Net Phosphate Uptake Research Articles

Regulation of phosphate uptake reveals cyanobacterial bloom resilience to shifting N:P ratios

Abstract The resilience of cyanobacterial blooms challenges lake restoration programmes based on nutrient load reduction. The survival of organisms may depend on episodic short‐term fluctuations of nitrogen (N) and phosphorus (P). Insight into physiological responses to shifts in nutrient limitation will improve our understanding of cyanobacterial bloom resilience. This study investigated the resilience and collapse of a long‐term cyanobacterial bloom dominated by Planktothrix agardhii and Raphidiopsis mediterranea, subjected to different periods of dissolved inorganic nitrogen (DIN) and phosphorus (SRP) inputs in Lago Rodó, a polymictic, hypereutrophic (6.0 ± 1.6 μmol total P/L) and turbid lake (attenuation coefficient: 4.7 ± 1.7 m−1). Phytoplankton composition, nutrient dynamics and physiological monitoring of [32P] phosphate uptake kinetics were studied over four summers. The influence of environmental nutrient supply on phytoplankton net phosphate uptake kinetics was analysed with a flow–force model that gives the threshold value of phosphate uptake ([Pe]A), a limiting concentration below which incorporation is not energetically possible by organisms, and the membrane conductivity coefficient (LP). The [Pe]A reflects the affinity and LP the activity of the cellular uptake systems. Nutrient supply into the lake sustained high DIN:SRP ratios and high cyanobacterial biomass that showed P‐deficiency features characterised by low [Pe]A (5.4 ± 0.5 nm [32P] phosphate) and high LP. High cyanobacterial biomass persisted after external nutrient inflows were interrupted for 14 months, which resulted in low dissolved DIN:SRP ratios; however, N2‐fixers did not develop. The collapse of cyanobacterial populations occurred under the lowest N:P ratios, low affinity and activity of phosphate uptake systems and strong water outflows. Our study suggests that the alleviation of N‐deficiency under high N:P ratios enhances the activation of phosphate uptake systems by cyanobacteria. The flexible physiological response results in more efficient exploitation of limiting nutrients favouring cyanobacterial resilience under suboptimal conditions.

CNP budgets of a coral-dominated fringing reef at La Réunion, France: coupling of oceanic phosphate and groundwater nitrate

Productivity, nutrient input, nutrient uptake, and release rates were determined for a coral-dominated reef flat at La Reunion, France, to assess the influence of groundwater nitrogen on carbon and nutrient budgets. Water samples were collected offshore in the ocean, at the reef crest and back reef for nutrients, picoplankton, pH, and total alkalinity. Volume transport of ocean water across the reef flat was measured using both current meters and drogues. Groundwater advected onto the reef flat and mixed with incoming ocean water. Metabolic rates for the reef community were determined to be: gross primary production = 1,000 mmol C m−2 d−1, community respiration = 960 mmol C m−2 d−1, and community calcification = 210 mmol C m−2 d−1. Across the reef flat, silicate behaved conservatively, there was net uptake of phosphate (0.06 mmol P m−2 d−1) and net release of nitrate, ammonia, dissolved and particulate organic nitrogen (total 7.0 mmol N m−2 d−1). Groundwater nitrate contributed 37% of the increase in nitrate plus ammonia. The first-order mass transfer coefficient of phosphate was 3.3 m d−1, and for nitrate plus ammonia, 5.9 m d−1. Gross N and P uptake from estimates of mass transfer and uptake of particles were 0.37 mmol P m−2 d−1 and 7.2 mmol N m−2 d−1, respectively giving an N:P uptake ratio of 20:1. Thus, the elevation of nitrogen across the reef flat maintains a high N:P flux, enhancing algal growth downstream of the transect. We conclude that net community production (40 mmol C m−2 d−1) was sustained by net uptake of phosphate from the ocean and net uptake of new nitrogen from groundwater.

Biofiltering efficiency in removal of dissolved nutrients by three species of estuarine macroalgae cultivated with sea bass (Dicentrarchus labrax) waste waters 1. Phosphate

The potential of three estuarine macroalgae (Ulvarotundata, Enteromorpa intestinalis andGracilaria gracilis) as biofilters for phosphate ineffluents of a sea bass (Dicentrarchus labrax) cultivationtank was studied. These seaweeds thrive in Cadiz Bay and were alsoselected because of their economic potential, so that environmental andeconomicadvantages may be achieved by future integrated aquaculture practices in thelocal fish farms. The study was designed to investigate the functioning of Pnutrition of the selected species. Maximum velocity of phosphate uptake (2.86μmol PO4 g−1 dry wth−1) was found in U. rotundata.This species also showed the highest affinity for this nutrient. At low flowrates (< 2 volumes d−1), the three species efficientlyfiltered the phosphate dissolved in the waste water, with a minimum efficiencyof 60.7% in U. rotundata. Net phosphate uptake rate wassignificantly affected by the water flow, being greatest at the highest rateassayed (2 volumes d−1). The marked decrease in tissue P shownby the three species during a flow-through experiment suggested that growth wasP limited. However, due to the increase in biomass, total P biomass increasedinthe cultures. A significant correlation was found between growth rates and thenet P biomass gained in the cultures. A three-stage design under low water flow(0.5 volumes d−1) showed that the highest growth rates (up to0.14 d−1) and integrated phosphate uptake rates(up to 5.8 μmol PO43− g−1dry wt d−1) were found in E.intestinalis in the first stage, with decreasing rates in thefollowing ones. As a result, phosphate become limiting and low increments oreven losses of total P biomass in these stages were found suggesting thatphosphate was excreted from the algae. The results show the potential abilityofthe three species to reduce substantially, at low water flow, the phosphateconcentration in waste waters from a D. labrax cultivationtank, and thus the quality of effluents from intensive aquaculture practices.

Oceanic vertical exchange and new production: a comparison between models and observations

This paper explores the relationship between large-scale vertical exchange and the cycling of biologically active nutrients within the ocean. It considers how the parameterization of vertical and lateral mixing effects estimates of newproduction (defined as the net uptake of phosphate). A baseline case is run with low vertical mixing in the pycnocline and a relatively lowlateral diffusion coefficient. The magnitude of the diapycnal diffusion coefficient is then increased within the pycnocline, within the pycnocline of the Southern Ocean, and in the top 50 m; while the lateral diffusion coefficient is increased throughout the ocean. It is shown that it is possible to change lateral and vertical diffusion coefficients so as to preserve the structure of the pycnocline while changing the pathways of vertical exchange and hence the cycling of nutrients. Comparisons between the different models reveal that new production is very sensitive to the level of vertical mixing within the pycnocline, but only weakly sensitive to the level of lateral and upper ocean diffusion. The results are compared with two estimates of new production based on ocean color and the annual cycle of nutrients. On a global scale, the observational estimates are most consistent with the circulation produced with a low diffusion coefficient within the pycnocline, resulting in a new production of around 10 GtC yr � 1 : On a regional level, however, large differences appear between observational and model based estimates. In the tropics, the models yield systematically higher levels of newproduction than the observational estimates. Evidence from the Eastern Equatorial Pacific suggests that this is due to both biases in the data used to generate the observational estimates and problems with the models. In the North Atlantic, the observational estimates vary more than the models, due in part to the methodology by which the nutrient-based climatology is constructed. In the North Pacific, the modelled values of newproduction are all much lower than the observational estimates, probably as a result of the failure to form intermediate

Phosphate Uptake in the Cyanobacterium Synechococcus R-2 PCC 7942

Phosphate uptake rates in Synechococcus R-2 in BG11 media (a nitrate-based medium, not phosphate limited) were measured using cells grown semi-continuously and in continuous culture. Net uptake of phosphate is proportional to external concentration. Growing cells at pH010 have a net uptake rate of about 600 pmol m~s phosphate, but the isotopk flux for P phosphate was about 4 nraol m~s~'. There appears to be a constitutive over-capacity for phosphate uptake. The Km and Vmtx of the saturable component were not significantly different at pH0 7.5 and 10, hence the transport system probably recognizes both H2PO4 and HPO ,. The intracellular inorganic phosphate concentration is about 3 to 10 mol m~, but there is an intracellular polyphosphate store of about 400 mol m~. Intracellular inorganic phosphate is 25 to 50 kJ mol' from electrochemical equilibrium in both the light and dark and at pHo 7.5 and 10. Phosphate uptake is very slow in the dark (»100 pmol m~s~) and is light-activated (pHo 7.5«1.3nmolms~, pHo 10«600 pmol m^ ). Uptake has an irreversible requirement for Mg in the medium. Uptake in the light is strongly Na-dependent. Phosphate uptake was negatively electrogenic (net negative charge taken up when transporting phosphate) at pHo 7.5, but positively electrogenic at pHo 10. This seems to exclude a sodium motive force driven mechanism. An ATP-driven phosphate uptake mechanism needs to have a stoichiometry of one phosphate taken up per ATP (1 PO4,0/ATP) to be thermodynamically possible under all the conditions tested in the present study.

Phosphate uptake by the component parts ofChara hispida

Mean daily rates of net phosphate uptake, as determined colorimetrically from phosphate depletion of the medium, were measured for Chara hispida shoots given 1 mmol m-3 phosphate and isolated (split chamber technique) rhizoid-node complexes given 1-, 50-, 100-, 500- and 1000 mmol m-3 phosphate. Under aerobic conditions phosphate uptake by the rhizoid-node complex expressed per g FW shoot increased with external phosphate concentration 1–100 mmol m-3. At external phosphate concentrations 100–1000 mmol m-3 uptake rates by the rhizoid-node complex were two to three times greater than that for the shoot at 1 mmol m-3 phosphate. Anaerobic conditions substantially reduced uptake by the rhizoid-node complex. It is concluded that in aerobic sediments, the rhizoid could play a substantial, possibly major role in phosphate uptake by the whole plant but, in aerobic sediments, this will be the case only when phosphate levels in the open water are extremely low. After 24-h exposure of the whole plant to 32P-labelled 1...

Effect of naphthalene and aqueous crude-oil extracts on the green flagellate Chlamydomonas angulosa. VI. Phosphate uptake and retention

Chlamydomonas angulosa when grown in normal Bold's basal medium (BBM) (1.7 mM Pi) has a very high cell P content (120 fg-at. P∙cell−1) and low C: P atomic ratio (35: 1) and is only able to show net Pi uptake in media with Pi concentrations higher than 0.1 mM when grown in the light. The presence of light enhances net phosphate uptake or decreases net phosphate loss under all external Pi concentrations. Cells transferred to low-Pi media will, however, grow rapidly while reducing their cell P to almost 1/10 of the initial level, indicating that most of the cell P in cells grown in high-P media represents reserve P, probably in the form of polyphosphates. The presence of naphthalene and crude-oil components in the culture media decreases net uptake of Pi at high external Pi concentrations and increases the rate of Pi loss at low external concentrations. Naphthalene present at 100% saturation level in BBM causes rapid loss of a large fraction of cell P under all conditions tested. The phosphorus lost appears as reactive phosphorus in the medium, suggesting that cell polyphosphates are rapidly converted to Pi, which then leaks out of the cells in response to the presence of saturating naphthalene concentrations in the medium. BBM with 50% naphthalene saturation causes much less loss of cell P under most of the incubation conditions, and net uptake can take place at the highest external Pi concentrations tested in the light. Media saturated with crude oil are even less effective than 50% naphthalene saturated media in causing P efflux, or in reducing net Pi uptake, although at low external P concentrations, uptake of P is decreased compared with the control.

Chemical and Radiotracer Measurements of Phosphorus Uptake by Lake Plankton

Either chemical or radioisotope methods can be used to measure the maximum uptake velocity for phosphorus in lake water but neither can measure uptake at ambient concentrations. Chemical estimates at ambient concentrations are insensitive and the isotope method provides the uptake rate constant only. By multiplying the uptake rate constant by the ambient phosphate concentration one obtains an estimate for phosphorus influx, but reliable estimates for ambient phosphate concentrations are still unattainable. At added phosphate levels even up to 10 μg P∙L−1, the isotope method overestimates net phosphate uptake because of release of phosphate from the plankton. Influx and efflux are practically equal under steady state conditions, and during periods of phosphate limitation a net uptake of phosphorus occurs only when there is an increase in the phosphorus supply. The uptake of phosphate is predominantly by small cells at low concentrations of added phosphate and by larger cells at the higher enrichments. This makes the use of the radiobioassay for estimating ambient phosphate concentrations difficult to interpret. Furthermore the half-saturation coefficients measured for whole lake water are a mean for the entire population and consist of small values for small algae and bacteria and larger values for larger algae.Key words: phosphorus, kinetics, plankton, algae, bacteria nutrition

A Relationship between Phosphate Uptake and Membrane Electrical Potential in Excised Roots ofHelianthus annuus

Phosphate uptake by excised roots of sunflower (Helianthus annuus) was determined by the disappearance of phosphate from the external solution and by the accumulation of phosphate labelled with 32P. Over a 24 h period it was observed that net phosphate uptake declined to zero whilst uptake of 32P continued unabated. The electrical PD of the cortical cell membranes declined in parallel with net phosphate uptake and it was found that both could be restored by creating a pH gradient across the plasmalemma. It was concluded that net phosphate uptake was responsible for a component of the membrane PD of the root cortical cells.

Plasma membrane phosphate transport and extracellular phosphate concentration in the regulation of cellular respiration in isolated perfused rat heart

The role of extracellular P i and transmembrane fluxes across the sarcolemma in the regulation of cellular respiration was studied in isolated Langendorff-perfused rat hearts. Extracellular phosphate did not significantly affect the oxygen consumption or cellular phosphorylation potential of the myocardium. K +-induced arrest was used to change the mechanical work load of the heart. Arresting the heart caused a rapid decrease in the unidirectional efflux of phosphate determined by in vitro prelabelling of the intracellular phosphate compounds with 32P and determining the specific radioactivity of the γ-P of ATP, and the label appearance into the perfusion medium. At normal or elevated perfusate phosphate concentration there was a fairly slow net uptake of phosphate. The decrease in phosphate fluxes upon the K +-induced arrest was probably not due to a decrease in the transmembrane Na + or K + gradients because a further increase in the perfusate K + concentration caused an increase in the K + efflux to the levels observed in contracting hearts. The use of higher than normal concentrations of phosphate necessitated a lowering of the extracellular Ca 2+ concentration, which caused a diminution of the oxygen consumption, accompanied by mitochondrial flavoprotein oxidation in the heart. This finding suggested that the extracellular Ca 2+ concentration may be involved in the substrate level regulation of mitochondrial metabolism.

Patterns of Oxygen Interchange between Water, Substrates, and Phosphate Compounds of Escherichia coli and Bacillus subtilis

Abstract The sources of oxygen in the phosphoryl moieties of the intracellular nucleotides and RNA under several conditions were examined with Bacillus subtilis and Escherichia coli. Oxygens of nucleotides and RNA are representative of those of the intracellular phosphate pool. Important findings are: 1. Under different conditions, from 50 to 80% of the oxygens of the intracellular phosphate are derived from the medium water. A steady state level of 18O in acid-labile nucleoside di- and triphosphates is reached within a few minutes after addition of H18OH to the growth medium. The principal routes of 18O incorporation from water likely occur via exchanges of oxidative phosphorylation, hydrolysis of phosphates, and transfer from substrates partially labeled with water oxygens. 2. Extracellular phosphate contributes only a small percentage of the phosphate oxygens in B. subtilis and even less with E. coli. This shows that turnover of oxygens of intracellular Pi and phosphorylated substances is very rapid compared to the net uptake of phosphate from the medium. 3. The remaining phosphate oxygens (nearly 30 to 50%) must be derived from glucose and exogenously supplied metabolites. Transfer from [18O]glutamate was shown and addition of amino acids to the medium reduced incorporation of 18O from water. The principal routes are likely through ATP-linked synthetases, and by dehydrogenases or phosphorylases yielding carboxyl phosphates followed by phosphoryl transfer. Only AMP among nucleotides appears to serve as a point of entry of substrate oxygens into the phosphate pool. 4. The 2' - or 3'-hydroxyl oxygens of ribose, or both, in nucleosides are derived in part from medium water. A tabulation is given of principal enzymic reactions participating in the interchange of phosphate oxygens.

Studies on the relation of the adenosinetriphosphate-inorganic phosphate exchange reaction of mitochondria to oxidative phosphorylation

The effects of a number of various agents on the inorganic phosphate-adenosinetriphosphate exchange (P i-ATP exchange) reaction catalyzed by rat-liver mitochondria have been studied. The types of agents included certain dyes, various respiratory inhibitors, and a number of other compounds of known interest in studies of oxidative phosphorylation. Oxidized, but not reduced, 2,6-dichlorophenolindophenol completely inhibited P i-ATP exchange and oxidative phosphorylation and partially depressed respiration supported by various substrates. The effect on the respiration was not eliminated by 2,4-dinitrophenol. Reduction of the dye after previous treatment of the mitochondria with the oxidized form partially restored the P i-ATP exchange. Methylene blue acted in all respects similarly to 2,6-dichlorophenolindophenol, while ferricyanide and a number of other one-electron acceptors were without inhibitory effects. Cyanide and antimycin A inhibited P i-ATP exchange to a maximal extent of 20–40%, whereas amytal gave an inhibition which was progressive with increasing concentration and could approach completeness. The progressive character of the amytal inhibition was not eliminated by the presence of antimycin A. The effect of amytal, in contrast to those of cyanide and antimycin A, was partially prevented by succinate; antimycin A, but not cyanide, abolished the succinate effect. The effects of adenosinemono- and diphosphate, p-chloromercuribenzoate, azide, fluoride, arsenate, ethylenediaminetetraacetate, deoxycholate and 2,4-dinitrophenol on P i-ATP exchange were investigated and compared with those on oxidative phosphorylation and/or mitochondrial adenosinetriphosphatase reactions. A short exposure of mitochondria to 2,4-dinitrophenol at 2°C resulted in a depression of the P i-ATP exchange with a maintenance of the net phosphate uptake upon the addition of substrate. On the basis of the data obtained it is concluded that the P i-ATP exchange reaction does not reflect all three phosphorylations occurring along the respiratory chain in a random manner, but is related mainly to one of these: that occurring at the diaphorase level. The implications of these conclusions for the mechanisms of respiratory chain phosphorylations and of dinitrophenol-activated adenosinetriphosphatase is discussed.