Fluorometric quantification of polyphosphate in environmental plankton samples: extraction protocols, matrix effects, and nucleic acid interference

Inorganic polyphosphate: from basic research to diagnostic and therapeutic opportunities in ALS/FTD

Inorganic polyphosphate (polyP) is a simple, negatively charged biopolymer with chain lengths ranging from just a few to over a thousand ortho-phosphate (Pi) residues. polyP is detected in every cell type across all organisms in nature thus far analyzed. Despite its structural simplicity, polyP has been shown to play important roles in a remarkably broad spectrum of biological processes, including blood coagulation, bone mineralization and inflammation. Furthermore, polyP has been implicated in brain function and the neurodegenerative diseases amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer's disease and Parkinson's disease. In this review, we first address the challenges associated with identifying mammalian polyP metabolizing enzymes, such as Nudt3, and quantifying polyP levels in brain tissue, cultured neural cells and cerebrospinal fluid. Subsequently, we focus on recent studies that unveil how the excessive release of polyP by human and mouse ALS/FTD astrocytes contributes to these devastating diseases by inducing hyperexcitability, leading to motoneuron death. Potential implications of elevated polyP levels in ALS/FTD patients for innovative diagnostic and therapeutic approaches are explored. It is emphasized, however, that caution is required in targeting polyP in the brain due to its diverse physiological functions, serving as an energy source, a chelator for divalent cations and a scaffold for amyloidogenic proteins. Reducing polyP levels, especially in neurons, might thus have adverse effects in brain functioning. Finally, we discuss how activated mast cells and platelets also can significantly contribute to ALS progression, as they can massively release polyP.

Membrane lipid remodeling and autophagy to cope with phosphorus deficiency in the dinoflagellate Prorocentrum shikokuense

Dinoflagellates, which are responsible for more than 80% of harmful algal blooms in coastal waters, are competitive in low-phosphate environments. However, the specific acclimated phosphorus strategies to adapt to phosphorus deficiency in dinoflagellates, particularly through intracellular phosphorus metabolism, remain largely unknown. Comprehensive physiological, biochemical, and transcriptomic analyses were conducted to investigate intracellular phosphorus modulation in a model dinoflagellate, Prorocentrum shikokuense, with a specific focus on membrane lipid remodeling and autophagy in response to phosphorus deficiency. Under phosphorus deficiency, P. shikokuense exhibited a preference to spare phospholipids with nonphospholipids. The major phospholipid classes of phosphatidylcholine and phosphatidylethanolamine decreased in content, whereas the betaine lipid class of diacylglyceryl carboxyhydroxymethylcholine increased in content. Furthermore, under phosphorus deficiency, P. shikokuense induced autophagy as a mechanism to conserve and recycle cellular phosphorus resources. The present study highlights the effective modulation of intracellular phosphorus in P. shikokuense through membrane phospholipid remodeling and autophagy and contributes to a comprehensive understanding of the acclimation strategies to low-phosphorus conditions in dinoflagellates.

Toolkit for cellular studies of mammalian mitochondrial inorganic polyphosphate

Introduction: Inorganic polyphosphate (polyP) is an ancient polymer which is extremely well-conserved throughout evolution, and found in every studied organism. PolyP is composed of orthophosphates linked together by high-energy bonds, similar to those found in ATP. The metabolism and the functions of polyP in prokaryotes and simple eukaryotes are well understood. However, little is known about its physiological roles in mammalian cells, mostly due to its unknown metabolism and lack of systematic methods and effective models for the study of polyP in these organisms. Methods: Here, we present a comprehensive set of genetically modified cellular models to study mammalian polyP. Specifically, we focus our studies on mitochondrial polyP, as previous studies have shown the potent regulatory role of mammalian polyP in the organelle, including bioenergetics, via mechanisms that are not yet fully understood. Results: Using SH-SY5Y cells, our results show that the enzymatic depletion of mitochondrial polyP affects the expression of genes involved in the maintenance of mitochondrial physiology, as well as the structure of the organelle. Furthermore, this depletion has deleterious effects on mitochondrial respiration, an effect that is dependent on the length of polyP. Our results also show that the depletion of mammalian polyP in other subcellular locations induces significant changes in gene expression and bioenergetics; as well as that SH-SY5Y cells are not viable when the amount and/or the length of polyP are increased in mitochondria. Discussion: Our findings expand on the crucial role of polyP in mammalian mitochondrial physiology and place our cell lines as a valid model to increase our knowledge of both mammalian polyP and mitochondrial physiology.

Variation in intracellular polyphosphate and associated gene expression in response to different phosphorus conditions in the dinoflagellate Karenia mikimotoi

Polyphosphate (polyP) has long been recognized as a crucial intracellular reservoir for phosphorus in microorganisms. However, the dynamics of polyP and its regulatory mechanism in eukaryotic phytoplankton in response to variations in external phosphorus conditions remain poorly understood. A comprehensive investigation was conducted to examine the intracellular polyP-associated metabolic response of the dinoflagellate Karenia mikimotoi, a harmful algal bloom species, through integrated physiological, biochemical, and transcriptional analyses under varying external phosphorus conditions. Comparable growth curves and Fv/Fm between phosphorus-replete conditions and phosphorus-depleted conditions suggested that K. mikimotoi has a strong capability to mobilize the intracellular phosphorus pool for growth under phosphorus deficiency. Intracellular phosphate (IPi) and polyP contributed approximately 6-23 % and 1-3 %, respectively, to the overall particulate phosphorus (PP) content under different phosphorus conditions. The significant decrease in PP and increase in polyP:PP suggested that cellular phosphorus components other than polyP are preferred for utilization under phosphorus deficiency. Genes involved in polyP synthesis and hydrolysis were upregulated to maintain phosphorus homeostasis in K. mikimotoi. These findings provide novel insights into the specific cellular strategies for phosphorus storage and the transcriptional response in intracellular polyP metabolism in K. mikimotoi. Additionally, these results also indicate that polyP may not play a crucial role in cellular phosphorus storage in phytoplankton, at least in dinoflagellates.

Isolation of phosphorus-hyperaccumulating microalgae from revolving algal biofilm (RAB) wastewater treatment systems

Excess phosphorus (P) in wastewater effluent poses a serious threat to aquatic ecosystems and can spur harmful algal blooms. Revolving algal biofilm (RAB) systems are an emerging technology to recover P from wastewater before discharge into aquatic ecosystems. In RAB systems, a community of microalgae take up and store wastewater P as polyphosphate as they grow in a partially submerged revolving biofilm, which may then be harvested and dried for use as fertilizer in lieu of mined phosphate rock. In this work, we isolated and characterized a total of 101 microalgae strains from active RAB systems across the US Midwest, including 82 green algae, 9 diatoms, and 10 cyanobacteria. Strains were identified by microscopy and 16S/18S ribosomal DNA sequencing, cryopreserved, and screened for elevated P content (as polyphosphate). Seven isolated strains possessed at least 50% more polyphosphate by cell dry weight than a microalgae consortium from a RAB system, with the top strain accumulating nearly threefold more polyphosphate. These top P-hyperaccumulating strains include the green alga Chlamydomonas pulvinata TCF-48 g and the diatoms Eolimna minima TCF-3d and Craticula molestiformis TCF-8d, possessing 11.4, 12.7, and 14.0% polyphosphate by cell dry weight, respectively. As a preliminary test of strain application for recovering P, Chlamydomonas pulvinata TCF-48 g was reinoculated into a bench-scale RAB system containing Bold basal medium. The strain successfully recolonized the system and recovered twofold more P from the medium than a microalgae consortium from a RAB system treating municipal wastewater. These isolated P-hyperaccumulating microalgae may have broad applications in resource recovery from various waste streams, including improving P removal from wastewater.

Inorganic polyphosphate accumulation protects a marine, filamentous cyanobacterium, Anabaena torulosa against uranium toxicity

The intricate dynamics of inorganic polyphosphate (polyP) in response to phosphorus (P) limitation and metal exposure typical of contaminated aquatic environments is poorly understood. Cyanobacteria are important primary producers in aquatic environments that are exposed to P stringency as well as metal contamination. There is a growing concern regarding migration of uranium, generated as a result of anthropogenic activities, into the aquatic environments owing to high mobility and solubility of stable aqueous complexes of uranyl ions. The polyP metabolism in cyanobacteria in context of uranium (U) exposure under P limitation has hardly been explored. In this study, we analyzed the polyP dynamics in a marine, filamentous cyanobacterium Anabaena torulosa under combination of variable phosphate concentrations (overplus and deficient) and uranyl exposure conditions typical of marine environments. Polyphosphate accumulation (polyP⁺) or deficient (polyP^-) conditions were physiologically synthesized in the A. torulosa cultures and were ascertained by (a) toulidine blue staining followed by their visualization using bright field microscopy and (b) scanning electron microscopy in combination with energy dispersive X-ray spectroscopy (SEM/EDX). On exposure to 100 μM of uranyl carbonate at pH 7.8, it was observed that the growth of polyP⁺ cells under phosphate limitation was hardly affected and these cells exhibited larger amounts of uranium binding as compared to polyP^- cells of A. torulosa. In contrast, the polyP^- cells displayed extensive lysis when exposed to similar U exposure. Our findings suggest that polyP accumulation played an important role in conferring uranium tolerance in the marine cyanobacterium, A. torulosa. The polyP-mediated uranium tolerance and binding could serve as a suitable strategy for remediation of uranium contamination in aquatic environments.

Comparison of photosynthetic responses between haptophyte Phaeocystis globosa and diatom Skeletonema costatum under phosphorus limitation

The diatom Skeletonema costatum and the haptophyte Phaeocystis globosa often form blooms in the coastal waters of the South China Sea. Skeletonema costatum commonly dominates in nutrient enrichment coastal waters, whereas P. globosa starts flourishing after the diatom blooms when phosphorus (P) is limited. Therefore, P limitation was proposed to be a critical factor affecting diatom-haptophyte transition. To elucidate the tolerance to P limitation in P. globosa compared with S. costatum, the effect of P limitation on their photosystem II (PSII) performance was investigated and their photosynthesis acclimation strategies in response to P limitation were evaluated. P limitation did not affect the growth of P. globosa over 7 days but decreased it for S. costatum. Correspondingly, the PSII activity of S. costatum was significantly inhibited by P limitation. The decline in PSII activity in S. costatum under P limitation was associated with the impairment of the oxygen-evolving complex (the donor side of PSII), the hindrance of electron transport from Q_A ^- to Q_B (the acceptor side of PSII), and the inhibition of electron transport to photosystem I (PSI). The 100% decrease in D1 protein level of S. costatum after P limitation for 6 days and PsbO protein level after 2 days of P limitation were attributed to its enhanced photoinhibition. In contrast, P. globosa maintained its photosynthetic activity with minor impairment of the function of PSII. With accelerated PSII repair and highly increased non-photochemical quenching (NPQ), P. globosa can avoid serious PSII damage under P limitation. On the contrary, S. costatum decreased its D1 restoration under P limitation, and the maximum NPQ value in S. costatum was only one-sixth of that in P. globosa. The present work provides extensive evidence that a close interaction exists between the tolerance to P limitation and photosynthetic responses of S. costatum and P. globosa.

Acclimation of Nodularia spumigena CCY9414 to inorganic phosphate limitation - Identification of the P-limitation stimulon via RNA-seq

Nodularia spumigena is a toxic, filamentous cyanobacterium capable of fixing atmospheric N₂, which is often dominating cyanobacterial bloom events in the Baltic Sea and other brackish water systems worldwide. Increasing phosphate limitation has been considered as one environmental factor promoting cyanobacterial mass developments. In the present study, we analyzed the response of N. spumigena strain CCY9414 toward strong phosphate limitation. Growth of the strain was diminished under P-deplete conditions; however, filaments contained more polyphosphate under P-deplete compared to P-replete conditions. Using RNA-seq, gene expression was compared in N. spumigena CCY9414 after 7 and 14 days in P-deplete and P-replete conditions, respectively. After 7 days, 112 genes were significantly up-regulated in P-deplete filaments, among them was a high proportion of genes encoding proteins related to P-homeostasis such as transport systems for different P species. Many of these genes became also up-regulated after 14 days compared to 7 days in filaments grown under P-replete conditions, which was consistent with the almost complete consumption of dissolved P in these cultures after 14 days. In addition to genes directly related to P starvation, genes encoding proteins for bioactive compound synthesis, gas vesicles formation, or sugar catabolism were stimulated under P-deplete conditions. Collectively, our data describe an experimentally validated P-stimulon in N. spumigena CCY9414 and provide the indication that severe P limitation could indeed support bloom formation by this filamentous strain.

Phosphate limitation intensifies negative effects of ocean acidification on globally important nitrogen fixing cyanobacterium

Growth of the prominent nitrogen-fixing cyanobacterium Trichodesmium is often limited by phosphorus availability in the ocean. How nitrogen fixation by phosphorus-limited Trichodesmium may respond to ocean acidification remains poorly understood. Here, we use phosphate-limited chemostat experiments to show that acidification enhanced phosphorus demands and decreased phosphorus-specific nitrogen fixation rates in Trichodesmium. The increased phosphorus requirements were attributed primarily to elevated cellular polyphosphate contents, likely for maintaining cytosolic pH homeostasis in response to acidification. Alongside the accumulation of polyphosphate, decreased NADP(H):NAD(H) ratios and impaired chlorophyll synthesis and energy production were observed under acidified conditions. Consequently, the negative effects of acidification were amplified compared to those demonstrated previously under phosphorus sufficiency. Estimating the potential implications of this finding, using outputs from the Community Earth System Model, predicts that acidification and dissolved inorganic and organic phosphorus stress could synergistically cause an appreciable decrease in global Trichodesmium nitrogen fixation by 2100.

Schindler's legacy: from eutrophic lakes to the phosphorus utilization strategies of cyanobacteria

David Schindler and his colleagues pioneered studies in the 1970s on the role of phosphorus in stimulating cyanobacterial blooms in North American lakes. Our understanding of the nuances of phosphorus utilization by cyanobacteria has evolved since that time. We review the phosphorus utilization strategies used by cyanobacteria, such as use of organic forms, alternation between passive and active uptake, and luxury storage. While many aspects of physiological responses to phosphorus of cyanobacteria have been measured, our understanding of the critical processes that drive species diversity, adaptation and competition remains limited. We identify persistent critical knowledge gaps, particularly on the adaptation of cyanobacteria to low nutrient concentrations. We propose that traditional discipline-specific studies be adapted and expanded to encompass innovative new methodologies and take advantage of interdisciplinary opportunities among physiologists, molecular biologists, and modellers, to advance our understanding and prediction of toxic cyanobacteria, and ultimately to mitigate the occurrence of blooms.

Excessive release of inorganic phosphate by ALS/FTD astrocytes causes non-cell-autonomous toxicity to motoneurons

Non-cell-autonomous mechanisms contribute to neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), in which astrocytes release unidentified factors that are toxic to motoneurons (MNs). We report here that mouse and patient iPSC-derived astrocytes with diverse ALS/FTD-linked mutations (SOD1, TARDBP, and C9ORF72) display elevated levels of intracellular inorganic polyphosphate (polyP), a ubiquitous, negatively charged biopolymer. PolyP levels are also increased in astrocyte-conditioned media (ACM) from ALS/FTD astrocytes. ACM-mediated MN death is prevented by degrading or neutralizing polyP in ALS/FTD astrocytes or ACM. Studies further reveal that postmortem familial and sporadic ALS spinal cord sections display enriched polyP staining signals and that ALS cerebrospinal fluid (CSF) exhibits increased polyP concentrations. Our in vitro results establish excessive astrocyte-derived polyP as a critical factor in non-cell-autonomous MN degeneration and a potential therapeutic target for ALS/FTD. The CSF data indicate that polyP might serve as a new biomarker for ALS/FTD.

Dissolved organic phosphorus utilization by the marine bacterium Ruegeria pomeroyi DSS-3 reveals chain length-dependent polyphosphate degradation

Dissolved organic phosphorus (DOP) is a critical nutritional resource for marine microbial communities. However, the relative bioavailability of different types of DOP, such as phosphomonoesters (P‐O‐C) and phosphoanhydrides (P‐O‐P), is poorly understood. Here we assess the utilization of these P sources by a representative bacterial copiotroph, Ruegeria pomeroyi DSS‐3. All DOP sources supported equivalent growth by R. pomeroyi, and all DOP hydrolysis rates were upregulated under phosphorus depletion (−P). A long‐chain polyphosphate (45polyP) showed the lowest hydrolysis rate of all DOP substrates tested, including tripolyphosphate (3polyP). Yet the upregulation of 45polyP hydrolysis under −P was greater than any other substrate analyzed. Proteomics revealed three common P acquisition enzymes potentially involved in polyphosphate utilization, including two alkaline phosphatases, PhoD and PhoX, and one 5′‐nucleotidase (5′‐NT). Results from DOP substrate competition experiments show that these enzymes likely have broad substrate specificities, including chain length‐dependent reactivity toward polyphosphate. These results confirm that DOP, including polyP, are bioavailable nutritional P sources for R. pomeroyi, and possibly other marine heterotrophic bacteria. Furthermore, the chain‐length dependent mechanisms, rates and regulation of polyP hydrolysis suggest that these processes may influence the composition of DOP and the overall recycling of nutrients within marine dissolved organic matter.

Fluorometric Quantification of Human Platelet Polyphosphate Using 4',6-Diamidine-2-phenylindole Dihydrochloride: Applications in the Japanese Population

Polyphosphate (polyP), a biopolymer of inorganic phosphate, is widely distributed in living organisms. In platelets, polyP is released upon activation and plays important roles in coagulation and tissue regeneration. However, the lack of a specific quantification method has delayed the in-depth study of polyP. The fluorescent dye 4′,6-diamidine-2-phenylindole dihydrochloride (DAPI) has recently received attention as a promising probe for the visualization and quantification of cellular polyP levels. In this study, we further optimized quantification conditions and applied this protocol in quantification of platelet polyP levels in a Japanese population. Blood samples were collected from non-smoking, healthy Japanese subjects (23 males, 23 females). Washed platelets were fixed and probed with DAPI for fluorometric determination. PolyP levels per platelet count were significantly higher in women than that in men. A moderate negative correlation between age and polyP levels was found in women. Responsiveness to CaCl₂ stimulation was also significantly higher in women than that in men. Overall, our optimized protocol requires neither purification nor degradation steps, reducing both the time and bias for reproducible quantification. Thus, we suggest that despite its low specificity, this DAPI-based protocol would be useful in routine laboratory testing to quantify platelet polyP levels efficiently and economically.

Critical Review of Polyphosphate and Polyphosphate Accumulating Organisms for Agricultural Water Quality Management

Despite ongoing management efforts, phosphorus (P) loading from agricultural landscapes continues to impair water quality. Wastewater treatment research has enhanced our knowledge of microbial mechanisms influencing P cycling, especially regarding microbes known as polyphosphate accumulating organisms (PAOs) that store P as polyphosphate (polyP) under oxic conditions and release P under anoxic conditions. However, there is limited application of PAO research to reduce agricultural P loading and improve water quality. Herein, we conducted a meta-analysis to identify articles in Web of Science on polyP and its use by PAOs across five disciplines (i.e., wastewater treatment, terrestrial, freshwater, marine, and agriculture). We also summarized research that provides preliminary support for PAO-mediated P cycling in natural habitats. Terrestrial, freshwater, marine, and agriculture disciplines had fewer polyP and PAO articles compared to wastewater treatment, with agriculture consistently having the least. Most meta-analysis articles did not overlap disciplines. We found preliminary support for PAOs in natural habitats and identified several knowledge gaps and research opportunities. There is an urgent need for interdisciplinary research linking PAOs, polyP, and oxygen availability with existing knowledge of P forms and cycling mechanisms in natural and agricultural environments to improve agricultural P management strategies and achieve water quality goals.

Platelet adhesion on commercially pure titanium plates in vitro III: effects of calcium phosphate-blasting on titanium plate biocompatibility

BACKGROUND

Platelet-rich plasma (PRP) is often used to improve surface biocompatibility. We previously found that platelets rapidly adhere to plain commercially pure titanium (cp-Ti) plates in the absence, but not in the presence, of plasma proteins. To further expand on these findings, in the present study, we switched titanium plates from a plain surface to a rough surface that is blasted with calcium phosphate (CaP) powder and then examined platelet adhesion and activation.

METHODS

Elemental distribution in CaP-blasted cp-Ti plates was analyzed using energy-dispersive X-ray spectroscopy. PRP samples prepared from anticoagulated blood samples of six healthy, non-smoking adult male donors were loaded on CaP-blasted cp-Ti plates for 1 h and fixed for examination of platelet morphology and visualization of PDGF-B and platelet surface markers (CD62P, CD63) using scanning electron microscopy and fluorescence microscopy. Plain SUS316L stainless steel plates used in injection needles were also examined for comparison.

RESULTS

Significant amounts of calcium and phosphate were detected on the CaP-blasted cp-Ti surface. Platelets rapidly adhered to this surface, leading to higher activation. Platelets also adhered to the plain stainless surface; however, the levels of adhesion and activation were much lower than those observed on the CaP-blasted cp-Ti plate.

CONCLUSIONS

The CaP-blasted cp-Ti surface efficiently entraps and activates platelets. Biomolecules released from the activated platelets could be retained by the fibrin matrix on the surface to facilitate regeneration of the surrounding tissues. Thus, PRP immersion could not only eliminate surface air bubbles but also improve the biocompatibility of the implant surface.

Bacterial Phosphate Granules Contain Cyclic Polyphosphates: Evidence from 31P Solid-State NMR

Polyphosphates (polyPs) are ubiquitous polymers in living organisms from bacteria to mammals. They serve a wide variety of biological functions, ranging from energy storage to stress response. In the last two decades, polyPs have been primarily viewed as linear polymers with varying chain lengths. However, recent biochemical data show that small metaphosphates, cyclic oligomers of [PO₃]^(-), can bind to the enzymes ribonuclease A and NAD kinase, raising the question of whether metaphosphates can occur naturally as products of biological activity. Before the 1980s, metaphosphates had been reported in polyPs extracted from various organisms, but these results are considered artifactual due to the extraction and purification protocols. Here, we employ nondestructive ³¹P solid-state NMR spectroscopy to investigate the chemical structure of polyphosphates in whole cells as well as insoluble fractions of the bacterium Xanthobacter autotrophicus. Isotropic and anisotropic ³¹P chemical shifts of hydrated whole cells indicate the coexistence of linear and cyclic phosphates. Under our cell growth conditions and the concentrated conditions of the solid-state NMR samples, we found substantial amounts of cyclic phosphates in X. autotrophicus, suggesting that in fresh cells metaphosphate concentrations can be significant. The cellular metaphosphates are identified by comparison with the ³¹P chemical shift anisotropy of synthetic metaphosphates of known structures. In X. autotrophicus, the metaphosphates have a chemical shift anisotropy that is consistent with an average size of 3-8 phosphate units. These metaphosphates are enriched in insoluble and electron-dense granules. Exogenous hexametaphosphate added to X. autotrophicus cell extracts is metabolized to trimetaphosphates, supporting the presence and biological role of metaphosphates in cells. The definitive evidence for the presence of metaphosphates, reported here in whole bacterial cells for the first time, opens the path for future investigations of the biological function of metaphosphates in many organisms.

Fixing the Broken Phosphorus Cycle: Wastewater Remediation by Microalgal Polyphosphates

Phosphorus (P), in the form of phosphate derived from either inorganic (Pi) or organic (Po) forms is an essential macronutrient for all life. P undergoes a biogeochemical cycle within the environment, but anthropogenic redistribution through inefficient agricultural practice and inadequate nutrient recovery at wastewater treatment works have resulted in a sustained transfer of P from rock deposits to land and aquatic environments. Our present and near future supply of P is primarily mined from rock P reserves in a limited number of geographical regions. To help ensure that this resource is adequate for humanity's food security, an energy-efficient means of recovering P from waste and recycling it for agriculture is required. This will also help to address excess discharge to water bodies and the resulting eutrophication. Microalgae possess the advantage of polymeric inorganic polyphosphate (PolyP) storage which can potentially operate simultaneously with remediation of waste nitrogen and phosphorus streams and flue gases (CO2, SOx, and NOx). Having high productivity in photoautotrophic, mixotrophic or heterotrophic growth modes, they can be harnessed in wastewater remediation strategies for biofuel production either directly (biodiesel) or in conjunction with anaerobic digestion (biogas) or dark fermentation (biohydrogen). Regulation of algal P uptake, storage, and mobilization is intertwined with the cellular status of other macronutrients (e.g., nitrogen and sulphur) in addition to the manufacture of other storage products (e.g., carbohydrate and lipids) or macromolecules (e.g., cell wall). A greater understanding of controlling factors in this complex interaction is required to facilitate and improve P control, recovery, and reuse from waste streams. The best understood algal genetic model is Chlamydomonas reinhardtii in terms of utility and shared resources. It also displays mixotrophic growth and advantageously, species of this genus are often found growing in wastewater treatment plants. In this review, we focus primarily on the molecular and genetic aspects of PolyP production or turnover and place this knowledge in the context of wastewater remediation and highlight developments and challenges in this field.

Polyphosphate: A Multifunctional Metabolite in Cyanobacteria and Algae

Polyphosphate (polyP), a polymer of orthophosphate (PO4 3-) of varying lengths, has been identified in all kingdoms of life. It can serve as a source of chemical bond energy (phosphoanhydride bond) that may have been used by biological systems prior to the evolution of ATP. Intracellular polyP is mainly stored as granules in specific vacuoles called acidocalcisomes, and its synthesis and accumulation appear to impact a myriad of cellular functions. It serves as a reservoir for inorganic PO4 3- and an energy source for fueling cellular metabolism, participates in maintaining adenylate and metal cation homeostasis, functions as a scaffold for sequestering cations, exhibits chaperone function, covalently binds to proteins to modify their activity, and enables normal acclimation of cells to stress conditions. PolyP also appears to have a role in symbiotic and parasitic associations, and in higher eukaryotes, low polyP levels seem to impact cancerous proliferation, apoptosis, procoagulant and proinflammatory responses and cause defects in TOR signaling. In this review, we discuss the metabolism, storage, and function of polyP in photosynthetic microbes, which mostly includes research on green algae and cyanobacteria. We focus on factors that impact polyP synthesis, specific enzymes required for its synthesis and degradation, sequestration of polyP in acidocalcisomes, its role in cellular energetics, acclimation processes, and metal homeostasis, and then transition to its potential applications for bioremediation and medical purposes.

A genetically validated approach for detecting inorganic polyphosphates in plants

Inorganic polyphosphates (polyPs) are linear polymers of orthophosphate units linked by phosphoanhydride bonds. Polyphosphates represent important stores of phosphate and energy, and are abundant in many pro- and eukaryotic organisms. In plants, the existence of polyPs has been established using microscopy and biochemical extraction methods that are now known to produce artifacts. Here we use a polyP-specific dye and a polyP-binding domain to detect polyPs in plant and algal cells. To develop the staining protocol, we induced polyP granules in Nicotiana benthamiana and Arabidopsis cells by heterologous expression of Escherichia coli polyphosphate kinase 1 (PPK1). Over-expression of PPK1 but not of a catalytically impaired version of the enzyme leads to severe growth phenotypes, suggesting that ATP-dependent synthesis and accumulation of polyPs in the plant cytosol is toxic. We next crossed stable PPK1-expressing Arabidopsis lines with plants expressing the polyP-binding domain of E. coli exopolyphosphatase (PPX1c), which co-localized with PPK1-generated polyP granules. These granules were stained by the polyP-specific dye JC-D7 and appeared as electron-dense structures in transmission electron microscopy sections. Using the polyP staining protocol derived from these experiments, we screened for polyP stores in different organs and tissues of both mono- and dicotyledonous plants. While we could not detect polyP granules in higher plants, we could visualize the polyP-rich acidocalcisomes in the green alga Chlamydomonas reinhardtii.

A genetically validated approach for detecting inorganic polyphosphates in plants

Inorganic polyphosphates (polyPs) are linear polymers of orthophosphate units linked by phosphoanhydride bonds. Polyphosphates represent important stores of phosphate and energy, and are abundant in many pro- and eukaryotic organisms. In plants, the existence of polyPs has been established using microscopy and biochemical extraction methods that are now known to produce artifacts. Here we use a polyP-specific dye and a polyP-binding domain to detect polyPs in plant and algal cells. To develop the staining protocol, we induced polyP granules in Nicotiana benthamiana and Arabidopsis cells by heterologous expression of Escherichia coli polyphosphate kinase 1 (PPK1). Over-expression of PPK1 but not of a catalytically impaired version of the enzyme leads to severe growth phenotypes, suggesting that ATP-dependent synthesis and accumulation of polyPs in the plant cytosol is toxic. We next crossed stable PPK1-expressing Arabidopsis lines with plants expressing the polyP-binding domain of E. coli exopolyphosphatase (PPX1c), which co-localized with PPK1-generated polyP granules. These granules were stained by the polyP-specific dye JC-D7 and appeared as electron-dense structures in transmission electron microscopy sections. Using the polyP staining protocol derived from these experiments, we screened for polyP stores in different organs and tissues of both mono- and dicotyledonous plants. While we could not detect polyP granules in higher plants, we could visualize the polyP-rich acidocalcisomes in the green alga Chlamydomonas reinhardtii.

Methods for the Analysis of Polyphosphate in the Life Sciences

Inorganic polyphosphate (polyP) is the polymer of orthophosphate and can be found in all living organisms. For polyP characterization, one or more of six parameters are of interest: the molecular structure (linear, cyclic, or branched), the concentration, the average chain length, the chain length distribution, the cellular localization, and the cation composition. Here, the merits, limitations, and critical parameters of the state-of-the-art methods for the analysis of the six parameters from the life sciences are discussed. With this contribution, we aim to lower the entry barrier into the analytics of polyP, a molecule with prominent, yet often incompletely understood, contributions to cellular function.

Characteristic Microbiomes Correlate with Polyphosphate Accumulation of Marine Sponges in South China Sea Areas

Some sponges have been shown to accumulate abundant phosphorus in the form of polyphosphate (polyP) granules even in waters where phosphorus is present at low concentrations. But the polyP accumulation occurring in sponges and their symbiotic bacteria have been little studied. The amounts of polyP exhibited significant differences in twelve sponges from marine environments with high or low dissolved inorganic phosphorus (DIP) concentrations which were quantified by spectral analysis, even though in the same sponge genus, e.g., Mycale sp. or Callyspongia sp. PolyP enrichment rates of sponges in oligotrophic environments were far higher than those in eutrophic environments. Massive polyP granules were observed under confocal microscopy in samples from very low DIP environments. The composition of sponge symbiotic microbes was analyzed by high-throughput sequencing and the corresponding polyphosphate kinase (ppk) genes were detected. Sequence analysis revealed that in the low DIP environment, those sponges with higher polyP content and enrichment rates had relatively higher abundances of cyanobacteria. Mantel tests and canonical correspondence analysis (CCA) examined that the polyP enrichment rate was most strongly correlated with the structure of microbial communities, including genera Synechococcus, Rhodopirellula, Blastopirellula, and Rubripirellula. About 50% of ppk genes obtained from the total DNA of sponge holobionts, had above 80% amino acid sequence similarities to those sequences from Synechococcus. In general, it suggested that sponges employed differentiated strategies towards the use of phosphorus in different nutrient environments and the symbiotic Synechococcus could play a key role in accumulating polyP.

Picoplankton accumulate and recycle polyphosphate to support high primary productivity in coastal Lake Ontario

Phytoplankton can accumulate polyphosphate (polyP) to alleviate limitation of essential nutrient phosphorus (P). Yet polyP metabolisms in aquatic systems and their roles in P biogeochemical cycle remain elusive. Previously reported polyP enrichment in low-phosphorus oligotrophic marine waters contradicts the common view of polyP as a luxury P-storage molecule. Here, we show that in a P-rich eutrophic bay of Lake Ontario, planktonic polyP is controlled by multiple mechanisms and responds strongly to seasonal variations. Plankton accumulate polyP as P storage under high-P conditions via luxury uptake and use it under acute P stress. Low phosphorus also triggers enrichment of polyP that can be preferentially recycled to attenuate P lost. We discover that picoplankton, despite their low production rates, are responsible for the dynamic polyP metabolisms. Picoplankton store and liberate polyP to support the high primary productivity of blooming algae. PolyP mechanisms enable efficient P recycling on ecosystem and even larger scales.

Polyphosphate accumulation dynamics in a population of Synechocystis sp. PCC 6803 cells under phosphate overplus

In this study, a simple and rapid DAPI-based protocol was developed and optimized to visualize polyphosphates (polyPs) in the cyanobacterium Synechocystis sp. PCC 6803. The optimum dye concentration and incubation time were determined, and formaldehyde fixation was shown to significantly improve polyP detection in Synechocystis cells. Using the developed protocol, for the first time, it was shown that 80% of Synechocystis cells under phosphate overplus were able to accumulate phosphorus as polyP 3 min after the addition of K₂HPO₄. After 1 h, the number of cells with polyP began to decrease, and after 24 h, polyP granules were detected in only 30% of the cells. Thus, the Synechocystis cells appeared to be heterogeneous in their ability to accumulate and mobilize polyP. Like other photosynthetic organisms, Synechocystis synthesized less polyP in the dark than in the light. The accumulation of polyP was not inhibited under conditions of cold and heat stresses, and some cells were even able to synthesize polyP at a temperature of approximately 0 °C.

Phosphorus strategy in bloom-forming cyanobacteria (Dolichospermum and Microcystis) and its role in their succession

Dolichospermum (formerly Anabaena) and Microcystis cause harmful cyanobacterial blooms in freshwater ecosystems worldwide. Input reduction of both nitrogen (N) and phosphorus (P) are commonly recognized as basic ways of controlling blooms, but little is known about the roles of nutrients and their using strategy among cyanobacteria in triggering the succession of diazotrophic to non-diazotrophic cyanobacteria. In this study, we investigated in situ responses of cyanobactria to ambient P status during the transition from Dolichospermum flos-aquae to Microcystis spp. in Lake Taihu and Lake Chaohu. While dominant in phytoplankton community, D. flos-aquae experienced P deficiency as evidenced by qualitative detection of extracellular phosphatase via enzyme labeled fluorescence (ELF). The percentage of ELF-labelled D. flos-aquae cells was 33% when it dominated the phytoplankton community, and was 78% when it co-dominated with Microcystis spp., indicating an increase in P deficiency. Meanwhile, no ELF-labelled Microcystis cells were observed while polyphosphate body (PPB) were present, suggesting that Microcystis spp. were not P deficient. Additionally, the percentages of Microcystis cells containing PPB showed an inverted "U-shaped" relationship with concentrations on soluble reactive phosphorus (SRP). To validate the field observation, a laboratory study of the monocultures of the dominant cyanobacteria was conducted. Extracellular alkaline phosphatase activity (APA) and PPB accumulation were regulated by P availability in monocultures of D. flos-aquae. Interestingly, no cell bound extracellular phosphatase was found on Microcystis aeruginasa even in the culture without P supply. Consistently, the expressions of phosphatase encoding gene phoX showed no differences among the treatments. The way in which PPB accumulation occurred in Microcystis spp. in response to P availability in the cultures was similar to that observed in the field, demonstrating a strategy of energy conservation over P accumulation. The competitive advantage of Microcystis spp. was displayed at low P concentrations: where it could rapidly uptake and store inorganic P, which also increased the P deficiency of the coexisting phytoplankton species. Responses of P-transport gene pstS confirmed this hypothesis. The physiological and molecular mechanisms mentioned above enable Microcystis to survive and proliferate in environment with low available P supply more efficiently. In conclusion, different cyanobacterial species have distinct ways of responding to P availability, suggesting that the control of cyanobacterial blooms by targeted nutrient reduction is largely dependent upon the dominant species. P reduction is more effective in controlling diazotrophic cyanobacteria than non-diazotrophic cyanobacteria.

Resolving the individual contribution of key microbial populations to enhanced biological phosphorus removal with Raman-FISH

Enhanced biological phosphorus removal (EBPR) is a globally important biotechnological process and relies on the massive accumulation of phosphate within special microorganisms. Candidatus Accumulibacter conform to the classical physiology model for polyphosphate accumulating organisms and are widely believed to be the most important player for the process in full-scale EBPR systems. However, it was impossible till now to quantify the contribution of specific microbial clades to EBPR. In this study, we have developed a new tool to directly link the identity of microbial cells to the absolute quantification of intracellular poly-P and other polymers under in situ conditions, and applied it to eight full-scale EBPR plants. Besides Ca. Accumulibacter, members of the genus Tetrasphaera were found to be important microbes for P accumulation, and in six plants they were the most important. As these Tetrasphaera cells did not exhibit the classical phenotype of poly-P accumulating microbes, our entire understanding of the microbiology of the EBPR process has to be revised. Furthermore, our new single-cell approach can now also be applied to quantify storage polymer dynamics in individual populations in situ in other ecosystems and might become a valuable tool for many environmental microbiologists.

Assaying for Inorganic Polyphosphate in Bacteria

Inorganic polyphosphate (polyP) is a biological polymer found in cells from all domains of life, and is required for virulence and stress response in many bacteria. There are a variety of methods for quantifying polyP in biological materials, many of which are either labor-intensive or insensitive, limiting their usefulness. We present here a streamlined method for polyP quantification in bacteria, using a silica membrane column extraction optimized for rapid processing of multiple samples, digestion of polyP with the polyP-specific exopolyphosphatase ScPPX, and detection of the resulting free phosphate with a sensitive ascorbic acid-based colorimetric assay. This procedure is straightforward, inexpensive, and allows reliable polyP quantification in diverse bacterial species. We present representative polyP quantification from the Gram-negative bacterium (Escherichia coli), the Gram-positive lactic acid bacterium (Lactobacillus reuteri), and the mycobacterial species (Mycobacterium smegmatis). We also include a simple protocol for nickel affinity purification of mg quantities of ScPPX, which is not currently commercially available.

Sulfurimonas subgroup GD17 cells accumulate polyphosphate under fluctuating redox conditions in the Baltic Sea: possible implications for their ecology

The central Baltic Sea is characterized by a pelagic redox zone exhibiting high dark CO₂ fixation rates below the chemocline. These rates are mainly driven by chemolithoautotrophic and denitrifying Sulfurimonas GD17 subgroup cells which are motile and fast-reacting r-strategists. Baltic Sea redox zones are unstable and a measurable overlap of nitrate and reduced sulfur, essential for chemosynthesis, is often only available on small scales and short times due to local mixing events. This raises the question of how GD17 cells gain access to electron donors or acceptors over longer term periods and under substrate deficiency. One possible answer is that GD17 cells store high-energy-containing polyphosphate during favorable nutrient conditions to survive periods of nutrient starvation. We used scanning electron microscopy with energy-dispersive X-ray spectroscopy to investigate potential substrate enrichments in single GD17 cells collected from Baltic Sea redox zones. More specific substrate enrichment features were identified in experiments using Sulfurimonas gotlandica GD1^T, a GD17 representative. Sulfurimonas cells accumulated polyphosphate both in situ and in vitro. Combined genome and culture-dependent analyses suggest that polyphosphate serves as an energy reservoir to maintain cellular integrity at unfavorable substrate conditions. This redox-independent energy supply would be a precondition for sustaining the r-strategy lifestyle of GD17 and may represent a newly identified survival strategy for chemolithoautotrophic prokaryotes occupying eutrophic redox zones.

Simple Silica Column-Based Method to Quantify Inorganic Polyphosphates in Cartilage and Other Tissues

OBJECTIVE

Inorganic polyphosphates (polyP) play a multitude of roles in mammalian biology. PolyP research is hindered by the lack of a simple and sensitive quantification method. The aim of this study was to develop a robust method for quantifying the low levels of polyP in mammalian tissue such as cartilage, which is rich in macromolecules that interfere with its determination.

DESIGN

Native and in vitro formed tissues were digested with proteinase K to release sequestrated polyP. The tissue digest was loaded on to silica spin columns, followed by elution of bound polyP and various treatments were assessed to minimize non-polyP fluorescence. The eluent was then quantified for polyP content using fluorometry based on DAPI (4',6-diamidino-2-phenylindole) fluorescence shift occurring with polyP.

RESULTS

Proteinase K pretreatment reduced the inhibitory effect of proteins on polyP recovery. The eluent was contaminated with nucleic acids and glycosaminoglycans, which cause extraneous fluorescence signals. These were then effectively eliminated by nucleases treatment and addition of concentrated Tris buffer. PolyP levels were quantified and recovery ratio determined using samples spiked with a known amount of polyP. This silica spin column method was able to recover at least 80% of initially loaded polyP, and detect as little as 10^-10 mol.

CONCLUSIONS

This sensitive, reproducible, easy to do method of quantifying polyP will be a useful tool for investigation of polyP biology in mammalian cells and tissues. Although the protocol was developed for mammalian tissues, this method should be able to quantify polyP in most biological sources, including fluid samples such as blood and serum.

Biogenic Polyphosphate Nanoparticles from a Marine Cyanobacterium Synechococcus sp. PCC 7002: Production, Characterization, and Anti-Inflammatory Properties In Vitro

Probiotic-derived polyphosphates have attracted interest as potential therapeutic agents to improve intestinal health. The current study discovered the intracellular accumulation of polyphosphates in a marine cyanobacterium Synechococcus sp. PCC 7002 as nano-sized granules. The maximum accumulation of polyphosphates in Synechococcus sp. PCC 7002 was found at the late logarithmic growth phase when the medium contained 0.74 mM of KH₂PO₄, 11.76 mM of NaNO₃, and 30.42 mM of Na₂SO₄. Biogenic polyphosphate nanoparticles (BPNPs) were obtained intact from the algae cells by hot water extraction, and were purified to remove the organic impurities by Sephadex G-100 gel filtration. By using 100 kDa ultrafiltration, BPNPs were fractionated into the larger and smaller populations with diameters ranging between 30–70 nm and 10–30 nm, respectively. 4′,6-diamidino-2-phenylindole fluorescence and orthophosphate production revealed that a minor portion of BPNPs (about 14–18%) were degraded during simulated gastrointestinal digestion. In vitro studies using lipopolysaccharide-activated RAW264.7 cells showed that BPNPs inhibited cyclooxygenase-2, inducible nitric oxide (NO) synthase expression, and the production of proinflammatory mediators, including NO, tumor necrosis factor-α, interleukin-6, and interleukin-1β through suppressing the Toll-like receptor 4/NF-κB signaling pathway. Overall, there is promise in the use of the marine cyanobacterium Synechococcus sp. PCC 7002 to produce BPNPs, an anti-inflammatory postbiotic.

Biogenic Polyphosphate Nanoparticles from Synechococcus sp. PCC 7002 Exhibit Intestinal Protective Potential in Human Intestinal Epithelial Cells In Vitro and Murine Small Intestine Ex Vivo

Polyphosphates are one of the active compounds from probiotics to maintain gut health. The current research extracted and purified intact biogenic polyphosphate nanoparticles (BPNPs) from Synechococcus sp. PCC 7002 cells. BPNPs were near-spherical anionic particles (56.9 ± 15.1 nm) mainly composed of calcium and magnesium salt of polyphosphate and were colloidally stable at near-neutral and alkaline pH. BPNPs survived gastrointestinal digestion in mice and could be absorbed and transported by polarized Caco-2 cell monolayers. They dose-dependently increased the tightness of intercellular tight junction and the expression of claudin-4, occludin, zonula occludens-1, and heat shock protein 27 in Caco-2 cell monolayers. BPNPs also effectively attenuated H₂O₂-induced cell death, plasma membrane impairment, and intracellular superoxide production in NCM460 cells. In addition, they conferred resistance to H₂O₂-induced barrier disruption in freshly excised mouse small intestine. Our results suggest that BPNPs are a promising postbiotic nanomaterial with potential applications in gut health maintenance.

Differences in the accumulation of phosphorus between vegetative cells and heterocysts in the cyanobacterium Nodularia spumigena

The cyanobacterium Nodularia spumigena is a species that frequently forms blooms in the Baltic Sea. Accumulation of the vital nutrient phosphorus (P) apparently plays an important role in the ability of this and other cyanobacteria to grow even when dissolved inorganic phosphorus is depleted. However, until now, this has not been studied in N. spumigena at the cellular level. Therefore, in this study, phosphorus incorporation and distribution in cyanobacterial filaments over time was examined by scanning electron microscopy in combination with energy dispersive X-ray analysis (SEM/EDX) and nanoscale secondary ion mass spectrometry (NanoSIMS). Immediately after phosphate addition to a phosphorus-depleted population, the phosphate concentration decreased in the water while intracellular polyphosphate accumulated. Microscopically, phosphorus in form of polyphosphate granules was stored preferentially in vegetative cells, whereas heterocysts remained low in intracellular phosphorus. This information is an essential step towards understanding the phosphorus dynamics of this species and demonstrates that the division of tasks between vegetative cells and heterocysts is not restricted to nitrogen fixation.

Lipidomics of Thalassiosira pseudonana under Phosphorus Stress Reveal Underlying Phospholipid Substitution Dynamics and Novel Diglycosylceramide Substitutes

Phytoplankton replace phosphorus-containing lipids (P-lipids) with non-P analogues, boosting growth in P-limited oceans. In the model diatom Thalassiosira pseudonana, the substitution dynamics of lipid headgroups are well described, but those of the individual lipids, differing in fatty acid composition, are unknown. Moreover, the behavior of lipids outside the common headgroup classes and the relationship between lipid substitution and cellular particulate organic P (POP) have yet to be reported. We investigated these through the mass spectrometric lipidomics of P-replete (P⁺) and P-depleted (P^-) T. pseudonana cultures. Nonlipidic POP was depleted rapidly by the initiation of P stress, followed by the cessation of P-lipid biosynthesis and per-cell reductions in the P-lipid levels of successive generations. Minor P-lipid degradative breakdown was observed, releasing P for other processes, but most P-lipids remained intact. This may confer an advantage on efficient heterotrophic lipid consumers in P-limited oceans. Glycerophosphatidylcholine (PC), the predominant P-lipid, was similar in composition to its betaine substitute lipid. During substitution, PC was less abundant per cell and was more highly unsaturated in composition. This may reflect underlying biosynthetic processes or the regulation of membrane biophysical properties subject to lipid substitution. Finally, levels of several diglycosylceramide lipids increased as much as 10-fold under P stress. These represent novel substitute lipids and potential biomarkers for the study of P limitation in situ, contributing to growing evidence highlighting the importance of sphingolipids in phycology. These findings contribute much to our understanding of P-lipid substitution, a powerful and widespread adaptation to P limitation in the oligotrophic ocean.IMPORTANCE Unicellular organisms replace phosphorus (P)-containing membrane lipids with non-P substitutes when P is scarce, allowing greater growth of populations. Previous research with the model diatom species Thalassiosira pseudonana grouped lipids by polar headgroups in their chemical structures. The significance of the research reported here is threefold. (i) We described the individual lipids within the headgroups during P-lipid substitution, revealing the relationships between lipid headgroups and hinting at the underlying biochemical processes. (ii) We measured total cellular P, placing P-lipid substitution in the context of the broader response to P stress and yielding insight into the implications of substitution in the marine environment. (iii) We identified lipids previously unknown in this system, revealing a new type of non-P substitute lipid, which is potentially useful as a biomarker for the investigation of P limitation in the ocean.

Overproduction, purification, and characterization of nanosized polyphosphate bodies from Synechococcus sp. PCC 7002

Background

Inorganic polyphosphate bodies (PPB) have recently been linked to a variety of functions in mammalian cells. To improve the yield of PPB from Synechococcus sp. PCC 7002 and characterize its form, in this study, a recombinant plasmid containing a polyphosphate kinase (ppk) gene was generated and transformed into Synechococcus sp. PCC 7002.

Results

PPB separated by Sephadex G-100 was characterized and added to polarized human intestinal epithelial (Caco-2) cells, and the absorption effect was assessed. The ppk gene was stably expressed by induction with 1 μM nickel, and the resulting PPB yield from Synechococcus sp. PCC 7002 cells increased by 89.66%. Transmission electron microscopy and dynamic light scattering analyses showed that PPB from these cells were nanosized, ranging from a few to approximately 100 nanometres in diameter. PPB can be taken up by Caco-2 cells and are mainly distributed around lipid droplets.

Conclusions

We determined that PPB can be overproduced in Synechococcus sp. PCC 7002 and that the resulting PPB were well absorbed by Caco-2 cells. Microalgae provide a promising “cell factory” for PPB production.

The biosorption of cadmium and cobalt and iron ions by yeast Cryptococcus humicola at nitrogen starvation

Yeasts Cryptococcus humicola accumulated cadmium, cobalt, and iron (~ 50, 17, and 4% of the content in the medium, respectively) from the medium containing glucose, phosphate, and 2 mmol/L of metal salts. The effects of metal absorption on the levels of orthophosphate (Pi) and inorganic polyphosphate (polyP) varied for the metals under study. The levels of Pi and polyP increased in the case of cadmium and cobalt, respectively. In the case of iron, no changes in the levels of Pi and polyP were observed. Multiple DAPI-stained polyP inclusions were observed in the cytoplasm of cadmium-containing cells. The intensity of DAPI staining of the cell wall especially increased in case of cobalt and iron accumulation.

Quantification of Polyphosphate in Microalgae by Raman Microscopy and by a Reference Enzymatic Assay

Polyphosphates have occurred in living cells early in evolution and microalgae contain these important polymers in their cells. Progress in research of polyphosphate metabolism of these ecologically as well as biotechnologically important microorganisms is hampered by the lack of rapid quantification methods. Experiments with the green alga Chlorella vulgaris presented here compared polyphosphate extraction in water, methanol-chloroform, and phenol-chloroform followed by polyphosphate purification by binding to silica columns or ethanol precipitation. The phenol-chloroform extraction of C. vulgaris followed by ethanol precipitation of polyphosphate was shown to be superior to the other tested method variants. Recovery test of added polyphosphate standard to algal biomass showed that the method is accurate. Using this biochemical assay as a validated reference, we show that 2-dimensional, confocal Raman microscopy can serve as a linear proxy for polyphosphate in C. vulgaris with R² up to 0.956. With this, polyphosphate quantification can be shortened by use of Raman microscopy from days to hours and, additionally, information about intracellular distribution of polyphosphate and heterogeneity among individual cells in algal culture can be obtained. This offers new insights into the dynamics and role of these polymers crucial for phosphorus uptake and storage. This analytical capability is of particular practical importance because algae aid phosphorus sequestration from wastewater and the thus enriched biomass may serve as organic fertilizer. Both these applications have a strong potential in a future sustainable, circular bioeconomy.

Improvement of biochemical methods of polyP quantification

Polyphosphate (polyP) is an abundant and physiologically important biomolecule for virtually any living cell. Therefore, determination of changes in cellular content of polyP is crucial for its functional characterization. Determination of cellular polyP has been performed by many different methods, and the lack of a standardized procedure is possibly responsible for the large dispersion of results found in the relevant literature. For a relatively simple organism, such as the yeast Saccharomyces cerevisiae, this variation can be up to 12-fold. polyP extraction and determination of free phosphate released by enzymatic degradation of the polymer is a method quite common and relatively straightforward for polyP determination. By using the yeast S. cerevisiae as model, we have experimentally evaluated the different steps in this procedure in order to identify critical issues that might explain the disparate reported results. As the main output of this evaluation we propose a straightforward and robust procedure that can be used as gold standard protocol for cellular polyP purification and determination from unicellular organisms, thus providing consistency to measurements and facilitating inter-laboratory comparisons and biological interpretation of the results.

A unique intracellular compartment formed during the oligotrophic growth of Rhodococcus erythropolis N9T-4

Rhodococcus erythropolis N9T-4, isolated from stored crude oil, shows extremely oligotrophic features and can grow on a basal medium without any additional carbon, nitrogen, sulfur, and energy sources, but requires CO₂ for its oligotrophic growth. Transmission electron microscopic observation showed that a relatively large and spherical compartment was observed in a N9T-4 cell grown under oligotrophic conditions. In most cases, only one compartment was observed per cell, but in some cases, it was localized at each pole of the cell, suggesting that it divides at cell division. We termed this unique bacterial compartment an oligobody. The oligobody was not observed or very rarely observed in small sizes under nutrient rich conditions, whereas additional carbon sources did not affect oligobody formation. Energy dispersive X-ray spectroscopy analysis revealed remarkable peaks corresponding to phosphorus and potassium in the oligobody. The oligobodies in N9T-4 cells could be stained by Toluidine blue, suggesting that the oligobody is composed of inorganic polyphosphate and is a type of acidocalcisome. Two genes-encoding polyphosphate kinases, ppk1 and ppk2, were found in the N9T-4 genome: ppk1 disruption caused a negative effect on the formation of the oligobody. Although it was suggested that the oligobody plays an important role for the oligotrophic growth, both ppk-deleted mutants showed the same level of oligotrophic growth as the wild-type strain.

Non-enzymatic quantification of polyphosphate levels in platelet lysates and releasates

Inorganic polyphosphate has been shown to be shed upon platelet activation inducing prothrombotic stimuli on the coagulation system. Several methods have been published to detect and quantify polyphosphate in various cells and tissues, but evaluation of platelet content has only been achieved by indirect detection of orthophosphate after enzymatic digestion, thus, relying heavily on specificity of an exopolyphosphatase that is not commercially available. We present a non-enzymatic method for quantification of platelet-derived polyphosphate featuring optimized extraction on silica spin-columns, followed by specific fluorescence detection using DAPI. This allowed us to quantify polyphosphate in platelet lysates, but also in releasates of TRAP-activated platelets for the first time. Extraction of exogenous polyphosphate from buffer and sample matrices resulted in quantitative yields while removing matrix effects observed with direct fluorescence detection. Treatment of eluted fractions with phosphatase completely abrogated polyphosphate-specific fluorescence arguing for no additional compounds influencing the fluorescence detection. This was confirmed by no change in fluorescence intensity in samples previously treated with DNase and RNase. Taken together, we developed a robust and easily standardizable method to quantify polyphosphate in platelet lysates and releasates that will facilitate polyphosphate related investigations of platelet physiology and coagulation.

Polyphosphate, platelets, and coagulation

While we have understood the basic outline of the enzymes and reactions that make up the traditional blood coagulation cascade for many years, recently our appreciation of the complexity of these interactions has greatly increased. This has resulted in unofficial 'revisions' of the coagulation cascade to include new amplification pathways and connections between the standard coagulation cascade enzymes, as well as the identification of extensive connections between the immune system and the coagulation cascade. The discovery that polyphosphate is stored in platelet dense granules and is secreted during platelet activation has resulted in a recent burst of interest in the role of this ancient molecule in human biology. Here we review the increasingly complex role of platelet polyphosphate in hemostasis, thrombosis, and inflammation that has been uncovered in recent years, as well as novel therapeutics centered on modulating polyphosphate's roles in coagulation and inflammation.

Variable phosphorus uptake rates and allocation across microbial groups in the oligotrophic Gulf of Mexico

Microbial uptake of dissolved phosphorus (P) is an important lever in controlling both microbial production and the fate and cycling of marine P. We investigated the relative role of heterotrophic bacteria and phytoplankton in P cycling by measuring the P uptake rates of individual microbial groups (heterotrophic bacteria and the phytoplankton groups Synechococcus, Prochlorococcus and picoeukaryotic phytoplankton) in the P-depleted Gulf of Mexico. Phosphorus uptake rates were measured using incubations with radiolabelled phosphate and adenosine triphosphate coupled with cell sorting flow cytometry. We found that heterotrophic bacteria were the dominant consumers of P on both a biomass basis and a population basis. Biovolume normalized heterotrophic bacteria P uptake rate per cell (amol P μm(-3) h(-1)) was roughly an order of magnitude greater than phytoplankton uptake rates, and heterotrophic bacteria were responsible for generally greater than 50% of total picoplankton P uptake. We hypothesized that this variation in uptake rates reflects variation in cellular P allocation strategies, and found that, indeed, the fraction of cellular P uptake utilized for phospholipid production was significantly higher in heterotrophic bacteria compared with cyanobacterial phytoplankton. These findings indicate that heterotrophic bacteria have a uniquely P-oriented physiology and play a dominant role in cycling dissolved P.

Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges

Marine sponges are major habitat-forming organisms in coastal benthic communities and have an ancient origin in evolution history. Here, we report significant accumulation of polyphosphate (polyP) granules in three common sponge species of the Caribbean coral reef. The identity of the polyP granules was confirmed by energy-dispersive spectroscopy (EDS) and by the fluorescence properties of the granules. Microscopy images revealed that a large proportion of microbial cells associated with sponge hosts contained intracellular polyP granules. Cyanobacterial symbionts cultured from sponges were shown to accumulate polyP. We also amplified polyphosphate kinase (ppk) genes from sponge DNA and confirmed that the gene was expressed. Based on these findings, we propose here a potentially important phosphorus (P) sequestration pathway through symbiotic microorganisms of marine sponges. Considering the widespread sponge population and abundant microbial cells associated with them, this pathway is likely to have a significant impact on the P cycle in benthic ecosystems.

In situ investigation of mammalian inorganic polyphosphate localization using novel selective fluorescent probes JC-D7 and JC-D8

Inorganic polyphosphate (polyP) is a polymer composed of many orthophosphates linked together by phosphoanhydride bonds. Recent studies demonstrate that in addition to its important role in the function of microorganisms, polyP plays multiple important roles in the pathological and physiological function of higher eukaryotes, including mammalians. However, due to the dramatically lower abundance of polyP in mammalian cells when comparing to microorganisms, its investigation poses an experimental challenge. Here, we present the identification of novel fluorescent probes that allow for specific labeling of synthetic polyP in vitro as well as endogenous polyP in living cells. These probes demonstrate high selectivity for the labeling of polyP that was not sensitive to a number of ubiquitous organic polyphosphates, notably RNA. Use of these probes allowed us to demonstrate the real time detection of polyP release from lysosomes in live cells. Furthermore, we have been able to detect the increased levels of polyP in cells with Parkinson's disease related mutations.

De novo assembly of Aureococcus anophagefferens transcriptomes reveals diverse responses to the low nutrient and low light conditions present during blooms

Transcriptome profiling was performed on the harmful algal bloom-forming pelagophyte Aureococcus anophagefferens strain CCMP 1850 to assess responses to common stressors for dense phytoplankton blooms: low inorganic nitrogen concentrations, low inorganic phosphorus concentrations, low light levels, and a replete control. The de novo assemblies of pooled reads from all treatments reconstructed ~54,000 transcripts using Trinity, and ~31,000 transcripts using ABySS. Comparison to the strain CCMP 1984 genome showed that the majority of the gene models were present in both de novo assemblies and that roughly 95% of contigs from both assemblies mapped to the genome, with Trinity capturing slightly more genome content. Sequence reads were mapped back to the de novo assemblies as well as the gene models and differential expression was analyzed using a Bayesian approach called Analysis of Sequence Counts (ASC). On average, 93% of significantly upregulated transcripts recovered by genome mapping were present in the significantly upregulated pool from both de novo assembly methods. Transcripts related to the transport and metabolism of nitrogen were upregulated in the low nitrogen treatment, transcripts encoding enzymes that hydrolyze organic phosphorus or relieve arsenic toxicity were upregulated in the low phosphorus treatment, and transcripts for enzymes that catabolize organic compounds, restructure lipid membranes, or are involved in sulfolipid biosynthesis were upregulated in the low light treatment. A comparison of this transcriptome to the nutrient regulated transcriptional response of CCMP 1984 identified conserved responses between these two strains. These analyses reveal the transcriptional underpinnings of physiological shifts that could contribute to the ecological success of this species in situ: organic matter processing, metal detoxification, lipid restructuring, and photosynthetic apparatus turnover.

Accumulation and enhanced cycling of polyphosphate by Sargasso Sea plankton in response to low phosphorus

Phytoplankton alter their biochemical composition according to nutrient availability, such that their bulk elemental composition varies across oceanic provinces. However, the links between plankton biochemical composition and variation in biogeochemical cycling of nutrients remain largely unknown. In a survey of phytoplankton phosphorus stress in the western North Atlantic, we found that phytoplankton in the phosphorus-depleted subtropical Sargasso Sea were enriched in the biochemical polyphosphate (polyP) compared with nutrient-rich temperate waters, contradicting the canonical oceanographic view of polyP as a luxury phosphorus storage molecule. The enrichment in polyP coincided with enhanced alkaline phosphatase activity and substitution of sulfolipids for phospholipids, which are both indicators of phosphorus stress. Further, polyP appeared to be liberated preferentially over bulk phosphorus from sinking particles in the Sargasso Sea, thereby retaining phosphorus in shallow waters. Thus, polyP cycling may form a feedback loop that attenuates the export of phosphorus when it becomes scarce, contributes bioavailable P for primary production, and supports the export of carbon and nitrogen via sinking particles.

Cytoplasmic inorganic polyphosphate participates in the heavy metal tolerance of Cryptococcus humicola

The basidiomycetous yeast Cryptococcus humicola was shown to be tolerant to manganese, cobalt, nickel, zinc, lanthanum, and cadmium cations at a concentration of 2.5 mmol/L, which is toxic for many yeasts. The basidiomycetous yeast Cryptococcus terreus was sensitive to all these ions and did not grow at the above concentration. In the presence of heavy metal cations, С. humicola, as opposed to C. terreus, was characterized by the higher content of acid-soluble inorganic polyphosphates. In vivo 4',6'-diamino-2-phenylindole dihydrochloride staining revealed polyphosphate accumulation in the cell wall and cytoplasmic inclusions of С. humicola in the presence of heavy metals. In C. terreus, polyphosphates in the presence of heavy metals accumulate mainly in vacuoles, which results in morphological changes in these organelles and, probably, disturbance of their function. The role of polyphosphate accumulation and cellular localization as factors of heavy metal tolerance of Cryptococcus humicola is discussed.

Coupled synthesis and translocation restrains polyphosphate to acidocalcisome-like vacuoles and prevents its toxicity

Eukaryotes contain inorganic polyphosphate (polyP) and acidocalcisomes, which sequester polyP and store amino acids and divalent cations. Why polyP is sequestered in dedicated organelles has been unknown. We show that polyP produced in the cytosol of yeast becomes toxic. Reconstitution of polyP translocation with purified vacuoles, the acidocalcisomes of yeast, showed that cytosolic polyP cannot be imported whereas polyP produced by the VTC complex, an endogenous vacuolar polyP polymerase, is efficiently imported and does not interfere with growth. PolyP synthesis and import require an electrochemical gradient, probably as a driving force for polyP translocation. VTC exposes its catalytic domain to the cytosol and carries nine vacuolar transmembrane domains. Mutations in the VTC transmembrane regions, which likely constitute the translocation channel, block not only polyP translocation but also synthesis. Since they are far from the cytosolic catalytic domain of VTC, this suggests that the VTC complex obligatorily couples synthesis of polyP to its import in order to avoid toxic intermediates in the cytosol. Sequestration of otherwise toxic polyP may be one reason for the existence of acidocalcisomes in eukaryotes.