Cell-bound and extracellular phosphatase activities of cyanobacterial isolates

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity

Cyanobacteria are harmful algae that are monitored worldwide to prevent the effects of the toxins that they can produce. Most research efforts have focused on direct or indirect effects on human populations, with a view to gain easy accurate detection and quantification methods, mainly in planktic communities, but with increasing interest shown in benthos. However, cyanobacteria have played a fundamental role from the very beginning in both the development of our planet's biodiversity and the construction of new habitats. These organisms have colonized almost every possible planktic or benthic environment on earth, including the most extreme ones, and display a vast number of adaptations. All this explains why they are the most important or the only phototrophs in some habitats. The negative effects of cyanotoxins on macroinvertebrates have been demonstrated, but usually under conditions that are far from natural, and on forms of exposure, toxin concentration, or composition. The cohabitation of cyanobacteria with most invertebrate groups is long-standing and has probably contributed to the development of detoxification means, which would explain the survival of some species inside cyanobacteria colonies. This review focuses on benthic cyanobacteria, their capacity to produce several types of toxins, and their relationships with benthic macroinvertebrates beyond toxicity.

Stringent Response of Cyanobacteria and Other Bacterioplankton during Different Stages of a Harmful Cyanobacterial Bloom

We conducted a field study to investigate the role of stringent response in cyanobacteria and coexisting bacterioplankton during nutrient-deprived periods at various stages of bloom in a freshwater lake (Utah Lake) for the first time. Using metagenomics and metatranscriptomics analyses, we examined the cyanobacterial ecology and expression of important functional genes related to stringent response, N and P metabolism, and regulation. Our findings mark a significant advancement in understanding the mechanisms by which toxic cyanobacteria survive and proliferate during nitrogen (N) and phosphorus (P) limitations. We successfully identified and analyzed the metagenome-assembled genomes (MAGs) of the dominant bloom-forming cyanobacteria, namely, Dolichospermum circinale, Aphanizomenon flos-aquae UKL13-PB, Planktothrix agardhii, and Microcystis aeruginosa. By mapping RNA-seq data to the coding sequences of the MAGs, we observed that these four prevalent cyanobacteria species activated multiple functions to adapt to the depletion of inorganic nutrients. During and after the blooms, the four dominant cyanobacteria species expressed high levels of transcripts related to toxin production, such as microcystins (mcy), anatoxins (ana), and cylindrospermopsins (cyr). Additionally, genes associated with polyphosphate (poly-P) storage and the stringent response alarmone (p)ppGpp synthesis/hydrolysis, including ppk, relA, and spoT, were highly activated in both cyanobacteria and bacterioplankton. Under N deficiency, the main N pathways shifted from denitrification and dissimilatory nitrate reduction in bacterioplankton toward N2-fixing and assimilatory nitrate reduction in certain cyanobacteria with a corresponding shift in the community composition. P deprivation triggered a stringent response mediated by spoT-dependent (p)ppGpp accumulation and activation of the Pho regulon in both cyanobacteria and bacterioplankton, facilitating inorganic and organic P uptake. The dominant cyanobacterial MAGs exhibited the presence of multiple alkaline phosphatase (APase) transcripts (e.g., phoA in Dolichospermum, phoX in Planktothrix, and Microcystis), suggesting their ability to synthesize and release APase enzymes to convert ambient organic P into bioavailable forms. Conversely, transcripts associated with bacterioplankton-dominated pathways like denitrification were low and did not align with the occurrence of intense cyanoHABs. The strong correlations observed among N, P, stringent response metabolisms and the succession of blooms caused by dominant cyanobacterial species provide evidence that the stringent response, induced by nutrient limitation, may activate unique N and P functions in toxin-producing cyanobacteria, thereby sustaining cyanoHABs.

Dissolved organic phosphorus bioremediation from food-waste centrate using microalgae

Dissolved organic phosphorus (DOP) accounts for a substantial proportion of the total phosphorus remaining in the wastewater discharge and remains a concern for the receiving environment. This study assessed the potential of wastewater microalgae for the bioremediation of DOP from anaerobically digested food-waste centrate. For high DOP to low DIP ratio, the microalgal consortia was able to remove over 98% of DOP and 95% of total dissolved phosphorus. However, under a 1:1 ratio of DOP to DIP, the microalgal consortia was only able to remove 5% of the organic phosphorus and 76% of total dissolved phosphorus. All five main microalgal species were capable of producing alkaline phosphatase to some degree, the enzyme responsible for hydrolysing the phosphorus. For the dominant species Desmodesmus communis, total phosphatase activity reduced from 46.0 ± 2.3 mmol L^-1 h^-1 in axenic cultures to only 6.3 ± 0.7 mmol L^-1 h^-1 in presence of its microbiome. This resulted in a reduction in biomass from 209 ± 13 g m^-3 to 73 ± 5 g m^-3. For Tetradesmus dimorphus, alkaline phosphatase increased from 6.5 ± 0.3 mmol L^-1 h^-1 in the axenic culture to 169.8 ± 40.1 mmol L^-1 h^-1 in presence of both its microbiome and centrate-sourced bacteria but had little impact on biomass production. DOP removal rates across all five species, in all treatments ranged from 17 to 91%. With the exception of D. communis, the nutrient removal efficiency of DOP per unit biomass suggested luxury uptake of phosphorus into the microalgal cell. For wastewaters with low inorganic and moderate to high organic phosphorus microalgal-based wastewater treatment systems may offer a cost-effective mechanism for the removal and recovery of dissolved organic phosphorus from wastewater. Further research on refining organic phosphorus bioremediation in a range of wastewater types, particularly at pilot and full-scale, is needed.

Organic P transformations and release from riparian soils responding to water level fluctuation

To manage eutrophication of reservoirs, it is important to consider the potential for unexpected releases of organic phosphorus (OP) from areas around the reservoir where the water level fluctuates. In this study, we investigated the absorption and release of OP from a riparian soil/sediment from the Miyun Reservoir under fluctuating water levels using laboratory simulations. The total organic phosphorus (TOP) content in the soils/sediments ranged from 250.76 to 298.62 mg/kg, which accounted for between 5.6 and 38.5% of the total phosphorus (TP) content. We measured three OP fractions and found that the concentration of moderately labile OP (MLOP) was the highest, followed by labile OP (LOP), and the concentration of non-labile OP (NLOP) was the lowest. As the soils and sediments dried, they adsorbed phosphorus (P). The inorganic phosphorus (IP) contents were significantly and negatively correlated with the LOP and MLOP contents, indicating exchange between IP with these two fractions when the concentrations of bioavailable phosphorus in the soil are low. During flooding, the physicochemical properties varied at the sediment-water interface, inducing the release of Fe/Al-P. Some of the LOP and MLOP in the sediments were mineralized to IP. Our results suggest that when there are external P inputs, P may be released when sediments around a reservoir are subjected to wetting and drying as water levels fluctuate, which may cause P enrichment in reservoirs, especially in areas with poor water exchange.

Roles of Phosphate Solubilizing Microorganisms from Managing Soil Phosphorus Deficiency to Mediating Biogeochemical P Cycle

Phosphorus (P) is a vital element in biological molecules, and one of the main limiting elements for biomass production as plant-available P represents only a small fraction of total soil P. Increasing global food demand and modern agricultural consumption of P fertilizers could lead to excessive inputs of inorganic P in intensively managed croplands, consequently rising P losses and ongoing eutrophication of surface waters. Despite phosphate solubilizing microorganisms (PSMs) are widely accepted as eco-friendly P fertilizers for increasing agricultural productivity, a comprehensive and deeper understanding of the role of PSMs in P geochemical processes for managing P deficiency has received inadequate attention. In this review, we summarize the basic P forms and their geochemical and biological cycles in soil systems, how PSMs mediate soil P biogeochemical cycles, and the metabolic and enzymatic mechanisms behind these processes. We also highlight the important roles of PSMs in the biogeochemical P cycle and provide perspectives on several environmental issues to prioritize in future PSM applications.

Significant influence of phosphorus resources on the growth and alkaline phosphatase activities of Microcystis aeruginosa

It is well-accepted that phosphorus, particularly orthophosphate, is a determinant factor in aquatic eutrophication. However, numerous kinds of phosphorus sources exist in real world scenario, and limited studies have characterized the pairwise relationships among abundant different phosphorus sources and the physiological behaviour of algae. The present study developed a high-throughput assay to investigate the effects of 59 different phosphorus sources (equal initial concentration of total phosphorus) on the growth and alkaline phosphatase (AKP) activities of Microcystis aeruginosa, a model cyanobacteria whose predominance holds sway in lake eutrophication. M. aeruginosa cultivated with nucleoside monophosphates (NMPs) had higher growth, relative AKP activities and residual orthophosphate, which were positively intercorrelated. Oppositely, non-NMPs cultivation of M. aeruginosa led to negative relationships between the relative AKP activities and their growth or residual orthophosphate. These results indicated distinct mechanisms for M. aeruginosa to utilize different phosphorus sources in real-world scenario, and both phosphorus source and content are determinant factors on the growth and physiological behaviour of M. aeruginosa. Given the complicated and vast phosphorus pool in the natural environment, phosphorus resources might significantly alter the abundance and physiological behaviour of M. aeruginosa and other bloom-forming algae, then influence the phytoplanktonic community structure and affect the possibility and intensity of algal bloom. Our work hints the underestimation of the restriction factors in lake eutrophication and provides a new tool to study the driven forces of phytoplanktonic community dynamics as phosphorus from both internal and external sources.

Effects of drought and water pulses on microbial functionality and the role of Cyanoprokaryota in the rhizospheres of gypsophytes

In the rhizospheres of three gypsophytes and in non-rhizospheric soil, two samplings were carried out - the first during a summer drought and the second during spring - to detect the responses to the availability of water in the soil. Urease and protease showed higher values after the drought whereas β-glucosidase was highest in the spring. This pattern was the same for all the rhizospheres tested. However, the arylsulfatase and alkaline phosphatase did not change. Surprising results were obtained when water retention and water loss were studied, with the highest values being obtained for the dry season due to the association of Cyanoprokaryota with the rhizospheres. The results are also explained by two water pulses that occurred before the samplings. Several parameters, whose values changed markedly due to the microbiological activation just after the drought and water pulses, are proposed as indicators of this activation: microbial biomass carbon and basal respiration rate, together with urease and protease. However, it was the dehydrogenase activity in spring that best reflected the microbiology associated with the carbon cycle, together with β-glucosidase. The interrelationships between carbon and nitrogen were shown through the indices: water soluble nitrogen and water soluble carbon. We propose three functional adaptation mechanisms of these plants associated with the Cyanoprokaryota in their rhizospheres and related to the water availability as determined by drought and water pulse effects. Herniaria fruticosa is a pioneer with the greatest diversity of Cyanoprokaryota, in both summer and spring (10 species and 11 species, respectively), and with high-medium abundance (5-30%). Teucrium balthazaris exhibits an intermediate strategy, with greater diversity of Cyanoprokaryota in spring (7 species) and predominance of high-medium abundance (5-30%). Finally, Helianthemum squamatum has lower diversity, with one species in summer (with low abundance, <5%) and no species in spring.

Differential strain response in alkaline phosphatase activity to available phosphorus in Microcoleus autumnalis

Toxic, benthic cyanobacterial proliferations have increased in frequency and severity globally and can have negative impacts on aquatic ecosystems, recreation and human health. Microcoleus autumnalis has been associated with numerous animal fatalities and is causing increasing concern. It tends to grow in systems with moderate dissolved inorganic nitrogen and very low dissolved reactive phosphorus. Acquisition of nutrients, particularly phosphorus, from organic sources may explain how M. autumnalis can reach the high biomass in these relatively nutrient deplete environments. In the present study the effect of phosphorus concentration and source on alkaline phosphatase activity was investigated in toxic and non-toxic M. autumnalis strains. Toxic strains exhibited significantly higher alkaline phosphatase activity than non-toxic strains (p <  0.05), and alkaline phosphatase activity increased in all strains under phosphorus-depleted conditions (p <  0.05). Alkaline phosphatase activity was also present in environmental M. autumnalis mats, though at lower levels than in laboratory experiments. The presence of alkaline phosphatase activity indicates that the acquisition of phosphorus from organic phosphorus sources may contribute to the ability of M. autumnalis to grow in systems with low dissolved reactive phosphorus.

Dissolved organic phosphorus enhances arsenate bioaccumulation and biotransformation in Microcystis aeruginosa

Only limited information is available on the effects of dissolved organic phosphorus (DOP) on arsenate (As(V)) bioaccumulation and biotransformation in organisms. In this study, we examined the influence of three different DOP forms (β-sodium glycerophosphate (βP), adenosine 5'-triphosphate (ATP), and D-Glucose-6-phosphate disodium (GP) salts) and inorganic phosphate (IP) on As(V) toxicity, accumulation, and biotransformation in Microcystis aeruginosa. Results showed that M. aeruginosa utilized the three DOP forms to sustain its growth. At a subcellular level, the higher phosphorus (P) distribution in metal-sensitive fractions (MSF) observed in the IP treatments could explain the comparatively lower toxic stress of algae compared to the DOP treatments. Meanwhile, the higher MSF distribution of arsenic (As) in M. aeruginosa in the presence of DOP could explain the higher toxicity with lower 96-h half maximal effective concentration (EC₅₀) values. Although we observed As(V) and P discrimination in M. aeruginosa under IP treatments with high intracellular P/As, we did not find this discrimination under the DOP treatments. As accumulation in algal cells was therefore greatly enhanced by DOP, especially βP, given its lower transformation rate to phosphate compared to ATP and GP in media. Additionally, As(V) reduction and, subsequently, As(III) methylation were greatly facilitated in M. aeruginosa by the presence of DOP, particularly GP, which was confirmed by the higher relative expression of its two functional genes (arsC and arsM). Our findings indicate that As(V) accumulation and its subsequent biotransformation were enhanced by organic P forms, which provides new insight into how DOP modulates As metabolism in algae.

Soil microalgae and cyanobacteria: the biotechnological potential in the maintenance of soil fertility and health

The soil microbiota plays a major role in maintaining the nutrient balance, carbon sink, and soil health. Numerous studies reported on the function of microbiota such as plant growth-promoting bacteria and fungi in soil. Although microalgae and cyanobacteria are ubiquitous in soil, very less attention has been paid on the potential of these microorganisms. The indiscriminate use of various chemicals to enhance agricultural productivity led to serious consequences like structure instability, accumulation of toxic contaminants, etc., leading to an ecological imbalance between soil, plant, and microbiota. However, the significant role of microalgae and cyanobacteria in crop productivity and other potential options has been so far undermined. The intent of the present critical review is to highlight the significance of this unique group of microorganisms in terms of maintaining soil fertility and soil health. Beneficial soil ecological applications of these two groups in enhancing plant growth, establishing interrelationships among other microbes, and detoxifying chemical agents such as insecticides, herbicides, etc. through mutualistic cooperation by synthesizing enzymes and phytohormones are presented. Since recombinant technology involving genomic integration favors the development of useful traits in microalgae and cyanobacteria for their potential application in improvement of soil fertility and health, the merits and demerits of various such advanced methodologies associated in harnessing the biotechnological potential of these photosynthetic microorganisms for sustainable agriculture were also discussed.

Tracking the rise of eukaryotes to ecological dominance with zinc isotopes

The biogeochemical cycling of zinc (Zn) is intimately coupled with organic carbon in the ocean. Based on an extensive new sedimentary Zn isotope record across Earth's history, we provide evidence for a fundamental shift in the marine Zn cycle ~800 million years ago. We discuss a wide range of potential drivers for this transition and propose that, within available constraints, a restructuring of marine ecosystems is the most parsimonious explanation for this shift. Using a global isotope mass balance approach, we show that a change in the organic Zn/C ratio is required to account for observed Zn isotope trends through time. Given the higher affinity of eukaryotes for Zn relative to prokaryotes, we suggest that a shift toward a more eukaryote-rich ecosystem could have provided a means of more efficiently sequestering organic-derived Zn. Despite the much earlier appearance of eukaryotes in the microfossil record (~1700 to 1600 million years ago), our data suggest a delayed rise to ecological prominence during the Neoproterozoic, consistent with the currently accepted organic biomarker records.

Bioavailable phosphorus (P) reduction is less than mobile P immobilization in lake sediment for eutrophication control by inactivating agents

Phosphorus (P) immobilization by inactivating agents in the sediment of eutrophic lakes to reduce immediately available P in lake water is often crucial for mitigating nuisance eutrophication symptoms, such as cyanobacterial blooms. Macrophytes and phytoplankton, however, can directly utilize P from the sediment for growth. Accordingly, a comprehensive analysis of the P bioavailability in lake sediment amended with two promising P-inactivation agents, namely Phoslock^® and drinking water treatment residue (DWTR), was investigated in both short- and long-term studies (20 and 180 d). Phosphorus-availability was assessed using six chemical extraction methods and Hydrilla verticillata and Microcystis aeruginosa growth tests. The results showed that Phoslock^® and DWTR significantly reduced mobile P (NH₄Cl and Na₂S₂O₄/NaHCO₃ extractable P) in lake sediment, while P bioavailability that was assessed by different methods showed considerable deviations. Interestingly, appropriate bioavailable P chemical extraction methods were determined based on linear correlation analysis, and further comparison indicated that reduction of bioavailable P by DWTR (<55% for macrophyte available P) and Phoslock^® (<17% for cyanobacteria available P) were clearly less than the mobile P immobilization (>75%) at recommended dosages, which was probably caused by the capability of macrophyte and cyanobacteria to utilize various fractions of P (except the residual P) in amended sediment under proper illumination. Therefore, DWTR and Phoslock^® can effectively reduce P release from lake sediment, but the potential bioavailable P may pose uncertainties for eutrophication control in lakes that typically have regular sediment re-suspension. Overall, an evaluation of the bioavailable P pool in the lake ecosystem should be essential for successful lake geo-engineering.

Effects of flow regime on benthic algae and macroinvertebrates - A comparison between regulated and unregulated rivers

Natural fluctuations in flow are important for maintaining the ecological integrity of riverine ecosystems. However, the flow regime of many rivers has been modified. We assessed the impact of water chemistry, habitat and streamflow characteristics on macroinvertebrates and benthic algae, comparing 20 regulated with 20 unregulated sites. Flow regime, calculated from daily averaged discharge over the five years preceding sampling, was generally more stable at regulated sites, with higher relative discharges in winter, lower relative discharges in spring and smaller differences between upper and lower percentiles. However, no consistent differences in benthic algal or macroinvertebrate structural and functional traits occurred between regulated and unregulated sites. When regulated and unregulated sites were pooled, overall flow regime, calculated as principal components of discharge characteristics over the five years preceding sampling, affected macroinvertebrate species assemblages, but not indices used for ecosystem status assessment or functional feeding groups. This indicates that, while species identity shifted with changing flow regime, the exchanged taxa had similar feeding habits. In contrast to macroinvertebrates, overall flow regime did not affect benthic algae. Our results indicate that overall flow regime affected the species pool of macroinvertebrates from which recolonization after extreme events may occur, but not of benthic algae. When individual components of flow regime were analyzed separately, high June (i.e. three months before sampling) flow maxima were associated with low benthic algal taxon richness, presumably due to scouring. Macroinvertebrate taxon richness decreased with lower relative minimum discharges, presumably due to temporary drying of parts of the riverbed. However, recolonization after such extreme events presumably is fast. Generally, macroinvertebrate and benthic algal assemblages were more closely related to water physico-chemical than to hydrological variables. Our results suggest that macroinvertebrate and benthic algal indices commonly used for ecological status assessment are applicable also in regulated rivers.

Fate, mass balance, and transport of phosphorus in the septic system drainfields

Septic systems can be a potential source of phosphorus (P) in shallow groundwater. Our objective was to investigate the fate, mass balance, and transport of P in the drainfield of a drip-dispersal septic system. Drainfields were replicated in lysimeters (152.4 cm long, 91.4 cm wide, and 91.4 cm high). Leachate and effluent samples were collected over 67 events (n = 15 daily; n = 52 weekly flow-weighted) and analyzed for total P (TP), orthophosphate (PO4P), and other P (TP - PO4P). Mean TP was 15 mg L(-1) (84% PO4P; 16% other P) in the effluent and 0.16 mg L(-1) (47% PO4P, 53% other P) in the leachate. After one year, 46.8 g of TP was added with effluent and rainfall to each drainfield, of which, <1% leached, 3.8% was taken up by St. Augustine grass, leaving >95% in the drainfield. Effluent dispersal increased water extractable P (WEP) in the drainfield from <5 to >10 mg kg(-1). Using the P sorption maxima of sand (118 mg kg(-1)) and soil (260 mg kg(-1)), we estimated that ∼18% of the drainfield P sorption capacity was saturated after one year of effluent dispersal. We conclude that despite the low leaching potential of P dispersed with effluent in the first year of drainfield operation, a growing WEP pool in the drainfield and low P sorption capacity of Florida's sandy soils may have the potential to transport P to shallow groundwater in long-running septic systems.

The dual role of nitrogen supply in controlling the growth and toxicity of cyanobacterial blooms

Historically, phosphorus (P) has been considered the primary limiting nutrient for phytoplankton assemblages in freshwater ecosystems. This review, supported by new findings from Lake Erie, highlights recent molecular, laboratory, and field evidence that the growth and toxicity of some non-diazotrophic blooms of cyanobacteria can be controlled by nitrogen (N). Cyanobacteria such as Microcystis possess physiological adaptations that allow them to dominate low-P surface waters, and in temperate lakes, cyanobacterial densities can be controlled by N availability. Beyond total cyanobacterial biomass, N loading has been shown to selectively promote the abundance of Microcystis and Planktothrix strains capable of synthesizing microcystins over strains that do not possess this ability. Among strains of cyanobacteria capable of synthesizing the N-rich microcystins, cellular toxin quotas have been found to depend upon exogenous N supplies. Herein, multi-year observations from western Lake Erie are presented demonstrating that microcystin concentrations peak in parallel with inorganic N, but not orthophosphate, concentrations and are significantly lower (p<0.01) during years of reduced inorganic nitrogen loading and concentrations. Collectively, this information underscores the importance of N as well as P in controlling toxic cyanobacteria blooms. Furthermore, it supports the premise that management actions to reduce P in the absence of concurrent restrictions on N loading may not effectively control the growth and/or toxicity of non-diazotrophic toxic cyanobacteria such as the cosmopolitan, toxin-producing genus, Microcystis.

Use of dissolved inorganic and organic phosphorus by axenic and nonaxenic clones of Karenia brevis and Karenia mikimotoi

Nearly annual blooms of the marine dinoflagellate Karenia brevis, which initiate offshore on the West Florida Shelf in oligotrophic waters, cause widespread environmental and economic damage. The success of K. brevis as a bloom-former is partially attributed to its ability to use a diverse suite of nutrients from natural and anthropogenic sources, although relatively little is known about the ability of K. brevis and the closely related Karenia mikimotoi to use a variety of organic sources of phosphorus, including phosphomonoesters, phosphodiesters, and phosphonates. Through a series of bioassays, this study characterized the ability of axenic and nonaxenic K. brevis and K. mikimotoi clones isolated from Florida waters to use a variety of organic phosphorus compounds as the sole source of phosphorus for growth, comparing this utilization to that of inorganic sources of phosphate. Differing abilities of axenic and nonaxenic K. brevis and K. mikimotoi cultures to use phosphorus from the compounds evaluated were documented. Specifically, growth of axenic cultures was greatest on inorganic phosphorus and was not supported on the phosphomonoester phytate, or generally on phosphodiesters or phosphonates. The nonaxenic cultures were able to use organic compounds that the axenic cultures were not able to use, often after lags in growth, highlighting a potential role of co-associated bacterial communities to transform nutrients to bioavailable forms. Given the ability of K. brevis and K. mikimotoi to use a diverse suite of inorganic and organic phosphorus, bloom mitigation strategies should consider all nutrient forms.

An in-depth assessment into simultaneous monitoring of dissolved reactive phosphorus (DRP) and low-molecular-weight organic phosphorus (LMWOP) in aquatic environments using diffusive gradients in thin films (DGT)

Long-term laborious and thus costly monitoring of phosphorus (P) fractions is required in order to provide reasonable estimates of the levels of bioavailable phosphorus for eutrophication studies. A practical solution to this problem is the application of passive samplers, known as Diffusive Gradient in Thin films (DGTs), providing time-average concentrations. DGT, with the phosphate adsorbent Fe-oxide based binding gel, is capable of collecting both orthophosphate and low molecular weight organic phosphorus (LMWOP) compounds, such as adenosine monophosphate (AMP) and myo-inositol hexakisphosphate (IP6). The diffusion coefficient (D) is a key parameter relating the amount of analyte determined from the DGT to a time averaged ambient concentration. D at 20 °C for AMP and IP6 were experimentally determined to be 2.9 × 10(-6) cm(2) s(-1) and 1.0 × 10(-6) cm(2) s(-1), respectively. Estimations by conceptual models of LMWOP uptake by DGTs indicated that this fraction constituted more than 75% of the dissolved organic phosphorus (DOP) accumulated. Since there is no one D for LMWOP, a D range was estimated through assessment of D models. The models tested for estimating D for a variety of common LMWOP molecules proved to be still too uncertain for practical use. The experimentally determined D for AMP and IP6 were therefore used as upper and lower D, respectively, in order to estimate minimum and maximum ambient concentrations of LMWOP. Validation of the DGT data was performed by comparing concentrations of P fractions determined in natural water samples with concentration of P fractions determined using DGT. Stream water draining three catchments with different land-use (forest, mixed and agriculture) showed clear differences in relative and absolute concentrations of dissolved reactive phosphorus (DRP) and dissolved organic P (DOP). There was no significant difference between water sample and DGT DRP (p > 0.05). Moreover, the upper and lower limit D for LMWOP proved reasonable as water sample determined DOP was found to lie in-between the limits of DGT LMWOP concentrations, indicating that on average DOP consists mainly of LMWOP. "Best fit" D was determined for each stream in order to practically use the DGTs for estimating time average DOP. Applying DGT in a eutrophic lake provided insight into P cycling in the water column.

Extreme phosphorus losses in drainage from grazed dairy pastures on marginal land

With the installation of artificial drainage and large inputs of lime and fertilizer, dairy farming can be profitable on marginal land. We hypothesized that this will lead to large phosphorus (P) losses and potential surface water impairment if the soil has little capacity to sorb added P. Phosphorous was measured in drainage from three "marginal" soils used for dairying: an Organic soil that had been developed out of scrub for 2 yr and used for winter forage cropping, a Podzol that had been developed into pasture for 10 yr, and an intergrade soil that had been in pasture for 2 yr. Over 18 mo, drainage was similar among all sites (521-574 mm), but the load leached to 35-cm depth from the Organic soil was 87 kg P ha (∼89% of fertilizer-P added); loads were 1.7 and 9.0 kg ha from the Podzol and intergrade soils, respectively. Soil sampling to 100 cm showed that added P leached throughout the Organic soil profile but was stratified and enriched in the top 15 cm of the Podzol. Poor P sorption capacity (<5%) in the Organic soil, measured as anion storage capacity, and tillage (causing mineralization and P release) in the Organic and intergrade soils were thought to be the main causes of high P loss. It is doubtful that strategies would successfully mitigate these losses to an environmentally acceptable level. However, anion storage capacity could be used to identify marginal soils with high potential for P loss for the purpose of managing risk.

Identification of inorganic and organic species of phosphorus and its bio-availability in nitrifying aerobic granular sludge

Phosphorus (P) recovery from sewage sludge is necessary for a sustainable development of the environment and thus the society due to gradual depletion of non-renewable P resources. Aerobic granular sludge is a promising biotechnology for wastewater treatment, which could achieve P-rich granules during simultaneous nitrification and denitrification processes. This study aimed to disclose the changes in inorganic and organic P species and their correlation with P mobility and bio-availability in aerobic granules. Two identical square reactors were used to cultivate aerobic granules, which were operated for 120 days with influent ammonia nitrogen (NH₄-N) of 100 mg/L before day 60 and then increased to 200 mg/L during the subsequent 60 days (chemical oxygen demand (COD) was kept constant at 600 mg/L). The aerobic granules exhibited excellent COD removal and nitrification efficiency. Results showed that inorganic P (IP) was about 61.4-67.7% of total P (TP) and non-apatite inorganic P (NAIP) occupied 61.9-70.2% of IP in the granules. The enrichment amount of NAIP and apatite P (AP) in the granules had strongly positive relationship with the contents of metal ions, i.e. Fe and Ca, respectively accumulated in the granules. X-ray diffraction (XRD) analysis and solution index calculation demonstrated that hydroxyapatite (Ca₅(PO₄)₃(OH)) and iron phosphate (Fe₇(PO₄)₆) were the major P minerals in the granules. Organic P (OP) content maintained around 7.5 mg per gram of biomass in the aerobic granules during the 120 days' operation. Monoester phosphate (21.8% of TP in extract), diester phosphate (1.8%) and phosphonate (0.1%) were identified as OP species by Phosphorus-31 nuclear magnetic resonance (³¹P NMR). The proportion of NAIP + OP to TP was about 80% in the granules, implying high potentially mobile and bio-available P was stored in the nitrifying aerobic granules. The present results provide a new insight into the characteristics of P species in aerobic granules, which could be helpful for developing P removal and recovery techniques through biological wastewater treatment.

Long-term impact of tillage practices and phosphorus fertilization on soil phosphorus forms as determined by p nuclear magnetic resonance spectroscopy

Conservation tillage practices have become increasingly common in recent years to reduce soil erosion, improve water conservation, and increase soil organic matter. Research suggests that conservation tillage can stratify soil test phosphorus (P), but little is known about the effects on soil organic P. This study was conducted to assess the long-term effects of tillage practices (no-till [NT] and mouldboard plowing) and P fertilization (0 and 35 kg P ha) on the distribution of P species in the soil profile. Soil samples from a long-term corn-soybean rotation experiment in Québec, Canada, were collected from three depths (0-5, 5-10, and 10-20 cm). These samples were analyzed for total P (TP), total C (TC), total N (TN), pH, and Mehlich-3 P (PM3); P forms were characterized with solution phosphorus-31 nuclear magnetic resonance spectroscopy (P-NMR). Results showed a stratification of TP, TC, TN, pH, PM3, and Mehlich-3-extractable aluminum and magnesium under NT management. The PM3 and orthophosphate concentrations were greater at the soil surface (0-5 cm) of the NT-P (soil treatment with 35 kg P ha) treatment. Organic P forms (orthophosphate monoesters, especially -IP, and nucleotides) had accumulated in the deep layer of NT treatment possibly due to preferential movement. We found evidence that the NT system and P fertilization changed the distribution of P forms along the soil profile, potentially increasing soluble inorganic P loss in surface runoff and organic P in drainage and decreasing bioavailability of inorganic and organic P in deeper soil layers.

Global transcriptional responses of the toxic cyanobacterium, Microcystis aeruginosa, to nitrogen stress, phosphorus stress, and growth on organic matter

Whole transcriptome shotgun sequencing (RNA-seq) was used to assess the transcriptomic response of the toxic cyanobacterium Microcystis aeruginosa during growth with low levels of dissolved inorganic nitrogen (low N), low levels of dissolved inorganic phosphorus (low P), and in the presence of high levels of high molecular weight dissolved organic matter (HMWDOM). Under low N, one third of the genome was differentially expressed, with significant increases in transcripts observed among genes within the nir operon, urea transport genes (urtBCDE), and amino acid transporters while significant decreases in transcripts were observed in genes related to photosynthesis. There was also a significant decrease in the transcription of the microcystin synthetase gene set under low N and a significant decrease in microcystin content per Microcystis cell demonstrating that N supply influences cellular toxicity. Under low P, 27% of the genome was differentially expressed. The Pho regulon was induced leading to large increases in transcript levels of the alkaline phosphatase phoX, the Pst transport system (pstABC), and the sphX gene, and transcripts of multiple sulfate transporter were also significantly more abundant. While the transcriptional response to growth on HMWDOM was smaller (5-22% of genes differentially expressed), transcripts of multiple genes specifically associated with the transport and degradation of organic compounds were significantly more abundant within HMWDOM treatments and thus may be recruited by Microcystis to utilize these substrates. Collectively, these findings provide a comprehensive understanding of the nutritional physiology of this toxic, bloom-forming cyanobacterium and the role of N in controlling microcystin synthesis.

Eco-physiological adaptations that favour freshwater cyanobacteria in a changing climate

Climate change scenarios predict that rivers, lakes, and reservoirs will experience increased temperatures, more intense and longer periods of thermal stratification, modified hydrology, and altered nutrient loading. These environmental drivers will have substantial effects on freshwater phytoplankton species composition and biomass, potentially favouring cyanobacteria over other phytoplankton. In this Review, we examine how several cyanobacterial eco-physiological traits, specifically, the ability to grow in warmer temperatures; buoyancy; high affinity for, and ability to store, phosphorus; nitrogen-fixation; akinete production; and efficient light harvesting, vary amongst cyanobacteria genera and may enable them to dominate in future climate scenarios. We predict that spatial variation in climate change will interact with physiological variation in cyanobacteria to create differences in the dominant cyanobacterial taxa among regions. Finally, we suggest that physiological traits specific to different cyanobacterial taxa may favour certain taxa over others in different regions, but overall, cyanobacteria as a group are likely to increase in most regions in the future.

Patterns of activities of root phosphomonoesterase and phosphodiesterase in wetland plants as a function of macrophyte species and ambient phosphorus regime

Phosphorus (P)-limited plants produce higher amounts of root phosphatases, but research has mostly focused on phosphomonoesterases (PMEs). Because phosphate diesters can form a significant proportion of organic P in wetlands, we aimed to determine whether wetland plants produce both root PMEs and root phosphodiesterases (PDEs), and, if so, what factors influence activities of these enzymes. We measured the activities of root PMEs and PDEs colorimetrically in a wide range of macrophytes from natural and P-enriched wetlands. Hydrolyzable P in sediments was analyzed using commercially available PMEs and PDEs. In all species, both root PMEs and PDEs were always present, and their activities were closely correlated. Sedges and broadleaved emergents had the highest activity of both enzymes, while those of floating-leaved plants were the lowest. Redundancy analysis revealed close association between root enzymes and the proportion of monoesterase- and diesterase-hydrolyzable dissolved unreactive P. Both enzymes were positively correlated with root tissue N : P ratio. Both plant and sediment traits were important when explaining differences in enzyme activities. Although the activities are related to ambient P regime, the relationship was not close enough to use root enzymes as reliable predictors of dissolved unreactive P that is hydrolyzed by sediment phosphomono- and diesterases.

Effect of mineral phosphate solubilization on biological nitrogen fixation by diazotrophic cyanobacteria

The ability of two diazotrophic cyanobacteria Westiellopsis prolifica and Anabaena variabilis were examined to solubilize extracellular insoluble tricalcium phosphate (TCP) and Mussorie rock phosphate (MRP). The two strains exhibited a differential response to insoluble forms of phosphorus used. W. prolifica showed better growth in presence of MRP while A. variabilis proliferated better in presence of TCP. Biological nitrogen fixation measured in terms of acetylene reduction (AR) activity showed significant variation among the concentrations of TCP or MRP and time of incubation. W. prolifica and A. variabilis showed maximum AR activity on 14 and 21 days of incubation respectively. In general AR activity in presence of MRP was always less than that in presence of TCP at all concentrations. Among the two cyanobacteria A. variabilis was best in terms of P-solubilization and nitrogen fixation and TCP (20 mg P l(-1)) was the best source of insoluble P rather than MRP or K(2)HPO(4).

Phosphorus release characteristics of different trophic lake sediments under simulative disturbing conditions

The effect of simulative disturbing on phosphorus (P) release characteristics and the differences of the P buffering capacity of different trophic lake sediments were investigated. The magnitudes of the dissolved total phosphorus (DTP), soluble reactive phosphorus (SRP) and dissolved organic phosphorus (DOP) released from the studied sediments increased with the increasing of disturbing intensity. The equilibrium time of the DTP release from the heavily polluted sediments was approximately 16 h, and that from the slightly polluted sediments was 8h. This may be related to the difference of P forms in the different trophic sediments. About 30% of the DTP released from Wuli Lake and Yue Lake was from DOP, about 60% and 50%, respectively, was from Gonghu Lake and East Taihu Lake. DOP was the important fraction of DTP released. The effect of disturbing on P release was related to both disturbing intensity and sediment pollution level. After the disturbing stop, the DTP, SRP and DOP concentrations in the overlying water of the different sediments decreased rapidly within 3, 10 and 3h, respectively, then gradually reached equilibrium at different time for the sediments with different pollution level. The different trophic lake sediments had different P buffering capacity, P buffering capacity of the slightly polluted sediments was lower at the initial lower SRP concentrations and was higher at the initial higher than that of the heavily polluted sediments.

Effects of organic matter on phosphorus release kinetics in different trophic lake sediments and application of transition state theory

Sediments have a significant influence on the overlying water, and phosphorus (P) release from sediments is an important source for the lake eutrophication, particularly in shallow ones. In this study, effects of organic matter on P release from sediments in different trophic lakes from the middle and lower reaches of Yangtze River, China, were investigated, and the release kinetics of different P fractions at different temperature were studied. The results show that the release kinetics of soluble reactive phosphorus (SRP), dissolved organic phosphorus (DOP) and dissolved total phosphorus (DTP) were similar for the studied sediments, the release rate increased rapidly in the initial hours, and it increased gradually after 10h. The release kinetics of SRP, DOP and DTP followed the Power Function model. SRP was the major fraction among the released DTP, while DOP was an important fraction in the heavily polluted sediments. Organic matter restricted the SRP and DTP release while it promoted the DOP release. Both DOP and SRP release processes were endothermic. The thermodynamic properties in the P release kinetics were calculated and discussed.

ATR-FTIR investigation on the complexation of myo-inositol hexaphosphate with aluminum hydroxide

The adsorption isotherm of and the pH effect on the adsorption of myo-inositol hexaphosphate (myo-IP6) on amorphous aluminum hydroxide was investigated. It was found that the adsorption isotherm of myo-IP6 on aluminum hydroxide could be well fitted with the Freundlich isotherm. The amount of myo-IP6 adsorbed remained almost constant in the range of pH 4.0 to 7.0, but it decreased considerably as the initial pH was over 7. The adsorption of myo-IP6 resulted in an increase in the pH level due to the release of OH(-) ions, which suggested that the adsorption of myo-IP6 on aluminum hydroxide was caused by a ligand exchange reaction. ATR-FTIR analysis of myo-IP6 in solution and adsorbed on aluminum hydroxide at different pH were performed. The ATR-FTIR investigation indicated that myo-IP6 was adsorbed onto aluminum hydroxide by forming inner-sphere complexes and adsorption facilitated the deprotonation of phosphate groups. The asymmetric vibration of the PO bond in AlPO(-)(3) appearing at a lower frequency than that in the terminal HPO(-)(3) indicated that Al bound to the O atom not as strongly as the H atom did. The ATR-FTIR investigation and theoretical calculation (with the Gaussian 03 program) revealed that three of the six phosphate groups in myo-IP6 molecules were bound to aluminum hydroxide while the other three remained free when myo-IP6 was adsorbed on aluminum hydroxide.

Phosphorus in fresh and dry dung of grazing dairy cattle, deer, and sheep: sequential fraction and phosphorus-31 nuclear magnetic resonance analyses

Knowledge of phosphorus (P) fractions in dung of animals (dairy cattle, deer, sheep) grazing pasture is important for soil fertility and the potential for P transport in runoff and subsequent surface water quality deterioration. We used sequential fractionation and 31P nuclear magnetic resonance (NMR) spectroscopy to determine P forms in fresh and air-dried (to simulate field conditions during grazing) dung. Sheep dung was richest in P (8 g kg(-1)), and cattle dung poorest (5.5 g kg(-1)). Data for sequential fractionation indicated that most P was extractable by water (15-36%) and bicarbonate (36-45%) in fresh dung, and shifted toward recalcitrant, HCl (12-28%), and residual P forms (15-31%) with drying. Organic P concentration in dung was poor (maximum of 15% of total P), probably due to the poor concentration of phytate in pasture. The 31P NMR spectra of NaOH-EDTA extracts supported this by detecting a low concentration of monoesters (9-19% of total P in extracts), of which phytate is a major component. The 31P NMR data also showed that changes in organic P concentration with drying could be due to the degradation of diesters. Data indicate the decreasing bioavailability of dairy cattle, deer, and sheep dung with drying and the need to consider this effect with respect to P returns for soil fertility and the potential for runoff.

Inositol phosphates in the environment

The inositol phosphates are a group of organic phosphorus compounds found widely in the natural environment, but that represent the greatest gap in our understanding of the global phosphorus cycle. They exist as inositols in various states of phosphorylation (bound to between one and six phosphate groups) and isomeric forms (e.g. myo, D-chiro, scyllo, neo), although myo-inositol hexakisphosphate is by far the most prevalent form in nature. In terrestrial environments, inositol phosphates are principally derived from plants and accumulate in soils to become the dominant class of organic phosphorus compounds. Inositol phosphates are also present in large amounts in aquatic environments, where they may contribute to eutrophication. Despite the prevalence of inositol phosphates in the environment, their cycling, mobility and bioavailability are poorly understood. This is largely related to analytical difficulties associated with the extraction, separation and detection of inositol phosphates in environmental samples. This review summarizes the current knowledge of inositol phosphates in the environment and the analytical techniques currently available for their detection in environmental samples. Recent advances in technology, such as the development of suitable chromatographic and capillary electrophoresis separation techniques, should help to elucidate some of the more pertinent questions regarding inositol phosphates in the natural environment.