Experiences on dual media filtration of WWTP effluent

This research is legislation driven by the European Water Framework Directive (WFD) and the Dutch Fourth Memorandum on Water Management. The objective of this research is to achieve the removal of total nitrogen and total phosphorus by Dual Media Filtration. The target value during this research for total nitrogen is 2.2 mg/L and for total phosphorus 0.15 mg/L. The results show that for NOx-N concentrations in the WWTP effluent up to 10 mg/L, a stable operation of the process can be reached with removal rates of 80% to 90%. The maximum nitrogen removal rate was 3.5 kg N/(m3.d). Above 10 mg/L a risk of filter bed clogging occurred. When the orthophosphorus concentration in the WWTP effluent exceeds the maximum of 0.3 mg/L, the total phosphorus concentration in the filtrate water will exceed the target value of 0.15 mg P-total/L. Temperature has a large impact in the phosphorus removal; the optimum temperature range is within 13 degrees C-18 degrees C. In conclusion, Dual Media Filtration is capable of producing reusable water with total phosphorus concentrations of <0.15 mg/L, under the condition that the wastewater treatment plant produces WWTP effluent with steady concentrations for orthophosphorus (<0.3 mg PO4-P/L). To reach total nitrogen concentrations in the filtrate water of <2.2 mg/L a NOx-N removal efficiency of nearly 100% is required.

Limiting factors in Escherichia coli fed-batch production of recombinant proteins

Fed-batch production of recombinant beta-galactosidase in E. coli was studied with respect to the specific growth rate at induction. The cultivations were designed to induce protein production by IPTG at a glucose feed rate corresponding to high mu = 0.5 h(-1)) or low (mu = 0.1 h(-1)) specific growth rate. Protein production rate was approximately 100% higher at the higher specific growth rate, resulting in the accumulation of beta-galactosidase up to 30% of the total cell protein. Transcription analysis showed that beta-galactosidase-specific messenger RNA was immediately formed after induction (<5 min), but the amount was the same in both cases and was thus not the initial limiting factor. The content of ribosomes, as represented by rRNA, rapidly decreased with specific growth rate from a relative level of 100%, at the high specific growth rate, to 20% at the low specific growth rate. At high specific growth rate, ribosomes were additionally degraded upon induction due to the high production level. Translation therefore seemed to be the initial limiting factor of the protein synthesis capacity. The alarmone guanosine tetraphosphate increased at both high and low feed level inductions, indicating an induction-forced starvation of charged tRNA and/or glucose. The altered physiological status was also detected by the formation of acetic acid. However, the higher production rate resulted in high-level accumulation of acetic acid, which was absent at low feed rate production. Acetic acid production is thus coupled to the high product formation rate and is proposed to be due either to a precursor drain of Krebs cycle intermediates and a time lag before induction of the glyoxalate shunt, or to single amino acid overflow, since the model product is relatively poor in glycin and alanin. In conclusion, it is proposed that production at high specific growth rate becomes precursor-limited, while production at low specific growth rate is carbon- and/or energy-limited.

Glycerol-3-phosphate-induced catabolite repression in Escherichia coli

The formation of glycerol-3-phosphate (G3P) in cells growing on TB causes catabolite repression, as shown by the reduction in malT expression. For this repression to occur, the general proteins of the phosphoenolpyruvate-dependent phosphotransferase system (PTS), in particular EIIA(Glc), as well as the adenylate cyclase and the cyclic AMP-catabolite activator protein system, have to be present. We followed the level of EIIA(Glc) phosphorylation after the addition of glycerol or G3P. In contrast to glucose, which causes a dramatic shift to the dephosphorylated form, glycerol or G3P only slightly increased the amount of dephosphorylated EIIA(Glc). Isopropyl-beta-D-thiogalactopyranoside-induced overexpression of EIIA(Glc) did not prevent repression by G3P, excluding the possibility that G3P-mediated catabolite repression is due to the formation of unphosphorylated EIIA(Glc). A mutant carrying a C-terminally truncated adenylate cyclase was no longer subject to G3P-mediated repression. We conclude that the stimulation of adenylate cyclase by phosphorylated EIIA(Glc) is controlled by G3P and other phosphorylated sugars such as D-glucose-6-phosphate and is the basis for catabolite repression by non-PTS compounds. Further metabolism of these compounds is not necessary for repression. Two-dimensional polyacrylamide gel electrophoresis was used to obtain an overview of proteins that are subject to catabolite repression by glycerol. Some of the prominently repressed proteins were identified by peptide mass fingerprinting. Among these were periplasmic binding proteins (glutamine and oligopeptide binding protein, for example), enzymes of the tricarboxylic acid cycle, aldehyde dehydrogenase, Dps (a stress-induced DNA binding protein), and D-tagatose-1,6-bisphosphate aldolase.

Startle response during smoking and 24 h after withdrawal predicts successful smoking cessation

RATIONALE

The startle response is thought to reflect changes in attentional processes in humans. The startle response shows a number of forms of plasticity, of which prepulse inhibition (PPI) refers to the attenuation of the startle response to a strong sensory stimulus (pulse), when such a pulse is preceded by a stimulus of lower intensity (prepulse). Recent studies have shown that nicotine modulates startle and PPI of the startle reflex in humans and animals. The present study examined individual differences in cognitive benefits obtained from smoking as indexed by startle response and PPI.

OBJECTIVES

We investigated, using a within-subjects design, the effects of cigarette smoking via a comparison of baseline and withdrawal measures of startle and PPI in 18 subjects wishing to quit cigarette smoking. The relapse of five of these subjects enabled a between-group comparison of these measures with the successful quitters.

METHODS

Startle and PPI were measured on three separate occasions: before quitting, 24 h after quitting and 1 month after quitting.

RESULTS

The presence of a high startle response amplitude while subjects were still engaged in their normal smoking patterns (baseline) and the occurrence of a significant drop of startle amplitude in withdrawal relative to baseline factors were found to be predictive of an individual's ability to quit smoking. Changes in PPI were found to reflect these changes in startle amplitude.

CONCLUSIONS

The observed response patterns are discussed in terms of individual differences in commitment to quitting and self-dosing to manipulate attentional mechanisms as measured by the acoustic startle response. Furthermore, it is suggested that these specific response profiles may be predictive of the ability to quit smoking.

The relationship between prepulse detection and prepulse inhibition of the acoustic startle reflex

Prepulse inhibition (PPI) of the startle reflex is defined as the attenuation of the startle response to a startling stimulus (pulse), when such a stimulus is briefly preceded by a stimulus of subthreshold intensity (prepulse). PPI is thought to be neither learned nor due to conscious response inhibition, as it occurs at stimulus onset asynchronies (SOAs) too short to enable the activation of a volitional response. The present study explored the latter of these assertions by investigating (a) the degree to which human subjects are able to detect prepulses at SOAs of 30, 60 and 120 ms, and (b) whether such detection is related to inhibition. Startle eyeblink reflex and detection were measured in 39 participants subjected to an acoustic startle paradigm. Results revealed a significant trend in prepulse detection according to SOA, with highest detection rates at the 120-ms SOA (75%). However, trials on which detection occurred did not differ from trials without detection on measures of startle inhibition. This suggests that PPI is independent of awareness of the prepulse.

Developmental prosopagnosia: should it be taken at face value?

This study presents a rare case of developmental prosopagnosia. Structural magnetic resonance imaging (MRI) revealed no overt brain abnormalities. EP's basic visual skills and visual memory were intact, as was his ability to judge age, sex and expression from faces, identify facial parts, and make face/non-face decisions. EP was impaired at recognizing famous and very familiar faces and describing visual images of famous faces. He also displayed an anterograde memory impairment for recently studied faces, and performed poorly on tests of unfamiliar face matching, most notably for chimeric faces. It is suggested that EP may be deficient at encoding configural representations of faces. EP appears to have a "pure" (i.e. specific to faces) prosopagnosia, as he shows normal object recognition from unusual viewpoints, good gestalt completion for objects, but not for faces, normal visual imagery for objects but not for faces, a disruption of the inversion effect for faces but not for houses, and performs within the normal range on tests of within-category discriminations, even with unique exemplars of object categories such as famous buildings.

CRP down-regulates adenylate cyclase activity by reducing the level of phosphorylated IIA(Glc), the glucose-specific phosphotransferase protein, in Escherichia coli

The cellular cAMP level is markedly down-regulated by cAMP receptor protein (CRP) in Escherichia coli. CRP regulates adenylate cyclase both at the level of transcription of its structural gene cya and at the level of enzyme activity. We established a method to determine the phosphorylation state of IIA(Glc), the glucose-specific phosphotransferase protein, in intact cells. We found that IIA(Glc) exists predominantly in the unphosphorylated form in wild-type cells growing in LB medium, while it is largely phosphorylated in crp or cya cells. Disruption of the ptsG gene that codes for the membrane component of the major glucose transporter (IICB(Glc)), and/or the fruF gene coding for FPr (fructose-specific hybrid phosphotransferase protein), did not affect the phosphorylation state of IIA(Glc). When IICB(Glc) was overproduced in the presence of glucose, the levels of both cAMP and phosphorylated IIA(Glc) in crp cells were concomitantly decreased to wild-type levels. In addition, when His-90 in IIA(Glc) was replaced by glutamine, both phosphorylation of IIA(Glc) and the overproduction of cAMP in crp cells were eliminated. We also found that extracts of crp+ cells markedly stimulate dephosphorylation of IIA(Glc)-P in vitro. We conclude that CRP-cAMP down-regulates adenylate cyclase primarily by reducing the level of phosphorylated IIA(Glc). The data suggest that unspecified proteins whose expression is under the control of CRP-cAMP are responsible for this regulation.

cAMP receptor protein-cAMP plays a crucial role in glucose-lactose diauxie by activating the major glucose transporter gene in Escherichia coli

The inhibition of beta-galactosidase expression in a medium containing both glucose and lactose is a typical example of the glucose effect in Escherichia coli. We studied the glucose effect in the lacL8UV5 promoter mutant, which is independent of cAMP and cAMP receptor protein (CRP). A strong inhibition of beta-galactosidase expression by glucose and a diauxic growth were observed when the lacL8UV5 cells were grown on a glucose-lactose medium. The addition of isopropyl beta-D-thiogalactoside to the culture medium eliminated the glucose effect. Disruption of the crr gene or overproduction of LacY also eliminated the glucose effect. These results are fully consistent with our previous finding that the glucose effect in wild-type cells growing in a glucose-lactose medium is not due to the reduction of CRP-cAMP levels but is due to the inducer exclusion. We found that the glucose effect in the lacL8UV5 cells was no longer observed when either the crp or the cya gene was disrupted. Evidence suggested that CRP-cAMP may not enhance directly the lac repressor action in vivo. Northern blot analysis revealed that the mRNA for ptsG, a major glucose transporter gene, was markedly reduced in a delta crp or delta cya background. The constitutive expression of the ptsG gene by the introduction of a multicopy plasmid restored the glucose effect in delta cya or delta crp cells. We conclude that CRP-cAMP plays a crucial role in inducer exclusion, which is responsible for the glucose-lactose diauxie, by activating the expression of the ptsG gene.

Increased production of recombinant pyrroloquinoline quinone (PQQ) glucose dehydrogenase by metabolically engineered Escherichia coli strain capable of PQQ biosynthesis

We have previously shown that the production of recombinant Escherichia coli PQQGDH was greatly improved by using a medium supplemented with the cofactor PQQ, which is not synthesized in E. coli. We show here that the increase in the accumulated PQQGDH is due to the increased stability of the holo-enzyme over apo-enzyme, using recombinant Acinetobacter calcoaceticus PQQGDH. In order to achieve cost-effective PQQGDH production, we incorporated the genes for PQQ biosynthetic pathway from Klebsiella pneumoniae into E. coli, which as a result allowed E. coli to produce PQQ. Using this metabolically engineered E. coli strain as a host, a 10-fold increase in the production of recombinant A. calcoaceticus PQQGDH was achieved, compared to the condition without PQQ and MgCl2.

Carbohydrate Utilization in Lactobacillus sake

The ability of Lactobacillus sake to use various carbon sources was investigated. For this purpose we developed a chemically defined medium allowing growth of L. sake and some related lactobacilli. This medium was used to determine growth rates on various carbohydrates and some nutritional requirements of L. sake. Mutants resistant to 2-deoxy-d-glucose (a nonmetabolizable glucose analog) were isolated. One mutant unable to grow on mannose and one mutant deficient in growth on mannose, fructose, and sucrose were studied by determining growth characteristics and carbohydrate uptake and phosphorylation rates. We show here that sucrose, fructose, mannose, N-acetylglucosamine, and glucose are transported and phosphorylated by the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). The PTS permease specific for mannose, enzyme II(supMan), was shown to be responsible for mannose, glucose, and N-acetylglucosamine transport. A second, non-PTS system, which was responsible for glucose transport, was demonstrated. Subsequent glucose metabolism involved an ATP-dependent phosphorylation. Ribose and gluconate were transported by PTS-independent permeases.

Control and regulation of metabolic fluxes in microbes by substrates and enzymes

The control of enzymes and substrates on the flux through microbial metabolic pathways can be quantified in terms of flux control coefficients. In pathways involving group transfer, the summation theorem for flux control by the enzymes has to be modified: the sum of control by all enzymes is between 1 and 2. The phosphoenolpyruvate:glucose phosphotransferase system is such a pathway. Experimental determination of the control by the enzymes in this pathway is under way. The control of the enzymes on the glycolytic flux in yeast is low, with the possible exception of the uptake step. In Klebsiella pneumoniae potassium and ammonium ions can simultaneously be 'limiting', (i.e. have significant control on growth) at pH6, but not at pH8. This may be due to the fact that at pH8 the high-affinity potassium uptake system is absent.

Resistance of the melibiose carrier to inhibition by the phosphotransferase system due to substitutions of amino acid residues in the carrier of Salmonella typhimurium

The melibiose carrier of Salmonella typhimurium is under the control of the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). We isolated mutants of the melibiose carrier that showed resistance to inhibition via the PTS. Growth of the mutants on melibiose was not inhibited by 2-deoxyglucose, a non-metabolizable substrate of the PTS, although growth of the parent strain was inhibited. Transport activity of the melibiose carrier in the mutants was fairly resistant to inhibition by 2-deoxyglucose, although the activity in the parent was sensitive to inhibition. We cloned the mutated melB gene that encodes the melibiose carrier, determined the nucleotide sequences, and identified replaced nucleotides. The mutations resulted in substitutions of Asp-438 with Tyr, Arg-441 with Ser, or Ile-445 with Asn. All of these residues are in the COOH-terminal region of the carrier. The secondary structure of this region is predicted to be an alpha-helix, and the mutated residues were on the same side of the helix. This region showed sequence similarity to a region of the MalK protein, in which substitution of amino acid residues also resulted in PTS-resistant mutants. Thus the COOH-terminal portion of the melibiose carrier is important for the interaction of dephosphorylated IIIGlc, which is an entity causing reversible inactivation of the carrier.

Regulation of the sacPA operon of Bacillus subtilis: identification of phosphotransferase system components involved in SacT activity

The sacT gene which controls the sacPA operon of Bacillus subtilis encodes a polypeptide homologous to the B. subtilis SacY and the Escherichia coli BglG antiterminators. Expression of the sacT gene is shown to be constitutive. The DNA sequence upstream from sacP contains a palindromic sequence which functions as a transcriptional terminator. We have previously proposed that SacT acts as a transcriptional antiterminator, allowing transcription of the sacPA operon. In strains containing mutations inactivating ptsH or ptsI, the expression of sacPA and sacB is constitutive. In this work, we show that this constitutivity is due to a fully active SacY antiterminator. In the wild-type sacT+ strain or in the sacT30 mutant, SacT requires both enzyme I and HPr of the phosphotransferase system (PTS) for antitermination. It appears that the PTS exerts different effects on the sacB gene and the sacPA operon. The general proteins of the PTS are not required for the activity of SacY while they are necessary for SacT activity.

Trehalose transport and metabolism in Escherichia coli

Trehalose metabolism in Escherichia coli is complicated by the fact that cells grown at high osmolarity synthesize internal trehalose as an osmoprotectant, independent of the carbon source, although trehalose can serve as a carbon source at both high and low osmolarity. The elucidation of the pathway of trehalose metabolism was facilitated by the isolation of mutants defective in the genes encoding transport proteins and degradative enzymes. The analysis of the phenotypes of these mutants and of the reactions catalyzed by the enzymes in vitro allowed the formulation of the degradative pathway at low osmolarity. Thus, trehalose utilization begins with phosphotransferase (IITre/IIIGlc)-mediated uptake delivering trehalose-6-phosphate to the cytoplasm. It continues with hydrolysis to trehalose and proceeds by splitting trehalose, releasing one glucose residue with the simultaneous transfer of the other to a polysaccharide acceptor. The enzyme catalyzing this reaction was named amylotrehalase. Amylotrehalase and EIITre were induced by trehalose in the medium but not at high osmolarity. treC and treB encoding these two enzymes mapped at 96.5 min on the E. coli linkage map but were not located in the same operon. Use of a mutation in trehalose-6-phosphate phosphatase allowed demonstration of the phosphoenolpyruvate- and IITre-dependent in vitro phosphorylation of trehalose. The phenotype of this mutant indicated that trehalose-6-phosphate is the effective in vivo inducer of the system.

Trehalase of Escherichia coli. Mapping and cloning of its structural gene and identification of the enzyme as a periplasmic protein induced under high osmolarity growth conditions

Escherichia coli can use the nonreducing disaccharide trehalose as a sole source of carbon and energy. Trehalose transport into the cell is mediated via the phosphotransferase system, and a mutant depleted in the nonspecific proteins enzyme I, HPr, and enzyme IIIGlc of this system was not only unable to grow on glucose or mannitol but also was strongly reduced in its ability to grow on trehalose. A pseudorevertant (PPA69) of such a deletion mutant was isolated that could again grow on glucose but not on mannitol. This revertant could now also use trehalose as a carbon source due to a constitutive galactose permease. PPA69 was subjected to Tn10 insertional mutagenesis, and a mutant (UE5) was isolated that no longer could use trehalose as a carbon source but could still grow on glucose. UE5 lacked a periplasmic trehalase that was present in PPA69. P1-mediated transduction of this Tn10 insertion (treA::Tn10) into a pts+ wild-type strain (MC4100) had no effect on the ability of MC4100 to grow on trehalose but resulted in loss of the periplasmic trehalase activity. The Tn10 insertion was mapped at 26 min on the E. coli linkage map and was 3% cotransducible with trp, in the order treA::Tn10, trp, cys. Trehalase activity in MC4100 was not induced by growth in the presence of trehalose but increased by about 10-fold when 0.6 M sucrose was added to minimal growth medium. Using the in vivo mini-Mu cloning system and growth on trehalose as selection, we cloned the treA gene. A 9-kilobase EcoRI fragment containing treA was subcloned into pBR322. Strains carrying this plasmid (pTRE5) contained about 100-fold higher periplasmic trehalase activity than PPA69 or MC4100. Using polyacrylamide gel electrophoresis, we found a protein of molecular weight 58,000 among the periplasmic proteins of the pTRE5-carrying strain that was absent in UE5. This protein was purified by ammonium sulfate precipitation and DEAE-Sepharose ion-exchange chromatography and contained all the trehalase activity. Minicells containing the treA+ plasmid produced, in addition to three other proteins, the 58,000-dalton protein. Thus, the plasmid carries the structural gene for the periplasmic trehalase and not just a gene involved in the regulation of the enzyme.

Virulence of urinary and faecal Escherichia coli in relation to serotype, haemolysis and haemagglutination

The virulence of faecal and urinary Escherichia coli strains was studied in relation to serotype, haemolysin production and haemagglutination pattern. By means of an experimental mouse model E. coli strains can be divided into avirulent (I), mouse nephropathogenic (II), and generally virulent (III) strains. Virulent group II and group III strains were more often haemolytic and haemagglutinating than avirulent group I strains. Presence of K antigen could not be associated with virulence. Discriminant analysis for qualitative variables revealed that no combination of the investigated properties contributed more to a strain's virulence level than did one single property. It is concluded that other virulence factors, apart from haemolysin production in group II strains and haemagglutinins in group III strains, must be involved in the determination of a strain's virulence level. All O2, O6 and O18 ac strains tested were virulent, and by far the most O75 strains were avirulent, whereas other O groups were more variable with regard to virulence. Pyelonephritis strains were more often mannose-resistance haemagglutinating than faecal and other urinary isolates, indicating that mannose-resistant adhesins may be important in the pathogenesis of pyelonephritis.

Haemolysis by urinary Escherichia coli and virulence in mice

The influence of haemolysin production on virulence was studied in an experimental mouse model. Urinary strains of Escherichia coli can be divided into three virulence groups by determining their kinetics in the mouse kidney after intravenous injection. Virulent strains of groups II and III were more often haemolytic than avirulent group-I strains. Haemolytic virulent strains often caused haemoglobinuria in the mice, and killed the mice more rapidly than did non-haemolytic virulent strains. No relationship was found between alpha-haemolytic activity and virulence in wild-type haemolytic strains. When haemolysin production was reduced or eliminated by treatment with actinomycin-D or rifampicin, six out of seven group-II strains tested gave the same results as avirulent group-I strains. However, the kinetics in the mouse kidney of four haemolytic group-III strains tested was not changed after reduction or elimination of haemolysin production; only a small decrease in toxicity was observed. It is concluded that haemolysin production by E. coli is a decisive virulence factor in most of the mouse-nephropathogenic group-II strains, but not in the virulent group-III strains.

Virulence of Escherichia coli strains isolated from urine of patients with acute cystitis and from faeces of healthy women

E. coli strains were isolated from the urine of patients with acute cystitis in general practice and from the faeces of a comparable reference group of healthy individuals. These strains were serotyped and tested for virulence in an experimental mouse model. Of 30 cystitis-strains 18 were virulent, and of 30 faeces-strains 15 were virulent. It is concluded that the cystitis-strains were not more often virulent than the faeces-strains. O antigens commonly found among urinary E. coli isolates were present in 60% of the cystitis-strains and in 37% of the faeces-strains. K antigens commonly found in urinary E. coli strains were present in 33% of the cystitis-strains and in 12% of the faeces-strains. Neither the presence of common urinary O-antigens, nor the presence of common urinary K antigens could be associated with virulence of the isolated strains. However, it is suggested that certain O and K antigens (O2,O6, K23) may be associated with virulence for the urinary tract.

Mannose-sensitive and mannose-resistant adherence to human uroepithelial cells and urinary virulence of Escherichia coli

The adherence to human uroepithelial cells of 23 Escherichia coli strains belonging to three groups with different levels of virulence was investigated, and the mechanism of adherence was studied. It was found that strains belonging to the most virulent group adhered better to human uroepithelial cells than did avirulent strains. Adherence of loss virulent but supposedly nephropathogenic strains was more variable. These results suggest that adherence is an important virulence factor, especially in the group of strains with the highest but a more general virulence. Piliated strains adhered better than did nonpiliated strains. We found strong evidence for the existence of at least two different mechanisms of adherence: (i) mannose-sensitive adherence by piliated strains, very likely mediated by type I pili because this mannose-sensitive adherence was associated with mannose-sensitive hemagglutination of guinea pig erythrocytes by broth cultures of the strains; (ii) mannose-resistant adherence by piliated strains, very likely mediated by non-type I pili because this mannose-resistant adherence was invariably associated with mannose-resistant hemagglutination of human group A erythrocytes by the strains, whether grown in broth or on plates. Additionally, one strain without pili and without hemagglutinating activity adhered well. Thus in most cases adherence seemed to be mediated by bacterial pili, although different types might be involved.

Virulence of Escherichia coli in acute pyelonephritis, acute cystitis and asymptomatic bacteriuria

E. coli strains were isolated from urine specimens of hospitalised patients with acute pyelonephritis, acute cystitis or asymptomatic bacteriuria (ABU), and tested for virulence in an experimental mouse model. Of 12 pyelonephritis-strains 11 were shown to be virulent and 1 avirulent; of 12 cystitis-strains 4 were virulent and 8 avirulent; of 12 ABU-strains 5 were virulent and 7 avirulent. It is concluded that, while no difference in virulence was found between cystitis- and ABU-strains, pyelonephritis-strains were more often virulent than cystitis- and ABU-strains. No associations could be shown between virulence of the isolated strains and the presence of antibody-coated bacteria in the urine. Common urinary O types were not more often virulent than other O types. No relationship was seen between virulence and the presence of K antigen or the presence of particular K types.