Phosphate Uptake Research Articles

Cerium-based sorbent with 100% Ce(III) and high dispersion for enhanced phosphate removal from wastewater

Under the double pressure of eutrophication and phosphorus deficiency, there is an urgent need to remove excess phosphate from wastewater efficiently. Preparing cerium-based materials with excellent application potential inevitably leads to Ce(III) oxidation to Ce(IV), which reduces the phosphate adsorption effect and restricts its development. To solve this problem, we introduced a protective agent and successfully synthesised cerium-modified activated carbon sorbent containing 100 % Ce(III) during the synthesis process. Compared with CeAC without a protecting agent, CeAC-A contained more Ce(III) (100 %) and exchange groups (–OH accounted for 82.76 %), achieving an adsorption capacity of up to 448.57 mg-P/g Ce, improving of 4.3 times. At the same time, the size of the cerium active component was reduced from the micron level to the nanometer level, and the mass transfer rate was significantly improved. In addition, with the enormous specific surface area and well-developed pore structure of activated carbon, it showed high dispersibility, with P/Ce molar ratio as high as 2.03, which is 1.1–4.8 times higher than other cerium-based adsorbents. Phosphate was removed primarily through electrostatic attraction and ligand exchange. In treating municipal wastewater with complex water quality, CeAC-A showed strong selectivity, a wide range of adaptability and easy repeat regeneration, making it a promising adsorbent for phosphate uptake from wastewater.

Characterization and stress-responsive regulation of CmPHT1 genes involved in phosphate uptake and transport in Melon (Cucumis melo L.)

BackgroundPhosphorus (P) deficiency, a major nutrient stress, greatly hinders plant growth. Phosphate (Pi) uptake in plant roots relies on PHT1 family transporters. However, melon (Cucumis melo L.) lacks comprehensive identification and characterization of PHT1 genes, particularly their response patterns under diverse stresses.ResultsThis study identified and analyzed seven putative CmPHT1 genes on chromosomes 3, 4, 5, 6, and 7 using the melon genome. Phylogenetic analysis revealed shared motifs, domain compositions, and evolutionary relationships among genes with close histories. Exon number varied from 1 to 3. Collinearity analysis suggested segmental and tandem duplications as the primary mechanisms for CmPHT1 gene family expansion. CmPHT1;4 and CmPHT1;5 emerged as a tandemly duplicated pair. Analysis of cis-elements in CmPHT1 promoters identified 14 functional categories, including putative PHR1-binding sites (P1BS) in CmPHT1;4, CmPHT1;6, and CmPHT1;7. We identified that three WRKY transcription factors regulated CmPHT1;5 expression by binding to its W-box element. Notably, CmPHT1 promoters harbored cis-elements responsive to hormones and abiotic factors. Different stresses regulated CmPHT1 expression differently, suggesting that the adjusted expression patterns might contribute to plant adaptation.ConclusionsThis study unveils the characteristics, evolutionary diversity, and stress responsiveness of CmPHT1 genes in melon. These findings lay the foundation for in-depth investigations into their functional mechanisms in Cucurbitaceae crops.

One-step microwave-assisted synthesis of MgO-modified magnetic biochar for enhanced removal of lead and phosphate from wastewater: Performance and mechanisms

Herein, magnesium oxide (MgO) and ferroferric oxide (Fe3O4) functionalized biochar (MgO@MBC) was synthetized through one-step pyrolysis method, which was used to decontaminate lead (Pb) and phosphate in contaminated water. Characterization results exhibited that MgO and Fe3O4 particles were successfully loaded on MgO@MBC, and the magnetism of MgO@MBC was in favor of recycling materials. Experimental results showed that MgO@MBC possessed outstanding adsorption performance with 556.62/303.08 mg/g for Pb(II)/phosphate. Furthermore, MgO@MBC had excellent anti-interference performance under the coexistence of various ions, and superior reusability with over 82 % adsorption efficiency for Pb(II)/phosphate after four regeneration cycles. It demonstrated that the high-efficiency capacity of Pb(II) adsorbed on MgO@MBC was attributable to complexation, electrostatic attraction, precipitation, and pore-filling, while the efficient uptake of phosphate was due to precipitation, pore-filling, and ligand exchange. Based on the above analysis, MgO@MBC was believed to be an outstanding adsorbent for remediating Pb(II)/phosphate wastewater.

SlDELLA interacts with SlPIF4 to regulate arbuscular mycorrhizal symbiosis and phosphate uptake in tomato.

Arbuscular mycorrhizal symbiosis (AMS), a complex and delicate process, is precisely regulated by a multitude of transcription factors. PHYTOCHROME-INTERACTING FACTORS (PIFs) are critical in plant growth and stress responses. However, the involvement of PIFs in AMS and the molecular mechanisms underlying their regulator functions have not been well elucidated. Here, we show that SlPIF4 negatively regulates the arbuscular mycorrhizal fungi (AMF) colonization and AMS-induced phosphate uptake in tomato. Protein-protein interaction studies suggest that SlDELLA interacts with SlPIF4, reducing its protein stability and inhibiting its transcriptional activity towards downstream target genes. This interaction promotes the accumulation of strigolactones (SLs), facilitating AMS development and phosphate uptake. As a transcription factor, SlPIF4 directly transcriptionally regulates genes involved in SLs biosynthesis, including SlCCD7, SlCDD8, and SlMAX1, as well as the AMS-specific phosphate transporter genes PT4 and PT5. Collectively, our findings uncover a molecular mechanism by which the SlDELLA-SlPIF4 module regulates AMS and phosphate uptake in tomato. We clarify a molecular basis for how SlPIF4 interacts with SLs to regulate the AMS and propose a potential strategy to improve phosphate utilization efficiency by targeting the AMS-specific phosphate transporter genes PTs.

Astrocytes modulate brain phosphate homeostasis via polarized distribution of phosphate uptake transporter PiT2 and exporter XPR1

Aberrant inorganic phosphate (Pi) homeostasis causes brain calcification and aggravates neurodegeneration, but the underlying mechanism remains unclear. Here, we found that primary familial brain calcification (PFBC)-associated Pi transporter genes Pit2 and Xpr1 were highly expressed in astrocytes, with importer PiT2 distributed over the entire astrocyte processes and exporter XPR1 localized to astrocyte end-feet on blood vessels. This polarized PiT2 and XPR1 distribution endowed astrocyte with Pi transport capacity competent for brain Pi homeostasis, which was disrupted in mice with astrocyte-specific knockout (KO) of either Pit2 or Xpr1. Moreover, we found that Pi uptake by PiT2, and its facilitation by PFBC-associated galactosidase MYORG, were required for the high Pi transport capacity of astrocytes. Finally, brain calcification was suppressed by astrocyte-specific PiT2 re-expression in Pit2-KO mice. Thus, astrocyte-mediated Pi transport is pivotal for brain Pi homeostasis, and elevating astrocytic Pi transporter function represents a potential therapeutic strategy for reducing brain calcification.

Mechanical activation of a natural calcite for enhanced orthophosphate sorption

We examined the effect of dry grinding on the properties of a calcite material and its sorption behaviour with respect to orthophosphate (OP). Limestone was ground in a planetary ball mill for 30 min using sample:ball mass ratio of 5:1 and grinding speed of 250–550 rpm. Specific surface area linearly developed from 7.2 m2 g-1 (initial material) to 15.6 m2 g-1 (550 rpm). Ground samples showed slightly lower content of calcite compared to the initial material (94.3–94.6 % vs 98.7 %), without evidence of an aragonite-like phase being formed, suggesting amorphization. Crystallite size in the samples linearly declined from 597 to 170 Å (initial material vs 550 rpm). Reactivity of limestone increased leading to higher dissolution with however only minor rise in the solution pH. Grinding distinctly enhanced maximum OP uptake from 14 % (initial material) to 60–92 % (250–550 rpm). Sorption kinetics accelerated with the grinding speed: reaction time needed to remove 50 % of the OP was reduced from 8 h (250 rpm) to only 5 h (550 rpm). This was due to increased surface area and enhanced reactivity. Mechanical processing of limestones by intense grinding is a promising solution to gain easily available, safe and relatively efficient calcite material for P control for environmental applications.

The cytoplasmic phosphate level has a central regulatory role in the phosphate starvation response of Caulobacter crescentus

In bacteria, the availability of environmental inorganic phosphate is typically sensed by the conserved PhoR-PhoB two-component signal transduction pathway, which uses the flux through the PstSCAB phosphate transporter as a readout of the extracellular phosphate level to control phosphate-responsive genes. While the sensing of environmental phosphate is well-investigated, the regulatory effects of cytoplasmic phosphate are unclear. Here, we disentangle the physiological and transcriptional responses of Caulobacter crescentus to changes in the environmental and cytoplasmic phosphate levels by uncoupling phosphate uptake from the activity of the PstSCAB system, using an additional, heterologously produced phosphate transporter. This approach reveals a two-pronged response of C. crescentus to phosphate limitation, in which PhoR-PhoB signaling mostly facilitates the utilization of alternative phosphate sources, whereas the cytoplasmic phosphate level controls the morphological and physiological adaptation of cells to growth under global phosphate limitation. These findings open the door to a comprehensive understanding of phosphate signaling in bacteria.

Total alkalinity change: The perspective of phytoplankton stoichiometry

AbstractMany biogeochemical processes change total alkalinity: this has been reported for carbonate precipitation and dissolution, uptake and release of various nitrogen‐containing compounds, uptake of phosphate, sulfate reduction combined with methane oxidation. However, the list is not exhaustive. Here we discuss additional processes, namely the uptake of Mg, K, Ca by phytoplankton, and calculate their contribution based on the explicit conservative expression for TA and an extended (compared to Redfield's C : N : P) stoichiometry of phytoplankton. These additional contributions are of the same order of magnitude as that of phosphate uptake and thus much smaller than the contribution from nitrate uptake and of opposite sign to the contribution by nitrate and phosphate uptake.

Phosphate overplus response in Chlamydomonas reinhardtii: Polyphosphate dynamics to monitor phosphate uptake and turnover

There is widespread interest in using microalgae to sustainably control and recover nutrients from wastewater to meet environmental discharge consents and recycle nutrients into agriculture or other applications. Like bacteria and yeasts, microalgae exhibit a phosphate (Pi) overplus response when Pi-deprived cells are resupplied with this nutrient. Quantitative and qualitative methods were used to follow the dynamics of polyP synthesis and turnover in four strains of Chlamydomonas reinhardtii during Pi deprivation followed by nutrient resupply (either as Pi or complete media). The lowest level of in-cell polyP during Pi deprivation, which correlates with the cessation of growth, is the key parameter for timing Pi resupply to maximise the Pi overplus response. Pi deprivation beyond this point leads to a reduced Pi uptake and reduced overplus response. Additional nutrients do not affect the magnitude of the overplus response but are important for continued growth and maximal Pi removal from the media. One strain tested shows enhanced Pi uptake and increased polyP and total in-cell P, suggesting that strain selection is also important. Although polyP levels are maintained after Pi resupply, the polymer is dynamically remodelled. Inositol hexakisphosphate (IP6) increases during this time but does not precede polyP synthesis as predicted by a model where inositol phosphates switch on polyP synthesis. Tracking polyP allows the correct time for nutrient resupply to be determined and therefore a reproducible Pi overplus response to be achieved. Depending on whether maximum cellular P content or maximum Pi removal is desired different strategies may be required. Pi deprivation until growth cessation then resupplying complete nutrients gives the best trade-off between high in-cell P accumulation, high Pi removal and algal biomass growth. This work provides robust measurements of quantitative physiological parameters, which allows reproducibility in laboratory studies and provides design parameters for algal-based nutrient recovery systems from waste waters.

Homeostatic coordination of cellular phosphate uptake and efflux requires an organelle-based receptor for the inositol pyrophosphate IP8

Phosphate (Pi) serves countless metabolic pathways and is involved in macromolecule synthesis, energy storage, cellular signaling, and bone maintenance. Herein, we describe the coordination of Pi uptake and efflux pathways to maintain mammalian cell Pi homeostasis. We discover that XPR1, the presumed Pi efflux transporter, separately supervises rates of Pi uptake. This direct, regulatory interplay arises from XPR1 being a binding partner for the Pi uptake transporter PiT1, involving a predicted transmembrane helix/extramembrane loop in XPR1, and its hitherto unknown localization in a subset of intracellular LAMP1-positive puncta (named "XLPVs"). A pharmacological mimic of Pi homeostatic challenge is sensed by the inositol pyrophosphate IP8, which functionalizes XPR1 to respond in a temporally hierarchal manner, initially adjusting the rate of Pi efflux, followed subsequently by independent modulation of PiT1 turnover to reset the rate of Pi uptake. These observations generate a unifying model of mammalian cellular Pi homeostasis, expanding opportunities for therapeutic intervention.

Biodegradable chelator GLDA intercalated magnesium/aluminum layered double hydroxides for efficient phosphate capture and removal from wastewater

Phosphate removal and recovery from wastewater play a vital role in controlling water eutrophication and facilitating resource recycling. Adsorbents of layered double hydroxides (LDHs) exhibit promising potential in the removal of phosphate; however, the removal efficiency often suffers insufficient as easy aggregation and inevitable loss of LDHs. Herein, a novel N, N–bis (carboxymethyl)–L–glutamic acid intercalated magnesium–aluminum LDH (GLDA@MgAl–LDH) were successfully synthesized. Intercalating with GLDA spawned dual functionality, i.e., the layer spacing expansion elevated the loading of phosphate, while GLDA also acted as additional binding sites toward phosphate. A higher phosphate capture (＞90%) was obtained in pH 5.0–8.0. Phosphate uptake was predominantly observed within the first1h, reaching equilibrium in approximately 4 h. The maximum adsorption capacity of 44.17 mg g–1 was attained for GLDA@MgAl–LDH at pH 6.70, which are far higher than that of pristine MgAl–LDH. GLDA@MgAl–LDH also had the excellent stability and reusability in five adsorption/desorption experiments. The GLDA@MgAl–LDH demonstrated significant efficacy in treating actual phosphate-containing wastewater in the fixed–bed adsorption column. Spectroscopic analysis, in conjunction with density functional theory, elucidated that GLDA intercalation enhanced the adsorption efficiency of MgAl–LDH. The key mechanisms facilitating phosphate removal included electrostatic attraction, anion and ligand exchange, and surface complexation. The above results highlight that GLDA@MgAl–LDH could serve as a promising and environmentally friendly candidate for phosphate treatment from the real wastewater.

The phosphate starvation response regulator PHR2 antagonizes arbuscule maintenance in Medicago.

Phosphate starvation response (PHR) transcription factors play essential roles in regulating phosphate uptake in plants through binding to the P1BS cis-element in the promoter of phosphate starvation response genes. Recently, PHRs were also shown to positively regulate arbuscular mycorrhizal colonization in rice and lotus by controlling the expression of many symbiotic genes. However, their role in arbuscule development has remained unclear. In Medicago, we previously showed that arbuscule degradation is controlled by two SPX proteins that are highly expressed in arbuscule-containing cells. Since SPX proteins bind to PHRs and repress their activity in a phosphate-dependent manner, we investigated whether arbuscule maintenance is also regulated by PHR. Here, we show that PHR2 is a major regulator of the phosphate starvation response in Medicago. Knockout of phr2 showed reduced phosphate starvation response, symbiotic gene expression, and fungal colonization levels. However, the arbuscules that formed showed less degradation, suggesting a negative role for PHR2 in arbuscule maintenance. This was supported by the observation that overexpression of PHR2 led to enhanced degradation of arbuscules. Although many arbuscule-induced genes contain P1BS elements in their promoters, we found that the P1BS cis-elements in the promoter of the symbiotic phosphate transporter PT4 are not required for arbuscule-containing cell expression. Since both PHR2 and SPX1/3 negatively affect arbuscule maintenance, our results indicate that they control arbuscule maintenance partly via different mechanisms. While PHR2 potentiates symbiotic gene expression and colonization, its activity in arbuscule-containing cells needs to be tightly controlled to maintain a successful symbiosis in Medicago.

Assessing the nitrate and phosphate uptake kinetics potential and growth performance of Gracilaria corticata var. cylindrica in shrimp farm water (SFW)

Gracilaria corticata var. cylindrica (GCC) was studied as a biofilter in shrimp farm water (SFW) and its growth and biochemical attributes in the medium were evaluated. GCC showed significant nutrient absorption from SFW, with maximum nitrate and phosphate uptake observed after the first 48 h. Nitrate depletion happened faster than phosphate, thus showing a higher affinity for nitrate uptake (78.4% removal) by GCC. Nutrient uptake kinetics followed the Michaelis–Menten curve, with Vmax values of 43.16 μM g dw−1 h−1 for nitrate and 67.50 μM g dw−1 h−1 for phosphate. Also, GCC’s low Km values (12.53 µM for nitrate, 1.91 µM for phosphate) indicated efficient nutrient utilization. GCC showed rapid growth in SFW, with a daily growth rate of 2.93 ± 0.19% d−1, comparable to the commercial MP1 media (3.54 ± 0.19% d−1) and greater to seawater (2.23 ± 0.13% d−1). Proximate analysis revealed consistent biochemical compositions across all three media, with carbohydrate and protein contents of 2.24 ± 0.41% and 0.76 ± 0.12%, respectively, in SFW. Pigment analysis revealed that pigment concentrations varied, with SFW having the greatest R-PE concentration (182.25 ± 32.77 µg g−1), followed by MP1 media and saltwater. R-PC concentrations followed a similar pattern, with SFW having the greatest concentration (85.73 ± 19.33 µg g−1). These findings highlight GCC’s potential as an efficient biofilter for reducing nitrate and phosphate levels in SFW, therefore offering a sustainable solution for aquaculture effluent management and the potential integration of GCC into shrimp farming practices.

Attenuated down-regulation of PHOSPHATE TRANSPORTER1 genes as a mechanism for phosphorus sensitivity in phosphorus-efficient Hakea prostrata (Proteaceae)

Abstract Background and aims Phosphorus (P) is an essential plant nutrient and integral for crop yield. However, plants adapted to P-impoverished environments, such as Hakea prostrata (Proteaceae), are often sensitive to P supplies that would be beneficial to other plants. The strategies for phosphate uptake and transport in P-sensitive species have received little attention. Methods Using a recently-assembled transcriptome of H. prostrata, we identified 10 putative members of the PHOSPHATE TRANSPORTER1 (PHT1) gene family, which is responsible for inorganic phosphate (Pi) uptake and transport in plants. We examined plant growth, organ P concentrations and the transcript levels for the eight PHT1 members that were expressed in roots of H. prostrata at Pi supplies ranging from P-impoverished to P-excess. Key results Hakea prostrata plants suppressed cluster root growth above ecologically-relevant Pi supplies, whilst non-cluster root mass ratios were constant. Root P concentrations increased with increasing Pi supply. Of the eight H. prostrata PHT1 genes tested, four had relatively high transcript amounts in young roots suggesting important roles in Pi uptake; however, a maximum five-fold difference in expression between P-impoverished and P-excess conditions indicated a low P-responsiveness for these genes. The HpPHT1;8 and HpPHT1;9 genes were paralogous to Pi-responsive Arabidopsis thaliana PHT1;8 and PHT1;9 orthologues involved in root-to-shoot translocation of P, but only HpPHT1;9 was P responsive. Conclusions An attenuated ability of H. prostrata to regulate PHT1 expression in response to Pi supply is likely responsible for its low capacity to control P uptake and contributes to its high P sensitivity.

Phosphate uptake in PhoX: Molecular mechanisms

PhoX is a high-affinity phosphate binding protein, present in Xanthomonas citri, a phytopathogen responsible for the citrus canker disease. Performing molecular dynamics simulations and different types of computational analyses, we study the molecular mechanisms at play in relation to phosphate binding, revealing the global functioning of the protein: PhoX naturally oscillates along its global normal modes, which allow it to explore both bound and unbound conformations, eventually attracting a nearby negative phosphate ion to the highly positive electrostatic potential on its surface, particularly close to the binding pocket. There, several hydrogen bonds are formed with the two main domains of the structure. Phosphate creates, in this way, a strong bridge that connects the domains, keeping itself between them, in a tight closed conformation, explaining its high binding affinity.

Phosphate Uptake and Its Relation to Arsenic Toxicity in Lactobacilli.

The use of probiotic lactobacilli has been proposed as a strategy to mitigate damage associated with exposure to toxic metals. Their protective effect against cationic metal ions, such as those of mercury or lead, is believed to stem from their chelating and accumulating potential. However, their retention of anionic toxic metalloids, such as inorganic arsenic, is generally low. Through the construction of mutants in phosphate transporter genes (pst) in Lactiplantibacillus plantarum and Lacticaseibacillus paracasei strains, coupled with arsenate [As(V)] uptake and toxicity assays, we determined that the incorporation of As(V), which structurally resembles phosphate, is likely facilitated by phosphate transporters. Surprisingly, inactivation in Lc. paracasei of PhoP, the transcriptional regulator of the two-component system PhoPR, a signal transducer involved in phosphate sensing, led to an increased resistance to arsenite [As(III)]. In comparison to the wild type, the phoP strain exhibited no differences in the ability to retain As(III), and there were no observed changes in the oxidation of As(III) to the less toxic As(V). These results reinforce the idea that specific transport, and not unspecific cell retention, plays a role in As(V) biosorption by lactobacilli, while they reveal an unexpected phenotype for the lack of the pleiotropic regulator PhoP.

Effects of salinity on glycerol conversion and biological phosphorus removal by aerobic granular sludge

Industrial wastewater often has high levels of salt, either due to seawater or e.g. sodium chloride (NaCl) usage in the processing. Previous work indicated that aerobic granular sludge (AGS) is differently affected by seawater or saline water at similar osmotic strength. Here we investigate in more detail the impact of NaCl concentrations and seawater on the granulation and conversion processes for AGS wastewater treatment. Glycerol was used as the carbon source since it is regularly present in industrial wastewaters, and to allow the evaluation of microbial interactions that better reflect real conditions. Long-term experiments were performed to evaluate and compare the effect of salinity on granulation, anaerobic conversions, phosphate removal, and the microbial community. Smooth and stable granules as well as enhanced biological phosphorus removal (EBPR) were achieved up to 20 g/L NaCl or when using seawater. However, at NaCl levels comparable to seawater strength (30 g/L) incomplete anaerobic glycerol uptake and aerobic phosphate uptake were observed, the effluent turbidity increased, and filamentous granules began to appear. The latter is likely due to the direct aerobic growth on the leftover substrate after the anaerobic feeding period. In all reactor conditions, except the reactor with 30 g/L NaCl, Ca. Accumulibacter was the dominant microorganism. In the reactor with 30 g/L NaCl, the relative abundance of Ca. Accumulibacter decreased to ≤1 % and an increase in the genus Zoogloea was observed. Throughout all reactor conditions, Tessaracoccus and Micropruina, both actinobacteria, were present which were likely responsible for the anaerobic conversion of glycerol into volatile fatty acids. None of the glycerol metabolizing proteins were detected in Ca. Accumulibacter which supports previous findings that glycerol can not be directly utilized by Ca. Accumulibacter. The proteome profile of the dominant taxa was analysed and the results are further discussed. The exposure of salt-adapted biomass to hypo-osmotic conditions led to significant trehalose and PO43−-P release which can be related to the osmoregulation of the cells. Overall, this study provides insights into the effect of salt on the operation and stability of the EBPR and AGS processes. The findings suggest that maintaining a balanced cation ratio is likely to be more important for the operational stability of EBPR and AGS systems than absolute salt concentrations.

Magnetic field-assisted adsorption of phosphate on biochar loading amorphous Zr–Ce (carbonate) oxide composite

For metal-based phosphate adsorbents, the dispersity and utilization of surface metal active sites are crucial factors in their adsorption performance and synthesis cost. In this study, a biochar material modified with amorphous Zr–Ce (carbonate) oxides (BZCCO-13) was synthesized for the phosphate uptake, and the adsorption process was enhanced by magnetic field. The beside-magnetic field was shown to have a better influence than under-magnetic field on adsorption, with maximum adsorption capacities (123.67 mg P/g) 1.14-fold greater than that without magnetic field. The beside-magnetic field could also accelerate the adsorption rate, and the time to reach 90% maximum adsorption capacity decreased by 83%. BZCCO-13 has a wide range of application pHs from 5.0 to 10.0, with great selectivity and reusability. The results of XPS and ELNES showed that the "magnetophoresis" of Ce3+ under the magnetic field was the main reason for the enhanced adsorption performance. In addition, increased surface roughness, pore size and oxygen vacancies, enhanced mass transfer by Lorentz force under a magnetic field, all beneficially influenced the adsorption process. The mechanism of phosphate adsorption by BZCCO-13 could be attributed to electrostatic attraction and CO32–dominated ligand exchange. This study not only provided an effective strategy for designing highly effective phosphate adsorbents, but also provides a new light on the application of rare earth metal-based adsorbent in magnetic field.

Biogeochemical Fluxes of Nickel in the Global Oceans Inferred From a Diagnostic Model

AbstractNickel (Ni) is a micronutrient that plays a role in nitrogen uptake and fixation in the modern ocean and may have affected rates of methanogenesis on geological timescales. Here, we present the results of a diagnostic model of global ocean Ni fluxes which addresses key questions about marine Ni cycling. Sparsely available observations of Ni concentration are first extrapolated into a global gridded climatology using tracers with better observational coverage such as macronutrients, and testing three different machine learning techniques. The physical transport of Ni is then estimated using the ocean circulation inverse model (OCIM2), revealing regions of net convergence or divergence. These diagnostics are not based on any assumption about Ni biogeochemical cycling, but their spatial patterns can be used to infer where biogeochemical processes such as biological Ni uptake and regeneration take place. Although Ni and silicate (Si) have similar concentration patterns in the ocean, we find that the spatial pattern of Ni uptake in the surface ocean is similar to phosphate (P) uptake but not to silicate (Si) uptake. This suggests that their similar distributions arise from different biogeochemical mechanisms, consistent with other evidence showing that Ni is not incorporated into diatom frustules. We find that Ni:P ratios at uptake do not decrease as Ni concentrations approach 2 nM, which challenges the hypothesis of a ∼2 nM pool of non‐bioavailable Ni in the surface ocean. Finally, we find that the net regeneration of Ni occurs deeper in the ocean than for P, though not as deeply as for Si.

Influence of operation sequences on phosphorus recovery by polyphosphate-accumulating organisms biofilm: Performance, kinetics and metabolic response

Two biofilm sequencing batch reactors (BSBRs) were conducted under alternating aerobic/anaerobic (Ae/An) sequence and alternating anaerobic/aerobic (An/Ae) sequence to investigate the effects of operation sequences on phosphorus removal and recovery performance. The Ae/An BSBR had advantages in phosphate enrichment, phosphorus concentration of enrichment solution can reach 99.08 mg/L. While An/Ae BSBR exhibited a higher kinetic rate for phosphate uptake and release up to 0.48 mmol/gVSS. In An/Ae BSBR, the remarkable increase of phosphate concentration in aerobic stage put a great strain on the phosphate uptake of biofilms that led to an increase of phosphorus accumulation in the biofilm (Pbiofilm). However, the poly-P proportion in TPbiofilm decreased which triggered the metabolisim of polyphosphate accumulating organisms (PAOs) shifting from polyphosphate accumulating metabolism (PAM) to glycogen accumulating metabolism (GAM) and suppressed the phosphorus enrichment performance of the An/Ae BSBR. The phosphate uptake rate (PUR) of biofilms was in alignment with the bulk phosphate concentration. PAOs were dominated by Rhodoplanes and Saprospiraceae in the Ae/An BSBR, whereas Thiothrix was predominant in the An/Ae BSBR. Notably, the Candidatus Competibacter, considered as a denitrifying glycogen accumulating organisms (DGAOs), showed a dominant proportion in the microbial community of both BSBRs. The higher expression of actP in the An/Ae system indicated a greater capacity for the uptake of acetate, while the Ae/An system was is more adept for degrading acetate represented by the higher relative abundance of ackA, pta and acsA genes The high phosphorus loading in the An/Ae system suppressed the ppk expression but enhanced the ppx expression.