Ambient Phosphate Research Articles

Reduction of the degradation activity of umami-enhancing purinic ribonucleotide supplement in miso by the targeted suppression of acid phosphatases in the Aspergillus oryzae starter culture

Miso (fermented soybean paste) is a traditional Japanese fermented food, and is now used worldwide. The solid-state culture of filamentous fungus, Aspergillus oryzae, grown on rice is known as rice-koji, and is important as a starter for miso fermentation because of its prominent hydrolytic enzyme activities. Recently, commercial miso products have been supplemented with purinic ribonucleotides, such as inosine monophosphate (IMP) and guanine monophosphate, to enhance the characteristic umami taste of glutamate in miso. Because the purinic ribonucleotides are degraded by enzymes such as acid phosphatases in miso, heat inactivation is required prior to the addition of these flavorings. However, heat treatment is a costly process and reduces the quality of miso. Therefore, an approach to lower acid phosphatase activities in koji culture is necessary. Transcriptional analysis using an A. oryzae KBN8048 rice-koji culture showed that eight of the 13 acid phosphatase (aph) genes were significantly down-regulated by the addition of phosphoric acid in the preparation of the culture in a concentration-dependent manner, while aphC expression was markedly up-regulated under the same conditions. The eight down-regulated genes might be under the control of the functional counterpart of the Saccharomyces cerevisiae transcriptional activator Pho4, which specifically regulates phosphatase genes in response to the ambient phosphate availability. However, the regulatory mechanism of aphC was not clear. The IMP dephosphorylation activities in rice-koji cultures of KBN8048 and the aphC deletion mutant (ΔaphC) were reduced by up to 30% and 70%, respectively, in cultures with phosphoric acid, while protease and amylase activity, which is important for miso fermentation, was minimally affected. The miso products fermented using the rice-koji cultures of KBN8048 and ΔaphC prepared with phosphoric acid had reductions in IMP dephosphorylation activity of 80% and 90%, respectively, without any adverse effects on amylase and protease activities. Thus, preparing the A. oryzae rice-koji culture under phosphate-sufficient conditions preferentially produces a fermentation starter of miso exhibiting low purinic ribonucleotide dephosphorylation activity. Moreover, aphC is a potential breeding target to reduce purinic ribonucleotide degradation activity further in commercial miso products.

Use of Benthic Algae and Bryophytes for Monitoring Rivers

Many countries have adopted a single, well-described approach to the use of phototrophs for monitoring river water quality, which involves the use of indices related to diatom composition at a site. Increasingly these indices have focussed on assessing ambient phosphate concentration. However, there is a wide range of other methods which can provide additional information to make up for any weaknesses in the standard method. Some of these methods are reviewed briefly here. They can be useful, for instance, when considering temporal and spatial variability in phosphate concentration at a particular site and providing much more insight on heavy metal or pesticide pollution than revealed by routine water analysis.

Steady‐state bioassay approach applied to phosphorus‐limited continuous cultures: A growth study of the marine chlorophyte Dunaliella salina

Phosphorus‐limited growth and phosphate uptake kinetics of the marine phytoplankter Dunaliella salina were studied using continuous‐culture techniques. Determination of residual phosphate concentrations in the cultures were made using a steady‐state bioassay approach in which short‐term phosphate uptake rates as measured by 33P‐radiotracer were balanced with the turnover of phosphorus in the culture. This allowed the determination of low‐nanomolar ambient phosphate concentrations (8–95 nmol P L−1) at seven unique specific growth rates, which agreed closely with an alternative kinetics bioassay phosphate determination. The relationship of specific growth rate to ambient phosphate concentration for the D. salina cultures was well‐described by the Monod growth equation with μmax = 1.8 d−1 and Kμ = 28 nmol P L−1. Phosphate uptake kinetics were evaluated at three growth rates and adhered to Michaelis‐Menten kinetics, with evidence of growth‐rate‐dependent variability of uptake affinities (1.9–3.0 L µmol−1 h−1) and half‐saturation constants (1.85–3.8 µmol P L−1). Maximum uptake rates were constant across growth rates when measured in either carbon‐specific (220 µmol P mol C−1 min−1), volume‐specific (7 amol P µm−3 min−1), cell‐specific (1 fmol P cell−1 min−1), or phosphorus‐specific units (7 h−1). This represents a phosphate uptake rate capacity between 200‐fold and 600‐fold greater than the requirements for growth. Finally, we compared the results from our study with previous studies across four phytoplankton species and found that the Monod half‐saturation constant for phosphorus‐limited growth (Kμ) is well‐predicted by the theoretical ratio of the maximum specific growth rate to the phosphorus‐specific uptake affinity.

Resistance of Hong Kong waters to nutrient enrichment: assessment of the role of physical processes in reducing eutrophication

Hong Kong waters receive high nutrient loading from year-round sewage effluent and Pearl River discharge during the summer wet season. We assessed the role of physical processes in reducing eutrophication by calculating a eutrophication reduction index for four different hydrographical areas and four seasons. We used outdoor incubation experiments to assess the response of phytoplankton when physical (mixing and dilution) processes and mesozooplankton grazing were reduced. The primary regulator of phytoplankton growth in low nutrient eastern waters (reference site) shifted from nutrients in the wet season to increased vertical mixing in the dry season. In the highly flushed western waters and Victoria Harbour, the majority (>86 %) of the eutrophication impacts were reduced by strong hydrodynamic mixing (turbulence, vertical mixing, and flushing effects) all year. In southern waters, eutrophication effects were severe (chlorophyll a of up to ~73 μg L−1) and was regulated by the ambient phosphate (PO4) concentration (~0.1 μM) during summer. In contrast, 62–96 % of the potential eutrophication impacts were reduced by physical processes during other seasons. Bioassays also revealed that the yield of chlorophyll from dissolved inorganic nitrogen (DIN) that was taken up by phytoplankton [1.1–3.3 g Chl (mol N)−1] was not significantly different in both N- and P-limited cases. In contrast, the uptake ratios of DIN:PO4 (26:1–105:1) and Chl:P ratios [42–150 g Chl (mol P)−1] in the P-limited cases were significantly (p < 0.05, t test) higher than the N-limited cases [~16DIN:1P and 22–48 g Chl (mol P)−1]. The C:Chl ratios ranged from 32 to 87 g g−1. These potential ranges in ratios need to be considered in future nutrient models.

Adaptive phosphate uptake behaviour of phytoplankton to environmental phosphate fluctuations

When phytoplankton growth in lakes is limited by the available phosphate, the external phosphate concentration fluctuates around a threshold value at which available energy is insufficient to drive phosphate incorporation into a polyphosphate pool. As a result, occasional increases in the external concentration are experienced by phytoplankton as a series of phosphate pulses. Based on [(32) P] phosphate uptake experiments with lake phytoplankton, we show that a community is able to process information about the experienced pattern of phosphate pulses via a complex regulation of the kinetic and energetic properties of cellular phosphate uptake systems. As a result, physiological adaptation to alterations of ambient phosphate concentration depends on the pattern of phosphate fluctuations to which the community had been exposed during its previous growth. In this process, the entire community exhibits coherent uptake behaviour with respect to a common threshold value. Thereby, different threshold values result from different antecedent pulse patterns, apparently unrestrained by the amount of previously stored phosphate. The coherent behaviour observed contradicts the basic assumptions of the competitive exclusion principle and provides an alternative perspective for explaining the paradoxical coexistence of many phytoplankton species.

Disruption of planktonic phosphorus cycling by ultraviolet radiation

Ultraviolet radiation (UVR) may alter phosphorous (P) cycling by plankton through changes in the acquisition and/or regeneration of dissolved P. However, to date an effect of UVR on the uptake of P has not been observed at ambient phosphate (PO43−) concentrations. This has lead to the conclusion that the uptake of P by plankton may be insensitive to UVR. Past research has been limited to a few individual systems, prolonged incubations in bags, or lab cultures. We suspect that experimentation with natural plankton assemblages across broader environmental and/or chemical gradients is required to appreciably understand how UVR may alter P kinetics. Therefore, our study aimed to determine the effect of UVR on the turnover time of the dissolved PO43− pool, the regeneration of dissolved P, the turnover rate of particulate P, and on PO43− concentrations in natural plankton assemblages across broad environmental and chemical gradients. Second we aimed to assess how UVR may alter phosphatase activity and, determine if a change in phosphatase activity under UVR irradiance is correlated with a change in P uptake as proposed in the literature. Studies were conducted on 18 thermally stratified or polymictic lakes located in Ontario and Saskatchewan, Canada. Lake water samples were exposed to one of three experimental treatments: control, photosynthetically active radiation (PAR), or photosynthetically active radiation plus ultraviolet radiation (PAR + UVR). Our study is the first to demonstrate that UVR exposure has the potential to alter P cycling at ambient (picomolar) PO43− concentrations. We have demonstrated that the turnover time of the PO43− pool increases under UVR irradiance (i.e., P uptake decreases), while the regeneration rate of dissolved P and turnover rate of planktonic P are generally not affected; with the net effect being an increase in steady state PO43− concentration (ssPO43−). Alkaline phosphatase activity (APA) in the dissolved and particulate fractions was significantly reduced in PAR + UVR treatments, but unrelated to changes in P uptake. In summary, we have demonstrated that the cycling of P may be disrupted by UVR, with a decrease in the uptake of P and the accumulation of PO43− in the dissolved pool. This, in turn may exacerbate planktonic P limitation, alter the nutrient stoichiometry of plankton and/or indirectly alter rates of primary production in limnetic systems.

Benthic nutrient fluxes along the Laurentian Channel: Impacts on the N budget of the St. Lawrence marine system

Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L−1), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L−1, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m−2 d−1 in the hypoxic western LSLE to 100 μmol m−2 d−1 in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m−2 d−1, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 106 t N, yielding an almost balanced N budget for the SL marine system.

NO EVIDENCE OF GENETIC ASSOCIATION BETWEEN DRD3 VARIANTS AND TARDIVE DYSKINESIA IN KOREAN SCHIZOPHRENIC PATIENTS

Stream nutrient uptake is an important ecosystem service, because it supplies human needs such as water purification. Uncertainty in nutrient uptake measurement determines, in combination with effect magnitude, whether effects of land use, stream restoration or climate change can be detected by this method. However, measurement uncertainty for nutrient uptake metrics is rarely reported. Here, we compared whole-stream phosphate and nitrate uptake among three pristine and three agricultural tropical Cerrado streams. We quantified uncertainty in uptake metrics estimated by kinetic nutrient-addition experiments and evaluated their potential to detect land-use effects. Ambient phosphate and nitrate uptake lengths (SW) ranged from 11 to 106 m and from 29 to 357 m, respectively, in pristine streams and from 41 to 586 m and from 76 to 1372 m in agricultural streams. Moderate measurement uncertainty in SW allowed for the detection of land-use impacts with this metric. However, derived nutrient uptake metrics, such as ambient uptake rates and uptake velocities, as well as parameters of whole-stream saturation kinetics, were associated with high measurement uncertainties that prevented the detection of potential land-use effects. Sensitivity analyses suggested that avoiding high enrichment levels in kinetic addition experiments and increasing sampling effort for plateau nutrient and tracer concentration at the first and last sampling stations of investigated stream reaches are the most promising strategies to reduce measurement uncertainty. Analyzing nutrient uptake without considering measurement uncertainty might lead to poor interpretation in case studies and meta-analyses, such as incorrect evaluations of human impacts or comparisons among systems.

Uptake kinetics and assimilation of phosphorus by Catenella nipae and Ulva lactuca can be used to indicate ambient phosphate availability

Uptake, assimilation and compartmentation of phosphate were studied in the opportunist green macroalgaUlva lactucaand the estuarine red algal epiphyteCatenella nipae. The Michaelis–Menten model was used to describe uptake rates of inorganic phosphate (Pi) at different concentrations. Maximum uptake rates (Vmax) of P-starved material exceededVmaxof P-enriched material; this difference was greater forC. nipae. Uptake and allocation of phosphorus (P) to internal pools was measured using trichloroacetic acid (TCA) extracts and32P. Both species demonstrated similar assimilation paths: when P-enriched, most32P accumulated as free phosphate. When unenriched,32P was rapidly assimilated into the TCA-insoluble pool.C. nipaeconsistently assimilated more32P into this pool thanU. lactuca, indicatingC. nipaehas a greater P-storage capacity. In both species,32P release data showed two internal compartments with very different biological half-lives. The rapidly exchanging compartment had a short half-life of ≈2 to 12 min, while the slowly exchanging compartment had a much longer half-life of 12 days in P-starvedC. nipaeor 4 days in P-starvedU. lactuca. In both species, the slowly exchanging compartment accounted for more than 90% of total tissue.U. lactucaandC. nipaeresponded differently to high external Pi.U. lactucarapidly took up Pi, transferring this Piinto tissue phosphate and TCA-soluble P in a few hours (≈90% of total P).C. nipaetook up Piat lower rates and stored much of this P in less mobile TCA-insoluble forms. Long-term storage of refractory forms of P makesC. nipaea useful bioindicator of the prevailing conditions of Piavailability over at least the previous 7 days, whereas the P-status ofU.lactucamay reflect conditions over no more than the previous few hours or days.C. nipaeis a more useful bioindicator for P status of estuarine and marine waters thanU. lactuca.

Biokinetics of cadmium, selenium, and zinc in freshwater alga Scenedesmus obliquus under different phosphorus and nitrogen conditions and metal transfer to Daphnia magna

The uptake of Cd, Se(IV) and Zn by the freshwater alga Scenedesmus obliquus and the subsequent transfer and release budget in Daphnia magna were investigated under different nutrient additions and cell incubation conditions. An increase in ambient phosphate concentrations from 0.5 micromol l(-1) to 50 micromol l(-1) significantly increased the intracellular accumulation of Cd (by 18x) and Zn (by 5x), but decreased the accumulation of Se (by 126x) in the alga. The percentage of these metals distributing in the intracellular pool of algae also increased substantially with increasing ambient P concentrations. Nitrate addition from 5.0 to 200 micromol l(-1) did not influence the uptake of any of the three metals, although a significant decrease in the intracellular Se distribution was observed. Radiolabeled algae under different nutrient manipulations (semi-continuous culture, starvation, and P-pulse treatments) were used to measure trophic transfer assimilation efficiency (AE) in Daphnia. When the algal cells were grown in a semi-continuous culture, starved for N and P, or were treated with P-pulse, the AEs of Cd and Zn were generally independent of the nutritional conditions, but the Se AE was significantly affected by different P levels. The efflux rate constants, determined during 10 d depuration following 7 days of dietary uptake, decreased significantly for Cd and Zn, but were relatively constant for Se with increasing P concentration. N-addition caused no effect on the metal efflux rate constants. P- or N-additions did not influence the release budget (including molting, neonates, excretion and feces) for all three elements in Daphnia. Our study indicated that phosphate enrichment may substantially increase metal uptake in green alga S. obliquus. Responses of trophic transfer in Daphnia to nutrient enrichment were metal specific. P-enrichment can possibly lead to considerable decrease on Se transfer from algae to zooplankton.

An ecosystem model of the global ocean including Fe, Si, P colimitations

Observations have shown that large areas of the world ocean are characterized by lower than expected chlorophyll concentrations given the ambient phosphate and nitrate levels. In these High Nutrient‐Low Chlorophyll regions, limitations of phytoplankton growth by other nutrients like silicate or iron have been hypothesized and further evidenced by in situ experiments. To explore these limitations, a nine‐component ecosystem model has been embedded in the Hamburg model of the oceanic carbon cycle (HAMOCC5). This model includes phosphate, silicate, dissolved iron, two phytoplankton size fractions (nanophytoplankton and diatoms), two zooplankton size fractions (microzooplankton and mesozooplankton), one detritus and semilabile dissolved organic matter. The model is able to reproduce the main characteristics of two of the three main HNLC areas, i.e., the Southern Ocean and the equatorial Pacific. In the subarctic Pacific, silicate and phosphate surface concentrations are largely underestimated because of deficiencies in ocean dynamics. The low chlorophyll concentrations in HNLC areas are explained by the traditional hypothesis of a simultaneous iron‐grazing limitation: Diatoms are limited by iron whereas nanophytoplankton is controlled by very efficient grazing by microzooplankton. Phytoplankton assimilates 18 × 109 mol Fe yr−1 of which 73% is supplied by regeneration within the euphotic zone. The model predicts that the ocean carries with it about 75% of the phytoplankton demand for new iron, assuming a 1% solubility for atmospheric iron. Finally, it is shown that a higher supply of iron to surface water leads to a higher export production but paradoxically to a lower primary productivity.

Metal accumulation in the green macroalga Ulva fasciata: effects of nitrate, ammonium and phosphate

Coastal organisms are often exposed to both metal pollution and nutrient enrichment. The influences of major nutrients (nitrate, ammonium, and phosphate) on the accumulation of trace metals (Cd, Cr, Zn and Se) in Ulva fasciata were examined. The relative accumulation of metals was quantified by the kinetic measurements of accumulated metal concentration over a short exposure period (8 h). Our study demonstrated that macronutrients could markedly influence the rate of metal accumulation in the macroalgae. An increase in ambient nitrate concentration resulted in a significant increase in Cd accumulation rate, whereas the rate of accumulation of Cr and Zn was not greatly affected by the ambient nitrate level (between 10 and 100 microM). Zn uptake in nitrate-enriched macroalgae was, however, significantly higher than its uptake in N-starved macroalgae. The accumulation of Cd, Cr and Zn was not appreciably affected by the concentration of ammonium. Se accumulation was significantly inversely related to the ambient phosphate concentration, presumably due to the competitive inhibition by a high P concentration. Cr accumulation in the macroalgae increased significantly with increasing phosphate concentration. These data implied that the influences of major nutrients on cationic and anionic metal accumulation were highly metal-specific. The dependence of metal accumulation on major nutrients will appreciably affect our prediction of metal accumulation in macroalgae and the interpretation of biomonitoring data using the Ulva species.

Effects of irradiance, water temperature and nutrients on the growth of sporelings of the crustose coralline alga Lithophyllum yessoense Foslie (Corallinales, Rhodophyceae)

SUMMARY Lithophyllum yessoense Foslie is a markedly dominant subtidal, crustose coralline alga in south–western Hokkaido, Japan. In this study, the effects of irradiance, water temperature and nutrients (nitrate and phosphate) on the growth of sporelings of the alga were examined. The relative growth rate (RGR) was saturated at 17.6% d−1 at a high irradiance (240 umol photon m2s−1). Even at a low irradiance (10.7–49.9 umol photon m−2s−1), RGR was 7.1–12.7% d−1 The survival rate of sporelings was greater than 80% at irradiance above 10.7 μmol photon m−2s−1 throughout the culture period. The growth of L. yessoense sporelings was promoted at 15°C and 20°C, but inhibited at 5°C. The half-saturation constants (Ks) for growth were about 0.5 umol L−1 and 0.14 umol L−1 for nitrate and phosphate, respectively. Saturated nitrate and phosphate concentrations for the growth were about 4.0 μmol L−1 and 0.4 μmol L−1, respectively, suggesting that L. yessoense is adaptable to a relatively high water temperature, a wide range of irradiance, and low ambient nitrate and phosphate concentrations. The results provide a possible explanation of why L. yessoense is dominant in the environments of south-western Hokkaido.

10.1016/s0967-0653(97)83701-5

10.1016/s0967-0653(97)83701-5

Latitudinal variability in phosphate uptake in the Central Atlantic

The role of P in regulating planktonic production in Atlantic waters was assessed by the examination of the phosphate turnover time and uptake rate along a latitudinal transect across the Central Atlantic Ocean (27° N to 36° S). Phosphate uptake rates and the affinity for phosphate were higher for small ( 0.8 pm. Phosphate uptake rates were relatively low, resulting in long phosphate turnover times (days), except in the surface waters south of 25° S, which were also characterized by the highest uptake rates and affinity for phosphate, and the smallest total P pools observed along the transect. The organisms were found to realize their maximal phosphate uptake rates at ambient phosphate concentrations, suggesting the adequacy of the P supply to support the requirements of organisms. These findings suggest that inorganic P was not limiting community production in most of the Central Atlantic, except for the area south of 25° S, where P uptake could possibly be limited by P supply. The long turnover times generally observed in the Central Atlantic Ocean are in agreement with previous observations in oceanic systems elsewhere, suggesting that the observation that P is unlikely to be a limiting resource for planktonic growth can be extrapolated to most of the open ocean. The combined rate of P excretion from planktonic organisms and their microbial grazers as dissolved organic phosphorus (DOP) represented 75% of the total phosphate uptake. This DOP does not reach a sufficient accumulation as to drive an important downward flux of DOP, which represents a loss of only 9% of the P inputs into the biogenic layer. Hence, the high P uptake rate of the planktonic community in the Central Atlantic provides P in excess to support primary production, leading to a release as DOP, which appears to be rapidly recycled in the biogenic layer, thereby maintaining an adequate P supply to fuel primary production.

Phosphorus and aquatic bryophytes in the Swale–Ouse river system, north-east England. 1. Relationship between ambient phosphate, internal N:P ratio and surface phosphatase activity

Abstract A study was made of the phosphorus content and surface phosphomonoesterase activities (PMEase) of two aquatic mosses, Fontinalis antipyretica and Rhynchostegium riparioides, in relation to the water chemistry of the River Swale–Ouse, NE England. The samples were taken from a headwater stream and three sites down the main river. Water and mosses (2-cm tips) were sampled monthly for 1 year from October 1995. Total inorganic combined nitrogen concentration and phosphate dissolved in the water both increased on passing downstream. Variability in concentrations of the various N and P fractions was greatest at the headwater site. The mosses showed their lowest concentrations of N and P at the headwater site, with both elements increasing on passing downstream. However, there was a marked shift in the N:P ratio (by mass), decreasing from 14.9 to 6.8 for F. antipyretica and from 12.5 to 5.5 for R. riparioides. PMEase assayed with 4-methylumbelliferyl phosphate as substrate was always greater at pH 5.5 than at pH 7.5 or 9.5. Differences in PMEase between sites were broadly similar for the two mosses, but F. antipyretica showed almost twice the activity (per unit mass) of R. riparioides. Material from the headwater site showed the most activity, though there were clear seasonal differences, with the highest activity in late summer; PMEase at all three pH values decreased on passing downstream. There was a marked increase in PMEase when the tissue P content was below about 0.3% or when the tissue N:P content was above about 9:1; the data were insufficient to establish which is the better predictor of PMEase. However, both mosses showed detectable activity at downstream sites. It is suggested that a combined programme of water analysis and moss PMEase assays provides the most efficient way of studying the nutrient status of streams showing highly variable nutrient conditions.

Nitrogen and phosphorus in east coast British rivers: Speciation, sources and biological significance

Abstract The data on nitrogen and phosphorus fractions obtained during the core study programme of the Land Ocean Interaction Study for rivers draining the central part of eastern UK are presented and assessed with respect to sources and potential biological effects. The approaches used include comparisons of: (1) overall speciation of nitrogen and phosphorus in the rivers by examining average values and ranges; (2) relationships between nitrogen and phosphorus fractions and flow; and (3) relationships between nitrate and total dissolved nitrogen and soluble reactive phosphorus and total dissolved phosphorus. In addition, comparisons are made between data from the LOIS study region and literature on rivers elsewhere in Europe and North America. Detailed consideration is given to N/P mass ratios in river water, because these can indicate conditions of potential N- or P-limitation for algal and other plant growth. A mid-river site in the Ure, a tributary of Yorkshire Ouse, showed 44% of samples with a N/P mass ratio of>24. Comparison of records for the `growing season' (April to September), when algal and other plant activity is highest, with those from the `dormant season' (October to March) showed a much higher N/P mass ratio during the growing season, indicating that conspicuous growths of Cladophora glomerata and other submerged plants may be reducing ambient phosphate to levels of marked phosphorus limitation.

Surface phosphatase activity of benthic algae in a stream with highly variable ambient phosphate concentrations

INGSTONE & WHITTON 1984). The majority of the phosphate was organic at the time of the spring maxima. Other studies have also reported high P concentrations in waters draining peat, exceeding 1 mg L' P during autumn in the incoming water from lowland peat into Tjeukemeer, The Netherlands (GOLTERMAN 1973). There is a number of reports of seasonal changes in P concentrations in flowing waters, but these mostly reflect seasonal changes in flow or use of the catchment. The cyanobacterium Rivularia was abundant in the three streams studied by LIVINGSTONE & WHITTON (1984) and some individual colonies persisted for several years. The colonies showed high alkaline phosphatase activity, suggesting that their trichomes were P-limited; there is considerable circumstantial evidence indicating that the multicellular hairs of this organism are the site of the phosphatase activity (WHITTON 1988). In view of the fact that the Rivularia streams showed a marked seasonal change in phosphate concentration and form, it seems likely that the cyanobacterium may show a marked seasonal change in phosphorus status and phosphatase activity. One stream, Red Sike, was therefore chosen for more intensive study of changes through the year in water chemistry, colony and trichome morphology and surface phosphomonoesterase activity (`alkaline phosphatase activity').

Study on phosphate uptake of the marine cyanophyte Synechococcus sp. NIBB 1071 in relation to oligotrophic environments in the open ocean

Inorganic phosphate (Pi) uptake by the marine cyanophyte Synechococcus sp. NIBB 1071 was studied using cells grown in an artificial seawater medium. The phosphate uptake was markedly enhanced in cells grown in the medium of low phosphate concentrations (phosphate-limited cells) than in cells grown in the phosphate-rich medium (phosphate-replete cells). The diagnosis of kinetics of instantaneous phosphate-uptake showed that V max of the former was more than two orders of magnitude greater than that of the latter, and the k m of the former was about 1/20 of that of the latter. The enhancement of the phosphate uptake was completed after a 40-h incubation of phosphate-replete cells in the phosphate-free medium. The activation was suppressed by chloramphenicol, an inhibitor of protein synthesis. The uptake developed in phosphate-limited cells was energy dependent and susceptive to osmotic shock, which suggests the involvement of a periplasmic phosphate-binding protein, analogous to that found in heterotrophic gram-negative eubacterial cells. The relationship between phosphate quota and growth rate, together with the kinetical data for phosphate uptake, predicted that ambient phosphate as low as 0.5 nM could support cell growth at a rate of one division per day. Results indicate that cells can grow rapidly even at phosphate concentrations as low as nanomolar levels. A possible regulatory mechanism of phosphate uptake in marine Synechococcus spp. is discussed in relation to a wide distribution of this picophytoplankton in the ocean environment.

Seasonal changes in ambient phosphate and phosphatase activities of the cyanobacterium Rivularia atra in intertidal pools at Tyne Sands, Scotland

(i) A study was made of Rivularia atra at a sheltered bay in S-E. Scotland, where it is frequent in summer in pools of the upper eulittoral. Monthly measurements of water chemistry and phosphate activities were made at the same stage in the tidal cycle during April 1992–October 1993, together with other short intensive studies. (ii) Drift seaweed deposited at high tide levels (>4.9 m) released high concentrations of inorganic nutrients to adjacent pools, where the water sometimes exceeded 6000 µg l−1 PO4−P. Combined inorganic N was, however, always low and the N:P ratio fell to 0.001–0.003:1 (by weight) in August, when the temperature was relatively high: much N was lost to the atmosphere as ammonia. (iii) Total P concentrations in the Rivularia pools (mostly covered by 4.5–4.8 m tides) were much lower than in the drift seaweed pools, but similar to the sea, though with higher % organic P in the former (means of 50% v. 28%): total N concentrations were much lower in the Rivularia pools than in seawater, leading to a very low N:P for most of the time. Aqueous organic P tended to increase (in summer) during the period between tidal cover, even in pools lacking input drainage, suggesting that much of the organic P may be autochthonous. (iv) All 9 Rivularia pools showed high concentrations of P in June in one or both years. At the same time the Rivularia colonies formed abundant hormogonia, followed 4–8 weeks later by a marked increase in macroscopically obvious colonies. (v) Assays of ‘surface’ phosphomonoesterase activity by Rivularia colonies showed different results according to whether p-nitrophenyl phosphate (pNPP) or 4-methylumbelliferyl phosphate (4-MUP) was used as substrate. Both substrates indicated obvious activity at intervals during the year. Using pNPP, activity was very low in June, usually followed by a very high value in July or August; use of 4-MUP showed a different response, with a high value one or two months later than with pNPP.