• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.426-429
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• 2001

The continuous production of L -proline was studied using L-histidine auxotrophic mutant of Corynebacterium acetoacidophilum under various substrate limited conditions. Among the $NH_4\;^+$ $PO_4\;^3$ and L -histidine limited conditions, the highest production of L -proline was observed under the L-histidine limited condition. Under $NH_4\;^+$ and $PO_4\;^3$ limited conditions, no or poor L-proline production was observed, respectively. For the kinetic parameters under L -histidine limitation the specific rate of L -proline production was increased with dilution rate upto $0.1hr^{-1}$ but decreased above $0.1hr^{-1}$. The volumetric rate of L -proline production was showed similar pattern with specific rate. The dried cell weight was gradually increased according to decrease the dilution rate. Specific rate of glucose consumption was proportionally increased with dilution rate. The results of continuous culture (higher production of L-proline at dilution rate $0.1hr^{-1}$) will be used in fed-batch culture for the control of cell growth rate and mass production of L-proline.

• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.666-670
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• 2001

Levofloxacin is L-form stereoisomer of ofloxacin. It has better antibacterial activity than D-oflxacin. In this study, levofloxacin was produced enantioselectively by using high density culture of recombinant E. coli containing a foreign esterase gene. Final cell concentration was 89 g/L at the end of fed-batch culture and the cells were used for levofloxacin production after IPTG induction at the optimized condition. For the immobilization of recombinant E. coli. 1.5% sodium alginate showed the best result to maintain enzyme activity and enantioselectivity.

• 한국생물공학회:학술대회논문집
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• 2003.04a
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• pp.213-217
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• 2003

The effects of glucose concentration on the production of PHB by fed-batch culture of Ralstonia eutropha were investigated. In the range of glucose concentration of $2.5\;{\sim}\;40\;g/l$, it was found that the high glucose concentration was not favorable for the PHB formation after the phosphate limitation. It was further confirmed by the specific PHB synthesis rates and yields. The PHB concentration decreased much with the increase of glucose concentration. But if the glucose concentration was very low, e.g. 2.5 g/l, the cell growth and PHB synthesis also could be limited because of inadequate glucose supply. Itwould be better to maintain the glucose concentration at about 9.0 g/l to obtain high DCW, PHB concentration and productivity.

• 한국생물공학회:학술대회논문집
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• 2002.04a
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• pp.257-260
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• 2002

Dissolved oxygen level of cell culture media has a critical effect on cellular metabolism, which governs specific productivity of recombinant proteins and mammalian cell growth However, in the cores of cell aggregates or cell-immobilized beads, oxygen level frequently goes below a critical level. Mammalian cells have a number of genes induced in the lower level of oxygen, and the genes contain a common cis-acting element (-RCGTG-), hypoxia response element (HRE). By binding of hypoxia inducible factor-l (HIF-I) to the HRE, promoters of hypoxia inducible genes are activated, which is a survival mechanism. In this work, to develop a CHO cell capable of producing recombinant proteins in immobilization and high density cell culture efficiently, mammalian expression vectors containing human tissue-type plasminogen activator (t-PA) gene controlled by HRE were constructed and stably transfected into the CHO cells. In $Ba^{2+}$ -alginate immobilization culture, CHO/pCl/dhfr/2HRE-t-PA cells produced 2 folds higher recombinant t-PA activity than CHO/pCl/dhfrlt-PA cells without $CoCl_2$ treatment. Furthermore, in repeated fed batch culture, productivity of t-PA in immobilized CHO/pCI/dhfr/2HRE-t-PA cells was 121 ng/ml/day, total production of 0.968 mg/day at 11 days culture while CHO/pCIIdhfrlt-PA cells was 22.8 ng/ml/day. All these results indicate that HRE is very useful for the enhancement of protein productivity in mammalian cell cultures.

• Journal of Microbiology and Biotechnology
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• v.22 no.3
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• pp.400-406
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• 2012

To improve the hydrogen yield from biological fermentation of organic wastewater, a co-culture system of dark- and photo-fermentation bacteria was investigated. In a pure-culture system of the dark-fermentation bacterium Clostridium butyricum, a pH of 6.25 was found to be optimal, resulting in a hydrogen production rate of 18.7 ml-$H_2/l/h$. On the other hand, the photosynthetic bacterium Rhodobacter sphaeroides could produce the most hydrogen at 1.81mol-$H_2/mol$-glucose at pH 7.0. The maximum specific growth rate of R. sphaeroides was determined to be 2.93 $h^{-1}$ when acetic acid was used as the carbon source, a result that was significantly higher than that obtained using either glucose or a mixture of volatile fatty acids (VFAs). Acetic acid best supported R. sphaeroides cell growth but not hydrogen production. In the co-culture system with glucose, hydrogen could be steadily produced without any lag phase. There were distinguishable inflection points in a plot of accumulated hydrogen over time, resulting from the dynamic production or consumption of VFAs by the interaction between the dark- and photo-fermentation bacteria. Lastly, the hydrogen production rate of a repeated fed-batch run was 15.9 ml-$H_2/l/h$, which was achievable in a sustainable manner.

• Applied Biological Chemistry
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• v.36 no.6
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• pp.488-494
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• 1993

A photosynthetic bacterium strain P17 having high growth rate and assimilating ability of organic acids was isolated from several soil samples, which was identified as Rhodospirillum rubrum. Cultural conditions of the strain P17 were examined for the production of starter culture used in the treatment of organic waste water. The addition of organic acids mixture as carbon source containing 0.2% Na-acetate, 0.1% Na-propionate and 0.2% Na-lactate and 0.1% of yeast extract as growth factor stimulated the cell growth. The maximal cell production was obtained at $30^{\circ}C$, pH 7.0, 2,500 lux of illumination and $50{\sim}100\;rpm$ of agitation. Under the optimal conditions of batch and fed-batch culture systems in a Jar fermentor, 5.17 g/l and 7.93 g/l of cells were obtained after S days of cultivation, respectively. In continuous culture system, the cell productivity was 0.206 g/l/h at a dilution rate of 0.21 $h^{-1}$. When R. rubrum P17 was cultivated in a soybean curd waste water, initial COD level(3,240 mg/l) of the waste water was reduced to 250 mg/l after 4 days of cultivation.

• 한국생물공학회:학술대회논문집
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• 2000.04a
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• pp.53-56
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• 2000

Two-stage fed-batch culture was peformed to improve the volumetric productivity of erythritol. In the growth phase dissolved oxygen was maintained to 20% and the feed medium was automatically supplied to the fermenter by pH-stat mode. The cell yield was 0.76 g-cell/g-glucose. In two-stage fed-batch culture, 41% of total erythritol conversion yield with 187 g/L of erythritol concentration and 2.79 g/L-h of maximum erythritol Productivity were obtained when 400 g/L of glucose was directly added in the form of non-sterile powder at production phase. The erythritol productivity increased in parallel with cell mass. The metabolic shift in the biosynthetic pathway of erythritol was caused by dissolved oxygen concentration. The production of gluconic acid was observed when the dissolved oxygen in the medium was maintained over 40% during the production phase, whereas the dissolved oxygen concentration lower than 40% caused the production of citric acid. But the butyric acid was produced independently with dissolved oxygen concentration in the medium. The production of organic acids such as gluconic acid, citric acid, and butyric acid was decreased by addition of mineral salts.

• Korean Journal of Microbiology
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• v.46 no.1
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• pp.46-51
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• 2010

Coenzyme Q10 (CoQ10) is an essential lipid-soluble component of membrane-bound electron transport chains. CoQ10 is involved in several aspects of cellular metabolism and is increasingly being used in therapeutic applications for several diseases. Despite the recent accomplishments in metabolic engineering of Escherichia coli for CoQ10 production, the production levels are not yet competitive with those by fermentation or isolation. So we tested several microorganisms obtained from the KCTC of Biological Resource Center to find novel sources of strain-development for CoQ10-production. Then we selected two strains, Paracoccus denitrificans (KCTC 2530) and Asaia siamensis (KCTC 12914), and tested to optimize the CoQ10 production conditions. Among the carbon sources tested, CoQ10 production was the highest when fructose was supplied about 4% concentration. Yeast extract produced the highest CoQ10 production about 2% concentration. The highest CoQ10 production was obtained at pH 6.0 for P. denitrificans and pH 8.0 for A. siamensis. And two strains showed the highest CoQ10 production at $30^{\circ}C$, but the highest DCW was obtained at $37^{\circ}C$. In the fed-batch culture, P. denitrificans yielded $14.34{\pm}0.473$ mg and A. siamensis yielded $12.53{\pm}0.231$ mg of final CoQ10 production.

• Journal of Microbiology and Biotechnology
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• v.13 no.3
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• pp.451-456
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• 2003

An expression vector system was developed for the secretory production of recombinant Bacillus stearothermophilus L1 lipase in Saccharomyces cerevisiae. The mature L1 lipase gene was fused to ${\alpha}-amylase$ signal sequence from Aspergillus oryzae for the effective secretion into the culture broth and the expression was controlled under GAL10 (the gene coding UDP-galactose epimerase of S. cerevisiae) promoter. S. cerevisiae harboring the resulting plasmid successfully secreted L1 lipase into the culture broth. To examine an optimum condition for L1 lipase expression in the fed-batch culture, L1 lipase expression was induced at three different growth phases (early, mid, and late-exponential growth phases). Maximum product on of L1 lipase (1,254,000 U/l, corresponding to 0.65/1) was found when the culture was induced at an early growth phase. Secreted recombinant L1 lipase was purified only through CM-Sepharose chromatography, and the purified enzyme showed 1,963 U/mg of specific activity and thermoalkalophilic properties similar to those reported for the enzyme expressed in Escherichia coli.

• Journal of Microbiology and Biotechnology
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• v.24 no.6
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• pp.781-787
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• 2014

2-Ketogluconic acid production by Klebsiella pneumoniae is a pH-dependent process, strictly proceeding under acidic conditions. Unfortunately, cell growth is inhibited by acidic conditions, resulting in low productivity of 2-ketogluconic acid. To overcome this deficiency, a two-stage fermentation strategy was exploited in the current study. During the first stage, the culture was maintained at neutral pH, favoring cell growth. During the second stage, the culture pH was switched to acidic conditions favoring 2-ketogluconic acid accumulation. Culture parameters, including switching time, dissolved oxygen levels, pH, and temperature were optimized for the fed-batch fermentation. Characteristics of glucose dehydrogenase and gluconate dehydrogenase were revealed in vitro, and the optimal pHs of the two enzymes coincided with the optimum culture pH. Under optimum conditions, a total of 186 g/l 2-ketogluconic acid was produced at 26 h, and the conversion ratio was 0.98 mol/mol. This fermentation strategy has successfully overcome the mismatch between optimum parameters required for cell growth and 2-ketogluconic acid accumulation, and this result has the highest productivity and conversion ratio of 2-ketogluconic and produced by microorganism.