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PubMed2005

An intracellular phosphate buffer filters transient fluctuations in extracellular phosphate levels.

To survive in a dynamic and unpredictable environment, cells must correctly interpret and integrate extracellular signals with internal factors. In particular, internal stores of nutrients must be managed for use during periods of nutrient limitation. To gain insight into this complex process, we combined biochemical and spectroscopic techniques to follow the dynamics of the phosphate responsive signaling pathway in both single yeast cells and populations. We demonstrate that the phosphate-responsive genes PHO5 and PHO84 exhibit different kinetics of transcriptional induction in response to phosphate starvation, and that transient phosphate limitation causes induction of PHO84 but not PHO5. This differential kinetic behavior is largely eliminated in cells that lack the ability to store phosphate internally in the form of polyphosphate, but the threshold of external phosphate required for induction of PHO5 and PHO84 is unaffected. Our observations indicate that polyphosphate acts as a buffer that can be mobilized during periods of phosphate limitation and enables the phosphate-responsive signaling pathway to filter transient fluctuations in extracellular phosphate levels.

Acid Phosphatase↗
PubMed1998

A 1-deoxy-D-xylulose 5-phosphate reductoisomerase catalyzing the formation of 2-C-methyl-D-erythritol 4-phosphate in an alternative nonmevalonate pathway for terpenoid biosynthesis.

Several eubacteria including Esherichia coli use an alternative nonmevalonate pathway for the biosynthesis of isopentenyl diphosphate instead of the ubiquitous mevalonate pathway. In the alternative pathway, 2-C-methyl-D-erythritol or its 4-phosphate, which is proposed to be formed from 1-deoxy-D-xylulose 5-phosphate via intramolecular rearrangement followed by reduction process, is one of the biosynthetic precursors of isopentenyl diphosphate. To clone the gene(s) responsible for synthesis of 2-C-methyl-D-erythritol 4-phosphate, we prepared and selected E. coli mutants with an obligatory requirement for 2-C-methylerythritol for growth and survival. All the DNA fragments that complemented the defect in synthesizing 2-C-methyl-D-erythritol 4-phosphate of these mutants contained the yaeM gene, which is located at 4.2 min on the chromosomal map of E. coli. The gene product showed significant homologies to hypothetical proteins with unknown functions present in Haemophilus influenzae, Synechocystis sp. PCC6803, Mycobacterium tuberculosis, Helicobacter pyroli, and Bacillus subtilis. The purified recombinant yaeM gene product was overexpressed in E. coli and found to catalyze the formation of 2-C-methyl-D-erythritol 4-phosphate from 1-deoxy-D-xylulose 5-phosphate in the presence of NADPH. Replacement of NADPH with NADH decreased the reaction rate to about 1% of the original rate. The enzyme required Mn2+, Co2+, or Mg2+ as well. These data clearly show that the yaeM gene encodes an enzyme, designated 1-deoxy-D-xylulose 5-phosphate reductoisomerase, that synthesizes 2-C-methyl-D-erythritol 4-phosphate from 1-deoxy-D-xylulose 5-phosphate, in a single step by intramolecular rearrangement and reduction and that this gene is responsible for terpenoid biosynthesis in E. coli.

Aldose-Ketose Isomerases↗
PubMed1998

Cloning and characterization of two phosphate transporters from Medicago truncatula roots: regulation in response to phosphate and to colonization by arbuscular mycorrhizal (AM) fungi.

Most vascular plants can acquire phosphate from the environment either directly, via the roots, or indirectly, via a fungal symbiont that invades the cortical cells of the root. Here we have identified two cDNA clones (MtPT1 and MtPT2) encoding phosphate transporters from a mycorrhizal root cDNA library (Medicago truncatula/Glomus versiforme). The cDNAs represent M. truncatula genes and the encoded proteins share identity with high-affinity phosphate transporters from Arabidopsis, potato, yeast, Neurospora crassa, and an arbuscular mycorrhizal (AM) fungus, G. versiforme. The function of the protein encoded by MtPT1 was confirmed by complementation of a yeast phosphate transport mutant (pho84). The K(m) of the MtPT1 transporter in this system is 192 microM. MtPT1 and MtPT2 transcripts are present in roots and transcript levels increase in response to phosphate starvation. MtPT transcripts were not detected in leaves. Following colonization of the roots by the AM fungus G. versiforme, both MtPT1 and MtPT2 transcript levels decrease significantly. Down-regulation of phosphate starvation-inducible genes in mycorrhizal roots appears to be a common occurrence and a homologue of a phosphate starvation-inducible purple acid phosphatase is also down-regulated in the mycorrhizal roots. The functional characteristics and expression patterns of the MtPT transporters are consistent with a role in the acquisition of phosphate from the environment but suggest that they may not be involved in phosphate uptake at the symbiotic interface in mycorrhizal roots.

Amino Acid Sequence↗
PubMed1985

Hepatic carbamoyl phosphate metabolism. Role of cytosolic and mitochondrial carbamoyl phosphate in de novo pyrimidine synthesis.

The interrelationship between the two carbamoyl phosphate pools in intact hepatocytes and intact liver was studied with respect to de novo pyrimidine synthesis by use of selective inhibitors of the mitochondrial and the cytosolic carbamoyl-phosphate synthetase. Inhibition of mitochondrial carbamoyl phosphate synthesis by 4-pentenoate was without effect on galactosamine-stimulated pyrimidine synthesis. Conditions favouring mitochondrial carbamoyl phosphate accumulation, like excess ammonium ions or L-norvaline, led to an increase in pyrimidine synthesis bypassing the feedback inhibition of cytosolic carbamoyl-phosphate synthetase by UTP. A stimulation of pyrimidine synthesis was not observed when the carbamoyl phosphate accumulation was due to aspartate deficiency in the presence of aminooxyacetate. The full response of pyrimidine synthesis to excess ammonium ions was restored, even in the presence of aminooxyacetate, when aspartate was substituted. This is explained by an inhibition of aspartate carbamoyltransferase flux [in view of the Km (aspartate = 0.7 mmol/l) of this enzyme] resulting from a 90% decrease in aspartate tissue levels. Acivicin, the inhibitor of cytosolic carbamoyl-phosphate synthetase, completely abolished the galactosamine-induced stimulation of pyrimidine synthesis, but was without effect on the stimulation of pyrimidine synthesis by ammonium ions and L-norvaline. It is concluded that experimental changes in mitochondrial carbamoyl phosphate content exert effects on de novo pyrimidine synthesis; however, it is considered unlikely that relevant amounts of mitochondrial carbamoyl phosphate are used for pyrimidine synthesis under physiological conditions. In addition the data point to a potential regulatory role of aspartate in hepatic pyrimidine synthesis.

Aminooxyacetic Acid↗
PubMed1996

Yeast mitochondria lacking the phosphate carrier/p32 are blocked in phosphate transport but can import preproteins after regeneration of a membrane potential.

Two different functions have been proposed for the phosphate carrier protein/p32 of Saccharomyces cerevisiae mitochondria: transport of phosphate and requirement for import of precursor proteins into mitochondria. We characterized a yeast mutant lacking the gene for the phosphate carrier/p32 and found both a block in the import of phosphate and a strong reduction in the import of preproteins transported to the mitochondrial inner membrane and matrix. Binding of preproteins to the surface of mutant mitochondria and import of outer membrane proteins were not inhibited, indicating that the inhibition of protein import occurred after the recognition step at the outer membrane. The membrane potential across the inner membrane of the mutant mitochondria was strongly reduced. Restoration of the membrane potential restored preprotein import but did not affect the block of phosphate transport of the mutant mitochondria. We conclude that the inhibition of protein import into mitochondria lacking the phosphate carrier/p32 is indirectly caused by a reduction of the mitochondrial membrane potential (delta(gamma)), and we propose a model that the reduction of delta(psi) is due to the defective phosphate import, suggesting that phosphate transport is the primary function of the phosphate carrier/p32.

Adenosine Triphosphate↗
PubMed1994

Low phosphate diet upregulates the renal and intestinal sodium-dependent phosphate transporter in vitamin D-resistant hypophosphatemic mice.

Renal and jejunal absorption of inorganic phosphate (P(i)) increases with dietary P(i) restriction in the rat. The defect in Na(+)-dependent phosphate transporter has been localized to the kidney of the Hyp mice; however, the adaptation to low-P(i) diet in both kidney and jejunum of the Hyp mice has not been well characterized. Therefore, the current studies were designed to characterize the adaptation of renal and jejunal Na(+)-dependent phosphate transport in the Hyp mice and compare it with normal mice. Low-P(i) diet significantly increased the slope of the initial rate of renal brush border membrane (BBM) phosphate uptake compared with corresponding values in mice raised on control-P(i) diet (0.035 vs 0.017) (P < 0.01). Kinetics of renal Na(+)-dependent phosphate uptake in Hyp mice showed a Vmax of 1.00 +/- 0.01 and 0.46 +/- 0.02 nmoles/mg protein/15 sec in low- and control-P(i) diets, respectively (P < 0.01), whereas, Km values were 0.07 +/- 0.04 and 0.02 +/- 0.01, respectively. Similar kinetic analysis in renal BBM of normal mice showed a Vmax of 2.4 +/- 0.17 and 1.18 +/- 0.09 (P < 0.01) and Km of 0.07 +/- 0.03 and 0.08 +/- 0.03 on low and control P(i) diets, respectively. Similarly, low-P(i) diet significantly increased the slope of the initial rate of intestinal phosphate uptake (0.013 and 0.007) (P < 0.01). Kinetics of jejunal Na(+)-dependent phosphate uptake in Hyp mice showed a Vmax of 0.36 +/- 0.01 and 0.2 +/- 0.02 nmoles/mg protein/15 sec, (P < 0.01) and Km of 0.13 +/- 0.06 and 0.06 +/- 0.01 mM in low- and in control-P(i) diet, respectively. Kinetic analysis in jejunal BBM of normal mice showed a Vmax of 0.47 +/- 0.04 and 0.18 +/- 0.01 nmoles/mg protein/15 sec (P < 0.01) and Km of 0.16 +/- 0.04 and 0.11 +/- 0.01 in low- and control-P(i) diets, respectively. The data indicates that low-phosphate diet upregulates the Vmax of the renal and jejunal Na(+)-dependent phosphate cotransporter in the hypophosphatemic mice.

Adaptation, Physiological↗
PubMedDate not supplied

The use of phosphate in detergents and possible replacements for phosphate.

About 5% of the total phosphate mined worldwide is used in detergents. The chemical form in which phosphate is used in detergents is predominantly pentasodium triphosphate (PSTP). The most significant feature for the use of PSTP in detergents is its ability to form soluble and strong complexes with calcium and magnesium ions. This provides a strong synergism with regard to detergency when PSTP is used in combination with synthetic surfactants. Other important features of PSTP are its ability to disperse dirt in the washing solution, its weak alkalinity, its crystalline form when dry (which enables production of crisp powders) and, last but not least, its toxicological acceptability. The development of PSTP for use in detergents has a history of over 25 years. In certain areas of highly developed countries where effluents from major centres of population can reach stagnant surface waters a rapid increase of eutrophication of these surface waters is observed. Phosphates are being recognized as one of the essential nutrients contributing to the eutrophication and detergents are one of the many sources of phosphate discharged to the environment. This is now causing demands for reduction in or even banning of the use of phosphates in detergents. Major reserach projects and some practical approaches to meeting these demands are described. The potential environmental impact of removing phosphate from detergents remains, however, doubtful, as it has been demonstrated in Sweden that phosphate removal by sewage treatment is the most effective measure to control phosphate discharges. This makes the case of phosphates in detergents an example of how science and technology can become entangled with politics.

Biodegradation, Environmental↗
PubMed1985

Response of tissue phosphate content to acute dietary phosphate deprivation in the X-linked hypophosphatemic mouse.

In order to evaluate a possible role for tissue phosphate or phosphorylated compounds in mediating the increase in plasma 1,25(OH)2D3 levels during dietary phosphate deprivation, renal cortical phosphate content has been measured in both normal and X-linked hypophosphatemic mice on a normal diet and also after acute dietary phosphate deprivation. We find that the metabolism of inorganic phosphate and phosphorylated organic compounds in the renal cortex of Hyp mice is not altered in response to their very low levels of serum phosphate. Skeletal muscle does not lose inorganic phosphate and/or phosphorylated metabolites to compensate for drastic loses of serum phosphate during acute dietary deprivation in either normal or Hyp mice. Furthermore, the chronic low level of serum phosphate and altered hormonal regulation in Hyp mice do not produce alterations in mineral composition of the bone with the possible exception that the stoichiometry of the apatite might be slightly different.

Animals↗
PubMed1986

Demonstration and chemical modification of a specific phosphate binding site in the phosphate-starvation-inducible outer membrane porin protein P of Pseudomonas aeruginosa.

The interaction of phosphate ions with the Pseudomonas aeruginosa anion-specific protein P channel was probed. The single-channel conductance of protein P incorporated into planar lipid bilayer membranes in the presence of 0.3 M H2PO-4 was shown to be 6.0 pS, demonstrating that protein P channels allowed the permeation of phosphate. When large numbers of protein P channels were incorporated into lipid bilayer membranes in the presence of 40 mM Cl-, addition of small concentrations of phosphate resulted in reduction of macroscopic Cl- conductance in a dose- (and pH-) dependent fashion. This allowed calculation of an I50 value of e.g. 0.46 mM at pH 7.0, suggesting that the affinity of protein P for its normal substrate phosphate was at least 60-100-fold greater than the affinity of the channel for other ions such as chloride. Pyrophosphate and the phosphate analogue, arsenate, also inhibited macroscopic Cl- conductance through protein P with I50 values at pH 7.0 of 4.9 mM and 1.3 mM, respectively. To probe the nature of the phosphate binding site, the epsilon-amino groups of available lysine residues of protein P were chemically modified. Acetylation and carbamylation which produced uncharged, modified lysines destroyed both the anion (e.g. Cl-) binding site and the phosphate binding site as determined by single-channel experiments and macroscopic conductance inhibition experiments respectively. Nevertheless, the modified proteins still retained their trimeric configuration and their ability to reconstitute single channels in lipid bilayer membranes. Methylation, which allowed retention of the charge on the modified lysine residues, increased the Kd of the channel for Cl- 33-fold and the I50 for phosphate inhibition of macroscopic Cl- conductance 2.5-4-fold. A molecular model for the phosphate binding site of the protein P channel is presented.

Acetylation↗
PubMed1980

Spectroscopic studies of complexes between pyridoxamine (pyridoxine)-5'-phosphate oxidase and pyridoxyl 5'-phosphate compounds differing at position 4'.

The absorbance spectrum of pyridoxamine (pyridoxine)-5'-phosphate oxidase (EC 1.4.3.5) is altered upon the binding of pyridoxal 5'-phosphate or analogs with different substituents at position 4'. The absorbance difference spectra are similar for complexes of the oxidase and pyridoxal 5'-phosphate, 4'-desoxypyridoxine 5'-phosphate, and 4-ethynyl-4-deformylpyridoxal 5'-phosphate; hence, these perturb the flavoprotein absorbance by similar interactions primarily involving the pyridoxyl 5'-phosphate moiety, and not specifically the 4-formyl group or other relatively small and uncharged functions at this position. A different type of spectral perturbation is caused by analogs with larger substituents at position 4' (i.e. 4'-methoxypyridoxine 5'-phosphate, 4-methyl-vinyl-4-deformylpyridoxal 5'-phosphate, and pyridoxal 5'-phosphate oxime and hydrazone). These analogs impose bulky groups in a region of the active site that critically influences the environment of the flavin, and, thus, may reflect positioning of this portion of the substrates close to the flavin ring, as is required for their redox interaction.

Animals↗
PubMed1994

Chloride- and alkali-containing calcium phosphates as basic materials to prepare calcium phosphate cements.

Combinations of an alkali-containing calcium phosphate-like rhenanite, sodium whitlockite or calcium potassium phosphate and a chloride-containing calcium phosphate-like spodiosite or chloroapatite with or without additions of other calcium phosphates like monocalcium phosphate monohydrate, dicalcium phosphate or dicalcium phosphate dihydrate were made and mixed with water into pastes. The setting time of these pastes was determined. After soaking for a day in Ringer's solution at 37 degrees C the compressive strength and the diametral tensile strength were determined. Two of the combinations tried in this study resulted in the formation of cements at room temperature. One cement was of the type dicalcium phosphate, whereas the other gave octocalcium phosphate as the solid reaction product. The byproducts formed were an aqueous solution of NaCl and one of K2HPO4, respectively. Applications for bone repair and augmentation are envisaged.

Alkalies↗
PubMed1993

A novel mono-branched lipid phosphate acts as a substrate for dolichyl phosphate mannose synthetase.

Dolichyl phosphate mannose synthetase (GDP-mannose: dolichyl-phosphate O-beta-D-mannosyltransferase; EC 2.4.1.83) is an enzyme that is involved in glycoconjugate biosynthesis and possesses a putatively conserved dolichol binding site. In order to probe the interaction between the enzyme and the dolichol chain, lipid phosphates varying in length and extent of branching have been tested as substrates in crude microsomal preparations from Saccharomyces cerevisiae. It was found that phytanyl (3,7,11,15-tetramethylhexadecanyl) phosphate was utilized at 60-70% of the efficiency of the natural dolichyl lipid in transfer of [3,4,-3H]mannose from GDP-Man to organic soluble material, whereas addition of S-3-methyloctadecanyl phosphate, which is of similar length to the phytanyl analogue but with only one branch, resulted in approximately 25% of the incorporation of the natural substrate. Incubations with the unbranched tetradecanyl phosphate and with the short, doubly branched R- and S-dihydrocitronellyl (3,7-dimethyloctanyl) phosphates exhibited levels of activity similar to incubations with no exogenous acceptor. These results were qualitatively confirmed with experiments on Escherichia coli harbouring the S. cerevisiae DPM1 gene. The [3H]mannosylated lipid-linked material from microsomal incubations was purified by anion-exchange chromatography. The major saccharide component recovered after hydrolysis was determined to be mannose, but a mannose-containing disaccharide was also present. It is concluded that branching of lipid phosphates is essential for substrates of dolichyl phosphate mannose synthetase and that significant transfer of mannose occurs even if only branching at C-3 is present.

Amino Acid Sequence↗
PubMed1999

Functional linkage between the glutaminase and synthetase domains of carbamoyl-phosphate synthetase. Role of serine 44 in carbamoyl-phosphate synthetase-aspartate carbamoyltransferase-dihydroorotase (cad).

Mammalian carbamoyl-phosphate synthetase is part of carbamoyl-phosphate synthetase-aspartate carbamoyltransferase-dihydroorotase (CAD), a multifunctional protein that also catalyzes the second and third steps of pyrimidine biosynthesis. Carbamoyl phosphate synthesis requires the concerted action of the glutaminase (GLN) and carbamoyl-phosphate synthetase domains of CAD. There is a functional linkage between these domains such that glutamine hydrolysis on the GLN domain does not occur at a significant rate unless ATP and HCO(3)(-), the other substrates needed for carbamoyl phosphate synthesis, bind to the synthetase domain. The GLN domain consists of catalytic and attenuation subdomains. In the separately cloned GLN domain, the catalytic subdomain is down-regulated by interactions with the attenuation domain, a process thought to be part of the functional linkage. Replacement of Ser(44) in the GLN attenuation domain with alanine increases the k(cat)/K(m) for glutamine hydrolysis 680-fold. The formation of a functional hybrid between the mammalian Ser(44) GLN domain and the Escherichia coli carbamoyl-phosphate synthetase large subunit had little effect on glutamine hydrolysis. In contrast, ATP and HCO(3)(-) did not stimulate the glutaminase activity, indicating that the interdomain linkage had been disrupted. In accord with this interpretation, the rate of glutamine hydrolysis and carbamoyl phosphate synthesis were no longer coordinated. Approximately 3 times more glutamine was hydrolyzed by the Ser(44) --> Ala mutant than that needed for carbamoyl phosphate synthesis. Ser(44), the only attenuation subdomain residue that extends into the GLN active site, appears to be an integral component of the regulatory circuit that phases glutamine hydrolysis and carbamoyl phosphate synthesis.

Adenosine Triphosphate↗
PubMed2005

The contribution of phosphate-phosphate repulsions to the free energy of DNA bending.

DNA bending is important for the packaging of genetic material, regulation of gene expression and interaction of nucleic acids with proteins. Consequently, it is of considerable interest to quantify the energetic factors that must be overcome to induce bending of DNA, such as base stacking and phosphate-phosphate repulsions. In the present work, the electrostatic contribution of phosphate-phosphate repulsions to the free energy of bending DNA is examined for 71 bp linear and bent-form model structures. The bent DNA model was based on the crystallographic structure of a full turn of DNA in a nucleosome core particle. A Green's function approach based on a linear-scaling smooth conductor-like screening model was applied to ascertain the contribution of individual phosphate-phosphate repulsions and overall electrostatic stabilization in aqueous solution. The effect of charge neutralization by site-bound ions was considered using Monte Carlo simulation to characterize the distribution of ion occupations and contribution of phosphate repulsions to the free energy of bending as a function of counterion load. The calculations predict that the phosphate-phosphate repulsions account for approximately 30% of the total free energy required to bend DNA from canonical linear B-form into the conformation found in the nucleosome core particle.

DNA↗
PubMed1980

Phenyl phosphate as a water-soluble analog of dolichyl phosphate in microsomal mannosyltransferase systems.

Incubation of rat liver microsomes with GDP-[14C]mannose and phenyl phosphate for 30 min, followed by paper-chromatographic analysis, revealed the presence of a new radioactive compound that was isolated and characterized as phenyl beta-D-mannosyl phosphate. The enzyme catalyzing this reaction was very closely related to a dolichyl beta-D-mannosyl phosphate-synthesizing activity found in the same microsomes. The two activities were affected in a parallel fashion by mild heating and were found in the same proportions in whole microsomes, in rough-surfaced microsomes, and in smooth-surfaced mirosomes. Increasing the concentration of phenyl phosphate from 0 to 15 mM resulted in a progressive reduction in the rate of mannose incorporation into endogenous dolichyl phosphate. It is concluded that the two reactions are catalyzed by a single enzyme. The labeled product from phenyl phosphate was rapidly excluded from the microsomes, while the product from dolichyl phosphate was retained in the microsomes, suggesting that phenyl phosphate may act as a mannose-trapping agent, thereby inhibiting mannosyltransferase reactions involving dolichyl phosphate as a glycosyl carrier.

Animals↗
PubMed1999

Apyrase functions in plant phosphate nutrition and mobilizes phosphate from extracellular ATP.

ATP, which is present in the extracellular matrix of multicellular organisms and in the extracellular fluid of unicellular organisms, has been shown to function as a signaling molecule in animals. The concentration of extracellular ATP (xATP) is known to be functionally modulated in part by ectoapyrases, membrane-associated proteins that cleave the gamma- and beta-phosphates on xATP. We present data showing a previously unreported (to our knowledge) linkage between apyrase and phosphate transport. An apyrase from pea (Pisum sativum) complements a yeast (Saccharomyces cerevisiae) phosphate-transport mutant and significantly increases the amount of phosphate taken up by transgenic plants overexpressing the gene. The transgenic plants show enhanced growth and augmented phosphate transport when the additional phosphate is supplied as inorganic phosphate or as ATP. When scavenging phosphate from xATP, apyrase mobilizes the gamma-phosphate without promoting the transport of the purine or the ribose.

Adenosine Triphosphate↗
PubMed1988

Human erythrocyte glucose-6-phosphate dehydrogenase. Identification of a reactive lysyl residue labelled with pyridoxal 5'-phosphate.

Human erythrocyte glucose-6-phosphate dehydrogenase contains a reactive lysyl residue, which can be labelled with pyridoxal 5'-phosphate. The binding of one mole of pyridoxal 5'-phosphate per mole of enzyme subunit produces substantial inactivation. The substrate glucose-6-phosphate prevents the loss of activity, suggesting that the reaction site is close to the substrate-binding site. A tryptic peptide containing the pyridoxal-5'-phosphate-binding lysyl residue has been isolated and characterised. The reactive lysyl residue has been identified in the glucose-6-phosphate dehydrogenase amino acid sequence. Comparison with glucose-6-phosphate dehydrogenase from other sources shows a high homology with a peptide containing a reactive lysyl residue, isolated from the enzyme from Saccharomyces cerevisiae; glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides also contains a region highly homologous with the sequence around the reactive lysyl residue in the human enzyme. The results of this communication provide the first direct evidence for the association of an essential catalytic function with a specific region of the molecule of human erythrocyte glucose-6-phosphate dehydrogenase.

Affinity Labels↗
PubMed1995

Bacterial community structures of phosphate-removing and non-phosphate-removing activated sludges from sequencing batch reactors.

The bacterial community structures of phosphate- and non-phosphate-removing activated sludges were compared. Sludge samples were obtained from two sequencing batch reactors (SBRs), and 16S rDNA clone libraries of the bacterial sludge populations were established. Community structures were determined by phylogenetic analyses of 97 and 92 partial clone sequences from SBR1 (phosphate-removing sludge) and SBR2 (non-phosphate-removing sludge), respectively. For both sludges, the predominant bacterial group with which clones were affiliated was the beta subclass of the proteobacteria. Other major groups represented were the alpha proteobacterial subclass, planctomycete group, and Flexibacter-Cytophaga-Bacteroides group. In addition, several clone groups unaffiliated with known bacterial assemblages were identified in the clone libraries. Acinetobacter spp., thought to be important in phosphate removal in activated sludge, were poorly represented by clone sequences in both libraries. Differences in community structure were observed between the phosphate- and non-phosphate-removing sludges; in particular, the Rhodocyclus group within the beta subclass was represented to a greater extent in the phosphate-removing community. Such differences may account for the differing phosphate-removing capabilities of the two activated sludge communities.

Acinetobacter↗