C. reinhardtii as a barrier and its influence on the sensitivity to CeO2 NP and cerium(III) was evaluated by testing both, the wild type and the cell wall free mutant of C. reinhardtii.Characterization showed that CeO2 NP had a surface charge of ∼0mV at physiological pH and agglomerated in exposure media. Phosphate stabilized CeO2 NP at pH 7.5 over 24h. This effect was exploited to test CeO2 NP dispersed in phosphate with a mean size of 140nm and agglomerated in absence of phosphate with a mean size of 2000nm. The level of dissolved cerium(III) in CeO2 NP suspensions was very low and between 0.1 and 27nM in all tested media.Exposure of C. reinhardtii to Ce(NO3)3 decreased the photosynthetic yield in a concentration dependent manner with EC50 of 7.5±0.84μM for wild type and EC50 of 6.3±0.53μM for the cell wall free mutant. The intracellular level of reactive oxygen species (ROS) increased upon exposure to Ce(NO3)3 with effective concentrations similar to those inhibiting photosynthesis. The agglomerated CeO2 NP caused a slight decrease of photosynthetic yield at the highest concentrations (100μM), while no effect was observed for dispersed CeO2 NP. The low toxicity of agglomerated CeO2 NP was attributed quantitatively to Ce3+ ions co-occurring in the nanoparticle suspension whereas for dispersed CeO2 NP, dissolved Ce3+ was precipitated with phosphate and not bioavailable. Furthermore CeO2 NP did not affect the intracellular ROS level. The cell wall free mutant and wild type of C. reinhardtii showed the same sensitivity to CeO2 NP and Ce(NO3)3, indicating a minor role of the cell wall on toxicity. For both algae strains, a flocculation of cells was observed upon exposure to agglomerated CeO2 NP and Ce(NO3)3, only algae exposed to agglomerated CeO2 NP were tightly packed in exopolymeric substances.

Overexpression of &amp;lt;i&amp;gt;OsMAPK2&amp;lt;/i&amp;gt; Enhances Low Phosphate Tolerance in Rice and &amp;lt;i&amp;gt;Arabidopsis thaliana&amp;lt;/i&amp;gt;

The mitogen-activated protein kinase (MAPK) cascade is the most important mechanism in environmental responses and developmental processes in plants. The OsMAPK2 gene has been found to function in plant tolerance to diverse biotic/abiotic stresses. This paper presents evidence that OsMAPK2 (Oryza sativa MAP kinase gene 2) is responsive to Pi deficiency and involved in Pi homeostasis. We found that full-length expression of OsMAPK2 was up-regulated in both rice plants and cell culture in the absence of inorganic phosphate (Pi). The transgenic rice and Arabidopsis plants overexpressing OsMAPK2 showed affected root development and increased plant Pi content compared with wild-type plants. Overexpression of OsMAPK2 controlled the expression of several Pi starvation-responsive genes. Our results indicated that OsMAPK2 enables tolerance phosphate deficiency and is involved in Pi homeostasis.