Low Phosphate Concentrations Research Articles

Risk of groundwater pollution in open dug wells in the Pungudutivu Island of the Jaffna Peninsula, Sri Lanka

Un-protected open dug wells of shallow groundwater environments are subjected to high risk of chemical and microbial pollution in many parts of the world. The present study was initiated in Pungudutivu, one of the surrounding islands of the Jaffna Peninsula, Sri Lanka, because the island totally relies on its limited groundwater resources extracted from open dug wells to meet all its needs. The study assessed the risk of pollution within the limited fresh groundwater found in unconfined aquifer systems of Pungudutivu, where high risk of pollution was expected mainly from organic sources, derived from human and animal wastes and easy infiltration and runoff returns. The fresh groundwater pockets of Pungudutivu were however found to be with less serious contamination risks other than high Fe2+ and high faecal coliform counts. Low nitrate and phosphate concentrations with high COD and low BOD demonstrated less pollution from biodegradable organic sources in the midst of high oxidising potentials in the shallow dug wells as implied by the stability field of Fe(OH)3 on the Eh-pH diagram; the argument of high Fe2+ in groundwater however, wasn't supported by the said oxidation potential. High faecal coliform counts with high DO in groundwater probably indicated conditions implied by on site waste disposal in groundwater of Pungudutivu.

Alkaline flocculation of Microcystis aeruginosa induced by calcium and magnesium precipitates

The biotechnological potential of Microcystis aeruginosa brings requirements for efficient cultivation and harvesting of biomass. Flocculation of M. aeruginosa at alkaline pH induced by calcium or magnesium precipitates was studied under model conditions, in culture medium with/without cellular organic matter (COM). The effect of independent variables (Ca2+, Mg2+, PO43−, and pH) on the zeta potential and turbidity of cells and inorganic precipitates was quantified by response surface methodology. The experimentally obtained flocculation efficiencies (FEs) were compared with predictions of physicochemical interaction (DLVO) models. The results presented here delimited the concentration ranges of Ca2+, Mg2+, PO43−, and pH, resulting in FE > 85%. The DLVO prediction model suggested that for high FE, positively charged precipitates and sufficient precipitate turbidity were required. At pH 10, alkaline flocculation was more advantageous using magnesium precipitates, since it required less phosphate. High FE with COM was achieved at pH 12 when precipitate formation was induced at a low phosphate concentration by the addition of magnesium hydroxide.

Mg2+ in β-TCP/Mg-Zn composite enhances the differentiation of human bone marrow stromal cells into osteoblasts through MAPK-regulated Runx2/Osx.

Inducing the osteogenic differentiation from bone marrow stromal cells (BMSCs) might be a potent strategy for treating bone loss and nonunion during fracture and improving fracture healing. Among several signaling pathways involved, mitogen-activated protein kinases (MAPKs) have been reported to play a critical role. Magnesium (Mg)-based alloys, including Mg-Zn alloy, have been used clinically as implants in the musculoskeletal field and could promote BMSC osteogenic differentiation. However, the underlying mechanisms remain unclear. In this study, we produced Mg-Zn alloy consists of Mg and low concentrations of Zn, calcium carbonate, and β-tricalcium phosphate (β-TCP; manifesting process not shown), prepared Mg, Zn, and Mg-Zn extracts, and investigated the specific effects of these extracts on human BMSC (hBMSC) osteogenic differentiation and MAPK signaling. Mg extracts and Mg-Zn extracts could significantly promote the osteogenic differentiation of hBMSCs as manifested as increased alkaline phosphatase levels, enhanced calcium nodules formation, and increased messenger RNA expression and protein levels of osteogenesis markers, including BMPs, Col-I, Runx2, and Osx; in the meantime, Mg culture medium (CM) and Mg-Zn CM both significantly enhanced the activation of MAPK signaling in hBMSCs. By adding ERK1/2 signaling, p38 signaling, or JNK signaling inhibitor to Mg-Zn CM, or conducting p38 MAPK silence in hBMSCs, we revealed that these extracts might promote hBMSC osteogenic differentiation via p38 MAPK signaling and MAPK-regulated Runx2/Osx. In conclusion, Mg2+ in β-TCP/Mg-Zn extract promotes the osteogenic differentiation of hBMSCs via MAPK-regulated Runx2/Osx interaction.

Feasibility of improving carbohydrate content of Chlorella S4, a native isolate from the Persian Gulf using sequential statistical designs

Microalgal carbohydrates can serve as feedstock for bioethanol production. Environmental and/or nutritional factors influence the carbohydrate content of microalgae and optimization of culture condition has a key role in the economic production of bioethanol. This research has evaluated the optimization of the carbohydrate content of a marine microalga isolate from the Persian Gulf. The Plackett-Burman design was used to screen the most effective parameters responsible for carbohydrate production. Then, the levels of two effective factors, total phosphate (KH2PO4+K2HPO4) and initial pH, were optimized by two types of Response Surface Method designs (Central Composite and historical data designs). Maximum carbohydrate production was obtained at a low concentration of phosphate (0.031 g/L) and initial pH of 5.95. Under optimal condition, the concentration of carbohydrate was increased by 1.9 folds, from 0.12 g/L (0.2 g/g of dry biomass) to 0.230 g/L (0.365 g/g of dry biomass). The carbohydrate content of microalga hydrolysate was also evaluated by the HPLC method, and the results showed that glucose made about 3.19% (w/w) of total carbohydrates. This study represents the isolation and determination of a promising native and non-invasive microalga for bioethanol production, and subsequently enhancement of its carbohydrate content for the same goal.

The Effectiveness of Phytochemical Components and Climatic Factors on Population Fluctuation of the Spider Mite, Tetranychus urticae Koch on Sweet Pea and Pea Crops

Studies were conducted to define the level infestations of sweet pea and pea crops to the infestation of the spider mite, Tetranychus urticae Koch, and its predatory mite Amblyseius swirskii (Athias-Henriot) during two successive seasons (2016-2017 and 2016-2017) at El- Ayyat - Giza Governorate. Results appeared that the infestation of two cultivars by T. urticae was begun in the first week of October under greenhouse conditions. Progressively increased till its peaks in the third week of June for (sweet pea) and in the first week of February for (pea) during the two successive seasons. Through two consecutive seasons, sweet pea cultivar was the most highly sensitive than pea, arranged in a descending order as follows: sweet pea (75.58, 74.37 and 74.19%), (76.30, 75.87 and 74.95%) and pea (24.41, 25.62 and 25.80%), (23.96, 23.51 and 25.04%). Subsequently, sweet pea cultivar highly susceptible (36.62±3.236), (47.75±4.395) and (45.73±4.193) adult, immature and egg, respectively in season 2017-2018 and the lowest infested are pea cultivar (10.71±1.249) (13.66±1.632 ) and (14.61±1.729) adult, immature and egg, respectively in season 2016-2017. Cultivars (sweet pea and pea) contain remarkable rates of the predatory mite, A. swirskii through two successive seasons. Phytochemical contents were evaluated in uninfested and infested leaves at peak infestation and the final season of 2017. In addition, there is a positive relationship between mite infestation levels and total carbohydrates and nitrogen in sweet pea and pea leaves, however a negative relationship found with total phenolic compounds. Infested leaves of sweet pea and pea cultivars contained a low concentration of phosphate and potassium (1.065, 2.165) & (0.54, 1.17) at the late season.

Modified biochar for phosphate adsorption in environmentally relevant conditions

Herein, we explored the modification of wheat straw biochar with chitosan, quaternary ammonium salt, and lanthanum for enhanced phosphate removal in environmentally relevant conditions. Specifically, a new amine protected cross-linking method was utilized to modify the absorbent material for maximum adsorption capacity, reaching 109 ± 4 mg P g−1. The high phosphate removal performance of the composite was not significantly affected in a broad range of temperature (15–45 °C) and pH (2.5–7). 30 min allowed reaching a 100% adsorption equilibrium for 100 mg P L−1, and 93% for 25 mg P L−1, thus, significantly reducing the treatment time compared to previous reports. The highest partition coefficient 172.1 mg g−1 μM−1 was obtained at a concentration of 25 mg L−1, and the phosphorus removal rate was as high as 99.98%, indicating La/GTB have great adsorption performance at low phosphate concentration. The adsorption mechanisms of the composite are extensively described, where electrostatic interaction, ligand exchange, and Lewis acid-base interaction contribute to the process. All of the above-mentioned advantages make the prepared composite of great interest for the development of materials for on-site phosphate removal.

A New Technique to Determine the Phosphate Oxygen Isotope Composition of Freshwater Samples at Low Ambient Phosphate Concentration.

The oxygen isotope composition of dissolved inorganic phosphate (δ18Op) offers new opportunities to understand the sources and the fate of phosphorus (P) in freshwater ecosystems. However, current analytical protocols for determining δ18Op are unable to generate reliable data for samples in which ambient P concentrations are extremely low, precisely the systems in which δ18Op may provide new and important insights into the biogeochemistry of P. In this Article, we report the development, testing and initial application of a new technique that enables δ18Op analysis to be extended into such ecosystems. The twist spinning mode (TSM) protocol described here enables >1000 L of sample with a P concentration <0.016 mg P L-1 to be initially processed within the field in approximately 24 h. Combined with a new freeze-drying method to maximize the yield and minimize the contamination of silver phosphate generated for isotope ratio mass spectrometry, the TSM protocol is able to generate accurate and precise δ18Op data. We evaluated the TSM protocol using synthetic test solutions and subsequently applied the protocol to samples from locations around the Saint Lawrence River in Montreal, Canada. We believe that the novel technique reported here offers the methodological basis for researchers to extend the application of δ18Op into a much wider range of freshwater ecosystems than has been possible to date.

Using Recycled Concrete as an Adsorbent to Remove Phosphate from Polluted Water.

Phosphate pollution remains a significant hazard to terrestrial and aquatic ecosystems. We developed an economical and efficient method for phosphate adsorption on waste construction concrete modified with seawater. Compared with raw concrete materials, the phosphate adsorption capacity of seawater-modified waste concrete was highly efficient, especially at low phosphate concentrations. The inflection point for seawater-modified concrete was 0.66 and 1.22 mg L for the raw material. The relative phosphate adsorption was 4.64 and 2.39 mg g, respectively. Phosphate removal was >90% over a pH range of 3 to 11 for the raw and modified materials. Chemical and physical analysis of the modified concrete indicated that Ca and Mg particles were uniformly sequestrated on the surface, and Ca was the determinant controlling phosphate uptake. Phosphate adsorption isotherms fit well using the Freundlich, Temkin, Elovich, Fowler-Guggenheim, and Hill-de Boer models and indicated that intermolecular forces in the concrete particles were enhanced by calcium oxides from seawater. This method can efficiently remove phosphate from polluted water and repurposes waste construction concrete.

Coccolithophore distributions of the North and South Atlantic Ocean

We present average coccolithophore and associated biogeochemical results from ten Atlantic Meridional Transect (AMT) cruises between 50oN-50oS, results that show a number of unique observations across this massive data set. Lowest concentrations of coccolithophores were consistently found in equatorial waters. Highest concentrations of coccolithophore cells and coccoliths were associated with temperate, sub-polar environments. Concentrations of detached coccoliths were dispersed to ∼300m depth and show low inter-cruise variance. Coccolithophore cell concentrations in the subtropics remain highest at < 200m depth in the S. Atlantic and 100m in the N. Atlantic, near the 26.5 to 27 sigma-theta (σθ) isopycnal, within the Subantarctic Mode Water (SAMW). Diversity and species richness of coccolithophore cells was greater than for the detached coccoliths and generally greater in surface populations than in the deep chlorophyll maximum (DCM). Placolith-bearing coccolithophore species dominated over the umbelliform and floriform coccolithophore groups in surface waters of the Southern Ocean at 50oS, as well as the DCM from 50oS to the equator. The DCM was strongly associated with the σθ, of ∼27 kg m-3, coincident with the top of the nitracline, within the SAMW. Concentrations of coccolithophore cells and detached coccoliths were much less related to the density field than chlorophyll was. Highest integrated euphotic coccolith concentrations were observed when the integrated POC:chlorophyll ratio was highest. PIC:POC ratios increased with depth and approached maximum values near the top of the nitracline. Great Calcite Belt waters (upper 300m) showed biogenic silica:particulate inorganic carbon ratios (BSi:PIC) >1 while all other waters showed BSi:PIC ratios <1. Peaks in PIC and BSi were observed within, and above the SAMW, in waters with low phosphate and silicate concentrations. The results of this study suggest that coccolithophore-rich SAMW in the Southern Ocean is being conditioned after its formation, such that by the time it upwells in the Atlantic equatorial region, the water is no longer conducive to coccolithophore growth.

Magnetically separable ZrO2@SiO2@Fe3O4 for selective phosphate removal from wastewater

Phosphorus (P), which is a non-renewable resource, has been extensively used in agricultural and industrial fields. However, the release of P into surface water through agricultural runoffs and wastewater can cause enrichment of P and eutrophication in confined water bodies. Hence, a novel technology that can remove phosphate (major species of P in water) from water bodies for eutrophication prevention and recover phosphate for minimising the loss of P resource is desired. Adsorption is a preferable approach for phosphate removal due to its simplicity of design, effectiveness even at low P concentrations, and potential for recovery. The use of zirconium-based adsorbents for phosphate removal from wastewater has received increasing attention. However, challenges remain to recover zirconium-based adsorbents. In this study, zirconium oxide-based superparamagnetic adsorbents (i.e. ZrO2@SiO2@Fe3O4) were developed for phosphate removal from wastewater. Magnetic separation efficiency, phosphate adsorption kinetics and isotherm, effects of coexisting anions and organic matters, and reusability are reported. The developed ZrO2@SiO2@Fe3O4 has an excellent magnetic separation efficiency of &gt; 98%, fast adsorption kinetics, high adsorption capacity at low phosphate concentrations, and strong selectivity for phosphate even at a competitive anion (i.e. Cl-, NO3-, SO42- and HCO3-) to phosphate molar ratio of 100:1 and humic acid (HA) concentration of 100 mg C/L. Adsorption-desorption cyclic experiments demonstrated the good reusability of the ZrO2@SiO2@Fe3O4.

A Haloarchaeal Small Regulatory RNA (sRNA) Is Essential for Rapid Adaptation to Phosphate Starvation Conditions.

The haloarchaeon Haloferax volcanii contains nearly 2800 small non-coding RNAs (sRNAs). One intergenic sRNA, sRNA132, was chosen for a detailed characterization. A deletion mutant had a growth defect and thus underscored the importance of sRNA132. A microarray analysis identified the transcript of an operon for a phosphate-specific ABC transporter as a putative target of sRNA132. Both the sRNA132 and the operon transcript accumulated under low phosphate concentrations, indicating a positive regulatory role of sRNA132. A kinetic analysis revealed that sRNA132 is essential shortly after the onset of phosphate starvation, while other regulatory processes take over after several hours. Comparison of the transcriptomes of wild-type and the sRNA132 gene deletion mutant 30 min after the onset of phosphate starvation revealed that sRNA132 controls a regulon of about 40 genes. Remarkably, the regulon included a second operon for a phosphate-specific ABC transporter, which also depended on sRNA132 for rapid induction in the absence of phosphate. Competitive growth experiments of the wild-type and ABC transporter operon deletion mutants underscored the importance of both transporters for growth at low phosphate concentrations. Northern blot analyses of four additional members of the sRNA132 regulon verified that all four transcripts depended on sRNA132 for rapid regulation after the onset of phosphate starvation. Importantly, this is the first example for the transient importance of a sRNA for any archaeal and bacterial species. In addition, this study unraveled the first sRNA regulon for haloarchaea.

Rapid release of internal carbon source from excess sludge with synergistic treatment via thermophilic microaerobic digestion and microcurrent

Synergistic treatment via thermophilic microaerobic digestion and microcurrent was adopted to release the internal carbon source from excess sludge, and the effects of the microcurrent on sludge digestion and carbon source release were investigated. Compared with the control group where no current was applied, the digestion supernatant in the tested R1-45 °C reactor maintained a relatively lower phosphate concentration. The optimal technical parameters included a digestion temperature of 45 °C, a current intensity of 175 mA, and a digestion time of 96 h; the concentrations of soluble chemical oxidation demand (SCOD), total nitrogen (TN), and total phosphate (TP) for the test group were 12 189, 903, and 105 mg L−1, respectively, and the ratios of SCOD/TN and SCOD/TP reached 13.5 and 116.1. The sludge flocs were disaggregated into smaller particles upon thermophilic treatment coupled with microcurrent application, and abundant organic matters were released into the digestion supernatant, resulting in a rapid increase in the SCOD. The hydroxyl radicals produced by the microcurrent could directly oxidize fatty acids into end molecules, and it also facilitated regeneration of NAD+ (nicotinamide adenine dinucleotide) through the oxidation of NADH; the orthophosphate in digestion supernatant could be continuously absorbed to synthesize ATP, accompanied by accumulation of acetic and propionic acids. In addition, synergistic treatment accelerated the production of humic acid-like substances and played an important role in the transformation of soluble microbial products.

Soil Quality Assessment Based on Different Properties of Remediated Soil Affected by Various Organic Amendments

Remediated soil can be one of valuable resources for sustainable agriculture after improving its quality and properties with proper treatments. Therefore, this study was conducted to estimate changes in soil properties and soil quality for improving remediated soil contaminated with petroleum as affected by the applications of various organic amendments as soil conditioners including biochar (BC), charcoal (CC), and livestock manure compost (LC). Two remediated soils, remediated soil A and B (RSA and RSB) that previously contaminated with different concentrations of total petroleum hydrocarbons, were alkaline soils with up to 8.5 of soil pH, very low soil organic matter (SOM) contents and available phosphate (available P2O5) concentrations, and very high exchangeable Ca concentrations. Thus, these soils had very unfavorable conditions for crop growth. RSA and RSB were treated with BC, CC, and LC in levels of 0.0%, 1.0%, and 5.0% on dry weight bases. The remediated soils treated with organic soil conditioners were incubated for 2, 4, 8 and 16 weeks at room temperature (24 ± 2°C). SOM contents increased with all the treatments. In particular, SOM in RSB increased up to 19.5 g kg-1 with BC 5.0% treatment (BC5, 16-week), which was 2 times higher than that in both RSA and RSB soils without BC applications (Control soils). Also, available P2O5 concentrations increased to 24.9 mg kg-1 (RSA, 16-week), and 17.0 mg kg-1 (RSB, 8-week) with BC5. However, available P2O5 concentration in the remediated soils was very lower than that of the optimal value for cultivating crops suggested by National Institute of Agricultural Sciences in the Republic of Korea. Available P2O5 was negatively correlated with soil pH (p < 0.01) and exchangeable Ca (p < 0.01). Soil quality index (SQI) and weight additive soil quality index (SQIW) were positively correlated with SOM (p < 0.01). The mean value of soil quality indices were 39.3, 56.0, 40.0, and 54.5 for RSA Control, RSA BC5, RSB Control, and RSB BC5, respectively. The highest soil quality index was found in the remediated soil with BC treatment. The remediated soils require the immediate solution for the poor soil quality, and thus should need methodical and continuous management. Soil quality index (SQI) and weight additive soil quality index (SQIW) of the two remediated soils (RSA and RSB) as influenced by the applications of various organic amendments. Treatment† RSA RSB SQI SQIW SQI SQIW Control 39.3 d‡ 32.6 d 40.0 d 32.4 c BC1 45.5 bc 39.5 bc 45.0 bc 37.2 bc BC5 56.0 a 51.0 a 54.5 a 47.6 a CC1 43.0 cd 36.6 cd 42.5 cd 35.6 bc CC5 48.0 b 42.7 b 47.5 b 40.9 b LC1 39.3 d 32.6 d 41.3 cd 34.0 c LC5 48.0 b 42.7 b 47.5 b 40.5 b †Control, no treated; BC1, 1% of biochar treated; BC5, 5% of biochar treated; CC1, 1% of charcoal treated; CC5, 5% of charcoal treated; LC1, 1% of livestock manure compost treated; LC5, 5% of livestock manure compost treated. ‡Numbers followed by the different letter within a column are significantly different at p <0.05 by Duncan's multiple range test.

Use of multiple isotopes to evaluate the impact of mariculture on nutrient dynamics in coastal groundwater.

Nitrogen and phosphate dynamics in groundwater and surface waters (aquaculture ponds and effluents and drainage channels) in the two seasons (April and September 2015) were investigated in a reclaimed coastal region in China. Multiple isotopes (δ15N-NO3-, δ18O-NO3-, δ2H-H2O, and δ18O-H2O) associated with the concentrations of dissolved inorganic nitrogen and phosphate were analyzed to assess the environmental impact of mariculture on coastal waters. Low phosphate concentration in the effluents was released from aquaculture ponds. Nitrate accounted for a larger proportion of dissolved inorganic nitrogen in September in aquaculture ponds and effluents and drainage channels. The groundwater in the mariculture zone was enriched with dissolved nitrogen components. In the offshore direction, seawater and precipitation were supplement of the groundwater, with nitrate deriving from mixing aquaculture effluents and wastewater. Denitrification occurred in groundwater in September 2015.

Quantification and isotherm modelling of competitive phosphate and silicate adsorption onto micro-sized granular ferric hydroxide.

Adsorption onto ferric hydroxide is a known method to reach very low residual phosphate concentrations. Silicate is omnipresent in surface and industrial waters and reduces the adsorption capacity of ferric hydroxides. The present article focusses on the influences of silicate concentration and contact time on the adsorption of phosphate to a micro-sized iron hydroxide adsorbent (μGFH) and fits adsorption data to multi-component adsorption isotherms. In Berlin drinking water (DOC of approx. 4 mg L−1) at pH 7.0, loadings of 24 mg g−1 P (with 3 mg L−1 initial PO43−–P) and 17 mg L−1 Si (with 9 mg L−1 initial Si) were reached. In deionized water, phosphate shows a high percentage of reversible bonds to μGFH while silicate adsorption is not reversible probably due to polymerization. Depending on the initial silicate concentration, phosphate loadings are reduced by 27, 33 and 47% (for equilibrium concentrations of 1.5 mg L−1) for 9, 14 and 22 mg L−1 Si respectively. Out of eight tested multi-component adsorption models, the Extended Freundlich Model Isotherm (EFMI) describes the simultaneous adsorption of phosphate and silicate best. Thus, providing the means to predict and control phosphate removal. Longer contact times of the adsorbent with silicate prior to addition of phosphate reduce phosphate adsorption significantly. Compared to 7 days of contact with silicate (c0 = 10 mg L−1) prior to phosphate (c0 = 3 mg L−1) addition, 28 and 56 days reduce the μGFH capacity for phosphate by 21 and 43%, respectively.

Use of Powdered Cockle Shell as a Bio‐Sorbent Material for Phosphate Removal from Water

In this study, powdered cockle shell was used as a bio‐sorbent material for the removal of phosphates in water. The SEM–EDX, XRD, and FT‐IR analyses showed that calcium carbonate (CaCO3) exists in aragonite state in powdered cockle shell. The influences of pH, initial phosphate concentrations and contact time were conducted in a series of batch sorption experiments. Among the various factors studied, the pH was turned out to be a key variable for phosphate removal. Based on the experimental results for pH, it was found that the phosphate is chemically sorbed onto aragonite surface. At lower phosphate concentration, roughly 88% of sorption efficiency was accomplished by powdered cockle shell. The Pseudo‐second‐order kinetic and the Langmuir isotherm model were fitted well to the sorption experimental data of phosphate because of their higher correlation coefficients (R2).

Single-cell imaging of phosphorus uptake shows that key harmful algae rely on different phosphorus sources for growth

Single-cell measurements of biochemical processes have advanced our understanding of cellular physiology in individual microbes and microbial populations. Due to methodological limitations, little is known about single-cell phosphorus (P) uptake and its importance for microbial growth within mixed field populations. Here, we developed a nanometer-scale secondary ion mass spectrometry (nanoSIMS)-based approach to quantify single-cell P uptake in combination with cellular CO2 and N2 fixation. Applying this approach during a harmful algal bloom (HAB), we found that the toxin-producer Nodularia almost exclusively used phosphate for growth at very low phosphate concentrations in the Baltic Sea. In contrast, the non-toxic Aphanizomenon acquired only 15% of its cellular P-demand from phosphate and ~85% from organic P. When phosphate concentrations were raised, Nodularia thrived indicating that this toxin-producer directly benefits from phosphate inputs. The phosphate availability in the Baltic Sea is projected to rise and therefore might foster more frequent and intense Nodularia blooms with a concomitant rise in the overall toxicity of HABs in the Baltic Sea. With a projected increase in HABs worldwide, the capability to use organic P may be a critical factor that not only determines the microbial community structure, but the overall harmfulness and associated costs of algal blooms.

Adsorption of phosphate by sediments in a eutrophic lake: Isotherms, kinetics, thermodynamics and the influence of dissolved organic matter

Adsorption and desorption of phosphorus (P) at sediment-water interface is one of the key processes of biogeochemical cycling of P in lakes. Thus, adsorption of phosphate by sediments from Lake Dianchi, a eutrophic lake, was investigated in this study. Importantly, the influence of dissolved organic matter (DOM) with fulvic acid (FA) as a representative example on these processes was further studied. The results showed that the presence of FA in the solution did not change the tendency of phosphate adsorption by sediments from Lake Dianchi. Compared with Freundlich equation, Langmuir model fitted better in describing the adsorption isotherms. And the pseudo-second-order kinetic model predicated well the adsorption kinetics for adsorption of phosphate by sediments. Under low concentrations of phosphate, FA promoted desorption of phosphate adsorbed on the sediments. However, adsorption behaviors including capacity and efficiency would be enhanced by presence of FA under high concentrations of phosphate. Based on adsorption thermodynamics, temperature and DOM (FA in this study) were two most important factors for adsorption of phosphate by sediments. Adsorption of phosphate on sediments was a spontaneous endothermic reaction process, which was a chemical-physical process rather than a simple physical adsorption. The influence of FA on the adsorption of phosphate by sediments was closely related with characteristics of sediments such as contents of Fe-Al oxides and organic matter. Aggressive results showed that increasing DOM due to algal blooming was likely an important way for dominant algae to maintain the nutrients such as P in lakes.

PE_PGRS3 of Mycobacterium tuberculosis is specifically expressed at low phosphate concentration, and its arginine-rich C-terminal domain mediates adhesion and persistence in host tissues when expressed in Mycobacterium smegmatis.

PE_PGRSs of Mycobacterium tuberculosis (Mtb) represent a family of complex and peculiar proteins whose role and function remain elusive. In this study, we investigated PE_PGRS3 and PE_PGRS4, two highly homologous PE_PGRSs encoded by two contiguous genes in the Mtb genome. Using a gene-reporter system in Mycobacterium smegmatis (Ms) and transcriptional analysis in Mtb, we show that PE_PGRS3, but not PE_PGRS4, is specifically expressed under low phosphate concentrations. Interestingly, PE_PGRS3, but not PE_PGRS4, has a unique, arginine-rich C-terminal domain of unknown function. Heterologous expression of PE_PGRS3 in Ms was used to demonstrate cellular localisation of the protein on the mycobacterial surface, where it significantly affects net surface charge. Moreover, expression of full-length PE_PGRS3 enhanced adhesion of Ms to murine macrophages and human epithelial cells and improved bacterial persistence in spleen tissue following infection in mice. Expression of the PE_PGRS3 functional deletion mutant lacking the C-terminal domain in Ms did not enhance adhesion to host cells, showing a phenotype similar to the Ms parental strain. Interestingly, enhanced persistence of Ms expressing PE_PGRS3 did not correlate with increased concentrations of inflammatory cytokines. These results point to a critical role for the ≈ 80 amino acids long, arginine-rich C-terminal domain of PE_PGRS3 in tuberculosis pathogenesis.

Low arsenate influx rate and high phosphorus concentration in wheat (Triticum aestivum L.): A mechanism for arsenate tolerance in wheat plants

Two wheat (Triticum aestivum L.) cultivars differing in arsenic (As)-tolerance were used to investigate the effects of phosphorus (P) concentration and nutrient solution pH on As(V) toxicity and As(V) uptake kinetics, and to illustrate the mechanism of As(V) tolerance in wheat seedlings. Low pH and low phosphate concentration enhanced wheat uptake of As, resulting in high As toxicity. The As(V)-tolerant cultivar MM45 exhibited higher relative root elongation than non-tolerant cultivar HM29 in all treatments, except that no genotypic difference was recorded for the solution P at 100 μmol L−1 or greater. Wheat seedling As(V) tolerance was positively correlated with P concentration in roots and shoots. In short-term (30 min) As(V)-uptake kinetics experiments, the maximum influx rate (Vmax) of As(V) increased with decreasing solution pH (from 7.0 to 6.0). Compared with HM29, although MM45 had lower Vmax, its Michaelis–Menten constant (Km) did not exceed that of HM29 in all treatments. The Vmax values of both cultivars were not significantly affected by phosphate treatments, except for HM29 which had significantly higher Vmax value in the presence of phosphate at pH 7.0. The Km values of the two cultivars increased by 9- to 20-fold when phosphate was present as opposed to absent from the uptake solution. This study showed that the Vmax values are mainly increased by high pH and As(V) uptake Km is mainly increased by phosphate presence. Decreased As(V) influx rates during early stages and increased P concentration in plant tissues are associated with increased As tolerance in wheat seedlings.