Publications by authors named "Ji-Hyeon Yeon"

8 Publications

  • Page 1 of 1

Long-term repeated-batch operation of immobilized Escherichia coli cells to synthesize galactooligosaccharide.

J Microbiol Biotechnol 2012 Nov;22(11):1486-93

Department of Biotechnology, Korea National University of Transportation, Jeungpyung, Chungbuk 368-701, Korea.

In this study, we investigated whether galactooligosaccharide (GOS) can be stably and steadily synthesized using immobilized beta-galactosidase (β-gal) inclusion body (IB)- containing E. coli cells during long-term repeated-batch operation. To improve the operational stability of this enzyme reactor system, immobilized E. coli cells were crosslinked with glutaraldehyde (GA) after immobilization of the E. coli. When we treated with 2% GA for E. coli crosslinking, GOS production continued to an elapsed time of 576 h, in which seven batch runs were operated consecutively. GOS production ranged from 51.6 to 78.5 g/l (71.2 ± 10.5 g/l, n = 7) during those batch operations. In contrast, when we crosslinked E. coli with 4% GA, GOS production ranged from 31.5 to 64.0 g/l (52.3 ± 10.8, n = 4), and only four consecutive batch runs were operated. Although we did not use an industrial β-gal for GOS production, in which a thermophile is used routinely, this represents the longest operation time for GOS production using E. coli β-gal. Improved stability and durability of the cell immobilization system were achieved using the crosslinking protocol. This strategy could be directly applied to other microbial enzyme reactor systems using cell immobilization to extend the operation time and/or improve the reactor system stability.
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http://dx.doi.org/10.4014/jmb.1204.04020DOI Listing
November 2012

Galactooligosaccharide synthesis by active β-galactosidase inclusion bodies-containing Escherichia coli cells.

J Microbiol Biotechnol 2011 Nov;21(11):1151-8

Department of Biotechnology, Chungju National University, Jeungpyung, Chungbuk 368-701, Republic of Korea.

In this study, galactooligosaccharide (GOS) was synthesized using active β-galactosidase (beta-gal) inclusion bodies (IBs)- containing Escherichia coli (E. coli) cells. Analysis by MALDI-TOF (matrix-assisted laser desorption/ionizationtime of flight) mass spectrometry revealed that a trisaccharide was the major constituent of the synthesized GOS mixture. Additionally, the optimal pH, lactose concentration, amounts of E. coli β-gal IBs, and temperature for GOS synthesis were 7.5, 500 g/l, 3.2 U/ml, and 37 °C, respectively. The total GOS yield from 500 g/l of lactose under these optimal conditions was about 32%, which corresponded to 160.4 g/l of GOS. Western blot analyses revealed that β-gal IBs were gradually destroyed during the reaction. In addition, when both the reaction mixture and E. coli β-gal hydrolysate were analyzed by high-performance thin-layer chromatography (HP-TLC), the trisaccharide was determined to be galactosyl lactose, indicating that a galactose moiety was most likely transferred to a lactose molecule during GOS synthesis. This GOS synthesis system might be useful for the synthesis of galactosylated drugs, which have recently received significant attention owing to the ability of the galactose molecules to improve the drugs solubility while decreasing their toxicity. β-Gal IB utilization is potentially a more convenient and economic approach to enzymatic GOS synthesis, since no enzyme purification steps after the transgalactosylation reaction would be required.
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http://dx.doi.org/10.4014/jmb.1105.05021DOI Listing
November 2011

Repeated-batch operation of immobilized β-galactosidase inclusion bodies-containing Escherichia coli cell reactor for lactose hydrolysis.

J Microbiol Biotechnol 2011 Sep;21(9):972-8

Department of Biotechnology, Chungju National University, Jeungpyung, Chungbuk 368-701, Korea.

In this study, we investigated the performance of an immobilized β-galactosidase inclusion bodies-containing Escherichia coli cell reactor, where the cells were immobilized in alginate beads, which were then used in repeated-batch operations for the hydrolysis of o-nitrophenyl-β-D-galactoside or lactose over the long-term. In particular, in the Tris buffer system, disintegration of the alginate beads was not observed during the operation, which was observed for the phosphate buffer system. The o-nitrophenyl-β-D-galactoside hydrolysis was operated successfully up to about 80 h, and the runs were successfully repeated at least eight times. In addition, hydrolysis of lactose was successfully carried out up to 240 h. Using Western blotting analyses, it was verified that the beta-galactosidase inclusion bodies were sustained in the alginate beads during the repeated-batch operations. Consequently, we experimentally verified that β-galactosidase inclusion bodies-containing Escherichia coli cells could be used in a repeated-batch reactor as a biocatalyst for the hydrolysis of o-nitrophenyl-β-D-galactoside or lactose. It is probable that this approach can be applied to enzymatic synthesis reactions for other biotechnology applications, particularly reactions that require long-term and stable operation.
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http://dx.doi.org/10.4014/jmb.1104.04029DOI Listing
September 2011

Repeated-batch operation of surface-aerated fermentor for bioethanol production from the hydrolysate of seaweed Sargassum sagamianum.

J Microbiol Biotechnol 2011 Mar;21(3):323-31

Department of Biotechnology, Chungju National University, Jeungpyung, Chungbuk, Korea.

In this study, we investigated the feasibility of sustainable long-term bioethanol production from the hydrolysate of a brown seaweed, Sargassum sagamianum. Because the hydrolysate was prepared as a liquid solution using a hightemperature liquefying system, a repeated-batch operation was utilized as the operational strategy for bioethanol production. Additionally, we used surface aeration to improve bioethanol production from the hydrolysate containing C5 monosaccharides such as xylose. In this study, the C5 monosaccharide-utilizable yeast strain Pichia stipitis was used for bioethanol production. Therefore, based on this repeated-batch flask culture, we designed a surface-aerated repeated-batch fermentor culture, in which the aeration was finely controlled at 100 ml/min and delivered into the headspace of a 2.5-l fermentor. When the medium was replaced every 48 h, bioethanol was continuously produced for 200 h under repeated-batch fermentor culture, where the level of bioethanol production was about 9~10 (g/l). Additionally, the bioethanol yield based on the reducing sugar was about 0.386, which was the average value throughout four consecutive cultures and was about 74.5% of the theoretical value. In addition, the bioethanol yield based on quantitative TLC analyses of glucose and xylose was about 0.431, which was the average value throughout four consecutive cultures and was about 84.3% of theoretical value. Consequently, throughout this repeated-batch operation, we demonstrated that it was actually feasible to produce bioethanol from the hydrolysate of seaweed S. sagamianum. In addition, the approach described here is a practical strategy for commercial bioethanol production from seaweed, particularly for finely controlling aeration through surface aeration.
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March 2011

Preparation of branched dextran microspheres of soluble interferon-alpha and its activity in vitro and in vivo.

J Microbiol Biotechnol 2011 Feb;21(2):176-82

Department of Medical Genetic Engineering, Keimyung University School of Medicine, Daegu 700-712, Korea.

The study objective was to prepare biodegradable branched dextran microspheres encapsulated with His-tagged interferon-alpha (BDM-hIFN-alpha) and evaluate its activity in vitro and in vivo. The glycidyl methacrylate derivatized dextrans (Dex-GMA) as precursor was primarily synthesized by substituting hydroxyl groups of either the branched or linear type of dextran with GMA. Dex-GMA microspheres loaded with hIFN-alpha was then prepared by the water-in-water emulsion technique. In vitro release and Western blotting experiments demonstrated the retained activity of hIFN-alpha released from branched dextran microspheres at 24 h by inducing phosphorylation of signal transducer and activator transcription-1 (STAT-1), a down-stream effector of IFN-alpha, in HepG2 cells. Animal data further revealed a peak of plasma levels of IFN-alpha in rats injected intravenously with BDM-hIFN-alpha at 10 min post-injection, but a sharp decline at 2 h. High plasma levels of neopterin, a plasma protein induced by IFN-alpha, were also detected in rats injected with BDM-hIFN-alpha at 10 min post-injection. Notably, plasma levels of neopterin remained high at 4 h, but largely declined thereafter.
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http://dx.doi.org/10.4014/jmb.1007.07060DOI Listing
February 2011

Bioethanol production from the hydrolysate of rape stem in a surface-aerated fermentor.

J Microbiol Biotechnol 2011 Jan;21(1):109-14

Department of Biotechnology, Chungju National University, Jeungpyung, Chungbuk 368-701, Korea.

In this study, we investigated the feasibility of producing bioethanol from the hydrolysate of rape stem. Specifically, the most ideal yeast strain was screened, and the microaeration was performed by surface aeration on a liquid medium surface. Among the yeast strains examined, Pichia stipitis CBS 7126 displayed the best performance in bioethanol production during the surface-aerated fermentor culture. Pichia stipitis CBS 7126 produced maximally 9.56 g/l of bioethanol from the initial total reducing sugars (about 28 g/l). The bioethanol yield was 0.397 (by the DNS method). Furthermore, this controlled surface aeration method holds promise for use in the bioethanol production from the xylose-containing lignocellulosic hydrolysate of biomass.
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http://dx.doi.org/10.4014/jmb.1008.08001DOI Listing
January 2011

Improving the yield of soluble 6xHis-tagged interferon-alpha via the addition of repressor of the araBAD promoter system in Escherichia coli.

Biotechnol Lett 2008 Sep 17;30(9):1577-82. Epub 2008 May 17.

Division of Food and Biotechnology, Chungju National University, Jeungpyung, Chungbuk 368-701, Republic of Korea.

The inhibition of inclusion body formation in Escherichia coli by the addition of alpha-D-glucopyranoside or D-fucose after induction improved the purification yield of soluble recombinant interferon-alpha. When D-fucose was added after induction, more soluble 6xHis-tagged interferon-alpha could be purified compared to when methyl alpha-D-glucopyranoside was added. It was shown that, on the basis of 1 mg dry cell weight, 16.6 microg of soluble 6xHis-tagged interferon-alpha was purified when D-fucose was added after induction and 6 ml nickel-chelated agarose gel column was used. This was about 15 times greater than when induction only was performed and 1 ml nickel-chelated agarose gel was used.
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http://dx.doi.org/10.1007/s10529-008-9741-2DOI Listing
September 2008

Methyl alpha-D-glucopyranoside enhances the enzymatic activity of recombinant beta-galactosidase inclusion bodies in the araBAD promoter system of Escherichia coli.

J Ind Microbiol Biotechnol 2008 Jul 4;35(7):695-701. Epub 2008 Mar 4.

Division of Food and Biotechnology, Chungju National University, Jeungpyung-Gun, Chungbuk 368-701, South Korea.

In this study, we utilized a catabolite repressor to improve the enzymatic activity of recombinant beta-galactosidase inclusion bodies (IBs) produced in Escherichia coli under the araBAD promoter system. Specifically, we employed methyl alpha-D: -glucopyranoside (alpha-MG) to lower the transcription rate of the beta-galactosidase structural gene. In deepwell microtiter plate and lab-scale fermentor culture systems, we demonstrated that the addition of alpha-MG after induction improved the specific beta-galactosidase production, even though beta-galactosidase was still produced as an IB. Particularly, the addition of 0.0025% alpha-MG led to the most significant increase in the specific activity of the beta-galactosidase. Interestingly, the beta-galactosidase IBs obtained in the presence of 0.0025% alpha-MG were more loosely packed, as determined by IB solubilization in guanidine hydrochloride solution. We propose that the reduced gene transcription rate was responsible for the increased specific beta-galactosidase activity and the loose packing that characterized the IBs produced in the presence of alpha-MG. This principle could be applied throughout the enzyme bioprocessing industry in order to enhance the activity of aggregate-prone enzymes within IBs.
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http://dx.doi.org/10.1007/s10295-008-0329-6DOI Listing
July 2008