Dissolved Organic Phosphorus Compounds Research Articles

Contrasting Roles of DOP as a Source of Phosphorus and Energy for Marine Diazotrophs

The oceanic dissolved organic phosphorus (DOP) pool is mainly composed of P-esters and, to a lesser extent, equally abundant phosphonate and P-anhydride molecules. In phosphate-limited ocean regions, diazotrophs are thought to rely on DOP compounds as an alternative source of phosphorus (P). While both P-esters and phosphonates effectively promote dinitrogen (N2) fixation, the role of P-anhydrides for diazotrophs is unknown. Here we explore the effect of P-anhydrides on N2 fixation at two stations with contrasting biogeochemical conditions: one located in the Tonga trench volcanic arc region (“volcano,” with low phosphate and high iron concentrations), and the other in the South Pacific Gyre (“gyre,” with moderate phosphate and low iron). We incubated surface seawater with AMP (P-ester), ATP (P-ester and P-anhydride), or 3polyP (P-anhydride) and determined cell-specific N2 fixation rates, nifH gene abundance, and transcription in Crocosphaera and Trichodesmium. Trichodesmium did not respond to any DOP compounds added, suggesting that they were not P-limited at the volcano station and were outcompeted by the low iron conditions at the gyre station. Conversely, Crocosphaera were numerous at both stations and their specific N2 fixation rates were stimulated by AMP at the volcano station and slightly by 3polyP at both stations. Heterotrophic bacteria responded to ATP and 3polyP additions similarly at both stations, despite the contrasting phosphate and iron availability. The use of 3polyP by Crocosphaera and heterotrophic bacteria at both low and moderate phosphate concentrations suggests that this compound, in addition to being a source of P, can be used to acquire energy for which both groups compete. P-anhydrides may thus leverage energy restrictions to diazotrophs in the future stratified and nutrient-impoverished ocean.

Dissolved organic phosphorus molecular weight fractionation and apparent bioavailability quantified via coupled sequential ultrafiltration and enzyme hydrolysis

AbstractAquatic organisms utilize dissolved organic phosphorus (DOP) when phosphate levels are insufficient to satisfy their P‐demand. Its critical role in supporting primary production has motivated efforts to characterize DOP composition and gain insight into its bioavailability. 31P nuclear magnetic resonance (31P‐NMR) spectroscopy, the principal tool currently used by aquatic geochemists to identify compositional aspects of the bulk marine DOP pool, has provided limited compositional detail beyond the immediate P‐bonding environment, and does not provide quantitative information on potential bioavailability of DOP. As a result, the DOP pool remains poorly characterized, limiting predictive power relative to DOP bioavailability. We have developed a sequential ultrafiltration (SUF) method to segregate the DOP pool into four distinct molecular weight ranges. The concentrated molecular weight fractions are then incubated with phosphohydrolytic enzymes to determine the potential bioavailability of monoester‐ and diester‐bound P. DOP molecular weight segregation was verified using commercially available DOP compounds of known molecular weight as analogues for naturally occurring DOP. We have applied the SUF method to surface water samples from a nearshore transect in Kāne'ohe Bay, Hawai'i, and surface waters from oligotrophic Station ALOHA (Hawai'i Ocean Time Series). Results of these field tests indicate that the coupled SUF‐bioavailability method reveals greater compositional complexity of the marine DOP pool than has been resolved by 31P‐NMR studies. Notably, the SUF‐bioavailability method does not require expensive, technically complicated instrumentation (e.g., 31P‐NMR), and thus is readily accessible to researchers wishing to probe marine DOP composition who do not have access to or expertise in 31P‐NMR.

Dissolved organic nutrient uptake by riverine phytoplankton varies along a gradient of nutrient enrichment

The concentration of dissolved organic matter (DOM) in freshwaters is increasing in large areas of the world. In addition to carbon, DOM contains nitrogen and phosphorus and there is growing concern that these organic nutrients may be bioavailable and contribute to eutrophication. However, relatively few studies have assessed the potential for dissolved organic nitrogen (DON) or dissolved organic phosphorus (DOP) compounds to be bioavailable to natural river phytoplankton communities at different locations or times. Temporal and spatial variations in uptake, relative to environmental characteristics were examined at six riverine sites in two contrasting catchments in the UK. This study also examined how the uptake by riverine phytoplankton of four DON and four DOP compounds commonly found in rivers, varied with concentration. Total nitrogen (TN) and phosphorus (TP) concentrations, the proportion of inorganic nutrient species, and nutrient limitation varied temporally and spatially, as did the potential for DON and DOP uptake. All eight of the DOM compounds tested were bioavailable, but to different extents. Organic nutrient use depended on the concentration of the organic compound supplied, with simple compounds (urea and glucose-6-phosphate) supporting algal growth even at very low concentrations. DON use was negatively correlated with the TN and ammonia concentration and DOP use was negatively correlated with soluble reactive phosphorus (SRP) and dissolved organic carbon (DOC) concentration. The evidence indicates that DOM in rivers has been overlooked as a potential source of nutrients to phytoplankton and therefore as an agent of eutrophication.

A simple spectrophotometric method to determine phytic acid in poultry wastewater without acid digestion

ABSTRACT Frequently, wastewater from treatment plants associated with animal husbandry, mainly animal feeding operations, are used to irrigate near agricultural lands based on nitrogen requirements. To avoid soil phosphorus accumulation owing to its long-term application, it is necessary to achieve lower levels of total phosphorus; one of the methods involve eliminating dissolved organic phosphorus (DOP) in treatment systems. The DOP in effluents and manure wastewater streams is commonly quantified without the identification of individual phosphorus species. Nevertheless, characterisation of the DOP is particularly important, because removal techniques, as well as soil sorption capacity and phosphorus transfer in the runoff to water bodies, differ for different DOP compounds. Particularly, phytic acid (PA), the main DOP compound in animal wastes, can strongly bind to soils making it unavailable for plant uptake. This work evaluates the application of a simple analytical procedure to the determination of the PA concentration in manure wastewater. The method does not require a prior acid digestion stage; in addition, sample colour removal, as well as the removal of potentially interfering compounds are not required. The results are in agreement with results obtained using 31P NMR. PA recoveries ranged between 87% and 97%, relative standard deviation was <8.5%, while the limits of detection and quantification for phosphorus as PA were 0.18 mg·L−1 and 0.55 mg·L−1 respectively.

Concentrations and Uptake of Dissolved Organic Phosphorus Compounds in the Baltic Sea

The dissolved organic phosphorus (DOP) pool in marine waters contains a variety of different compounds. Knowledge of the distribution and utilization of DOP by phyto- and bacterioplankton is limited, but critical to our understanding of the marine phosphorus cycle. In the Baltic Sea, detailed information about the composition of DOP and its turnover is lacking. This study reports the concentrations and uptake rates of DOP compounds, namely, adenosine triphosphate (dATP), deoxyribonucleic acid (dDNA), and phospholipids (dPL), in the Baltic Proper and in Finnish coastal waters in the summers of 2011 and 2012. Both areas differed in their dissolved inorganic phosphorus (DIP) concentrations (0.16 and 0.02–0.04 μM), in the C:P (123–178) and N:P (18–27) ratios, and in abundances of filamentous cyanobacteria and of autotrophic and heterotrophic picoplankton. The mean concentrations of dATP-P, dDNA-P, and dPL-P were 4.3–6.4, 0.05–0.12, and 1.9–6.8 nM, respectively, together contributing between 2.4 and 5.2% of the total DOP concentration. The concentrations of the compounds varied between and within the investigated regions and the distribution patterns of the individual components are not linked to each other. DIP was taken up at rates of 10.1–380.8 nM d-1. dATP-P and dDNA-P were consumed simultaneously with DIP at rates of 6.9–24.1 and 0.09–0.19 nM d-1, respectively, with the main proportion taken up by the size fraction <3 μm and with DIP to be the dominant source. Groups of hydrographical and biological parameters were identified in the multiple regression analysis to impact the concentrations and uptake rates. It points to the complexity of the regulation. Our results indicate that the investigated DOP compounds, particularly dATP-P, can make significant contributions to the P nutrition of microorganisms and their use seems to be not intertwined. Therefore, more detailed knowledge of all DOP components including variation of concentrations and the utilization is required to understand the roles of DOP in marine ecosystems.

Differential utilization patterns of dissolved organic phosphorus compounds by heterotrophic bacteria in two mountain lakes

Although phosphorus limitation is common in freshwaters and bacteria are known to use dissolved organic phosphorus (DOP), little is known about how efficiently DOP compounds are taken up by individual bacterial taxa. Here, we assessed bacterial uptake of three model DOP substrates in two mountain lakes and examined whether DOP uptake followed concentration-dependent patterns. We determined bulk uptake rates by the bacterioplankton and examined bacterial taxon-specific substrate uptake patterns using microautoradiography combined with catalyzed reporter deposition–fluorescence in situ hybridization. Our results show that in the oligotrophic alpine lake, bacteria took up ATP, glucose-6-phosphate and glycerol-3-phosphate to similar extents (mean 29.7 ± 4.3% Bacteria), whereas in the subalpine mesotrophic lake, ca. 40% of bacteria took up glucose-6-phosphate, but only ∼20% took up ATP or glycerol-3-phosphate. In both lakes, the R-BT cluster of Betaproteobacteria (lineage of genus Limnohabitans) was over-represented in glucose-6-phosphate and glycerol-3-phosphate uptake, whereas AcI Actinobacteria were under-represented in the uptake of those substrates. Alphaproteobacteria and Bacteroidetes contributed to DOP uptake proportionally to their in situ abundance. Our results demonstrate that R-BT Betaproteobacteria are the most active bacteria in DOP acquisition, whereas the abundant AcI Actinobacteria may either lack high affinity DOP uptake systems or have reduced phosphorus requirements.

Sorption of dissolved inorganic and organic phosphorus compounds onto iron-doped ceramic sand

Sorption-based processes are widely used in the wastewater treatment. We present results of a study contrasting the sorption behavior of several dissolved organic phosphorus (DOP) compounds and phosphate onto three ceramic sands with different physicochemical properties. The synthesized sorbent materials were characterized by nitrogen adsorption analyses, X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The DOP compounds were chosen to represent different molecular weights and structures. The effects of solution pH, P concentration and contact time on sorption capacity was investigated by kinetic and equilibrium sorption isotherm studies. The order of maximum sorption capacity observed for the three P compounds onto iron-doped ceramic sand samples, on a per gram dry weight basis, is phosphate (DIP)>β-glycerophosphate disodium salt hydrate (β-GP)>adenosine 5′-triphosphate disodium salt hydrate (ATP-P). Langmuir isotherm sorption equation well describes the experimental sorption isotherms. Kinetic studies revealed that the sorption process followed both pseudo-first order and pseudo-second order kinetic models. The iron-doped ceramic sand samples had a higher phosphorus removal capacity than the raw, which could be attributed to its better intra-particle diffusion and higher binding energy. P compound size and structure, and the nature of the sorbents all appear to play a role dictating relative sorption capacity. The sorption process was complex; both surface sorption and intra-particle diffusion were simultaneously occurring and contribute to the sorption mechanism.

Response of &amp;lt;i&amp;gt;Nodularia spumigena&amp;lt;/i&amp;gt; to &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; – Part 3: Turnover of phosphorus compounds

Abstract. Diazotrophic cyanobacteria form extensive summer blooms in the Baltic Sea driving the surrounding surface waters into phosphate limitation. One of the main bloom-forming species is the heterocystous cyanobacterium Nodularia spumigena. N. spumigena exhibits accelerated uptake of phosphate through the release of the extracellular enzyme alkaline phosphatase whose activity also serves as an indicator of the hydrolysis of dissolved organic phosphorus (DOP). The present study investigated the utilisation of DOP and its compounds (e.g., ATP) by N. spumigena during growth under different CO2 concentrations, in order to estimate potential consequences of ocean acidification on the cell's supply with phosphorus (P). Cell growth, the phosphorus pool, and four DOP compounds (ATP, DNA, RNA, and phospholipids) were determined in three setups with different CO2 concentrations (average 341 μatm, 399 μatm, and 508 μatm) during a 15-day batch experiment. The results showed stimulated growth of N. spumigena and a rapid depletion of dissolved inorganic phosphorus (DIP) in all pCO2 treatments. DOP uptake was enhanced by a factor of 1.32 at 399 μatm and of 2.25 at 508 μatm compared to the lowest CO2 concentration. Among the measured DOP compounds, none was found to accumulate preferentially during the incubation or in response to a specific pCO2 treatment. However, at the beginning 61.9 &amp;amp;pm; 4.3% of total DOP were not characterised but comprised the most utilised fraction. This is demonstrated by the decrement of this fraction to 27.4 &amp;amp;pm; 9.9% of total DOP during the growth phase with a preference at high pCO2. Our results indicate a stimulated growth of diazotrophic cyanobacteria at increasing CO2 concentrations which is accompanied by increasing utilisation of DOP as an alternative P source.

The marine phosphorus cycle

The marine phosphorus cycle

The importance of bacteria in promoting algal growth in eutrophic lakes with limited available phosphorus

Surface waters in Lake Taihu are increasingly threatened by phosphorus (P)-related eutrophication, with a considerable proportion of organic P. A simple experimental model was proposed to characterize “bacterial services” to cyanobacteria. We used the digested solutions of three dissolved organic phosphorus (DOP) compounds (i.e., glucose-6-phosphate, adenosine triphosphate and lecithin) to test the stimulatory effects of nutrient regeneration by bacteria. The growth-promoting effects of six digested solutions on the microalga Microcystis aeruginosa (Ma) were studied. Of these six digested solutions, four had significantly growth-promoting effects on Ma, including the digested solutions of the three DOP compounds by bacteria Gordonia sp. txj1302RI and glucose-6-phosphate by bacteria Burkholderia sp. txj1302Y4. These results demonstrated that bacteria played important roles in decomposing the unavailable organic P into DIP, suggesting that natural bacteria contribute to algal blooms in Lake Taihu.

Utilization of dissolved organic phosphorus by different groups of phytoplankton taxa

The utilization of nine dissolved organic phosphorus (DOP) compounds by five bloom-causing phytoplankton species was studied under batch culture conditions. The DOP compounds included were adenosine 5-triphosphate (ATP), adenosine 5-monophosphate (AMP), cytidine 5-monophosphate (CMP), guanosine 5-monophosphate (GMP), uridine 5-monophosphate (UMP), glucose-6-phosphate (G6P), sodium glycerophosphate (GYP), 4-nitrophenyl phosphate (NPP), and triethyl phosphate (TEP), and the phytoplankton taxa were Skeletonema costatum, Prorocentrum micans, Alexandrium tamarense, Chattonella marina, and Heterosigma akashiwo. The four flagellate taxa, P. micans, A. tamarense, C. marina, and H. akashiwo, grew well under various DOP regimes. P. micans and C. marina were the most capable of using DOP compounds, sustaining better growth on a majority of nucleotides (ATP, AMP, CMP, GMP, and UMP) and phosphomonoesters (G6P and GYP) than in inorganic phosphorus (P) controls. A. tamarense and H. akashiwo showed equivalent growth in most organic and inorganic P cultures, while the diatom species, S. costatum, could only utilize AMP and GMP. Furthermore, A. tamarense and C. marina could endure N, P-depleted conditions. Among the nine DOP compounds tested, the nucleotide compounds had the highest nutritional value for algal cell growth, while TEP could not sustain growth as the sole source of P. These results suggest that enhanced DOP utilization and the endurance of nutrient-limitation by harmful flagellate taxa offer their competitive advantages, which may account for the frequent occurrence of their blooms in coastal waters.

Sorption and desorption of dissolved organic phosphorus onto iron (oxyhydr)oxides in seawater

Sorption of phosphorus (P) onto particulate surfaces significantly influences dissolved P concentrations in aquatic environments. We present results of a study contrasting the sorption behavior of several dissolved organic phosphorus (DOP) compounds and phosphate onto three commonly occurring iron (oxyhydr)oxides (Fe ox): ferrihydrite, goethite, and hematite. The DOP compounds were chosen to represent a range of molecular weights and structures, and include: adenosine triphosphate (ATP), adenosine monophosphate (AMP), glucose-6-phosphate (G6P), and aminoethylphosphonic acid (AEP). All P compounds displayed decreasing sorption as a function of crystallinity of the Fe ox substrate, with ferrihydrite adsorbing the most, hematite the least. In general, maximum sorption density decreased with increasing molecular weight of P compound; sorption of G6P onto goethite and hematite excepted. P compound size and structure, and the nature of the Fe ox substrate all appear to play a role dictating relative sorption capacity. Failure of a simple, 1-step sorption–desorption model to describe the data suggests that P sorption cannot be explained by a simple balance between sorption and desorption. Instead, the data are consistent with a 2-step sorption model consisting of an initial rapid surface sorption, followed by a slow, solid-state diffusion of P from surface sites into particle interiors. Desorption experiments provide additional support for the 2-step sorption model. Without exception, DOP compounds showed less efficient sorption than did orthophosphate. This suggests that in aquatic systems enriched in reactive Fe ox, whether as suspended particulates in the water column or in benthic sediments, DOP bioavailability may exceed that of orthophosphate. Since biological uptake of P from DOP requires enzymatic cleavage of orthophosphate, a system enriched in DOP relative to orthophosphate may impact ecosystem community structure.

A Protocol to Assess the Enzymatic Release of Dissolved Organic Phosphorus Species in Waters under Environmentally Relevant Conditions

A protocol to assess the potential release of dissolved reactive phosphorus (DRP) by enzymatic hydrolysis of dissolved organic phosphorus (DOP) in waters (sediment porewater and sewage liquors in this study) under environmental conditions is presented. This protocol enables the quantification of different classes of DOP compounds using a variety of phosphatase enzymes, i.e., alkaline phosphatase, phosphodiesterase, and phytase. All experiments were carried out within the pH range of most natural waters, i.e., at neutral (pH 7) or slightly alkaline pH (pH 9). Tri-sodium citrate and sodium dodecyl sulfate (SDS) were used in the assays to prevent interferences due to adsorption processes in the presence of multivalent metallic cations and to minimize protein binding. Applying this protocol revealed that labile phosphate monoesters always represented the largest fraction of enzymatically hydrolyzed P in sewage liquors and sediment porewater. Total enzymatically hydrolyzable P (EHP) represented only 16% of the TDP in the sediment porewater but up to 43% in sewage liquors. Because most of the enzymes used in this study are likely to exist in aquatic ecosystems, the EHP fraction might represent a source of potentially bioavailable P of similar magnitude to DRP.

Bioavailability of dissolved organic phosphorus compounds to typical harmful dinoflagellate Prorocentrum donghaiense Lu

The bioavailability of dissolved organic phosphorus (DOP) compounds to harmful alga Prorocentrum donghaiense Lu and its alkaline phosphatase activity (APA) were studied. Results showed that P. donghaiense could utilize the test DOP compounds such as glucose-6-phosphate (G-6-P), adenosine triphosphate (ATP) and ribonucleic acid (RNA) to sustain its growth. Nutrition between the test DOP compounds and orthophosphate was comparable. P. donghaiense could utilize intracellular phosphorus to sustain growth under depletion of dissolved phosphorus. Variation of APA in different test DOP compounds was addressed; the controlling mechanism of APA in different DOP media was discussed.

Utilization of dissolved organic phosphorus by the two toxic dinoflagellates, Alexandrium tamarense and Gymnodinium catenatum (Dinophyceae)

The utilization of dissolved organic phosphorus (DOP) by the two toxic dinoflagellates Alexandrium tamarense (Lebour) Balech and Gymnodinium catenatum Grahamm which were isolated from Hiroshima Bay, Japan, was studied. Alexandrium tamarense grew poorly on fructose- 6-phophate, glucose-1-phosphate, glycerophosphate, and ribose-5-phosphate with a phosphomo- noester bond, although it grew well on the nucleotides adenosine-5-diphosphate (ADP) and adenosine triphosphate (ATP), as well as on dissolved inorganic phosphorus (DIP; as metaphos- phate, pyrophosphate, tripolyposphate and orthophosphate). The results imply that A. tamarense was able to utilize DOP and DIP from ambient water using nucleotidase, pyrophosphatase and poly- phosphatase, which hydrolyze phosphodiesters. In contrast, G. catenatum was able to utilize DOP compounds of various molecular weights and structures as well as DIP. In time-course experiments, alkaline phosphatase activity (APA) was induced at orthophosphate concentrations of 0.43 mmol/L and 3.3 mmol/L for A. tamarense and G. catenatum, respectively, and APA increased with orthophos- phate depletion. The experiments also demonstrated that APA was maximum at the optimum temperatures for the growth of A. tamarense and G. catenatum; that is, 15∞C and 25∞C, respectively. These results suggest that the DIP-depleted conditions in Hiroshima Bay might have led to the outbreaks of noxious dinoflagellates in recent years.

Electrospray ionization fourier transform ion cyclotron resonance mass spectrometry of dissolved organic phosphorus species in a treatment wetland after selective isolation and concentration.

A method for the selective concentration of dissolved organic phosphorus (DOP) from complex surface water samples for the first time allows mass spectral characterization of individual DOP compounds in phosphorus-limited ecosystems. The entire dissolved organic matter (DOM) pool is first separated according to molecular weight by tangential cross-flow ultrafiltration (CFF). DOP is selectively isolated and concentrated from CFF fractions by a barium precipitation procedure. The DOP precipitate is then reconstituted in distilled water and excess barium, and other cations are removed with an ion-exchange resin. The DOP isolation/concentration step can provide up to 15-fold concentration and 300-fold concentration of high molecular weight DOP when combined with the inherent concentration provided by CFF. The procedure also removes cations and most of the background DOM, leaving DOP in a matrix suitable for electrospray ionization and mass spectral characterization. Model organic phosphate standards representative of DOP species expected in aquatic environments were used to evaluate the technique. It was then applied to a series of high molecular weight (>1000) CFF retentates isolated from sites within the Everglades Nutrient Removal (ENR) treatment wetland. The elemental compositions of several individual DOP compounds observed at different sites within the ENR were determined by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

Dissolved organic phosphorus in the coastal ocean: Reassessment of available methods and seasonal phosphorus profiles from the Eel River Shelf

Methods for quantifying total dissolved phosphorus (TDP) were reevaluated. High‐temperature ashing/hydrolysis (Ash/Hydrol.) and Acid Persulfate methods were examined for their ability to quantitatively convert a range of organic‐P compounds to orthophosphate. The Ash/Hydrol. method recovered on average 99% of organic‐P compounds tested, including phosphonates (compounds with C‐P bonds). Contrary to concerns voiced in prior studies, we found no P loss due to volatilization in seawater samples. Poor recovery by the Acid Persulfate method was observed for two compound classes: phosphonates and phospholipids. The Ash/Hydrol. method is recommended for routine TDP analyses.The hydrolysis of dissolved organic phosphorus (DOP) during the phosphomolybdate‐blue reaction and the subsequent overestimation of dissolved inorganic phosphorus (DIP) have long been a concern. Extent of hydrolysis of standard DOP compounds was evaluated both during this reaction and over long‐term acidified (pH 1.0)/refrigerated and unacidified/frozen storage. Eleven of 12 compounds tested hydrolyzed &lt;2% during the phosphomolybdate‐blue reaction. Phospholipid, phosphosugar, and nucleotide mono‐ and diphosphate standards stored acidified/refrigerated over 2.5 months were &lt;5% hydrolyzed; compounds with higher energy phosphate bonds (e.g., phosphocreatine) hydrolyzed to a greater extent. A natural seawater sample showed no hydrolysis over 80 d, however, suggesting that refrigerated storage of acidified samples is a viable option.Seasonal DOP profiles from the Eel River Shelf quantified by the Ash/Hydrol. and Acid Persulfate methods yielded comparable results, indicating that the DOP pool at this site did not contain significant phospholipids or phosphonates, which are underrecovered by the Persulfate method. Recoveries using a third method, Nitrate Oxidation, were on average 7% lower. Surface‐water DOP exceeded DIP in summer and was apparently related to biological productivity, underscoring the need to include organic species when evaluating nutrient limitation and creating nutrient budgets.

Alkaline Phosphatase Activity and Utilization of Dissolved Organic Phosphorus by Algae in Subtropical Coastal Waters

Alkaline phosphatase activity (APA) and the availability of dissolved organic phosphorus (DOP) to marine algae were determined in Xiamen Bay and in algal batch culture systems. Results showed that APA changed with seasons, increasing to the highest value in summer and decreasing to the lowest in autumn and spring in Xiamen Bay. Tests on natural populations of planktonic algae and bacteria community showed that algae were mostly responsible for DOP utilization, while bacteria could not take up DOP compounds. Results from algal batch cultures also supported the above conclusion. Relationships between APA and environmental factors indicated that APA was negatively correlated with phosphorus level such as phosphate and small molecular DOP, and APA played an important role in utilization of DOP by algae. All the results emphasized the ecological significance of DOP in subtropical coastal waters.

Dissolved organic substrates as phosphorus and nitrogen sources for axenic batch cultures of freshwater green algae

The growth and yields of four green algae (Pediastrum duplex Meyen, Scenedesmus sp., Tetraedron sp. and Selenastrum sp.) were examined in axenic batch cultures with either dissolved organic phosphorus (DOP) or dissolved organic nitrogen (DON) compounds as sources of phosphorus (P) or nitrogen (N), respectively. These algae, which are major components of the summer-autumn phytoplankton in Lake Kinneret, Israel, showed marked differences in growth response. Scenedesmus and Tetraedron strains grew most rapidly, with highest yields on some DOP compounds, such as ribose phosphate and ATP, whereas Pediastrum was most effective in exploiting some DON sources, such as tryptophan. These observations are consistent with the hypothesis that the differentialability of microalgae to utilize DOP and DON as P and N sources may be ecologically significant, and may playa role in determining the species composition of phytoplankton assemblages in aquatic systems.

Characterization of orthophosphate release from dissolved organic phosphorus by gel filtration and several hydrolytic enzymes

The molecular weight distribution of dissolved organic phosphorus (DOP) and the possible mechanisms of orthophosphate (Pi) release were examined by gel filtration and incubation with some hydrolytic enzymes. Sixty five percent of the DOP appeared to have apparent molecular weights between 300 to 10000 daltons. Less than 10% of the DOP estimated higher molecules greater than 10000 daltons. Alkaline phosphatase released Pi more easily from low molecular weight (< 1500 daltons) DOP than from high molecular weight fractions. While, addition of nucleases or phosphodiesterase alone did not appear Pi release from high molecular weight DOP compounds. Pi release from those DOP compounds increased markedly (more than 30%) when alkaline phosphatase was incubated with nucleases or phosphodiesterase. However, 60% of DOP did not release Pi when alkaline phosphatase was incubated with either enzymes.