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Biomedical subjects

H N Chang

Publications and source records attributed to H N Chang.

At least 19 recordsLinked to original sources
PubMed2003

Batch and continuous cultures of Mannheimia succiniciproducens MBEL55E for the production of succinic acid from whey and corn steep liquor.

Mannheimia succiniciproducens MBEL55E isolated from bovine rumen is able to produce a large amount of succinic acid in a medium containing glucose, peptone, and yeast extract. In order to reduce the cost of the medium, whey and corn steep liquor (CSL) were used as substrates for the production of succinic acid by M. succiniciproducens MBEL55E. Anaerobic batch cultures of M. succiniciproducens MBEL55E in a whey-based medium containing CSL resulted in the production of succinic acid with a yield of 71% and productivity of 1.18 g/l/h, which are similar to those obtained in a whey-based medium containing yeast extract (72% and 1.21 g/l/h). Anaerobic continuous culture of M. succiniciproducens MBEL55E in a whey-based medium containing CSL resulted in a succinic acid yield of 69% and a succinic acid productivity as high as 3.90 g/l/h. These results show that succinic acid can be produced efficiently and economically by M. succiniciproducens MBEL55E from whey and CSL.

Animals↗
PubMed2002

Isolation and characterization of a new succinic acid-producing bacterium, Mannheimia succiniciproducensMBEL55E, from bovine rumen.

A novel succinic acid-producing bacterium was isolated from bovine rumen. The bacterium is a non-motile, non-spore-forming, mesophilic and capnophilic gram-negative rod or coccobacillus. Phylogenetic analysis based on the 16S rRNA sequence and physiological analysis indicated that the strain belongs to the recently reclassified genus Mannheimia as a novel species, and has been named Mannheimia succiniciproducens MBEL55E. Under 100% CO(2) conditions, it grows well in the pH range of 6.0-7.5 and produces succinic acid, acetic acid and formic acid at a constant ratio of 2:1:1. When M. succiniciproducensMBEL55E was cultured anaerobically in medium containing 20 g l(-1) glucose as carbon source, 13.5 g l(-1) of succinic acid was produced.

Acetic Acid↗
PubMed2001

High-rate continuous production of lactic acid by Lactobacillus rhamnosus in a two-stage membrane cell-recycle bioreactor.

It is important to produce L(+)-lactic acid at the lowest cost possible for lactic acid to become a candidate monomer material for promising biodegradable polylactic acid. In an effort to develop a high-rate bioreactor that provides high productivity along with a high concentration of lactic acid, the performance of membrane cell-recycle bioreactor (MCRB) was investigated via experimental studies and simulation optimization. Due to greatly increased cell density, high lactic acid productivity, 21.6 g L(-1) h(-1), was obtained in the reactor. The lactic acid concentration, however, could not be increased higher than 83 g/L. When an additional continuous stirred tank reactor (CSTR) was attached next to the MCRB a higher lactic acid concentration of 87 g/L was produced at significant productivity expense. When the two MCRBs were connected in series, 92 g/L lactic acid could be produced with a productivity of 57 g L(-1) h(-1), the highest productivity among the reports of L(+)-lactic acid that obtained lactic acid concentration higher than 85 g/L using glucose substrate. Additionally, the investigation of lactic acid fermentation kinetics resulted in a successful model that represents the characteristics of lactic acid fermentation by Lactobacillus rhamnosus. The model was found to be applicable to most of the existing data with MCRBs and was in good agreement with Levenspiel's product-inhibition model, and the Luedeking-Piret equation for product-formation kinetics appeared to be effective in representing the fermentation kinetics. There was a distinctive difference in the production potential of cells (cell-density-related parameter in Luedeking-Piret equation) as lactic acid concentration increases over 55 g/L, and this finding led to a more precise estimation of bioreactor performance.

Bioreactors↗
PubMed2001

Chemoenzymatic synthesis of sucrose-containing aromatic polymers.

A chemoenzymatic approach was developed to prepare sucrose-containing aromatic polymers. The protease from Bacillus licheniformis catalyzed the transesterification of sucrose with a diester of terephthalic acid in pyridine to give the mono- and diester products. At 45 degrees C, >70% of sucrose was consumed after 1 day and sucrose diester began to form after 6 days when >95% of sucrose had been converted to sucrose monoester. The final yield of sucrose diester after 20 days was 13.8%. The sucrose monoester was identified as sucrose 1'-terephthalate and the diester products consisted of sucrose 6,1'-diterephthalate and sucrose 6',1'-diterephthalate in a ratio of 2:1. The sucrose diester products were polymerized with ethylene-glycol and ethylene-diamine to give poly(ethylene-terephthalate) and poly(ethylene-terephthalamide), with sucrose contained in the polymer backbone. The polycondensation reactions were carried out in dimethylsulfoxide (DMSO) at 70 degrees C using zinc acetate as a catalyst. The sucrose-containing polyester and polyamide were obtained at 65% yield for 24 h and at 73% yield for 12 h, respectively. End-group analysis of the polymers by (13)C-NMR or (1)H-NMR in DMSO provided a number average molecular weight of 3200 and 4300 Da, respectively. Structural analyses of the polymers were performed with (1)H-NMR, (13)C-NMR, and FTIR. On the basis of (13)C-NMR, acylation of the C1', C6, and C6' hydroxyls were maintained in the polymer backbones.

Bacillus↗
PubMed2001

Characterization of an oxygen-dependent inducible promoter, the nar promoter of Escherichia coli, to utilize in metabolic engineering.

The nar promoters, whose transcription is maximally induced under microaerobic conditions in the presence of nitrate ion, were characterized in fed-batch culture to determine whether they can be used for metabolic engineering, by which overall production of valuable chemicals can be increased. For this purpose, we tested whether the expression level of a reporter gene, the lacZ gene from the nar promoter, could be maintained constant throughout the induction period by manipulation of dissolved oxygen (DO) levels at a given nitrate ion concentration. First, E. coli was grown under aerobic conditions (DO 80%) to absorbance at 600 nm (OD(600)) of 35, then the nar promoter was induced by reduction of DO to different levels, combined with different frequencies and duration of alternating microaerobic and aerobic conditions throughout the entire induction period. For a wild-type nar promoter (pMW61) in a mutant host E. coli with a mutation in the narG gene on the chromosome of the host (RK5265), it was possible to maintain production of beta-galactosidase activity per cell (specific beta-galactosidase activity) at a constant rate at 5000, 10,000, 15,000, and 20,000 Miller units, using different combinations of nitrate ion concentrations (0.1%, 0.5%, and 1%) and DO levels. In addition, it was possible to maintain production of specific beta-galactosidase activity at a constant rate at about 10,000 Miller units in the absence of nitrate ion when a nitrate-independent nar promoter (pMW618) in the narL(-) mutant of the W3110 E. coli strain (W3110narL(-)) was used. Based on these results, we conclude that the nar promoter system provides a convenient expression system for metabolic engineering as well as for maximal production of recombinant proteins under conditions of fed-batch culture.

Chromosomes, Bacterial↗
PubMed2001

Characteristics and glycerol metabolism of fumarate-reducing Enterococcus faecalis RKY1.

Enterococcus faecalis RKY1, which converts fumarate to succinate with a high yield, was identified on the basis of a phylogenetic analysis of the 16S rDNA gene sequence. The strain was incubated at 38 degrees C for 18 h to examine the possible diversion of glucose or glycerol fermentation by fumarate. The products of glucose and glycerol fermentation with fumarate were quite different from those of normal fermentation, which ultimately produces lactate, in that mainly succinate is produced. Metabolic pathway stoichiometry was used to analyze the oxidation of glycerol to succinate by Enterococcus faecalis RKY1. The stoichiometric relationship between glycerol and fumarate was used as a guideline to accumulate succinate more efficiently.

DNA, Ribosomal↗
PubMed2001

Succinic acid production with reduced by-product formation in the fermentation of Anaerobiospirillum succiniciproducens using glycerol as a carbon source.

Succinic acid was produced by fermentation of Anaerobiospirillum succiniciproducens using glycerol as a carbon source. When cells were anaerobically cultured in a medium containing 6.5 g/L glycerol, a high succinic acid yield (133%) was obtained while avoiding the formation of by-product acetic acid. The gram ratio of succinic acid to acetic acid was 25.8:1, which is 6.5 times higher than that obtained using glucose (ca. 4:1) as a carbon source. Therefore, succinic acid can be produced with much less by-product formation by using glycerol as a carbon source, which will facilitate its purification. When glucose and glycerol were cofermented with the increasing ratio of glucose to glycerol, the gram ratio of succinic acid to acetic acid and succinic acid yield decreased, suggesting that glucose enhanced acetic acid formation irrespective of the presence of glycerol. Glycerol consumption by A. succiniciproducens required unidentified nutritional components present in yeast extract. By intermittently feeding yeast extract along with glycerol, a high succinic acid yield (160%) could be obtained while still avoiding acetic acid formation. This resulted in the highest ratio of succinic acid to acetic acid (31.7:1).

Acetic Acid↗
PubMed2001

Efficient recovery of gamma-poly (glutamic acid) from highly viscous culture broth.

An efficient strategy for the separation and recovery of gamma-polyglutamic acid (gamma-PGA) from highly viscous broth was developed. This strategy was divided into two processes: The first was to separate gamma-PGA from highly viscous culture broth; the second was to concentrate gamma-PGA solution by ultrafiltration for the reduction of the amount of alcohol required during recovery process with precipitation. By lowering the pH value of culture broth to 3, the viscosity of culture broth and the zeta potential of cell could be reduced to a sixth of the original value at 35 degrees C and a third, respectively. After the acidification of culture broth the energy demand for the separation of gamma-PGA from culture broth by centrifugation could be reduced to 17% of that without it when the centrifugal force was 22,000g. The amount of alcohol required for precipitation could be reduced to a fourth of that generally used without concentration by concentrating 20 g gamma-PGA/L solution to 60 g gamma-PGA/L at pH 5 by ultrafiltration with hollow-fiber membrane cartridge (MWCO 500,000).

Bacillus↗
PubMed2000

Development and characterization of an oxygen-dependent inducible promoter system, the modified nar promoter in a mutant Escherichia coli.

A nar promoter system (a modified nar promoter in a mutant host Escherichia coli (pMW618/W3110narL(-))), which is maximally induced under microaerobic conditions, was developed and characterized through batch and fed-batch culture to see whether the modified nar promoter can be used as an oxygen-dependent inducible promoter in the absence of nitrate ion. The modified nar promoter (pMW618) derived by mutations at -10 and -35 regions of the wild-type nar promoter does not require nitrate ion for the full induction, while a mutant host E. coli, W3110narL(-), does not express nitrate-dependent regulatory protein, NARL, from the host chromosome. In this study, it was found from fed-batch culture that the specific beta-galactosidase activity expressed from the lacZ gene fused to the modified nar promoter in the absence of nitrate ion was maximal when E. coli was grown under aerobic conditions (dissolved oxygen (DO) at 80%) to absorbance at 600 nm (OD(600)) of 35, and then the modified nar promoter was induced by lowering DO to 1-2% with alternating microaerobic and aerobic conditions. The maximal specific beta-galactosidase activity became 58,000 Miller at OD(600) of 160 with an induction ratio of 20. On the basis of these results, we conclude that the modified nar promoter system (pMW618/W3110narL(-)), requiring only reduction of DO for the full induction, provides a convenient and effective high-level expression system under conditions of fed-batch culture.

Bacteriological Techniques↗
PubMed2000

Desulfurization of light gas oil in immobilized-cell systems of Gordona sp. CYKS1 and Nocardia sp. CYKS2.

Desulfurizations of a model oil (hexadecane containing dibenzothiophene (DBT)) and a diesel oil by immobilized DBT-desulfurizing bacterial strains, Gordona sp. CYKS1 and Nocardia sp. CYKS2, were carried out. Celite bead was used as a biosupport for cell immobilization. Seven-eight cycles of repeated-batch desulfurization were conducted for each strain. Each batch reaction was carried out for 24 h. In the case of model oil treatment with strain CYKS1, about 4.0 mM of DBT in hexadecane (0.13 g sulfur l(oil)(-1)) was desulfurized during the first batch, while 0.25 g sulfur l(oil)(-1) during the final eighth batch. The mean desulfurization rate increased from 0.24 for the first batch to 0.48 mg sulfur l(dispersion)(-1) h(-1) for the final batch. The sulfur content in the light gas oil was decreased from 3 to 2.1 g l(oil)(-1) by strain CYKS1 in the first batch. The mean desulfurization rate was 1.81 mg sulfur l(dispersion)(-1) h(-1), which decreased slightly when the batch reaction was repeated. No significant changes in desulfurization rate were observed with strain CYKS2 when the batch reaction was repeated. When the immobilized cells were stored at 4 degrees C in 0.1 M phosphate buffer (pH 7.0) for 10 days, the residual desulfurization activity was about 50 approximately 70% of the initial value.

Actinomycetales↗
PubMed2000

Batch and continuous cultivation of Anaerobiospirillum succiniciproducens for the production of succinic acid from whey.

Batch and continuous cultivation of Anaerobiospirillum succiniciproducens were systematically studied for the production of succinic acid from whey. Addition of 2.5 g l(-1) yeast extract and 2.5 g l(-1) polypeptone per 10 g l(-1) whey was most effective for succinic acid production from both treated and nontreated whey. When 20 g l(-1) nontreated whey and 7 g l(-1) glucose were used as cosubstrates, the yield and productivity of succinic acid reached at the end of fermentation were 95% and 0.46 g (1 h)(-1), respectively. These values were higher than those obtained using nontreated whey alone [93% and 0.24 g (1 h)(-1) for 20 g l(-1) whey]. Continuous fermentation of A. succiniciproducens at an optimal dilution rate resulted in the production of succinic acid with high productivity [1.35 g (1 h)(-1)], high conversion yield (93%), and higher ratio of succinic acid to acetic acid (5.1:1) from nontreated whey.

Bacteria, Anaerobic↗
PubMed2000

Microencapsulation of microbial cells.

The high level of biocatalysts such as microbial cells and enzymes plays an important role in increasing the productivity of a bioreactor. The beads entrapped with microbial cells are not strong enough for long-term use. The small void space of polymer matrix and the leakage of cells limit a final cell loading in the beads. The recent success of encapsulating microbial cells makes it possible to prepare dense biocatalyst composed of recombinant microbial cells. In addition to encapsulating microbial cells, immobilization of animal and plant cells in capsules is also briefly described.

Journal Article↗
PubMed1999

Ethanol production using concentrated oak wood hydrolysates and methods to detoxify.

Ethanol production from concentrated oak wood hydrolysate was carried out to obtain a high ethanol concentration and a high ethanol yield. The effect of added inhibitory compounds, which are typically produced in the pretreatment step of steam-explosion on ethanol fermentation, was also examined. p-Hydroxybenzoic aldehyde, a lignin-degradation product, was the most inhibitory compound tested in this study. Compounds with additional methyl groups had reduced toxicity and the aromatic acids were less toxic than the corresponding aldehydes. The lignin-degradation products were more inhibitory than the sugar-derived products, such as furfural and 5-hydroxymethylfurfural (HMF). Adaptation of yeast cells to the wood hydrolysate and detoxification methods, such as using charcoal and overlime, had some beneficial effects on ethanol production using the concentrated wood hydrolysate. After treatment with charcoal and low-temperature sterilization, the yeast cells could utilize the concentrated wood hydrolysate with 170 as well as 140 g/L glucose, and produce 69.9 and 74.2 g/L ethanol, respectively, with a yield of 0.46-0.48 g ethanol/g glucose. In contrast, the cells could not completely utilize untreated wood hydrolysate with 100 g/L glucose. Low-temperature sterilization, with or without charcoal treatment, was very effective for ethanol production when highly concentrated wood hydrolysates were used. Low-temperature sterilization has advantages over traditional detoxification methods, such as using overlime, ion exchange, and charcoal, because of the reduction in the total cost of ethanol production.

Journal Article↗
PubMed1998

Effect of post-induction nutrient feeding strategies on the production of bioadhesive protein in Escherichia coli.

The effect of post-induction nutrient feeding strategies on the production of bioadhesive protein using an IPTG inducible expression system in Escherichia coli was investigated. Cells were cultured in an exponential fed-batch mode to the OD600 of ca. 100 (48 gDCW/L) prior to induction. Six different post-induction nutrient feeding strategies (pH-stat, exponential, constant and linear change in feeding rate with three different slopes) were then applied, and bioadhesive protein production was examined. It was found that post-induction cell growth was independent of nutrient feeding rate. However, bioadhesive protein production was significantly affected by post-induction feeding strategies. Linearly changing post-induction feeding rate with a suitable slope allowed production of bioadhesive protein up to 5.3 g/L, which was higher than that obtained by the other post-induction feeding strategies.

Animals↗
PubMed1998

Fed-batch cultivation of an oxygen-dependent inducible promoter system, the nar promoter in Escherichia coli with an inactivated nar operon.

The nar promoter of Escherichia coli is maximally induced under anaerobic or microaerobic conditions in the presence of nitrate. We previously demonstrated in batch experiments that the intact nar promoter of E. coli cloned into a pBR322-based plasmid serves as a high-level expression system in a nar mutant of E. coli (Lee et al., 1996b). In this study, we extend characterization of the nar promoter expression system to the fed-batch culture mode, which is widely used in industrial-scale fermentation. From these experiments, it was found that the specific beta-galactosidase activity expressed from the lacZ gene fused to the nar promoter was maximal when host cells were grown under aerobic conditions [dissolved oxygen, (DO) = 80%] to absorbance at 600 nm (OD600) = 35 before induction of the nar promoter by lowering DO to 1-2% with alternating microaerobic and aerobic conditions. Approximately 15 h after induction, the OD600 of the culture reached 135 and the specific beta-galactosidase activity increased to 40,000 Miller units, equivalent to approximately 35% of the total cellular proteins. The specific beta-galactosidase activity before induction was approximately 1,000 Miller units, giving an induction ratio of approximately 40. Based on these results, we conclude that the nar promoter provides a convenient and effective high level expression system under conditions of fed-batch culture.

Cell Culture Techniques↗
PubMed1997

Angiogenesis and osteogenesis in an orthopedically expanded suture.

The purpose of this study was to examine the angiogenic and the subsequent osteogenic responses during a 96-hour time-course after sutural expansion. Fifty rats were divided into: (1) a control group that received only angiogenic induction through injection of 5 ng/gm recombinant human endothelial cell growth factor (rhECGF); (2) an experimental group that received orthopedic expansion and rhECGF; (3) a sham group that received expansion and sodium chloride (NaCl) injection; and (4) a baseline group that received no expansion or injection. All rats were injected with 3H-thymidine (1.0 microCi/gm) 1 hour before death to label the DNA of S-phase cells. Demineralized sections (4 microm thick) were stained with hematoxylin and eosin. Angiogenesis and cell migration were analyzed with a previously established cell kinetics model. Analysis of variance was used to test the hypothesis that enhancement of angiogenesis stimulates reestablishment of osteogenic capability. Blood vessel number, area, and endothelial cell-labeled index significantly increased in experimental groups, but no difference was found between control and baseline groups. Labeled-pericyte index and activated pericyte numbers in the experimental group were also higher than in the sham groups. These results show that supplemental rhECGF enhances angiogenesis in expanded sutures but not in nonexpanded sutures. Data also suggest that pericytes are the source of osteoblasts in an orthopedically expanded suture.

Analysis of Variance↗