Phosphate Depletion Research Articles

Comparison of growth and toxicity responses between non-toxic and toxic strains of Prorocentrum hoffmannianum

We aimed to study the growth and toxicity responses of non-toxic (CCMP683) and toxic (CCMP2804) strains of Prorocentrum hoffmannianum under various nitrate and phosphate concentrations. The 2 strains were cultured in L1-Si medium with standard, depleted or 10-fold repleted nitrate or phosphate. CCMP683 cultured in standard L1-Si medium exhibited delayed growth. Nitrate or phosphate depletion decreased the cell density of both strains. Repletion of nitrate slightly increased the cell density of both strains. Repletion of phosphate also slightly increased the cell density of CCMP2804 but surprisingly decreased the cell density of CCMP683. Okadaic acid (OA) and its derivatives were not detected in CCMP683. OA was detected only in CCMP2804. Depletion of nitrate or phosphate increased the cellular concentration of OA, and repletion of nitrate or phosphate had no effect on the cellular concentration of OA. Correlation analysis indicated that the cellular concentration of OA was negatively correlated with cell density. Differences in the growth response to phosphate repletion and in the ability to produce OA suggest that the 2 strains may be good candidates for comparative studies related to phosphate metabolism and OA toxicity.

Optimization of heterotrophic cultivation of Chlorella sp. HS2 using screening, statistical assessment, and validation

The heterotrophic cultivation of microalgae has a number of notable advantages, which include allowing high culture density levels as well as enabling the production of biomass in consistent and predictable quantities. In this study, the full potential of Chlorella sp. HS2 is explored through optimization of the parameters for its heterotrophic cultivation. First, carbon and nitrogen sources were screened in PhotobioBox. Initial screening using the Plackett-Burman design (PBD) was then adopted and the concentrations of the major nutrients (glucose, sodium nitrate, and dipotassium phosphate) were optimized via response surface methodology (RSM) with a central composite design (CCD). Upon validation of the model via flask-scale cultivation, the optimized BG11 medium was found to result in a three-fold improvement in biomass amounts, from 5.85 to 18.13 g/L, in comparison to a non-optimized BG11 medium containing 72 g/L glucose. Scaling up the cultivation to a 5-L fermenter resulted in a greatly improved biomass concentration of 35.3 g/L owing to more efficient oxygenation of the culture. In addition, phosphorus feeding fermentation was employed in an effort to address early depletion of phosphate, and a maximum biomass concentration of 42.95 g/L was achieved, with biomass productivity of 5.37 g/L/D.

Environmental and health co-benefits for advanced phosphorus recovery

Worldwide food production is largely dependent on rock phosphate, a finite raw material used for the production of concentrated phosphorus fertilizers. With the aim to close the biogeochemical phosphorus cycle across regions and urban–rural systems, advanced phosphorus recovery applies thermochemical and precipitation techniques to transform locally available biogenic materials into concentrated phosphorus fertilizers. Due to insufficient insights into the consequential impacts of these circular processes, opportunities to align advanced phosphorus recovery with agricultural sustainability are still widely unknown. Here we show that environmental and health life cycle impacts are often lower for phosphorus fertilizers sourced from secondary raw materials than for rock phosphate-derived products, especially in areas of high livestock and population density. Including externalities from rock phosphate extraction and avoided current-day management of biogenic materials in the comparative product life cycle severely alters the cost assessment relative to an analysis that considers only internal costs from manufacturers’ production processes. Societal costs incurred for circular products derived from sewage sludge, manure and meat and bone meal are up to 81%, 50% and 10% lower than for rock-derived superphosphate, respectively. Even without accounting for rock phosphate depletion risks, short-term and local environmental and health co-benefits might underlie the societal cost effectiveness of advanced phosphorus recovery. Agriculture depends critically on phosphorus fertilizer from rock phosphate. This study finds environmental and health benefits from instead recovering phosphorus from secondary sources, such as sewage and manure.

Eryptosis (quasi-apoptosis) the human red blood cells. Its role in medicinal therapy

In the course of circulation erythrocytes can test damages, which compromises their integrity and thus triggers suicidal erythrocyte death or eryptosis. This mechanism is characterised by cell shrinkage, cell membrane blebbing, and cell membrane phospholipid scrambling after phosphatidylserine exposure on the cell surface that is identified by macrophages, which engulf and degrade the eryptotic cells. The term eryptosis also includes typical mechanisms, which contribute to the triggering of this process, such as oxidative stress, Ca2+ entry with an increase in cytosolic Ca2+ activity and the activation of p38 kinase, which is a kinase expressed in human erythrocytes and activated after hyperosmotic shock. Enhanced eryptosis has been observed in several clinical conditions such as diabetes, renal insufficiency, haemolytic uremic syndrome, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anaemia, beta-thalassemia, glucose-6-phosphate dehydrogenase (G6PD)-deficiency, hereditary spherocytosis, paroxysmal nocturnal haemoglobinuria, Wilson’s disease, myelodysplastic syndrome, and phosphate depletion. Therefore, eryptosis may be considered as a useful mechanism of removal of defective erythrocytes to prevent haemolysis. Moreover, the clearance of infected erythrocytes in diseases such as malaria may counteract parasitemia. Indeed it is known that sickle-cell trait, beta-thalassemia trait, G6PD-deficiency and iron deficiency confer some protection against a severe course of malaria. Importantly, strategies to control Plasmodium infection by inducing eryptosis are not expected to generate resistance of the pathogen, as the proteins involved in suicidal death of the host cell are not encoded by the pathogen and thus cannot be modified by mutations of its genes. However, excessive eryptosis could compromise microcirculation and lead to anemia. Besides, adhesion of eryptosis erythrocytes to a vascular wall also can lead to microcirculation infringement.Thus, modern representations about eryptosis expand our knowledge about the programmed death of blood cells and is more directed to create new therapeutic schemes of treatment of patients.

Antagonistic co-limitation through ion promiscuity – On the metal sensitivity of Thalassiosira oceanica under phosphorus stress

Nutrient limitation of primary producers is a fundamental principle in biogeochemical oceanography and has been used with great success in prescribing understanding to patterns of marine primary productivity. In recent years the paradigm of nutrient limitation has expanded from single nutrient limitation towards concepts of co-limitation by multiple resources. Interactive effects between multiple limiting resources are now thought commonplace in marine microbial communities. Here we investigate the response exhibited by phosphate-limited Thalassiosira oceanica to elevated concentrations of the phosphate analogs vanadate, arsenate and molybdate. Enrichments in external arsenate and vanadate to phosphate-limited cultures act to suppress growth rates entirely, an effect not seen in phosphate replete conditions. Retardation of growth rates is attributed to mistaken uptake through ion promiscuity as evidenced by observations of significant intracellular accumulation of both arsenic and vanadium under phosphate limited conditions. We describe this novel co-limitation scenario as dependent antagonistic co-limitation (DAC), and suggest that this phenomenon of non-deliberate intracellular accumulation could be used as both a proxy of phosphate stress in the modern ocean and a possible marker of phosphate depletion limiting the duration of oceanic anoxic events.

Molecular Basis and Ecological Relevance of Caulobacter Cell Filamentation in Freshwater Habitats.

All living cells are characterized by certain cell shapes and sizes. Many bacteria can change these properties depending on the growth conditions. The underlying mechanisms and the ecological relevance of changing cell shape and size remain unclear in most cases. One bacterium that undergoes extensive shape-shifting in response to changing growth conditions is the freshwater bacterium Caulobacter crescentus When incubated for an extended time in stationary phase, a subpopulation of C. crescentus forms viable filamentous cells with a helical shape. Here, we demonstrated that this stationary-phase-induced filamentation results from downregulation of most critical cell cycle regulators and a consequent block of DNA replication and cell division while cell growth and metabolism continue. Our data indicate that this response is triggered by a combination of three stresses caused by prolonged growth in complex medium, namely, the depletion of phosphate, alkaline pH, and an excess of ammonium. We found that these conditions are experienced in the summer months during algal blooms near the surface in freshwater lakes, a natural habitat of C. crescentus, suggesting that filamentous growth is a common response of C. crescentus to its environment. Finally, we demonstrate that when grown in a biofilm, the filamentous cells can reach beyond the surface of the biofilm and potentially access nutrients or release progeny. Altogether, our work highlights the ability of bacteria to alter their morphology and suggests how this behavior might enable adaptation to changing environments.IMPORTANCE Many bacteria drastically change their cell size and morphology in response to changing environmental conditions. Here, we demonstrate that the freshwater bacterium Caulobacter crescentus and related species transform into filamentous cells in response to conditions that commonly occur in their natural habitat as a result of algal blooms during the warm summer months. These filamentous cells may be better able to scavenge nutrients when they grow in biofilms and to escape from protist predation during planktonic growth. Our findings suggest that seasonal changes and variations in the microbial composition of the natural habitat can have profound impact on the cell biology of individual organisms. Furthermore, our work highlights that bacteria exist in morphological and physiological states in nature that can strongly differ from those commonly studied in the laboratory.

Sustained Release of Phosphates From Hydrogel Nanoparticles Suppresses Bacterial Collagenase and Biofilm Formation in vitro.

Intestinal disease or surgical intervention results in local changes in tissue and host-derived factors triggering bacterial virulence. A key phenotype involved in impaired tissue healing is increased bacterial collagenase expression which degrades intestinal collagen. Antibiotic administration is ineffective in addressing this issue as it inadvertently eliminates normal flora while allowing pathogenic bacteria to “bloom” and acquire antibiotic resistance. Compounds that could attenuate collagenase production while allowing commensal bacteria to proliferate normally would offer major advantages without the risk of the emergence of resistance. We have previously shown that intestinal phosphate depletion in the surgically stressed host is a major cue that triggers P. aeruginosa virulence which is suppressed under phosphate abundant conditions. Recent findings indicate that orally administered polyphosphate, hexametaphosphate, (PPi) suppresses collagenase, and biofilm production of P. aeruginosa and S. marcescens in animal models of intestinal injury but does not attenuate E. faecalis induced collagenolytic activity (Hyoju et al., 2017). Systemic administration of phosphates, however, is susceptible to rapid clearance. Given the diversity of collagenase producing bacteria and the variation of phosphate metabolism among microbial species, a combination therapy involving different phosphate compounds may be required to attenuate pathogenic phenotypes. To address these barriers, we present a drug delivery approach for sustained release of phosphates from poly(ethylene) glycol (PEG) hydrogel nanoparticles. The efficacy of monophosphate (Pi)- and PPi-loaded NPs (NP-Pi and NP-PPi, respectively) and a combination treatment (NP-Pi + NP-PPi) in mitigating collagenase and biofilm production of gram-positive and gram-negative pathogens expressing high collagenolytic activity was investigated. NP-PPi was found to significantly decrease collagenase and biofilm production of S. marcescens and P. aeruginosa. Treatment with either NP-Pi or NP-Pi + NP-PPi resulted in more prominent decreases in E. faecalis collagenase compared to NP-PPi alone. The combination treatment was also found to significantly reduce P. aeruginosa collagenase production. Finally, significant attenuation in biofilm dispersal was observed with NP-PPi or NP-Pi + NP-PPi treatment across all test pathogens. These findings suggest that sustained release of different forms of phosphate confers protection against gram-positive and gram-negative pathogens, thereby providing a promising treatment to attenuate expression of tissue-disruptive bacterial phenotypes without eradicating protective flora over the course of intestinal healing.

Phosphate-limited ocean regions select for bacterial populations enriched in the carbon-phosphorus lyase pathway for phosphonate degradation.

SummaryIn tropical and subtropical oceanic surface waters phosphate scarcity can limit microbial productivity. However, these environments also have bioavailable forms of phosphorus incorporated into dissolved organic matter (DOM) that microbes with the necessary transport and hydrolysis metabolic pathways can access to supplement their phosphorus requirements. In this study we evaluated how the environment shapes the abundance and taxonomic distribution of the bacterial carbon–phosphorus (C–P) lyase pathway, an enzyme complex evolved to extract phosphate from phosphonates. Phosphonates are organophosphorus compounds characterized by a highly stable C–P bond and are enriched in marine DOM. Similar to other known bacterial adaptions to low phosphate environments, C–P lyase was found to become more prevalent as phosphate concentrations decreased. C–P lyase was particularly enriched in the Mediterranean Sea and North Atlantic Ocean, two regions that feature sustained periods of phosphate depletion. In these regions, C–P lyase was prevalent in several lineages of Alphaproteobacteria (Pelagibacter, SAR116, Roseobacter and Rhodospirillales), Gammaproteobacteria, and Actinobacteria. The global scope of this analysis supports previous studies that infer phosphonate catabolism via C–P lyase is an important adaptive strategy implemented by bacteria to alleviate phosphate limitation and expands the known geographic extent and taxonomic affiliation of this metabolic pathway in the ocean.

Arsenate and microbial dynamics in different phosphorus regimes of the subtropical Pacific Ocean

Biologically toxic arsenate is physicochemically similar to biologically essential phosphate. Because arsenate and phosphate are indiscriminately incorporated by microbes, their ambient concentration ratios can be an important factor controlling microbial growth and metabolism. This study investigated the spatial distributions of arsenate and phosphate and the associated biogeochemical dynamics in the subtropical North and South Pacific Ocean. Vertical arsenate and phosphate profiles (≤ 150 m) in most of the study areas showed a nutrient-type distribution where the concentrations increased below the euphotic zone. The arsenate and phosphate concentrations in the surface waters ranged from the detection limits (5 nM and 4 nM, respectively) to approximately 40 nM and 400 nM, respectively. The surface arsenate:phosphate ratios were typically lower than 1, but those in the western subtropical North Pacific (WSNP) were frequently higher than 1 due to phosphate depletion. In the WSNP surface waters, Prochlorococcus and Pelagibacter arsenic detoxification and phosphorus acquisition genes were abundant. Results of the onboard bioassays involving the addition of arsenate or phosphate to the surface water indicated that microbes throughout the study areas possessed arsenate resistance and those in the WSNP during summer were under serious phosphate limitation. Although phosphate limitation likely accelerates the relative cellular accumulation of toxic arsenate, the lowest particulate As:P ratios were observed in the summer WSNP, concurrent with the lowest dissolved organic P (DOP) concentrations and the highest alkaline phosphatase activities. These results imply that active As excretion and/or DOP utilization could alleviate As accumulation while maintaining the cellular P quota.

The Role of PHT1 Family Transporters in the Acquisition and Redistribution of Phosphorus in Plants

Phosphorus (P) is one of the most important macronutrients for plant growth and yield. Low availability of inorganic phosphate (Pi) in soil substantially curbs crop production, whereas excessive Pi fertilization causes economic and ecological problems. The rapid depletion of global rock phosphate (RP) reserves calls for efficient plant Pi-management. To cope with low Pi (LP) stress, plants have evolved morphological, physiological, molecular, and biochemical adaptations. Apart from arbuscular mycorrhizal fungi (AMF)-mediated Pi acquisition, Pi uptake, it's export, utilization, and remobilization depend on transport processes mediated by membrane bound PHosphate Transporters (PHTs), which are grouped into five families. Among these, the PHT1 family is the primary transporter involved in the acquisition of Pi from soil and redistribution within plants. In this review, we present a brief account on 5 PHTs (PHT1 to PHT5) and focus on PHT1s. We cover in detail the PHT1s identified and characterized until now in various plants including their phylogenetic relationships, induction by AMF, localization, and affinity. We also discuss the extant understanding of the regulation of PHT1s at transcriptional, post-transcriptional, and post-translational levels. Further exploitation of PHT1s will help overcome the problems associated with LP soils and assist in improving crop yields through sustainable agriculture.

Phosphate depletion controls lipid content and accumulation of heterotrophic bacteria during growth of Synechocystis sp. PCC 6803.

During the culturing of cyanobacteria, heterotrophic bacteria can compete for nutrients, compromise the quality of the harvested biomass, or cause culture crashes. We systematically investigated the effects of depleting inorganic phosphate (Pi) on the growth of the cyanobacterium Synechocystis sp. PCC 6803, its community of heterotrophic bacteria, and the biomass's chemical composition. On the one hand, depleting Pi had minimal impact on total biomass, extracellular polymeric substances (ESP), soluble microbial products (SMP), and most types of intracellular organic polymers production. On the other hand, depleting Pi led to markedly less lipid content, less heterotrophic biomass, and a shift in the heterotrophic community from Burkholderiales to Sphingobacteriales and Saprospirales. The causes of the large impacts were that Synechocystis was much better at scavenging a very low Pi concentration and lowering the Pi available to the heterotrophs. This work lays a foundation for controlling the accumulation of heterotrophs and reducing their deleterious effects in cyanobacteria culturing.

Peak phosphate in Jordan

The benefits and impacts of mineral resource extraction and processing in Jordan are changing and whilst our vast endowment of phosphate will not be exhausted soon, extraction and production are becoming more challenging. This paper establishes a conceptual analysis of peak phosphate as a powerful tool and it uses Gompertz and logistic models for measuring Jordan's phosphate peak year, peak production and depletion time. Our results showed that based on logistic and Gompertz models results, Jordan's phosphate is likely to peak in 2044 and 2048, respectively. Phosphate production has already passed the peak year in Al-Hasa and Al-Abiad mines. The logistic model for Jordan phosphate which has a peak year of 2048 and a production volume of 15.2 million tonnes matched exactly the Gompertz model for Al-Shidiyah mine which confirms that Jordan's future phosphate production will totally depend on Al-Shidiyah mine.

Peak phosphate in Jordan

The benefits and impacts of mineral resource extraction and processing in Jordan are changing and whilst our vast endowment of phosphate will not be exhausted soon, extraction and production are becoming more challenging. This paper establishes a conceptual analysis of peak phosphate as a powerful tool and it uses Gompertz and logistic models for measuring Jordan's phosphate peak year, peak production and depletion time. Our results showed that based on logistic and Gompertz models results, Jordan's phosphate is likely to peak in 2044 and 2048, respectively. Phosphate production has already passed the peak year in Al-Hasa and Al-Abiad mines. The logistic model for Jordan phosphate which has a peak year of 2048 and a production volume of 15.2 million tonnes matched exactly the Gompertz model for Al-Shidiyah mine which confirms that Jordan's future phosphate production will totally depend on Al-Shidiyah mine.

Genome-scale characterization of the vacuole nitrate transporter Chloride Channel (CLC) genes and their transcriptional responses to diverse nutrient stresses in allotetraploid rapeseed.

The Chloride Channel (CLC) gene family is reported to be involved in vacuolar nitrate (NO3-) transport. Nitrate distribution to the cytoplasm is beneficial for enhancing NO3- assimilation and plays an important role in the regulation of nitrogen (N) use efficiency (NUE). In this study, genomic information, high-throughput transcriptional profiles, and gene co-expression analysis were integrated to identify the CLCs (BnaCLCs) in Brassica napus. The decreased NO3- concentration in the clca-2 mutant up-regulated the activities of nitrate reductase and glutamine synthetase, contributing to increase N assimilation and higher NUE in Arabidopsis thaliana. The genome-wide identification of 22BnaCLC genes experienced strong purifying selection. Segmental duplication was the major driving force in the expansion of the BnaCLC gene family. The most abundant cis-acting regulatory elements in the gene promoters, including DNA-binding One Zinc Finger, W-box, MYB, and GATA-box, might be involved in the transcriptional regulation of BnaCLCs expression. High-throughput transcriptional profiles and quantitative real-time PCR results showed that BnaCLCs responded differentially to distinct NO3- regimes. Transcriptomics-assisted gene co-expression network analysis identified BnaA7.CLCa-3 as the core member of the BnaCLC family, and this gene might play a central role in vacuolar NO3- transport in crops. The BnaCLC members also showed distinct expression patterns under phosphate depletion and cadmium toxicity. Taken together, our results provide comprehensive insights into the vacuolar BnaCLCs and establish baseline information for future studies on BnaCLCs-mediated vacuolar NO3- storage and its effect on NUE.

Phosphate‐Loaded Hydrogel Nanoparticles for Sepsis Prevention Prepared via Inverse Miniemulsion Polymerization

AbstractLocal depletion of intestinal phosphate triggers changes in bacterial phenotypes that adversely affect the health of the host. This article describes a process for encapsulating phosphates in crosslinked poly(ethylene glycol) diacrylate (PEGDA) nanoparticles using inverse miniemulsion polymerization as a drug delivery approach for sustained release of phosphates to the intestinal epithelium. The effects of crosslinker, PEGDA co‐monomer, N‐vinyl pyrrolidone, (NVP) and surfactant concentrations on the nanoparticle size distribution, swelling ratio and monomer conversion are investigated. Increased surfactant and PEGDA concentrations result in smaller particle size and swelling ratio. A copolymerization model of crosslinking is used to predict conversion and gelation dynamics as a function of polymerization conditions. The model assumes that bulk polymerization can be used to approximate inverse miniemulsion polymerization with an aqueous‐phase initiator. The initiator efficiency is used as an adjustable parameter to simulate the conversion dynamics, thus accounting for radical confinement effects and interaction with emulsifier molecules.

A proposed mechanism for material-induced heterotopic ossification

Abstract Repairing large bone defects caused by severe trauma or tumor resection remains one of the major challenges in orthopedics and maxillofacial surgery. A promising therapeutic approach is the use of osteoinductive materials, i.e. materials able to drive mesenchymal stem cells into the osteogenic lineage. Even though the mechanism of this so-called intrinsic osteoinduction or material-induced heterotopic ossification has been studied for decades, the process behind it remains unknown, thus preventing any design of highly potent osteoinductive materials. We propose and demonstrate for the first time that intrinsic osteoinduction is the result of calcium and/or phosphate depletion, thus explaining why not only the material (surface) composition but also the material volume and architecture (e.g. porosity, pore size) play a decisive role in this process.

Rice single cropping or ratooning agro-system: which one is more environment-friendly?

Sustainable development of food production depends on damping the environmental impacts of agricultural production. The aim of this study was to investigate the environmental performance of rice production in single crop and ratooning (main rice + ratoon crop) agro-systems through life cycle assessment (LCA) methodology in Guilan province, Northern Iran, in 2015. The flooding irrigation regime was the dominant irrigation method for single cropping system and main crop rising in ratooning agro-system. The data were gathered through a face to face interview with 215 single crop and 115 ratoon breeder paddy farmers. The environmental risks were determined in six impact categories including global warming, terrestrial eutrophication, acidification, and depletion of fossil fuels, phosphate, and potash resources. The functional unit (FU) was set as 100kg protein. Results indicated that the CO2, N2O, and CH4 emissions of the rice ratooning agro-system (661.44, 1.96, and 5.42kg 100kg-1 protein) were less than the corresponding values in the rice single cropping agro-system (1341.63, 2.88, and 9.20kg 100kg-1 protein, respectively). Among all the environmental impact categories, the terrestrial eutrophication had the widest negative environmental effect followed by depletion of phosphate resources in single cropping agro-system with weighted indices of 0.51 and 0.41, respectively. Moreover, the terrestrial eutrophication had the largest negative environmental effect followed by acidification in rice ratooning agro-system with weighted indices of 0.48 and 0.29, respectively. Overall, the results highlighted that the rice ratooning ago-system is more environmentally beneficial than the single cropping system, particularly in terms of depletion of fossil fuels, global warming, and depletion of phosphate and potash resources categories. This priority may be improved through adopting proper management of agronomic practices for main and ratoon rice in ratooning agro-system. Graphical abstract ᅟ.

Effects of Organic Compounds on Dissolution of the Phosphate Minerals Chlorapatite, Whitlockite, Merrillite, and Fluorapatite: Implications for Interpreting Past Signatures of Organic Compounds in Rocks, Soils and Sediments.

Phosphate is an essential nutrient for life on Earth, present in adenosine triphosphate (ATP), deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and phospholipid membranes. Phosphorus does not have a significant volatile phase, and its release from minerals is therefore critical to its bioavailability. Organic ligands can enhance phosphate release from minerals relative to release in inorganic solutions, and phosphorus depletion in paleosols has consequently been used as a signature of the presence of ligands secreted by terrestrial organisms on early Earth. We performed batch dissolution experiments of the Mars-relevant phosphate minerals merrillite, whitlockite, chlorapatite, and fluorapatite in solutions containing organic compounds relevant to Mars. We also analyzed these phosphate minerals using the ChemCam laboratory instrument at Los Alamos, providing spectra of end-member phosphate phases that are likely present on the surface of Mars. Phosphate release rates from chlorapatite, whitlockite, and merrillite were enhanced by mellitic, oxalic, succinic, and acetic acids relative to inorganic controls by as much as >35 × . The effects of the organic compounds could be explained by the denticity of the ligand, the strength of the complex formed with calcium, and the solution saturation state. Merrillite, whitlockite, and chlorapatite dissolution rates were more strongly enhanced by acetic and succinic acids relative to inorganic controls (as much as >10 ×) than were fluorapatite dissolution rates (≲2 ×). These results suggest that depletion of phosphate in soils, rocks or sediments on Mars could be a sensitive indicator of the presence of organic compounds.

Adaptive response of yeast cells to triggered toxicity of phosphoribulokinase

Adjustment of plasmid copy number resulting from the balance between positive and negative impacts of borne synthetic genes, plays a critical role in the global efficiency of multistep metabolic engineering. Differential expression of co-expressed engineered genes is frequently observed depending on growth phases, metabolic status and triggered adjustments of plasmid copy numbers, constituting a dynamic process contributing to minimize global engineering burden. A yeast model involving plasmid based expression of phosphoribulokinase (PRKp), a key enzyme for the reconstruction of synthetic Calvin cycle, was designed to gain further insights into such a mechanism. A conditional PRK expression cassette was cloned either onto a low (ARS-CEN based) or a high (2-micron origin based) copy number plasmid using complementation of a trp1 genomic mutation as constant positive selection. Evolution of plasmid copy numbers, PRKp expressions, and cell growth rates were dynamically monitored following gene de-repression through external doxycycline concentration shifts. In the absence of RubisCO encoding gene permitting metabolic recycling, PRKp expression that led to depletion of ribulose phosphate, a critical metabolite for aromatic amino-acids biosynthesis, and accumulation of the dead-end diphosphate product contribute to toxicity. Triggered copy number adjustment was found to be a dynamic process depending both on plasmid types and levels of PRK induction. With the ARS-CEN plasmid, cell growth was abruptly affected only when level PRKp expression exceeded a threshold value. In contrast, a proportional relationship was observed with the 2-micron plasmid consistent with large copy number adjustments. Micro-compartment partitioning of bulk cultures by embedding individual cells into inverse culture medium/oil droplets, revealed the presence of slow and fast growing subpopulations that differ in relative proportions for low and high copy number plasmids.

Ketohexokinase C blockade ameliorates fructose-induced metabolic dysfunction in fructose-sensitive mice.

Increasing evidence suggests a role for excessive intake of fructose in the Western diet as a contributor to the current epidemics of metabolic syndrome and obesity. Hereditary fructose intolerance (HFI) is a difficult and potentially lethal orphan disease associated with impaired fructose metabolism. In HFI, the deficiency of aldolase B results in the accumulation of intracellular phosphorylated fructose, leading to phosphate sequestration and depletion, increased adenosine triphosphate (ATP) turnover, and a plethora of conditions that lead to clinical manifestations such as fatty liver, hyperuricemia, Fanconi syndrome, and severe hypoglycemia. Unfortunately, there is currently no treatment for HFI, and avoiding sugar and fructose has become challenging in our society. In this report, through use of genetically modified mice and pharmacological inhibitors, we demonstrate that the absence or inhibition of ketohexokinase (Khk), an enzyme upstream of aldolase B, is sufficient to prevent hypoglycemia and liver and intestinal injury associated with HFI. Herein we provide evidence for the first time to our knowledge of a potential therapeutic approach for HFI. Mechanistically, our studies suggest that it is the inhibition of the Khk C isoform, not the A isoform, that protects animals from HFI.