NITRATE AND PHOSPHATE UPTAKE INTERACTIONS IN A MARINE PRYMNESIOPHYTE1

The short- and long-term uptake of nitrate and phosphate ions, and their interactions, were studied as functions of the preconditioning of Pavlova lutheri (Droop) Green. Populations were preconditioned in continuous culture at a variety of growth rates and N:P supply ratios. The maximum uptake rates cell^?1 for nitrate and phosphate were of similar magnitudes, in spite of the forty-fold smaller requirement for phosphorus. Short-term phosphate uptake was independent of the nitrate concentration, but the short-term nitrate uptake rate was reduced in the presence of phosphate. The severity of inhibition of nitrate uptake by phosphate was positively correlated with the preconditioning N:P supply ratio and the preconditioning growth rate. In response to large additions of nutrients, P. lutheri was able to increase its phosphorus content sixty-fold, but was only able to take up enough nitrate to double its nitrogen content. The high rate of phosphate uptake relative to its requirement, the inhibition of nitrate uptake by phosphate, and the large capacity for phosphorus storage relative to its requirement, all of which were observed even under N limitation, may imply that even where nitrogen is limiting there can be interspecific competition for available phosphate.     

Nutritional control of actinorhodin production byStreptomyces coelicolor A3(2): suppressive effects of nitrogen and phosphate

Summary Actinorhodin production inStreptomyces coelicolor A3(2) was relatively insensitive to the carbon source concentration but was elicited by nitrogen or phosphate depletion, or by a decline in the growth rate. In starch-glutamate media with nitrogen limitation, increasing the nitrogen supply delayed the onset of antibiotic synthesis and, at concentrations above 30 mM, decreased its rate. In a similar medium with phosphate limitation, increasing the initial phosphate concentration delayed actinorhodin formation and, above 2.5 mM, reduced the rate of synthesis. Experiments in which actinorhodin synthesis was elicited by phosphate depletion at various nitrogen concentrations demonstrated strong suppression by residual glutamate. Cultures in which actinorhodin biosynthesis was initiated by nitrogen depletion were not similarly suppressed by increasing amounts of residual phosphate. The results suggest that actinorhodin production inS. coelicolor A3(2) responds to interacting physiological controls, notable among which is nitrogen catabolite regulation.     

Seasonal Variations in Chlorophyll a Concentrations in Relation to Potentials of Sediment Phosphate Release by Different Mechanisms in a Large Chinese Shallow Eutrophic Lake (Lake Taihu)

The relationship between chlorophyll a and fractionation of sediment phosphorus, inorganic phosphate-solubilizing bacteria (IPB), and organic phosphate-mineralizing bacteria (OPB) was evaluated in a large Chinese shallow eutrophic lake (Lake Taihu) and its embayment (Wuli Bay). At the three study sites, the increase of chlorophyll a concentrations in April paralleled those of the iron bound phosphate accounting for major portion of sediment inorganic phosphate, and in June significantly higher OPB and IPB numbers (especially OPB) in sediment were main contributors to the peaks of chlorophyll a concentration. Even though IPB peaked from February to June, it should serve as an unimportant P source due to the irrelevancy with chlorophyll a and soluble reactive phosphorus (SRP). By contrast, at the other site in the embayment, the calcium-bound phosphate was predominant and solid, which was difficult to be released, and neither IPB nor OPB were detectable in the sediment, indicating weak potential for phosphorus release from the sediment, which was reflected in the small seasonal variation in SRP concentration in water column. Hence, the extents to which the three general mechanisms behind phosphate release from sediment (desorption of iron bound phosphate, solubilization by IPB and enzymatic hydrolysis by OPB) operated were different depending on seasons and sites in Lake Taihu, they may jointly drive phosphate release and accelerate the eutrophication processes.     

Biological Activities of p-Ethylphenyl and p-Acetylphenyl Phosphates and their Thiono Analogs

Sixteen phosphate or phosphorothioate esters related to neurotoxic tri-p-ethylphenyl phosphate and its active metabolites were synthesized and their biological activities including inhibitory activity against cholinesterases, insecticidal activity, toxicity to mammals and neurotoxicity were examined. Dialkyl p-ethylphenyl phoshates, p-acetylphenyl phosphates and their thiono analogs showed insecticidal activity, but did not show the ataxic sign by any sublethal doses in hens. When a methyl group was introduced on p-acetylphenyl ring, the biological activity changed remarkably by its position. The introduction of a methyl group into o-position made the ester inactive, while the introduction into m-position made it active to insects selectively.     

Regulation of cephalosporin synthesis in Cephalosporium acremonium by phosphate and glucose

The regulation of cephalosporin synthesis in Cephalosporium acremonium was studied in a simple chemically-defined medium with glucose as the carbon source. Antibiotic synthesis depended on the phosphate content of the medium. At phosphate concentrations above 2.75 mM maximum antibiotic titres were not reached while glucose uptake and growth rates were increased. Phosphate exerted its effect indirectly by regulating the rate of glucose consumption. The negative effect of high phosphate concentrations could be overcome completely by controlling the sugar supply in fed-batch and chemostat experiments. High actual concentrations of phosphate or of glucose alone had no direct negative effect on antibiotic synthesis.     

Development and assessment of fusarium oxysporum-based mycoherbicide for control of Striga Hermonthica in sorghum

Abstract

Experiments were carried out from 2002 to 2003 to determine the most suitable form of fungal delivery for possible use by farmers in biological control of Striga hermonthica. Six mycoherbicides were developed, based on Fusarium oxysporum isolated from wilted S. hermonthica. In mycoherbicide formulation, rock phosphate powder, sorghum bran and gum arabic powder were used as carriers. Besides its role as a carrier, gum arabic powder was used as a sticker. There were three carriers with two formulations each, making six treatments altogether. Living propagule studies were based on colony, mycelium and conidium number of F. oxysporum. In greenhouse evaluation of mycoherbicides, each kg sorghum seed was coated with 10 g mycoherbicide before sowing. Carrier rock phosphate powder with gum arabic powder as a sticking agent was the most suitable form of its delivery for use by peasant farmers.     

Investigations on phosphate uptake and polyphosphate metabolism by mycorrhized and nonmycorrhized roots of beech and pine as investigated by in vivo 31P-NMR

Comparative in vivo ³¹P-NMR studies of mycorrhized and nonmycorrhized roots of Fagus sylvatica and Pinus sylvestris and of the fungus Suillus bovinus in pure culture have produced interesting new data. With respect to intracellular compartments and pH, ³¹P-NMR spectroscopy showed that the spectrum of the mycorrhiza results from simple superimposition of the spectra of its symbionts. A special method of cyclic phosphate supply followed by block averaging of the NMR spectra was used to determine the kinetic behaviour of phosphate uptake and storage and its incorporation into polyphosphate at a constant external pH of 5.5. Mycorrhized roots and pure fungus showed transformation of accumulated inorganic phosphate into mobile polyphosphate with a medium chain length. Transformation of mobile into immobile polyphosphate either with a long chain length or in a granular state was also observed. Thus, two different types of fungal polyphosphate could be verified. Deficiency of external phosphate initiated the mobilization of internal phosphate, transforming stored polyphosphate into phosphate. It could be shown that a high fungal mass renders mycorrhizal phosphate metabolism less sensitive to external variation in nutrient concentration. The central role of the fungus in regulating mycorrhizal phosphate metabolism is discussed.     

Characterization of the mineral phosphate solubilizing activity of <Emphasis Type="Italic">Serratia marcescens</Emphasis> CTM 50650 isolated from the phosphate mine of Gafsa

The mineral phosphate solubilizing (MPS) ability of a Serratia marcescens strain, namely CTM 50650, isolated from the phosphate mine of Gafsa, was characterized on a chemically defined medium (NBRIP broth). Various insoluble inorganic phosphates, including rock phosphate (RP), calcium phosphate (CaHPO₄), tri-calcium phosphate (Ca₃(PO₄)₂) and hydroxyapatite were tested as sole sources of phosphate for bacterial growth. Solubilization of these phosphates by S. marcescens CTM 50650 was very efficient. Indeed, under optimal conditions, the soluble phosphorus (P) concentration it produced reached 967, 500, 595 and 326 mg/l from CaHPO₄, Ca₃(PO₄)₂, hydroxyapatite and RP, respectively. Study of the mechanisms involved in the MPS activity of CTM 50650, showed that phosphate solubilization was concomitant with significant drop in pH. HPLC-analysis of culture supernatants revealed the secretion of gluconic acid (GA) resulting from direct oxidation pathway of glucose when the CTM 50650 cells were grown on NBRIP containing glucose as unique carbon source. This was correlated with the simultaneous detection by PCR for the first time in a S. marcescens strain producing GA, of a gene encoding glucose dehydrogenase responsible for GA production, as well as the genes pqqA, B, C and E involved in biosynthesis of its PQQ cofactor. This study is expected to lead to the development of an environmental-friendly process for fertilizer production considering the capacity of S. marcescens CTM 50650 to achieve yields of P extraction up to 75% from the Gafsa RP.     

Effect of environmental phosphate concentration on protein export by Bacillus licheniformis NCIB 6346

Bacillus licheniformis NCIB 6346 was grown under phosphate or magnesium limitation in continuous culture and forward and reverse transitions carried out to examine their effects upon extracellular enzyme production. Analysis of the observed kinetics allowed a distinction to be made between the effects of phenotypic variation and of genetic selection upon exoenzyme production. Furthermore, increases in the phosphate concentration (0.3–30 mM) were directly related to increased phenotypic expression of alpha-amylase. By contrast, penicillinase production was reduced under these conditions but analysis revealed that its phenotypic expression was only indirectly influenced by the concentrations of either magnesium or phosphate present during the transitions.     

Performance of improved bacterial cellulose application in the production of functional paper

Aim: The purpose of this work was to study the feasibility of producing economic flame retardant bacterial cellulose (BC) and evaluating its behaviour in paper production. Methods and Results: This type of BC was prepared by Gluconacetobacter subsp. xylinus and substituting the glucose in the cultivation medium by glucose phosphate as a carbon source; as well as using corn steep liquor as a nitrogen source. The investigated processing technique did not dispose any toxic chemicals that pollute the surroundings or cause unacceptable effluents, making the process environmentally safe. The fire retardant behaviour of the investigated BC has been studied by non‐isothermal thermogravimetric analysis (TGA & DTGA). The activation energy of each degradation stage and the order of degradation were estimated using the Coats–Redfern equation and the least square method. Strength, optical properties, and thermogravimetric analysis of BC‐phosphate added paper sheets were also tested. Conclusions: The study confirmed that the use of glucose phosphate along with glucose was significant in the high yield production of phosphate containing bacterial cellulose (PCBC1); more so than the use of glucose phosphate alone (PCBC2). Incorporating 5% of the PCBC with wood pulp during paper sheet formation was found to significantly improve kaolin retention, strength, and fire resistance properties as compared to paper sheets produced from incorporating bacterial cellulose (BC). Significance and Impact of the Study: This modified BC is a valuable product for the preparation of specialized paper, in addition to its function as a fillers aid.     

Phosphorus relations of roots and mycorrhizas of Rhododendron maximum L. in the southern Appalachians,North Carolina

Summary The mycorrhizal associations of Rhododendron maximum in the southern Appalachian mountains were studied in relation to the supply and demand of phosphate at three altitudes. A variety of mycorrhizal associations are described together with the ability of the differing mycorrhizal types to produce phosphatase enzyme, which was inversely related to the availability of inorganic phosphate determined by a root bioassay, as Ectomycorrhizal associations were shown to have a higher phosphatase production potential than other mycorrhizas. The availability of inorganic phosphate at different altitudes is related to turnover of organic matter and fixation capacity of the mineral soil. It is speculated that the ability of R. maximum to associate with a range of mycorrhizal associates is likely to improve species' fitness and enhance its competitive ability.     

The identification and classification ofAcinetobacter strains exhibiting variations in phosphate accumulation by SDS-PAGE and numerical analysis

The limitation of phosphate concentrations in effluents is of international concern because of the risk of eutrophication.Acinetobacter spp. have often been isolated from activated sludge plants exhibiting enhanced phosphate removal. The ability to remove phosphate from mixed liquor byAcinetobacter isolates and reference strains was, therefore, determined. The ability to remove phosphate was found to vary among theAcinetobacter strains. The taxonomic relationships among these various strains were elucidated by SDS-PAGE and numerical analysis, and the correlation between their taxonomy and phosphate uptake ability was determined. The ability to remove large amounts of phosphate was found to be strain specific rather than species specific. The classification ofA. haemolyticus andA. baumannii as separate species is questioned.     

Impact of MtrA on phosphate metabolism genes and the response to altered phosphate conditions in Streptomyces

Phosphate metabolism is known to be regulated by the PhoPR regulatory system in Streptomyces and some other bacteria. In this study, we report that MtrA also regulates phosphate metabolism in Streptomyces. Our data showed that, in Streptomyces coelicolor, MtrA regulates not only phosphate metabolism genes such as phoA but also phoP under different phosphate conditions, including growth on rich complex media without added inorganic phosphate and on defined media with low or high concentrations of inorganic phosphate. Cross-regulation was also observed among mtrA, phoP and glnR under these conditions. We demonstrated both in vitro and in vivo binding of MtrA to the promoter regions of genes associated with phosphate metabolism and to the intergenic region between phoR and phoU, indicating that these phosphate metabolism genes are targets of MtrA. We further showed that MtrA in S. lividans and S. venezuelae has detectable regulatory effects on expression of phosphate metabolism genes. Additionally, the MtrA homologue from Corynebacterium glutamicum bound predicted MtrA sites of multiple phosphate metabolism genes, implying its potential for regulating phosphate metabolism in this species. Overall, our findings support MtrA as a major regulator for phosphate metabolism in Streptomyces and also potentially in other actinobacteria.     

Isolation and characterization of mutants of the facultative methylotroph Arthrobacter P1 blocked in one-carbon metabolism

Among methylamine and/or ethylamine minus mutants of Arthrobacter P1 four different classes were identified, which were blocked either in the methylamine transport system, amine oxidase, hexulose phosphate synthase or acetaldehyde dehydrogenase. The results indicated that a common primary amine oxidase is involved in the metabolism of methylamine and ethylamine. Growth on ethylamine, however, was not dependent on the presence of the methylamine transport system. In mutants lacking amine oxidase, methylamine was unable to induce the synthesis of hexulose phosphate synthase, thus confirming the view that the actual inducer for the latter enzyme is not methylamine, but its oxidation product formaldehyde. Contrary to expectation, when the formaldehyde fixing enzyme hexulose phosphate synthase was deleted (mutant Art 11), accumulation of formaldehyde during growth on choline or on glucose plus methylamine as a nitrogen source did not occur. Evidence was obtained to indicate that under these conditions formaldehyde may be oxidized to carbon dioxide via formate, a sequence in which peroxidative reactions mediated by catalase are involved. In addition, a specific NAD-dependent formaldehyde dehydrogenase was detected in choline-grown cells of wild type Arthrobacter P1 and strain Art 11. This enzyme, however, does not play a role in methylamine or formaldehyde metabolism, apparently because these compounds do not induce its synthesis.Abbreviations RuMP ribulose monophosphate - HPS hexulose phosphate synthase - HPI hexulose phosphate isomerase     

Bacterial Synthesis of Nucleotides

5′-Phosphoribosyl 5-amino-4-imidazole carboxamide was prepared by incubating 5-amino-4-imidazole carboxamide riboside and a phosphate compound with the bacteria characterized to phosphorylate at C_5′ via the phosphoryl transfer reaction. Aromatic phosphate compounds and 5′-nucleotides were able to act as the phosphate donor. This material was isolated chromatographically and its properties were studied. The other bacteria characterized to phosphorylate at C_{3′ (or 2′)} also phosphorylated a little probably at C_{3′ (or 2′)} of 5-amino-4-imidazole carboxamide riboside.

The phosphoryl interconversion between nucleotides and nucleosides was studied to be carried out via the phosphoryl transfer reaction observed in bacteria. The phosphotransferase activity of Ps. trifolii mediated reversibly the phosphoryl transfer between 5′-nucleotides and nucleosides, and its optimal pH was at around 8.5, whereas that of Prot. mirabilis did transfer the phosphoryl radical from 2′- and 3′-nucleotide to nucleoside at its optimal pH, around 5.0.

These donor- and product-isomer specificities of both bacteria were evident to be invariable, regardless of reaction pH and cultural conditions. These reactions, especially using the bacteria characterized to phosphorylate at C_5′ of nucleoside, were demonstrated to catalyze the phosphoryl interconversion between 5′-purine nucleotides and pyrimidine nucleosides or vice versa.     

A novel coenzymatic function of pyridoxal 5'-phosphate

Pyridoxal 5′-phosphate, the vitamin B₆ derivative, acts as the coenzyme of many enzymes involved in amino acid metabolism. Exceptionally, this compound was found covalently bound to glycogen phosphorylase, the key enzyme in the regulation of glycogen metabolism. Although it is essential for the function of phosphorylase, its direct role has remained an enigma. We have recently found that the glucose moiety of pyridoxal (5′)diphospho (1)-α-D -glucose, a conjugate of pyridoxal 5′-phosphate and glucose 1-phosphate through a pyrophosphate linkage, is transferred to the nonreducing end of glycogen, forming a new α-1,4-glucosidic linkage. This finding emphasizes the importance of the direct phosphate-phosphate interaction between the coenzyme and the substrate in the phosphorylase catalytic reaction. We have proposed a catalytic mechanism for phosphorylase in which the phosphate group of pyridoxal 5′-phosphate acts as an electrophile to the phosphate group of glucose 1-phosphate. This appears to represent the first instance of the direct involvement of a phosphate group in catalysis by enzymes.