Characterisation of Phosphate Accumulating Organisms and Techniques for Polyphosphate Detection: A Review

Demystifying polyphosphate-accumulating organisms relevant to wastewater treatment: A review of their phylogeny, metabolism, and detection

Currently, the most cost-effective and efficient method for phosphorus (P) removal from wastewater is enhanced biological P removal (EPBR) via polyphosphate-accumulating organisms (PAOs). This study integrates a literature review with genomic analysis to uncover the phylogenetic and metabolic diversity of the relevant PAOs for wastewater treatment. The findings highlight significant differences in the metabolic capabilities of PAOs relevant to wastewater treatment. Notably, Candidatus Dechloromonas and Candidatus Accumulibacter can synthesize polyhydroxyalkanoates, possess specific enzymes for ATP production from polyphosphate, and have electrochemical transporters for acetate and C4-dicarboxylates. In contrast, Tetrasphaera, Candidatus Phosphoribacter, Knoellia, and Phycicoccus possess PolyP-glucokinase and electrochemical transporters for sugars/amino acids. Additionally, this review explores various detection methods for polyphosphate and PAOs in activated sludge wastewater treatment plants. Notably, FISH-Raman spectroscopy emerges as one of the most advanced detection techniques. Overall, this review provides critical insights into PAO research, underscoring the need for enhanced strategies in biological phosphorus removal.

Grow now, pay later: When should a bacterium go into debt?

Microbes grow in a wide variety of environments and must balance growth and stress resistance. Despite the prevalence of such trade-offs, understanding of their role in nonsteady environments is limited. In this study, we introduce a mathematical model of "growth debt," where microbes grow rapidly initially, paying later with slower growth or heightened mortality. We first compare our model to a classical chemostat experiment, validating our proposed dynamics and quantifying Escherichia coli's stress resistance dynamics. Extending the chemostat theory to include serial-dilution cultures, we derive phase diagrams for the persistence of "debtor" microbes. We find that debtors cannot coexist with nondebtors if "payment" is increased mortality but can coexist if it lowers enzyme affinity. Surprisingly, weak noise considerably extends the persistence of resistance elements, pertinent for antibiotic resistance management. Our microbial debt theory, broadly applicable across many environments, bridges the gap between chemostat and serial dilution systems.

Cultivation of microalgae-bacteria consortium by waste gas-waste water to achieve CO2 fixation, wastewater purification and bioproducts production

The cultivation of microalgae and microalgae-bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae-bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae-bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae-bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing.

Performance of a modified and intermittently operated slow sand filter with two different mediums in removing turbidity, ammonia, and phosphate with varying acclimatization periods

The present study investigated the utilization of blood clam shells as a potential substitute for conventional media, as well as the influence of the acclimation time on the efficacy of an intermittent slow sand filter (ISSF) in the treatment of real domestic wastewater. ISSF was operated with 16 h on and 8 h off, focusing on the parameters of turbidity, ammonia, and phosphate. Two media combinations (only blood clam shells [CC] and sand + blood clam shells [SC]) were operated under two different acclimatization periods (14 and 28 d). Results showed that SC medium exhibited significantly higher removal of turbidity (p < 0.05) as compared to CC medium (45.99 ± 26.84 % vs. 3.79 ± 9.35 %), while CC exhibited slightly higher (p > 0.05) removal of ammonia (23.12 ± 20.2 % vs. 16.77 ± 16.8 %) and phosphate (18.03 ± 11.96 % vs 13.48 ± 12 %). Comparing the acclimatization periods, the 28 d of acclimatization period showed higher overall performances than the 14 d. Further optimizations need to be conducted to obtain an effluent value below the national permissible limit, since the ammonia and phosphate parameters are still slightly higher. SEM analysis confirmed the formation of biofilm on both mediums after 28 d of acclimatization; with further analysis of schmutzdecke formation need to be carried out to enrich the results.

Transitions in nitrogen and organic matter form and concentration correspond to bacterial population dynamics in a hypoxic urban estuary

Nitrogen (N) inputs to developed coastlines are linked with multiple ecosystem and socio-economic impacts worldwide such as algal blooms, habitat/resource deterioration, and hypoxia. This study investigated the microbial and biogeochemical processes associated with recurrent, seasonal bottom-water hypoxia in an urban estuary, western Long Island Sound (WLIS), that receives high N inputs. A 2-year (2020-2021) field study spanned two hypoxia events and entailed surface and bottom depth water sampling for dissolved nutrients as inorganic N (DIN; ammonia-N and nitrite + nitrate (N + N)), organic N, orthophosphate, organic carbon (DOC), as well as chlorophyll a and bacterial abundances. Physical water quality data were obtained from concurrent conductivity, temperature, and depth casts. Results showed that dissolved organic matter was highest at the most-hypoxic locations, DOC was negatively and significantly correlated with bottom-water dissolved oxygen (Pearson's r = -0.53, p = 0.05), and ammonia-N was the dominant DIN form pre-hypoxia before declining throughout hypoxia. N + N concentrations showed the reverse, being minimal pre-hypoxia then increasing during and following hypoxia, indicating that ammonia oxidation likely contributed to the switch in dominant DIN forms and is a key pathway in WLIS water column nitrification. Similarly, at the most hypoxic sampling site, bottom depth bacteria concentrations ranged ~ 1.8 × 10⁴-1.1 × 10⁵ cells ml^-1 pre-hypoxia, declined throughout hypoxia, and were positively and significantly correlated (Pearson's r = 0.57; p = 0.03) with ammonia-N, confirming that hypoxia influences N-cycling within LIS. These findings provide novel insight to feedbacks between major biogeochemical (N and C) cycles and hypoxia in urban estuaries.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-023-01021-2.

The Role of Flavobacterium enshiense R6S-5-6 in the Wetland Ecosystem Revealed by Whole-Genome Analysis

The wetland is an important ecosystem for purifying pollutants and circulating nutrients. Numerous microorganisms contribute to maintaining this function. We obtained Flavobacterium enshiense R6S-5-6 which was isolated from Ungok (Ramsar) Wetland and conducted whole-genome sequencing to investigate what contribution R6S-5-6 could make to the wetland community. The complete genome sequence of R6S-5-6 has a size of 3,251,289 bp with 37.68% of GC content. Gene annotation revealed that R6S-5-6 has several pathways to break down pollutants, including denitrification, assimilatory sulfate reduction (ASR), and polyphosphate-accumulating process. Furthermore, R6S-5-6 has genes that can have a positive effect on plants living in wetlands, such as storing essential nutrients, promoting plant growth, and protecting plants against pathogens.

Enhanced Bio-P removal: Past, present, and future - A comprehensive review

Excess amounts of phosphorus (P) and nitrogen (N) from anthropogenic activities such as population growth, municipal and industrial wastewater discharges, agriculture fertilization and storm water runoffs, have affected surface water chemistry, resulting in episodes of eutrophication. Enhanced biological phosphorus removal (EBPR) based treatment processes are an economical and environmentally friendly solution to address the present environmental impacts caused by excess P present in municipal discharges. EBPR practices have been researched and operated for more than five decades worldwide, with promising results in decreasing orthophosphate to acceptable levels. The advent of molecular tools targeting bacterial genomic deoxyribonucleic acid (DNA) has also helped us reveal the identity of potential polyphosphate-accumulating organisms (PAO) and denitrifying PAO (DPAO) responsible for the success of EBPR. Integration of process engineering and environmental microbiology has provided much-needed confidence to the wastewater community for the successful implementation of EBPR practices around the globe. Despite these successes, the process of EBPR continues to evolve in terms of its microbiology and application in light of other biological processes such as anaerobic ammonia oxidation and on-site carbon capture. This review provides an overview of the history of EBPR, discusses different operational parameters critical for the successful operation of EBPR systems, reviews current knowledge of EBPR microbiology, the influence of PAO/DPAO on the disintegration of microbial communities, stoichiometry, EBPR clades, current practices, and upcoming potential innovations.

Update on platelet procoagulant mechanisms in health and in bleeding disorders

Platelet procoagulant mechanisms are emerging to be complex and important to achieving haemostasis. The mechanisms include the release of procoagulant molecules from platelet storage granules, and strong agonist-induced expression of procoagulant phospholipids on the outer platelet membrane for tenase and prothrombinase assembly. The release of dense granule polyphosphate is important to platelet procoagulant function as it promotes the activation of factors XII, XI and V, inhibits tissue factor pathway inhibitor and fibrinolysis, and strengthens fibrin clots. Platelet procoagulant function also involves the release of partially activated factor V from platelets. Scott syndrome has provided important insights on the mechanisms that regulate procoagulant phospholipids expression on the external platelet membrane, which require strong agonist stimulation that increase cystolic calcium levels, mitochondrial calcium uptake, the loss of flippase function and activation of the transmembrane scramblase protein anoctamin 6. There have been advances in the methods used to directly and indirectly assess platelet procoagulant function in health and disease. Assessments of thrombin generation with platelet rich plasma samples has provided new insights on how platelet procoagulant function is altered in inherited platelet disorders, and how platelets influence the bleeding phenotype of a number of severe coagulation factor deficiencies. Several therapies, including desmopressin and recombinant factor VIIa, improve thrombin generation by platelets. There is growing interest in targeting platelet procoagulant function for therapeutic benefit. This review highlights recent advances in our understanding of platelet-dependent procoagulant mechanisms in health and in bleeding disorders.

Phosphorus mining from eutrophic marine environment towards a blue economy: The role of bio-based applications

Global phosphorus reserves are under pressure of depletion in the near future due to increased consumption of primary phosphorus reservoirs and improper management of phosphorus. At the same time, a considerable portion of global marine water bodies has been suffering from eutrophication due to excessive nutrient loading. The marine environment can be considered as a valuable phosphorus source due to nutrient rich eutrophic seawater and sediment which could potentially serve as phosphorus mines in the near future. Hence, sustainable phosphorus recovery strategies should be adapted for marine systems to provide phosphorus for the growing market demand and simultaneously control eutrophication. In this review, possible sustainable strategies for phosphorus removal and recovery from marine environments are discussed in detail. Bio-based strategies relying on natural phosphorus uptake/release metabolism of living organisms are suggested as promising options that can provide both phosphorus removal and recovery from marine waters for achieving a sustainable marine ecosystem. Among them, the utilization of microorganisms seems promising to develop novel strategies. However, the research gap for the technical applicability of these strategies is still considerably big. Therefore, future research should focus on the technical development of the strategies through laboratory and/or field studies. Coupling phosphorus mining with other valorisation pathways (i.e., metal recovery, energy production) is also suggested to improve overall sustainability and economic viability. Environmental, economic and societal challenges should altogether be well addressed prior to real scale applications.

Exploring the Extent of Phosphorus and Heavy Metal Uptake by Single Cells of Saccharomyces cerevisiae and Their Effects on Intrinsic Elements by SC-ICP-TOF-MS

The effect of six heavy metals, namely, silver (Ag), lead (Pb), palladium (Pd), copper (Cu), nickel (Ni), and chromium (Cr), on phosphorus (P) uptake by yeast was investigated by single-cell analysis using inductively coupled plasma time-of-flight mass spectrometry (SC-ICP-TOF-MS). It was found that the P content in cells with 1.55 g L^–1 P feeding after P starvation was increased by ∼70% compared to control cells. Heavy metals at 10 ppm, except Cu, had a negative impact on P accumulation by cells. Pd reduced the P content by 26% in single cells compared to control cells. Metal uptake was strongest for Ag and Pd (0.7 × 10^–12 L cell^–1) and weakest for Cr (0.05 × 10^–12 L cell^–1). Exposure to Cr markedly reduced (−50%) Mg in cells and had the greatest impact on the intrinsic element composition. The SC-ICP-TOF-MS shows the diversity of elemental content in single cells: for example, the P content under standard conditions varied between 12.4 and 890 fg cell^–1. This technique allows studying both the uptake of elements and sublethal effects on physiology at a single-cell level.

Novel Chloroflexi genomes from the deepest ocean reveal metabolic strategies for the adaptation to deep-sea habitats

BACKGROUND

The deep sea harbors the majority of the microbial biomass in the ocean and is a key site for organic matter (OM) remineralization and storage in the biosphere. Microbial metabolism in the deep ocean is greatly controlled by the generally depleted but periodically fluctuating supply of OM. Currently, little is known about metabolic potentials of dominant deep-sea microbes to cope with the variable OM inputs, especially for those living in the hadal trenches-the deepest part of the ocean.

RESULTS

In this study, we report the first extensive examination of the metabolic potentials of hadal sediment Chloroflexi, a dominant phylum in hadal trenches and the global deep ocean. In total, 62 metagenome-assembled-genomes (MAGs) were reconstructed from nine metagenomic datasets derived from sediments of the Mariana Trench. These MAGs represent six novel species, four novel genera, one novel family, and one novel order within the classes Anaerolineae and Dehalococcoidia. Fragment recruitment showed that these MAGs are globally distributed in deep-sea waters and surface sediments, and transcriptomic analysis indicated their in situ activities. Metabolic reconstruction showed that hadal Chloroflexi mainly had a heterotrophic lifestyle, with the potential to degrade a wide range of organic carbon, sulfur, and halogenated compounds. Our results revealed for the first time that hadal Chloroflexi harbor pathways for the complete hydrolytic or oxidative degradation of various recalcitrant OM, including aromatic compounds (e.g., benzoate), polyaromatic hydrocarbons (e.g., fluorene), polychlorobiphenyl (e.g., 4-chlorobiphenyl), and organochlorine compounds (e.g., chloroalkanes, chlorocyclohexane). Moreover, these organisms showed the potential to synthesize energy storage compounds (e.g., trehalose) and had regulatory modules to respond to changes in nutrient conditions. These metabolic traits suggest that Chloroflexi may follow a "feast-or-famine" metabolic strategy, i.e., preferentially consume labile OM and store the energy intracellularly under OM-rich conditions, and utilize the stored energy or degrade recalcitrant OM for survival under OM-limited condition.

CONCLUSION

This study expands the current knowledge on metabolic strategies in deep-ocean Chlorolfexi and highlights their significance in deep-sea carbon, sulfur, and halogen cycles. The metabolic plasticity likely provides Chloroflexi with advantages for survival under variable and heterogenic OM inputs in the deep ocean. Video Abstract.

Microalgal Cultures for the Bioremediation of Urban Wastewaters in the Presence of Siloxanes

Microalgae are widely used in the bioremediation of wastewaters due to their efficient removal of pollutants such as nitrogen, phosphorus, and contaminants of emerging concern (CECs). Siloxanes are CECs that reach wastewater treatment plants (WWTPs), leading to the production of biogas enriched with these compounds, associated with the breakdown of cogeneration equipment. The biological removal of siloxanes from wastewaters could be a sustainable alternative to the costly existing technologies, but no investigation has been performed using microalgal cultures for this purpose. This study evaluated the ability of Chlorella vulgaris to bioremediate primary (PE) and secondary (SE) urban effluents and remove volatile methylsiloxanes (VMSs). C. vulgaris grew successfully in both effluents, and approximately 86% of nitrogen and 80% of phosphorus were efficiently removed from the PE, while 52% of nitrogen and 87% of phosphorus were removed from the SE, and the presence of VMSs does not seem to have a negative influence on nutrient removal. Three out of the seven of the analysed VMSs were detected in the microalgal biomass at the end of the PE assay. However, dodecamethylcyclohexasiloxane (D6) was the one that accumulated to a greater extent, since 48% of the initial mass of D6 was detected in the biomass samples. D6 is one of the most lipophilic VMSs, which might contribute to the higher adsorption onto the surface of microalgae. Overall, the results indicate C. vulgaris’ potential to remove specific VMSs from effluents.

Functional Genetic Diversity and Plant Growth Promoting Potential of Polyphosphate Accumulating Bacteria in Soil

Polyphosphate (polyP) accumulation is an important trait of microorganisms. Implication of polyP accumulating bacteria (PAB) in enhanced biological phosphate removal, heavy metal sequestration, and dissolution of dental enamel is well studied. Phosphorous (P) accumulated within microbial biomass also regulates labile P in soil; however, abundance and diversity of the PAB in soil is still unexplored. Present study investigated the genetic and functional diversity of PAB in rhizosphere soil. Here, we report the abundance of Pseudomonas spp. as high PAB in soil, suggesting their contribution to global P cycling. Additional subset analysis of functional genes i.e., polyphosphate kinase (ppk) and exopolyphosphatase (ppx) in all PAB, indicates their significance in bacterial growth and metabolism. Distribution of functional genes in phylogenetic tree represent a more biologically realistic discrimination for the two genes. Distribution of ppx gene disclosed its phylogenetic conservation at species level, however, clustering of ppk gene of similar species in different clades illustrated its environmental condition mediated modifications. Selected PAB showed tolerance to abiotic stress and strong correlation with plant growth promotary (PGP) traits viz. phosphate solubilization, auxin and siderophore production. Interaction of PAB with A. thaliana enhanced the growth and phosphate status of the plant under salinity stress, suggestive of their importance in P cycling and stress alleviation.

IMPORTANCE Study discovered the abundance of Pseudomonas genera as a high phosphate accumulator in soil. The presence of functional genes (polyphosphate kinase [ppk] and exopolyphosphatase [ppx]) in all PAB depicts their importance in polyphosphate metabolism in bacteria. Genetic and functional diversity reveals conservation of the ppx gene at species level. Furthermore, we found a positive correlation between PAB and plant growth promotary traits, stress tolerance, and salinity stress alleviation in A. thaliana.

Repurposing anaerobic digestate for economical biomanufacturing and water recovery

Due to mounting impacts of climate change, particularly increased incidence of drought, hence water scarcity, it has become imperative to develop new technologies for recovering water from nutrient-rich, water-replete effluents other than sewage. Notably, anaerobic digestate could be harnessed for the purpose of water recovery by repurposing digestate-borne minerals as nutrients in fermentative processes. The high concentrations of ammonium, phosphate, sulfate, and metals in anaerobic digestate are veritable microbial nutrients that could be harnessed for bio-production of bulk and specialty chemicals. Tethering nutrient sequestration from anaerobic digestate to bio-product accumulation offers promise for concomitant water recovery, bio-chemical production, and possible phosphate recovery. In this review, we explore the potential of anaerobic digestate as a nutrient source and as a buffering agent in fermentative production of glutamine, glutamate, fumarate, lactate, and succinate. Additionally, we discuss the potential of synthetic biology as a tool for enhancing nutrient removal from anaerobic digestate and for expanding the range of products derivable from digestate-based fermentations. Strategies that harness the nutrients in anaerobic digestate with bio-product accumulation and water recovery could have far-reaching implications on sustainable management of nutrient-rich manure, tannery, and fish processing effluents that also contain high amounts of water. KEY POINTS: • Anaerobic digestate may serve as a source of nutrients in fermentation. • Use of digestate in fermentation would lead to the recovery of valuable water.

Fatty acid signatures of sediment microbial community in the chronically polluted mangrove ecosystem

Phospholipid fatty acid (PLFA) analysis was used to examine variation in the distribution of microbial communities in heavily polluted mangrove sediments of Thane creek, west coast of India. A total of 40 individual PLFAs representing 11 functional groups were identified in the sediment and were mainly dominated by saturated fatty acids (anaerobic prokaryotes) >50%. Significant dominance of PUFA, 16:3 ω6c (34.2%) indicators of micro-eukaryotes, in subsurface depth (p < 0.05) suggests input from the remnants of marine microalgae. Declined mean relative abundance of fungi (<6%) and actinomycetes (<1%) were detected in the sediment indicating their sensitivity to anthropic stressors. Homogenous profile of microbial diversity indicating active bioturbation. Cumulative metabolic stress evident from SAT/MUFA (>1), B/F (>1) and G⁺/G^- (<1) ratio and prolonged hypoxia to be prevalent in the creek during the study. In conclusion, PLFA signatures can thus be used as potential biomarkers of environmental monitoring and proxy for interpreting ecosystem health.

Status and advances in technologies for phosphorus species detection and characterization in natural environment- A comprehensive review

Poor recovery of phosphorus (P) across natural environment (water, soil, sediment, and biological sources) is causing rapid depletion of phosphate rocks and continuous accumulation of P in natural waters, resulting in deteriorated water quality and aquatic lives. Accurate detection and characterization of various P species using suitable analytical methods provide a comprehensive understanding of the biogeochemical cycle of P and thus help its proper management in the environment. This paper aims to provide a comprehensive review of the analytical methods used for P speciation in natural environment by dividing them into five broad categories (i.e., chemical, biological, molecular, staining microscopy, and sensors) and highlighting the suitability (i.e., targeted species, sample matrix), detection limit, advantages-limitations, and reference studies of all methods under each category. This can be useful in designing studies involving P detection and characterization across environmental matrices by providing insights about a wide range of analytical methods based on the end user application needs of individual studies.

Isolation and Purification of Organophosphorus Hydrolases Secreted from Acetone-acclimated Phosphorus Accumulating Organisms and Study of Their Properties for Hydrophobic Organophosphorus Sensor

The present work studied an acclimation method for phosphorus accumulating organisms (PAOs) with a high content of acetone in culture solutions to develop microbial-based enzyme sensors for highly hydrophobic organophosphorus (OP) pesticides. Through three steps of cultivation and acclimation, only rod-shaped bacteria survived among the various PAOs. The extracellular enzymes released from the acclimated PAOs were salted out by using ammonium sulfate, then purified by a dialysis membrane and a DEAE-Sepharose FF anion exchange column. Two enzyme components were successfully separated-both of which showed hydrolase activity on disodium p-nitrophenyl phosphate (enzyme I, 1.57 μmol/(min·μg); enzyme II, 0.88 μmol/(min·μg) at 45°C). Further, SDS-PAGE gel electrophoresis results showed that the molecular weights of enzymes I and II were about 15.11 and 11.98 kDa, respectively. On this basis, the applicability of the enzyme in hydrophobic OP biosensors was demonstrated.

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.

Waste to phosphorus: A transdisciplinary solution to P recovery from wastewater based on the TRIZ approach

Phosphorus (P) is a limited yet essential resource. P cannot be replaced, but it can be recovered from waste. We proposed the TRIZ approach (Teoria reszenija izobretatielskich zadacz - Rus., Theory of Inventive Problem Solving - Eng.) to identify a feasible solution. We aimed at minimizing the environmental impact and, by eliminating contradictions, proposed viable technical solutions. P recovery can be more sustainable based on circular economy and 4Rs (reduction, recovery, reuse, and recycling). The TRIZ approach identified sewage sludge (SS) as waste with a large potential for P recovery (up to 90%). Successful selection and application of SS management and P recovery require a transdisciplinary approach to overcome the various socio-economic, environmental, technical, and legal aspects. The review provides an understanding of principles that must be taken to improve understanding of the whole process of P recovery from wastewater while building on the last two decades of research.

Enzymatic Behavior Regulation-Based Colorimetric and Electrochemiluminescence Sensing of Phosphate Using the Cobalt Oxyhydroxide Nanosheet

In this work, a convenient and flexible assay for colorimetric and electrochemiluminescence (ECL) sensing of phosphate was proposed based on the enzymatic behavior regulation of the cobalt oxyhydroxide (CoOOH) nanosheet. CoOOH as a novel nanoenzyme exhibited a peroxidase-like activity, which could catalyze different substrates such as 2, 2'-azinobis-3-ethylbenzthiazoline-6-sulfonate (ABTS) and 4-chloro-1-naphthol (4-CN) with hydrogen peroxide (H₂O₂) as the electron acceptor. Phosphate could specifically regulate the enzymatic behavior of the CoOOH nanosheet via the deactivating effect. A high level of phosphate enabled a weak color change of ABTS, which offered a "turn-off" model of the colorimetric assay with a limit of detection of 0.673 μM. Based on the similar enzymatic behavior, this strategy could then be applied in the ECL assay utilizing l-arginine-6-aza-2-thiothymine-protected gold nanoclusters (Arg-ATT-AuNCs) as ECL signal indicators. Specifically, 4-CN was catalyzed to generate the precipitate and lead to the quenching on ECL emission. Different from colorimetric behavior, phosphate with a high concentration could induce strong ECL performance, which enabled the "turn-on" model of the ECL assay with a more sensitive determination down to 0.434 nM. This flexible enzymatic behavior regulation could then allow the phosphate measurement in environmental samples including tap water and river water with satisfactory accuracy, which holds the potential in the field of environmental protection.

Phosphate, Microbiota and CKD

Phosphate is a key uremic toxin associated with adverse outcomes. As chronic kidney disease (CKD) progresses, the kidney capacity to excrete excess dietary phosphate decreases, triggering compensatory endocrine responses that drive CKD-mineral and bone disorder (CKD-MBD). Eventually, hyperphosphatemia develops, and low phosphate diet and phosphate binders are prescribed. Recent data have identified a potential role of the gut microbiota in mineral bone disorders. Thus, parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched in the Th17 cell-inducing taxa segmented filamentous bacteria. Furthermore, the microbiota was required for PTH to stimulate bone formation and increase bone mass, and this was dependent on bacterial production of the short-chain fatty acid butyrate. We review current knowledge on the relationship between phosphate, microbiota and CKD-MBD. Topics include microbial bioactive compounds of special interest in CKD, the impact of dietary phosphate and phosphate binders on the gut microbiota, the modulation of CKD-MBD by the microbiota and the potential therapeutic use of microbiota to treat CKD-MBD through the clinical translation of concepts from other fields of science such as the optimization of phosphorus utilization and the use of phosphate-accumulating organisms.

Phosphorus and nitrogen removal by a novel phosphate-accumulating organism, Arthrobacter sp. HHEP5 capable of heterotrophic nitrification-aerobic denitrification: Safety assessment, removal characterization, mechanism exploration and wastewater treatment

A novel phosphate-accumulating organism (PAO), Arthrobacter sp. HHEP5 was isolated from mariculture effluents. It produced no hemolysin and was susceptible to most antibiotics. It had removal efficiencies of above 99% for 1-10 mg/L phosphorus at 18-28 °C, pH 5.5-8.5, salinities 0-3%, C/N ratios 5-20, P/N ratios 0.1-0.2 and 20-260 rpm. It exhibited simultaneous aerobic phosphorus removal, nitrification and denitrification with the highest ammonium, nitrite, nitrate removal efficiencies of 99.87%, 100%, 99.37%. Phosphorus removal was accomplished by assimilating phosphate with the existence of polyphosphate kinase completely under aerobic condition. Genes involved in nitrogen removal were amplified. 99% of phosphorus and 95% of nitrogen in both mariculture and domestic wastewater were removed by HHEP5. This study provided sound methods for future screening of PAOs and new perspectives for renewed cognition of phosphorus removal process. Wide adaptation and remarkably aerobic phosphorus, nitrogen removal performances would make HHEP5 a promising candidate in wastewater treatment.

Stress-induced assays for polyphosphate quantification by uncoupling acetic acid uptake and anaerobic phosphorus release

Phosphorus has been successfully eliminated from wastewater by biological techniques of enhanced biological phosphorus removal (EBPR) process, which relies on a specific microbiota of polyphosphate accumulating organisms (PAOs) that accumulate phosphate as polyphosphates (poly-P). Most methods for quantification of poly-P pools suffer from low accuracy and specificity. More powerful and implementable P-analysis tools are required for poly-P quantification, which will help in improved evaluation of processes in laboratory and full-scale EBPR systems. This study developed two methods to quantify poly-P pools by releasing the poly-P from the cell. During experimental optimization, it was observed that two different methods resulted in the highest phosphate release: acetate addition at a pH of 4.8 and exposure to EDTA solution with a concentration of 1% (w/v). Treatment with EDTA resulted in a higher amount of phosphate release from all sludge samples. This was characterized by P-release of 1.5-2.5 times higher than the control tests. In contrast, treatments with acetate addition at a low pH exhibited that P-release depended upon the types of the sludge samples. The highest P-release amount and rate were found in highly-enriched PAO sludge samples, but with fewer influences on the sludge collected from WWTP, which may be attributed to the lower fraction of PAOs in the sludge. Overall, the proposed approaches to quantify the poly-P concentration can be applied in simple, user-friendly, and cost-effective ways.

Phosphorus removal from landfill leachate by microalgae

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Microalgae were able to grow in high N-NH₄⁺ landfill leachate

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P-PO₄⁻³ removal was quicker than N-NH₄⁺ and N-NO₃

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Microalgal species stored P-PO₄⁻³ as intracellular poly-P granules

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100% P-PO₄⁻³ was removed before reaching the end of experiment

Phosphorus is an essential constituent of all living organisms but it is non-renewable and its natural reserves are fast depleting. Phosphorus discharged in wastewater could be sustainably reused by microalgae. Knowledge about cellular phosphorus dynamics in microalgae has been rapidly advancing and luxury phosphorus (poly-P) uptake phenomenon by microalgae is becoming the focus point for many research studies. Ultra-membrane treated landfill leachate was used as a nutrient medium for the growth of indigenous microalgal species with simultaneous removal of phosphorus (P-PO₄⁻³) and nitrogen (N-NH₄⁺ and N-NO₃). Different concentrations of phosphorus (15–100 mg. L^-1 P-PO₄⁻³) was added to leachate. Highest nitrogen removal (69.03% N-NH₄⁺) was observed for 100 mg. L^-1 P-PO₄⁻³ supplemented medium. P removal efficiency was 100% for all the tested P-PO₄^-3 concentrations. Intracellular poly-P was detected by florescence microscopy. Microalgae can be grown and utilized for the sustainable recovery of P and N from landfill leachate.

The PolS-PolR Two-Component System Regulates Genes Involved in Poly-P Metabolism and Phosphate Transport in Microlunatus phosphovorus

Microlunatus phosphovorus NM-1 is a polyphosphate (poly-P)-accumulating bacterium that accumulates poly-P under aerobic conditions and degrades poly-P under anaerobic conditions. In this study, the two-component system (TCS) PolS-PolR was identified in NM-1, and the response regulator PolR was found to directly bind to the promoters of genes related to phosphate transport (MLP_RS00235, MLP_RS23035, and MLP_RS24590); poly-P catabolism (MLP_RS12905) and poly-P synthesis (MLP_RS23025). RT-qPCR assays showed that ppgk (MLP_RS12905), ppk (MLP_RS23025), pstS (MLP_RS23035), and pit (MLP_RS24590) were down-regulated during the aerobic-anaerobic shift. The sequence GTTCACnnnnnGTTCaC was identified as a recognition sequence for PolR by MEME analysis and DNase I footprinting. EMSAs and ChIP-qPCR assays indicated that PolR binds to the promoters of pit (MLP_RS00235), ppgk (MLP_RS12905), ppk (MLP_RS23025), pstS (MLP_RS23035) and pit (MLP_RS24590), and ChIP-qPCR further suggested that the binding affinity of PolR was lower under anaerobic conditions than under aerobic conditions in vivo. These findings indicate that the PolS-PolR TCS in M. phosphovorus may be involved in the regulation of poly-P metabolism in response to levels of dissolved oxygen in the environment, and our results provide insights into new approaches for understanding the mechanisms of phosphorus accumulation and release.

Treatment of triethyl phosphate wastewater by Fenton oxidation and aerobic biodegradation

The conventional (i.e., aerobic biodegradation) and advanced (i.e., Fenton oxidation) treatment methods with implementation potentials were in parallel investigated for the treatment of industrial wastewater rich in organic phosphorus (Org.-P, dominated by triethyl phosphate (TEP)). Fenton effectively reduced Org.-P from 58 to 5 mg/L under the optimal reaction conditions of 20 mM H₂O₂, 14 mM Fe²⁺, pH 3.0, 120 mins' reaction time and the continuous dosing method (N = 4), following the first order kinetic model with a reaction rate constant of 0.07 min^-1. Nevertheless, the pretreatment prior to Fenton reaction (e.g., desalination) is recommended since high salinity significantly hindered TEP degradation, possibly due to the formation of Fe-Cl complexation and its scavenging effect to ∙OH. The Org.-P mineralization rate of ~98% was achieved by aerobic biodegradation. The excellent performance was maintained up to a salinity of 4.6% (w/w), higher than which the mineralization was seriously deteriorated. The high salinity could inhibit the microbial growth. This property might be responsible for the insufficient Org.-P removal during the on-site wastewater biological treatment. The Org.-P and COD concentrations were 6 and 405 mg/L respectively after the realistic wastewater treatment by biodegradation and coagulation, which meets with the municipal sewer discharge standard (GB/T 31962-2015).

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.

Optimization of organics to nutrients (COD:N:P) ratio for aerobic granular sludge treating high-strength organic wastewater

The present study attempted to optimize the nutrients required for biological growth and biomass synthesis in the treatment of high-strength organics wastewater using aerobic granular sludge (AGS). Three identical sequencing batch reactors (SBRs) were used to cultivate aerobic granules at COD concentration of ~5000 mg/L at COD:N:P ratios of 100:2.8:0.4, 100:4.4:0.5, and 100:5:0.7. Results indicated that the amount of nutrients needed for biomass growth does not follow the conventional organics to nutrients ratio (COD:N:P) of 100:5:1 when dealing with high-strength organics wastewater. The highest removal efficiency was achieved at COD:N:P ratio of 100:2.8:0.4, where COD, TN, and P removal was 98.8 ± 0.3%, 100.0 ± 0.0%, and 99.3 ± 1.0%, respectively. Moreover, the presence of high amounts of organics led to the dominance of the fast-growing heterotrophs in all SBRs, with the genus Thauera identified as the most abundant genera (23-40%), while autotrophic nitrifiers disappeared. The observed biomass yield at COD:N ratio of 100:2.8 suggested that heterotrophic nitrification may have occurred, while at COD:N ratios of 100:4.4 and 100:5, all the nitrogen was used for biomass synthesis. Moreover, at COD:N ratio of 100:5, almost 1/5 of the organics were utilized by the biomass cells to produce EPS as defensive action against the effects of free ammonia. Batch optimization experiments showed that the fastest rate of removal occurred at COD:N:P ratio of 100:1.1:0.4. After 4 h, the COD, TN, and P removal efficiencies were 95%, 99%, and 96%, achieving overall removal efficiencies of 98%, 100%, and 97% respectively, at HRT of 8 h. The bacterial behavior in consuming the organics was altered under nutrient-deficient conditions, where faster degradation rates were observed as the amounts of nutrients decreased, with higher relative abundance of heterotrophs and diazotrophic bacterial populations.

Optimal strategies for bioremediation of nitrate-contaminated groundwater and microalgae biomass production

Optimizing the mono-cultivation and mixed cultivation of Chlamydomonas reinhardtii, Chlorella vulgaris, and an Ettlia sp. was evaluated for treating nitrate-contaminated groundwater and biomass production. Ettlia sp. showed the highest nutrient assimilation and growth rate among the three microalgae during bioremediation. Light-dark cycle was the effective condition for nutrient removal and COD mitigation by microalgae. Mixed microalgae with a larger presence of the Ettlia sp. exhibited the highest biomass productivity, nitrate-nitrogen, and phosphate-phosphorus removal rates of 0.21 g/L/d, 16.6, and 3.06 mg/L/d, respectively. An N:P mass ratio of 5 was necessary to increase the mixed-microalgal performance. The settling efficiency of the mixed microalgae increased up to 0.55 when using pH modulation during 30 min. Therefore, applying an Ettlia sp.-dominant consortium was the optimum strategy for the bioremediation of nitrate-contaminated groundwater in 3 days.

Two-Armed Activation of Bone Mineral Deposition by the Flavones Baicalin and Baicalein, Encapsulated in Polyphosphate Microparticles

In this study, we investigated the effect of the two flavonoids, baicalin (baicalein 7-O-[Formula: see text]- d-glucuronic acid) and its aglycone, baicalein (5,6,7-trihydroxyflavone), after encapsulation into amorphous calcium polyphosphate (Ca-polyP) microparticles on mineralization of primary human osteoblasts (phOSB). Both flavonoids, which come from root extracts of Scutellaria baicalensis Georgi, are used in Traditional Chinese Medicine, and are nontoxic in cells up to a concentration of 3[Formula: see text][Formula: see text]g/ml. The morphogenetically active, energy-rich Ca-polyP particles with a stoichiometric P:Ca ratio of 1:2 are degraded by cellular alkaline phosphatase (ALP) to ortho-phosphate used for bone hydroxyapatite formation. Here we show that the flavone-loaded Ca-polyP microparticles are readily taken up by phOSB, resulting in the accumulation of polyP around the nuclei and the formation of intracellular vesicles containing the ALP. In addition, we demonstrate that baicalin/baicalein causes a rise of the intracellular calcium [Ca[Formula: see text]]_i a level which markedly is augmented after encapsulation into Ca-polyP, through activation of the phospholipase C. Moreover, both flavones, either alone or associated with Ca-polyP microparticles, upregulate the expression of the osteoblast calcium efflux channel, the plasma membrane Ca[Formula: see text]-ATPase (PMCA), while the expression of ALP, which promotes bone mineralization, is induced by Ca-polyP and by the flavones only if present in the Ca-polyP-microparticle-associated form. As a result, the extent of bone mineralization is markedly enhanced. Based on the two-armed activating function, new applications of baicalin/baicalein as a component of nutriceuticals for osteoporosis prevention or bone implants can be envisaged.

Looking for phosphate-accumulating bacteria in activated sludge processes: a multidisciplinary approach

Over the past decades, an increasing need in renewable resources has progressively appeared. This trend concerns not only fossil fuels but also mineral resources. Wastewater and sewage sludge contain significant concentrations in phosphate and can be considered as a fertilizer source of the utmost importance. In wastewater treatment plants, the biological uptake of phosphate is performed by a specific microbiota: the phosphate-accumulating organisms. These microorganisms are recovered in sewage sludge. Here, we aimed to investigate the occurrence of phosphate accumulators in four wastewater treatment plants. A 16S metagenetic analysis identified the main bacterial phyla extracted from the aerobic treatment: α-Proteobacteria, β-Proteobacteria, and Sphingobacteria. An enrichment stage was performed to stimulate the specific growth of phosphate-accumulating bacteria in an acetate medium. An analysis of metabolic activities of sulfur and phosphorus highlighted strong modifications related to phosphorus and much less distinguishable effects with sulfur. A solid acetate medium containing 5-Br-4-Cl-3-indolyl phosphate was used to select potential phosphate-accumulating bacteria from the enriched consortia. The positive strains have been found to belong in the genera Acinetobacter, Corynebacterium, and Pseudomonas. Finally, electron microscopy was applied to the strains and allowed to confirm the presence of polyphosphate granules. Some of these bacteria contained granules the size of which exceeded 100 nm.