Inorganic polyphosphate occurs in the cell wall of Chlamydomonas reinhardtii and accumulates during cytokinesis

Elemental and macromolecular plasticity of Chlamydomonas reinhardtii (Chlorophyta) in response to resource limitation and growth rate

With the ongoing differential disruption of the biogeochemical cycles of major elements that are essential for all life (carbon, nitrogen, and phosphorus), organisms are increasingly faced with a heterogenous supply of these elements in nature. Given that photosynthetic primary producers form the base of aquatic food webs, impacts of changed elemental supply on these organisms are particularly important. One way that phytoplankton cope with the differential availability of nutrients is through physiological changes, resulting in plasticity in macromolecular and elemental biomass composition. Here, we assessed how the green alga Chlamydomonas reinhardtii adjusts its macromolecular (e.g., carbohydrates, lipids, and proteins) and elemental (C, N, and P) biomass pools in response to changes in growth rate and the modification of resources (nutrients and light). We observed that Chlamydomonas exhibits considerable plasticity in elemental composition (e.g., molar ratios ranging from 124 to 971 for C:P, 4.5 to 25.9 for C:N, and 15.1 to 61.2 for N:P) under all tested conditions, pointing to the adaptive potential of Chlamydomonas in a changing environment. Exposure to low light modified the elemental and macromolecular composition of cells differently than limitation by nutrients. These observed differences, with potential consequences for higher trophic levels, included smaller cells, shifts in C:N and C:P ratios (due to proportionally greater N and P contents), and differential allocation of C among macromolecular pools (proportionally more lipids than carbohydrates) with different energetic value. However, substantial pools of N and P remained unaccounted for, especially at fast growth, indicating accumulation of N and P in forms we did not measure.

Avoiding and allowing apatite precipitation in oxygenic photolithotrophs

The essential elements Ca and P, taken up and used metabolically as Ca²⁺ and H₂ PO₄ ^- /HPO₄ ^2- respectively, could precipitate as one or more of the insoluble forms calcium phosphate (mainly apatite) if the free ion concentrations and pH are high enough. In the cytosol, chloroplast stroma, and mitochondrial matrix, the very low free Ca²⁺ concentration avoids calcium phosphate precipitation, apart from occasionally in the mitochondrial matrix. The low free Ca²⁺ concentration in these compartments is commonly thought of in terms of the role of Ca²⁺ in signalling. However, it also helps avoids calcium phosphate precipitation, and this could be its earliest function in evolution. In vacuoles, cell walls, and xylem conduits, there can be relatively high concentrations of Ca²⁺ and inorganic orthophosphate, but pH and/or other ligands for Ca²⁺ , suggests that calcium phosphate precipitates are rare. However, apatite is precipitated under metabolic control in shoot trichomes, and by evaporative water loss in hydathodes, in some terrestrial flowering plants. In aquatic macrophytes that deposit CaCO₃ on their cell walls or in their environment as a result of pH increase or removal of inhibitors of nucleation or crystal growth, phosphate is sometimes incorporated in the CaCO₃ . Calcium phosphate precipitation also occurs in some stromatolites.

Failure of Micractinium simplicissimum Phosphate Resilience upon Abrupt Re-Feeding of Its Phosphorus-Starved Cultures

Microalgae are naturally adapted to the fluctuating availability of phosphorus (P) to opportunistically uptake large amounts of inorganic phosphate (P_i) and safely store it in the cell as polyphosphate. Hence, many microalgal species are remarkably resilient to high concentrations of external P_i. Here, we report on an exception from this pattern comprised by a failure of the high P_i-resilience in strain Micractinium simplicissimum IPPAS C-2056 normally coping with very high P_i concentrations. This phenomenon occurred after the abrupt re-supplementation of P_i to the M. simplicissimum culture pre-starved of P. This was the case even if P_i was re-supplemented in a concentration far below the level toxic to the P-sufficient culture. We hypothesize that this effect can be mediated by a rapid formation of the potentially toxic short-chain polyphosphate following the mass influx of P_i into the P-starved cell. A possible reason for this is that the preceding P starvation impairs the capacity of the cell to convert the newly absorbed P_i into a "safe" storage form of long-chain polyphosphate. We believe that the findings of this study can help to avoid sudden culture crashes, and they are also of potential significance for the development of algae-based technologies for the efficient bioremoval of P from P-rich waste streams.

C:N:P stoichiometric variations of herbs and its relationships with soil properties and species relative abundance along the Xiaokai River irrigation in the Yellow River Delta, China

INTRODUCTION

Soil salinity is known to affect plant performance and nutrient stoichiometry by altering their ecophysiology, and thus playing a crucial role in determining plant distribution patterns and nutrient cycles in salinized ecosystems. However, there was little consensus on the effects of salinity stress on plant C, N, and P stoichiometries. Moreover, determining the relationships between species relative species abundance and plant C, N, and P stoichiometries can help to understand the different adaptive strategies between the common and rare species as well as the community assembly process.

METHODS

We determined the plant C, N, P stoichiometries at the community and species levels and the relative abundance of species as well as the corresponding soil properties from five sampling sites along a soil salinity gradient in the Yellow River Delta, China.

RESULTS AND DISCUSSION

We found that the C concentration of belowground part increased with soil salinity. Meanwhile, plant community N concentration and C:N ratio tended to decrease with soil salinity, whereas the P concentration, C:P, and N:P ratios exhibited the opposite trends. This indicated that N use efficiency increased, while P use efficiency decreased with soil salinity. Moreover, the decreased N:P ratio indicated that N limitation was gradually aggravated along the soil salinity gradient. The soil C:P ratio and P concentration were the major factors of plant C, N, and P stoichiometries in the early growth stage, whereas the soil pH and P concentration were the major factors of plant C, N, and P stoichiometries in the late growth stage. Compared with that of the rare species, the C:N:P stoichiometry of the most common species was medium. Moreover, the intraspecific variations in the aboveground part N:P ratio and belowground part C concentration showed a significant correlation with species' relative abundance, which indicated that higher intraspecific trait variation might facilitate greater fitness and survival opportunities in environments with high heterogeneity.

CONCLUSION

Our results revealed that the plant community C:N:P stoichiometry and its determining soil properties varied with plant tissues as well as sampling seasons, and emphasized the importance of intraspecific variation in determining the functional response of plant communities to salinity stress.

Truncated hemoglobin 2 modulates phosphorus deficiency response by controlling of gene expression in nitric oxide-dependent pathway in Chlamydomonas reinhardtii

Truncated hemoglobin 2 is involved in fine-tuning of PSR1-regulated gene expression during phosphorus deprivation. Truncated hemoglobins form a large family found in all domains of life. However, a majority of physiological functions of these proteins remain to be elucidated. In the model alga Chlamydomonas reinhardtii, macro-nutritional deprivation is known to elevate truncated hemoglobin 2 (THB2). This study investigated the role of THB2 in the regulation of a subset of phosphorus (P) limitation-responsive genes in cells suffering from P-deficiency. Underexpression of THB2 in amiTHB2 strains resulted in downregulation of a suite of P deprivation-induced genes encoding proteins with different subcellular location and functions (e.g., PHOX, LHCSR3.1, LHCSR3.2, PTB2, and PTB5). Moreover, our results provided primary evidence that the soluble guanylate cyclase 12 gene (CYG12) is a component of the P deprivation regulation. Furthermore, the transcription of PSR1 gene for the most critical regulator in the acclimation process under P restriction was repressed by nitric oxide (NO). Collectively, the results indicated a tight regulatory link between the THB2-controlled NO levels and PSR1-dependent induction of several P deprivation responsive genes with various roles in cells during P-limitation.

Phycoremediation mechanisms of heavy metals using living green microalgae: physicochemical and molecular approaches for enhancing selectivity and removal capacity

Heavy metal (HM) contamination of water bodies is a serious global environmental problem. Because they are not biodegradable, they can accumulate in food chains, causing various signs of toxicity to exposed organisms, including humans. Due to its effectiveness, low cost, and ecological aspect, phycoremediation, or the use of microalgae's ecological functions in the treatment of HMs contaminated wastewater, is one of the most recommended processes. This study aims to examine in depth the mechanisms involved in the phycoremediation of HMs by microalgae, it also provides an overview of the prospects for improving the productivity, selectivity, and cost-effectiveness of this bioprocess through physicochemical and genetic engineering applications. Firstly, this review proposes a detailed examination of the biosorption interactions between cell wall functional groups and HMs, and their complexation with extracellular polymeric substances released by microalgae in the extracellular environment under stress conditions. Subsequently, the metal transporters involved in the intracellular bioaccumulation of HMs as well as the main intracellular mechanisms including compartmentalization in cell organelles, enzymatic biotransformation, or photoreduction of HMs were also extensively reviewed. In the last section, future perspectives of physicochemical and genetic approaches that could be used to improve the phytoremediation process in terms of removal efficiency, selectivity for a targeted metal, or reduction of treatment time and cost are discussed, which paves the way for large-scale application of phytoremediation processes.

Model systems for studying polyphosphate biology: a focus on microorganisms

Polyphosphates (polyP) are polymers of inorganic phosphates joined by high-energy bonds to form long chains. These chains are present in all forms of life but were once disregarded as 'molecular fossils'. PolyP has gained attention in recent years following new links to diverse biological roles ranging from energy storage to cell signaling. PolyP research in humans and other higher eukaryotes is limited by a lack of suitable tools and awaits the identification of enzymatic players that would enable more comprehensive studies. Therefore, many of the most important insights have come from single-cell model systems. Here, we review determinants of polyP metabolism, regulation, and function in major microbial systems, including bacteria, fungi, protozoa, and algae. We highlight key similarities and differences that may aid in our understanding of how polyP impacts cell physiology at a molecular level.

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.

A Phosphite Dehydrogenase Variant with Promiscuous Access to Nicotinamide Cofactor Pools Sustains Fast Phosphite-Dependent Growth of Transplastomic Chlamydomonas reinhardtii

Heterologous expression of the NAD⁺-dependent phosphite dehydrogenase (PTXD) bacterial enzyme from Pseudomonas stutzerii enables selective growth of transgenic organisms by using phosphite as sole phosphorous source. Combining phosphite fertilization with nuclear expression of the ptxD transgene was shown to be an alternative to herbicides in controlling weeds and contamination of algal cultures. Chloroplast expression of ptxD in Chlamydomonas reinhardtii was proposed as an environmentally friendly alternative to antibiotic resistance genes for plastid transformation. However, PTXD activity in the chloroplast is low, possibly due to the low NAD⁺/NADP⁺ ratio, limiting the efficiency of phosphite assimilation. We addressed the intrinsic constraints of the PTXD activity in the chloroplast and improved its catalytic efficiency in vivo via rational mutagenesis of key residues involved in cofactor binding. Transplastomic lines carrying a mutagenized PTXD version promiscuously used NADP⁺ and NAD⁺ for converting phosphite into phosphate and grew faster compared to those expressing the wild type protein. The modified PTXD enzyme also enabled faster and reproducible selection of transplastomic colonies by directly plating on phosphite-containing medium. These results allow using phosphite as selective agent for chloroplast transformation and for controlling biological contaminants when expressing heterologous proteins in algal chloroplasts, without compromising on culture performance.

Quantifying nutrient throughput and DOM production by algae in continuous culture

Freshwater and marine algae can balance nutrient demand and availability by regulating uptake, accumulation and exudation. To obtain insight into these processes under nitrogen (N) and phosphorus (P) limitation, we reanalyze published data from continuous cultures of the chlorophyte Selenastrum minutum. Based on mass budgets, we argue that much of the non-limiting N and P had passed through the organisms and was present as dissolved organic phosphorus or nitrogen (DOP or DON). We construct a model that describes the production of biomass and dissolved organic matter (DOM) as a function of the growth rate. A fit of this model against the chemostat data suggests a high turnover of the non-limiting N and P: at the highest growth rates, N and P atoms spent on average only about 3 h inside an organism, before they were exuded as DON and DOP, respectively. This DOM exudation can explain the observed trends in the algal stoichiometric ratios as a function of the dilution rate. We discuss independent evidence from isotope experiments for this apparently wasteful behavior and we suggest experiments to quantify and characterize DON and DOP exudation further.

Identity and functions of inorganic and inositol polyphosphates in plants

Inorganic polyphosphates (polyPs) and inositol pyrophosphates (PP-InsPs) form important stores of inorganic phosphate and can act as energy metabolites and signaling molecules. Here we review our current understanding of polyP and inositol phosphate (InsP) metabolism and physiology in plants. We outline methods for polyP and InsP detection, discuss the known plant enzymes involved in their synthesis and breakdown, and summarize the potential physiological and signaling functions for these enigmatic molecules in plants.

Molecular characterization of CHAD domains as inorganic polyphosphate-binding modules

A domain of unknown function termed CHAD, present in all kingdoms of life, is characterized as a specific inorganic polyphosphate-binding domain.

Inorganic polyphosphates (polyPs) are linear polymers of orthophosphate units linked by phosphoanhydride bonds. Here, we report that bacterial, archaeal, and eukaryotic conserved histidine α-helical (CHAD) domains are specific polyP-binding modules. Crystal structures reveal that CHAD domains are formed by two four-helix bundles, giving rise to a central pore surrounded by conserved basic surface patches. Different CHAD domains bind polyPs with dissociation constants ranging from the nano- to mid-micromolar range, but not nucleic acids. A CHAD—polyP complex structure reveals the phosphate polymer binding across the central pore and along the two basic patches. Mutational analysis of CHAD—polyP interface residues validates the complex structure. The presence of a CHAD domain in the polyPase ygiF enhances its enzymatic activity. The only known CHAD protein from the plant Ricinus communis localizes to the nucleus/nucleolus when expressed in Arabidopsis and tobacco, suggesting that plants may harbor polyPs in these compartments. We propose that CHAD domains may be used to engineer the properties of polyP-metabolizing enzymes and to specifically localize polyP stores in eukaryotic cells and tissues.

The putative G protein-coupled receptor GrlD mediates extracellular polyphosphate sensing in Dictyostelium discoideum

Five or more orthophosphates bound together by high-energy phosphoanhydride bonds are highly ubiquitous inorganic molecules called polyphosphate. Polyphosphate acts as a signaling molecule eliciting a number of responses in eukaryotic cells, but the mechanisms mediating these effects are poorly understood. Proliferating Dictyostelium discoideum cells accumulate extracellular polyphosphate. At extracellular concentrations similar to those observed in stationary phase cells, polyphosphate inhibits proteasome activity and proliferation, and induces aggregation. Here we identify GrlD as a putative G protein–coupled receptor that mediates binding of extracellular polyphosphate to the cell surface. Cells lacking GrlD do not respond to polyphosphate-induced proteasome inhibition, aggregation, or proliferation inhibition. Polyphosphate also elicits differential effects on cell-substratum adhesion and cytoskeletal F-actin levels based on nutrient availability, and these effects were also mediated by GrlD. Starving cells also accumulate extracellular polyphosphate. Starved cells treated with exopolyphosphatase failed to aggregate effectively, suggesting that polyphosphate also acts as a signaling molecule during starvation-induced development of Dictyostelium. Together, these results suggest that a eukaryotic cell uses a G protein–coupled receptor to mediate the sensing and response to extracellular polyphosphate.

Degradation of phosphate polymer polyP enhances lactic fermentation in mice

In bacteria, a polymer of inorganic phosphate (Pi) (inorganic polyphosphate; polyP) is enzymatically produced and consumed as an alternative phosphate donor for adenosine triphosphate (ATP) production to protect against nutrient starvation. In vertebrates, polyP has been dismissed as a "molecular fossil" due to the lack of any known physiological function. Here, we have explored its possible role by producing transgenic (TG) mice widely expressing Saccharomyces cerevisiae exopolyphosphatase 1 (ScPPX1), which catalyzes hydrolytic polyP degradation. TG mice were produced and displayed reduced mitochondrial respiration in muscles. In female TG mice, the blood concentration of lactic acid was enhanced, whereas ATP storage in liver and brain tissues was reduced significantly. Thus, we suggested that the elongation of polyP reduces the intracellular Pi concentration, suppresses anaerobic lactic acid production, and sustains mitochondrial respiration. Our results provide an insight into the physiological role of polyP in mammals, particularly in females.

Microalgae-bacteria biofilms: a sustainable synergistic approach in remediation of acid mine drainage

Microalgae and bacteria offer a huge potential in delving interest to study and explore various mechanisms under extreme environments. Acid mine drainage (AMD) is one such environment which is extremely acidic containing copious amounts of heavy metals and poses a major threat to the ecosystem. Despite its extreme conditions, AMD is the habitat for several microbes and their activities. The use of various chemicals in prevention of AMD formation and conventional treatment in a larger scale is not feasible under different geological conditions. It implies that microbe-mediated approach is a viable and sustainable alternative technology for AMD remediation. Microalgae in biofilms play a pivotal role in such bioremediation as they maintain mutualism with heterotrophic bacteria. Synergistic approach of using microalgae-bacteria biofilms provides supportive metabolites from algal biomass for growth of bacteria and mediates remediation of AMD. However, by virtue of their physiology and capabilities of metal removal, non-acidophilic microalgae can be acclimated for use in AMD remediation. A combination of selective acidophilic and non-acidophilic microalgae together with bacteria, all in the form of biofilms, may be very effective for bioremediation of metal-contaminated waters. The present review critically examines the nature of mutualistic interactions established between microalgae and bacteria in biofilms and their role in removal of metals from AMDs, and consequent biomass production for the yield of biofuel. Integration of microalgal-bacterial consortia in fuel cells would be an attractive emerging approach of microbial biotechnology for AMD remediation.

Microalgae-bacteria biofilms: a sustainable synergistic approach in remediation of acid mine drainage

Microalgae and bacteria offer a huge potential in delving interest to study and explore various mechanisms under extreme environments. Acid mine drainage (AMD) is one such environment which is extremely acidic containing copious amounts of heavy metals and poses a major threat to the ecosystem. Despite its extreme conditions, AMD is the habitat for several microbes and their activities. The use of various chemicals in prevention of AMD formation and conventional treatment in a larger scale is not feasible under different geological conditions. It implies that microbe-mediated approach is a viable and sustainable alternative technology for AMD remediation. Microalgae in biofilms play a pivotal role in such bioremediation as they maintain mutualism with heterotrophic bacteria. Synergistic approach of using microalgae-bacteria biofilms provides supportive metabolites from algal biomass for growth of bacteria and mediates remediation of AMD. However, by virtue of their physiology and capabilities of metal removal, non-acidophilic microalgae can be acclimated for use in AMD remediation. A combination of selective acidophilic and non-acidophilic microalgae together with bacteria, all in the form of biofilms, may be very effective for bioremediation of metal-contaminated waters. The present review critically examines the nature of mutualistic interactions established between microalgae and bacteria in biofilms and their role in removal of metals from AMDs, and consequent biomass production for the yield of biofuel. Integration of microalgal-bacterial consortia in fuel cells would be an attractive emerging approach of microbial biotechnology for AMD remediation.

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.

Critical function of a Chlamydomonas reinhardtii putative polyphosphate polymerase subunit during nutrient deprivation

Forward genetics was used to isolate Chlamydomonas reinhardtii mutants with altered abilities to acclimate to sulfur (S) deficiency. The ars76 mutant has a deletion that eliminates several genes, including VACUOLAR TRANSPORTER CHAPERONE1 (VTC1), which encodes a component of a polyphosphate polymerase complex. The ars76 mutant cannot accumulate arylsulfatase protein or mRNA and shows marked alterations in levels of many transcripts encoded by genes induced during S deprivation. The mutant also shows little acidocalcisome formation compared with wild-type, S-deprived cells and dies more rapidly than wild-type cells following exposure to S-, phosphorus-, or nitrogen (N)-deficient conditions. Furthermore, the mutant does not accumulate periplasmic L-amino acid oxidase during N deprivation. Introduction of the VTC1 gene specifically complements the ars76 phenotypes, suggesting that normal acidocalcisome formation in cells deprived of S requires VTC1. Our data also indicate that a deficiency in acidocalcisome function impacts trafficking of periplasmic proteins, which can then feed back on the transcription of the genes encoding these proteins. These results and the reported function of vacuoles in degradation processes suggest a major role of the acidocalcisome in reshaping the cell during acclimation to changing environmental conditions.

The effects of different coatings on zinc oxide nanoparticles and their influence on dissolution and bioaccumulation by the green alga, C. reinhardtii

Determining the environmental risk of nanoparticles (NPs) requires an in-depth understanding of the NP core, the particle surface coatings and the interactions of the two with environmental matrices. Non-coated ZnO NPs (nZnO) are known to release ionic Zn, contributing directly to the toxicity of these particles. On the other hand, relatively less data are available for particles that have coatings designed to increase particle stability. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Zn salt or nZnO with different stabilizers: (i) bare nZnO, (ii) polyacrylic acid-stabilized, nZnO-PAA, or a (iii) sodium hexametaphosphate-stabilized, nZnO-HMP. Multiple techniques were used to quantify particle agglomeration and dissolution. The dissolution of the NPs depended on the stabilizer, with the largest dissolution obtained for the bare nZnO (near total dissolution), followed by the nZnO-PAA. When exposed to the bare and PAA-stabilized nZnOs, bioaccumulation was largely accounted for by free Zn. On the other hand, the bioaccumulation of nZnO-HMP was greater than could be attributed to the release of free Zn from the particles. The increased Zn bioaccumulation was hypothesized to have resulted from the biological stimulation of C. reinhardtii due to phosphate from the particle coating.

Systems Analysis of the Response of Photosynthesis, Metabolism, and Growth to an Increase in Irradiance in the Photosynthetic Model Organism Chlamydomonas reinhardtii

We investigated the systems response of metabolism and growth after an increase in irradiance in the nonsaturating range in the algal model Chlamydomonas reinhardtii. In a three-step process, photosynthesis and the levels of metabolites increased immediately, growth increased after 10 to 15 min, and transcript and protein abundance responded by 40 and 120 to 240 min, respectively. In the first phase, starch and metabolites provided a transient buffer for carbon until growth increased. This uncouples photosynthesis from growth in a fluctuating light environment. In the first and second phases, rising metabolite levels and increased polysome loading drove an increase in fluxes. Most Calvin-Benson cycle (CBC) enzymes were substrate-limited in vivo, and strikingly, many were present at higher concentrations than their substrates, explaining how rising metabolite levels stimulate CBC flux. Rubisco, fructose-1,6-biosphosphatase, and seduheptulose-1,7-bisphosphatase were close to substrate saturation in vivo, and flux was increased by posttranslational activation. In the third phase, changes in abundance of particular proteins, including increases in plastidial ATP synthase and some CBC enzymes, relieved potential bottlenecks and readjusted protein allocation between different processes. Despite reasonable overall agreement between changes in transcript and protein abundance (R2 = 0.24), many proteins, including those in photosynthesis, changed independently of transcript abundance.

Biochemical and biomedical aspects of metabolic imidazoles

The imidazole structure is involved in the formation of several compounds in the human metabolism including methyl imidazole, imidazole acetic acid, histidine, histamine, carnosine and homocarnosine. A number of these compounds are widely distributed metabolites such as histamine which is present in basophil and mast cells as well as being present in muscle and brain cells. This work advances detailed proposals on the metabolic chemical reactions which produce and decompose the compounds. The activity of these compounds in detrimental allergic medical conditions is discussed and the origin of the medical observations of the imidazole based medical compound known as cimetidine is discussed.

The function of oxalic acid in the human metabolism

Biochemical reactions in cells which involve oxalic acid are described. It is shown that this compound is required for the formation of uracil and orotic acid. The former is a component of RNA which is common to all cells in the human metabolism. On the basis of the biochemical reactions described a possible treatment to relieve the effects of calcium oxalate renal calculi whose origin is related to the metabolic concentration of oxalic acid is proposed.

Genetic interactions between regulators of Chlamydomonas phosphorus and sulfur deprivation responses

The Chlamydomonas reinhardtii PSR1 gene is required for proper acclimation of the cells to phosphorus (P) deficiency. P-starved psr1 mutants show signs of secondary sulfur (S) starvation, exemplified by the synthesis of extracellular arylsulfatase and the accumulation of transcripts encoding proteins involved in S scavenging and assimilation. Epistasis analysis reveals that induction of the S-starvation responses in P-limited psr1 cells requires the regulatory protein kinase SNRK2.1, but bypasses the membrane-targeted activator, SAC1. The inhibitory kinase SNRK2.2 is necessary for repression of S-starvation responses during both nutrient-replete growth and P limitation; arylsulfatase activity and S deficiency-responsive genes are partially induced in the P-deficient snrk2.2 mutants and become fully activated in the P-deficient psr1snrk2.2 double mutant. During P starvation, the sac1snrk2.2 double mutants or the psr1sac1snrk2.2 triple mutants exhibit reduced arylsulfatase activity compared to snrk2.2 or psr1snrk2.2, respectively, but the sac1 mutation has little effect on the abundance of S deficiency-responsive transcripts in these strains, suggesting a post-transcriptional role for SAC1 in elicitation of S-starvation responses. Interestingly, P-starved psr1snrk2.2 cells bleach and die more rapidly than wild-type or psr1 strains, suggesting that activation of S-starvation responses during P deprivation is deleterious to the cell. From these results we infer that (i) P-deficient growth causes some internal S limitation, but the S-deficiency responses are normally inhibited during acclimation to P deprivation; (ii) the S-deficiency responses are not completely suppressed in P-deficient psr1 cells and consequently these cells synthesize some arylsulfatase and exhibit elevated levels of transcripts for S-deprivation genes; and (iii) this increased expression is controlled by regulators that modulate transcription of S-responsive genes during S-deprivation conditions. Overall, the work strongly suggests integration of the different circuits that control nutrient-deprivation responses in Chlamydomonas.

Allometry and stoichiometry of unicellular, colonial and multicellular phytoplankton

Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organisms, span a huge size range. The smallest unicells are less than 1 microm3 (e.g. cyanobacteria), while large unicellular diatoms may attain 10(9) microm3, being visible to the naked eye. Phytoplankton includes chemo-organotrophic unicells, colonies and multicellular organisms that depend on symbionts or kleptoplastids for their capacity to photosynthesize. Analyses of physical (transport within cells, diffusion boundary layers, package effect, turgor, and vertical movements) and biotic (grazing, viruses and other parasitoids) factors indicate potential ecological constraints and opportunities that differ among the life forms. There are also variations among life forms in elemental stoichiometry and in allometric relations between biovolume and specific growth. While many of these factors probably have ecological and evolutionary significance, work is needed to establish those that are most important, warranting explicit description in models. Other factors setting limitations on growth rate (selecting slow-growing species) await elucidation.