PubMed Health⌕ Search

Biomedical subjects

P Xu

Publications and source records attributed to P Xu.

At least 19 recordsLinked to original sources
PubMed2006

Statistical optimization of medium components for enhanced acetoin production from molasses and soybean meal hydrolysate.

The nutritional requirements for acetoin production by Bacillus subtilis CICC 10025 were optimized statistically in shake flask experiments using indigenous agroindustrial by-products. The medium components considered for initial screening in a Plackett-Burman design comprised a-molasses (molasses submitted to acidification pretreatment), soybean meal hydrolysate (SMH), KH(2)PO(4).3H(2)O, sodium acetate, MgSO(4).7H(2)O, FeCl(2), and MnCl(2), in which the first two were identified as significantly (at the 99% significant level) influencing acetoin production. Response surface methodology was applied to determine the mutual interactions between these two components and optimal levels for acetoin production. In flask fermentations, 37.9 g l(-1) acetoin was repeatedly achieved using the optimized concentrations of a-molasses and SMH [22.0% (v/v) and 27.8% (v/v), respectively]. a-Molasses and SMH were demonstrated to be more productive than pure sucrose and yeast extract plus peptone, respectively, in acetoin fermentation. In a 5-l fermenter, 35.4 g l(-1) of acetoin could be obtained after 56.4 h of cultivation. To our knowledge, these results, i.e., acetoin yields in flask or fermenter fermentations, were new records on acetoin fermentation by B. subtilis.

Acetoin↗
PubMed2006

Tetramethylpyrazine production from glucose by a newly isolated Bacillus mutant.

2,3,5,6-Tetramethylpyrazine (TTMP) was produced using a newly isolated Bacillus mutant. Culture medium optimization studies showed that soytone, an enzyme-hydrolysate of soybean meal, with the supplementation of vitamins, can fully replace yeast extract plus peptone in supporting TTMP production from glucose. In a 5-l fermenter, using the optimized medium which contained 20% glucose, 5% soytone, 3% (NH(4))(2)HPO(4), and vitamin supplements, fermentations were carried out with stirring at 700 rpm, air flow at 1.0 vvm, controlled pH at 7.0, and temperature at 37 degrees C. TTMP reached 4.33 g l(-1) after 64.6 h cultivation. A product recovery method was described, which involved evaporation, crystallization, and lyophilization. The product purity was 99.88%, determined by GC with the normalization method. The main impurities were 2,3,5-trimethylpyrazine (0.09%) and 2-ethyl-3,5,6-trimethylpyrazine (0.02%), which were identified by GC/MS. (13)C NMR determination also gave a consistent result. Natural and high purity of the product and the utilization of cheap green renewable materials make this process promising to compete with TTMP chemical synthetic methods.

Bacillus↗
PubMed2006

Channel catfish BAC-end sequences for marker development and assessment of syntenic conservation with other fish species.

In the present study, 25 195 BAC ends for channel catfish (Ictalurus punctatus) were sequenced, generating 20 366 clean BAC-end sequences (BES), with an average read length of 557 bp after trimming. A total of 11 414 601 bp were generated, representing approximately 1.2% of the catfish genome. Based on this survey, the catfish genome was found to be highly AT-rich, with 60.7% A+T and 39.3% G+C. Approximately 12% of the catfish genome consisted of dispersed repetitive elements, with the Tc1/mariner transposons making up the largest percentage by base pair (4.57%). Microsatellites were detected in 17.5% of BES. Catfish BACs were anchored to the zebrafish and Tetraodon genome sequences by BLASTN, generating 16% and 8.2% significant hits (E < e(-5)) respectively. A total of 1074 and 773 significant hits were unique to the zebrafish and Tetraodon genomes, respectively, of which 417 and 406, respectively, were identified as known genes in other species, providing a major genome resource for comparative genomic mapping.

Animals↗
PubMed2005

Recovery of pyruvic acid from biotransformation solutions.

The aim of this investigation was to separate pyruvic acid of biotransformation solutions from lactic acid through complex extraction. For this purpose, complex extraction was investigated from model solutions. Tri-n-octanylamine (TOA) was used as the extractant. The effects of various diluents, the stoichiometry of pyruvic acid to TOA, and the initial pH of the aqueous phase on the extraction process were investigated in this study. The effects of sodium hydroxide (NaOH) and trimethylamine (TMA) on the back extraction process were also studied, respectively. The optimal conditions attained from the model solutions proved efficient on the biotransformation solutions of different concentrations. A total recovery of 71-82% of pyruvic acid was obtained, whereas 89-92% of lactic acid was removed. The purity of pyruvic acid reached 97% after the removal of TMA by a simple distillation.

Acinetobacter↗
PubMed2005

Analysis of cellular response to protein overexpression.

The overexpression of secreted proteins is of critical importance to the biotechnology and biomedical fields. A common roadblock to high yields of proteins is in the endoplasmic reticulum (ER) where proofreading for properly folded proteins is often rate limiting. Heterologous expression of secreted proteins can saturate the cell's capacity to properly fold protein, initiating the unfolded protein response (UPR), and resulting in a loss of protein expression. An obvious method for overcoming this block would be to increase the capacity of the folding process (overexpressing chaperones) or decreasing the proofreading process (blocking the down-regulation by the UPR). Unfortunately, these processes are tightly interlinked, whereby modification of one mechanism has unknown effects on the other. Although some success has been achieved in improving expression via co-overexpressing ER chaperones, the results have not lead to a global method for increasing all heterologously overexpressed proteins. Further, many diseases have been linked to extended periods of stress and are not treatable by these approaches. This work utilises both experimental analysis of the interactions within the ER and modelling in order to understand how these interactions affect early secretory pathway dynamics. This study shows that overexpression of the ER chaperone binding protein does not regulate Ire1p and the UPR as predicted by a model based on the published understanding of the molecular mechanism. A new model is proposed for Ire1p regulation and the UPR that better fits the experimental data and recent studies on Ire1p.

Computer Simulation↗
PubMed2004

Conical second harmonic generation in a two-dimensional chi(2) photonic crystal: a hexagonally poled LiTaO3 crystal.

A new type of conical second-harmonic generation was discovered in a 2D chi((2)) photonic crystal-a hexagonally poled LiTaO3 crystal. It reveals the presence of another type of nonlinear interaction-a scattering involved optical parametric generation in a nonlinear medium. Such a nonlinear interaction can be significantly enlarged in a modulated chi((2)) structure by a quasi-phase-matching process. The conical beam records the spatial distribution of the scattering signal and discloses the structure information and symmetry of the 2D chi((2)) photonic crystal.

Journal Article↗
PubMed2004

An enzymatic route to produce pyruvate from lactate.

A bacterial strain of Acinetobacter sp., which was capable of enzymatic production of pyruvate from lactate, was cultured in a 5-l reactor with a basal salt medium. After 14 h of fed-batch fermentation, 9.56 g l(-1) cell concentration in the broth was obtained with 20 g l(-1) (178 mM) sodium lactate and 4 g l(-1) NH(4)Cl in the medium; and the biotransformation ability was 2.51 units ml(-1). The cells were harvested from one reactor and then used for pyruvate production from lactate in the same reactor. l-lactate at a concentration about 527 mM was almost stoichiometrically converted to pyruvate in 28 h. After a total 42 h of cell culture and biotransformation, the transformative yield was about 0.72 g g(-1) pyruvate from lactate and the rate of pyruvate production was calculated as 1.33 g l(-1) h(-1) during the process. The results suggested this simple enzymatic production of pyruvate from lactate should be a promising process and may bring a yield higher than that by microbial fermentation. By this process, the recovery of pyruvate from such a simple reaction liquid is relatively easy and inexpensive to perform.

Acinetobacter↗
PubMed2004

Degradation of carbazole in the presence of non-aqueous phase liquids by Pseudomonas sp.

Biodegradation of carbazole was enhanced by the presence of a non-aqueous phase liquid (logKo/w > or = 3.1) at phase ratio of 1:1 (organic/aqueous). In a cyclohexane/aqueous phase system, the maximum specific degradation rate (3.34 mg carbazole min(-1) g dry cell(-1)) was at an organic/aqueous ratio of 1:1. Pseudomonas sp. XLDN4-9 degraded 47% (w/w) of 1 g carbazole l(-1) in cyclohexane phase directly within 1 h.

Biodegradation, Environmental↗
PubMed2003

Microbial fed-batch production of 1,3-propanediol by Klebsiella pneumoniae under micro-aerobic conditions.

The microbial production of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae under micro-aerobic conditions was investigated in this study. The experimental results of batch fermentation showed that the final concentration and yield of 1,3-PD on glycerol under micro-aerobic conditions approached values achieved under anaerobic conditions. However, less ethanol was produced under microaerobic than anaerobic conditions at the end of fermentation. The batch micro-aerobic fermentation time was markedly shorter than that of anaerobic fermentation. This led to an increment of productivity of 1,3-PD. For instance, the concentration, molar yield, and productivity of 1,3-PD of batch micro-aerobic fermentation by K. pneumoniae DSM 2026 were 17.65 g/l, 56.13%, and 2.94 g l(-1) h(-1), respectively, with a fermentation time of 6 h and an initial glycerol concentration of 40 g/l. Compared with DSM 2026, the microbial growth of K. pneumoniae AS 1.1736 was slow and the concentration of 1,3-PD was low under the same conditions. Furthermore, the microbial growth in fed-batch fermentation by K. pneumoniae DSM 2026 was faster under micro-aerobic than anaerobic conditions. The concentration, molar yield, and productivity of 1,3-PD in fed-batch fermentation under micro-aerobic conditions were 59.50 g/l, 51.75%, and 1.57 g l(-1) h(-1), respectively. The volumetric productivity of 1,3-PD under microaerobic conditions was almost twice that of anaerobic fed-batch fermentation, at 1.57 and 0.80 g l(-1) h(-1), respectively.

Aerobiosis↗
PubMed2003

Convergent evolution of perenniality in rice and sorghum.

Annual and perennial habit are two major strategies by which grasses adapt to seasonal environmental change, and these distinguish cultivated cereals from their wild relatives. Rhizomatousness, a key trait contributing to perenniality, was investigated by using an F(2) population from a cross between cultivated rice (Oryza sativa) and its wild relative, Oryza longistaminata. Molecular mapping based on a complete simple sequence-repeat map revealed two dominant-complementary genes controlling rhizomatousness. Rhz3 was mapped to the interval between markers OSR16 [1.3 centimorgans (cM)] and OSR13 (8.1 cM) on rice chromosome 4 and Rhz2 located between RM119 (2.2 cM) and RM273 (7.4 cM) on chromosome 3. Comparative mapping indicated that each gene closely corresponds to major quantitative trait loci (QTLs) controlling rhizomatousness in Sorghum propinquum, a wild relative of cultivated sorghum. Correspondence of these genes in rice and sorghum, which diverged from a common ancestor approximately 50 million years ago, suggests that the two genes may be key regulators of rhizome development in many Poaceae. Many additional QTLs affecting abundance of rhizomes in O. longistaminata were identified, most of which also corresponded to the locations of S. propinquum QTLs. Convergent evolution of independent mutations at, in some cases, corresponding genes may have been responsible for the evolution of annual cereals from perennial wild grasses. DNA markers closely linked to Rhz2 and Rhz3 will facilitate cloning of the genes, which may contribute significantly to our understanding of grass evolution, advance opportunities to develop perennial cereals, and offer insights into environmentally benign weed-control strategies.

Biological Evolution↗
PubMed2003

Improved method for measurement of human plasma xanthine oxidoreductase activity.

The XOR activity in human plasma was measured by quantifying the XOR-derived uric acid (UA) in plasma using the high-performance liquid chromatography (HPLC) equipped with a UV detector. Chromatographic separation consisted of the mobile phase (a mixture of 0.1% trifluoroacetic acid in Milli-Q water and 0.085% trifluoroacetic acid in acetonitrile in a mix ratio of 99:1) running through a Zorbax StableBond SB-C(18) column at a flow-rate of 1 ml/min. Deproteinization with heat-treatment of plasma samples after the reaction was used in the assay to avoid splitting of the UA and xanthine peaks caused by acid deproteinization that could interfere the accurate determination of human plasma XOR activity in our case. Based on the examination of the dependence of XOR activity on added amounts of xanthine and reaction times, the amount of xanthine and reaction time for XOR activity assay were determined to prevent the errors caused by the limiting effect of substrates and plateau phase of the reaction. Using this method, human plasma XOR activities of 25 healthy people were measured. The average human plasma XOR activity was 2.1+/-0.8 (x10(-3) U/ml).

Chromatography, High Pressure Liquid↗
PubMed2002

Non-steady-state modelling of faecal coliform removal in deep tertiary lagoons.

In Noirmoutier, a French island off the Atlantic coast, secondary effluents flow into a series of four lagoons, 1.4-2.8 m deep, and are reused for agricultural irrigation. The excess water is disposed of to the sea. The aim of this study was to provide a model capable of predicting the microbiological quality of the water pumped for irrigation or discharged to the sea. Meteorological variables, flow rates, physical-chemical characteristics and faecal coliform (FC) contents were monitored for a year and a half. The hydraulic pattern of each lagoon was assumed to be that of completely mixed reactor because of the calculated dispersion numbers and the wind mixing effect. Coliform decay was assumed to follow first order kinetics in each lagoon. Die-off coefficients were calculated in each lagoon using a non-steady-state model. The main bacterial removal mechanism was shown to be solar irradiation. Empirical equations were established to calculate die-off coefficients as a function of received solar energy and temperature. FC die-off rates were higher in the first lagoon and then decreased successively in those following. FC numbers in the different lagoons were predicted with reasonable accuracy in spite of high variation in inlet water quality. The model will facilitate the prediction of water quality under various climatic conditions and different water reuse scenarios and will help to optimise reclamation and storage facilities.

Atlantic Ocean↗
PubMed2002

Design of a climate-dependent water reuse project.

Reclaimed water storage is imperative in water reuse management. Climate is a primary factor controlling reclaimed water storage design by its significant influence on irrigation water needs as well as on stored water quality. This study presents a modelling approach that has been applied to assist the design of a climate-dependent water reuse project on an Atlantic island. Models for predicting irrigation water needs and water quality in tertiary lagoons were coupled with a technical-economic model to design reclaimed water storage facilities. Three scenarios corresponding to different augmentation of current reclaimed water reuse were investigated. According to the modelling, the storage sizes to meet the water quantity required for irrigation increased with water deficit--the difference between evapotranspiration and precipitation. The size of tertiary lagoons to meet required water quality was found to be larger than the size to meet required water quantity. To meet both quantitative irrigation needs and <1,000 FC/100 ml irrigation and disposal regulation, extending the tertiary lagoon system would be more cost-effective than storage calculated to meet only quantitative irrigation needs supplemented with UV disinfection. The reliability of reclaimed water storage design was estimated with 40 years historic climatic records.

Climate↗
PubMed2001

[Relationship between serum 1,25-dihydroxyvitamin D and bone loss in postmenopausal women].

OBJECTIVE: To study the correlations between loss of activity and/or amont of serum 1,25-dihydroxyvitamin D(1,25(OH)2D) and 25-dihydroxyvitamin D(1,25(OH)2D) and bone loss in postmenopausal women, in order to reveal the possible pathophysiology of postmenopausal osteoporosis. METHODS: The serum levels of 1,25 (OH)2D, 25 (OH) D, PTH, and E2 in 57 postmenopausal women with osteoporosis and 37 postmenopausal women without osteoporosis were measured by radioimmunology. Their Dpd/Cr in urine was measured by ELISA. The bone mineral density (BMD) at lumbar spine (L2-4) was measured in each subject by DEXA. RESULTS: The serum 1,25(OH)2D in postmenopausal oeteoporotic women and non-osteoporotic women were 18 pg/ml +/- 6 pg/ml and 31 pg/ml +/- 14 pg/ml respectively (P < 0.01) The serum 25 (OH)2D in postmenopausal oeteoporotic women and non-osteoporotic women were 32 ng/ml +/- 9 ng/ml and 46 ng/ml +/- 17 ng/ml respectively (P < 0.01). Postmenopausal osteoporotic women had a lower estrogen concentration (P < 0.01), higher serum parathyroid hormone (PTH) (P < 0.01) and higher urinary Dpd/Cr level (P < 0.01). The level of serum 1,25(OH)2D was highly correlated with BMD in L2-4 for postmenopausal women (r = 0.693, P < 0.001). There was a close relationship between the serum level of 1,25(OH)2D and serum level of 25(OH)2D, suggesting an association between the two factors. CONCLUSION: The lower bone mass density was associated with lower level of serum 1,25-dihydroxyvitamin D, accompanied by reduced serum estrogen and elevated serum PTH in postmenopausal women. Those may be among the important pathphysiological changes of postmenopausal osteoporosis.

Aged↗
PubMed2001

A new type of class I bacterial 5-enopyruvylshikimate-3-phosphate synthase mutants with enhanced tolerance to glyphosate.

Glyphosate or Roundup is the most extensively used herbicide for broad-spectrum control of weeds. Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a key enzyme in the aromatic amino acid biosynthetic pathway in microorganisms and plants. Applying the staggered extension process, we randomly mutated and recombined the aroA genes of Salmonella typhimurium and Escherichia coli to obtain four variants that exhibit significantly enhanced tolerance to glyphosate. All four mutants are chimeras of the two parental genes and, in addition, three of them carry one or more de novo point mutations. None of the amino acid substitutions in the mutants was in a position previously known to be important for catalysis or substrate binding. Kinetic analysis of EPSPS activity from these mutants indicated that the tolerance was attributed to a 2-10-fold increased specific activity, 0.4-8-fold reduced affinity to glyphosate, and 2.5-19-fold decreased K(m) for phosphoenolpyruvate. Such mutants will be instrumental for the structural and function study of the enzyme and for the generation of transgenic crops resistant to the herbicide.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed2001

Molecular interactions of the Gbeta binding domain of the Ste20p/PAK family of protein kinases. An isolated but fully functional Gbeta binding domain from Ste20p is only partially folded as shown by heteronuclear NMR spectroscopy.

The transmission of the mating signal of the budding yeast Saccharomyces cerevisiae requires Ste20p, a member of the serine/threonine protein kinases of the Ste20p/PAK family, to link the Gbeta subunit of the heterotrimeric G protein to the mitogen-activated protein kinase cascades. The binding site of Ste20p to the Gbeta subunit was mapped to a consensus sequence of SSLphiPLI/VXphiphibeta (X for any residue; phi for A, I, L, S or T; beta for basic residues), which was shown to be a novel Gbeta binding (GBB) motif present only in the noncatalytic C-terminal domains of the Ste20p/PAK family of protein kinases (Leeuw, T., Wu, C., Schrag, J. D., Whiteway, M., Thomas, D. Y., and Leberer, E. (1998) Nature 391, 191-195; Leberer, E., Dignard, D., Thomas, D. Y., and Leeuw, T. (2000) Biol. Chem. 381, 427-431). Here, we report the results of an NMR study on two GBB motif peptides and the entire C-terminal domain derived from Ste20p. The NMR data show that the two peptide fragments are not uniquely structured in aqueous solution, but in the presence of 40% trifluoroethanol, the longer 37-residue peptide exhibited two well defined, but flexibly linked helical structure elements. Heteronuclear NMR data indicate that the fully functional 86-residue C-terminal domain of Ste20p is again unfolded in aqueous solution but has helical secondary structure preferences similar to those of the two peptide fragments. The NMR results on the two GBB peptides and the entire GBB domain all indicate that the two important binding residues, Ser(879) and Ser(880), are located at the junction between two helical segments. These experimental observations with the prototype GBB domain of a novel family of Gbeta-controlled effectors may have important implications in understanding the molecular mechanisms of the signal transduction from the heterotrimeric G protein to the mitogen-activated protein kinase cascade.

Electrophoresis, Polyacrylamide Gel↗
PubMed2001

Antioxidant activity of water-soluble chitosan derivatives.

Water-soluble chitosan derivatives were prepared by graft copolymerization of maleic acid sodium onto hydroxypropyl chitosan and carboxymethyl chitosan sodium. Their scavenging activities against hydroxyl radical *OH were investigated by chemiluminescence technique. They exhibit IC(50) values ranging from 246 to 498 microg/mL, which should be attributed to their different contents of hydroxyl and amino groups and different substituting groups.

Antioxidants↗