title: Enhanced production of gamma-aminobutyrate (GABA) in recombinant Corynebacterium glutamicum by expressing glutamate decarboxylase active in expanded pH range.
abstract: BACKGROUND
  Gamma-aminobutylate (GABA) is an important chemical in pharmacetucal field and chemical industry. GABA has mostly been produced in lactic acid bacteria by adding L-glutamate to the culture medium since L-glutamate can be converted into GABA by inherent L-glutamate decarboxylase. Recently, GABA has gained much attention for the application as a major building block for the synthesis of 2-pyrrolidone and biodegradable polyamide nylon 4, which opens its application area in the industrial biotechnology. Therefore, Corynebacterium glutamicum, the major L-glutamate producing microorganism, has been engineered to achieve direct fermentative production of GABA from glucose, but their productivity was rather low.
  
  
  RESULTS
  Recombinant C. glutamicum strains were developed for enhanced production of GABA from glucose by expressing Escherichia coli glutamate decarboxylase (GAD) mutant, which is active in expanded pH range. Synthetic PH36, PI16, and PL26 promoters, which have different promoter strengths in C. glutamicum, were examined for the expression of E. coli GAD mutant. C. glutamicum expressing E. coli GAD mutant under the strong PH36 promoter could produce GABA to the concentration of 5.89±0.35 g/L in GP1 medium at pH 7.0, which is 17-fold higher than that obtained by C. glutamicum expressing wild-type E. coli GAD in the same condition (0.34±0.26 g/L). Fed-bath culture of C. glutamicum expressing E. coli GAD mutant in GP1 medium containing 50 μg/L of biotin at pH 6, culture condition of which was optimized in flask cultures, resulted in the highest GABA concentration of 38.6±0.85 g/L with the productivity of 0.536 g/L/h.
  
  
  CONCLUSIONS
  Recombinant C. glutamicum strains developed in this study should be useful for the direct fermentative production of GABA from glucose, which allows us to achieve enhanced production of GABA suitable for its application area in the industrial biotechnology.
authors.affiliation: Department of Chemical and Biomolecular Engineering (BK21 Plus Program), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon, 305-701, Republic of Korea. jwoongci@kaist.ac.kr.
authors.forename: Jae Woong
authors.initials: JW
authors.lastname: Choi
authors.affiliation: Department of Chemical and Biomolecular Engineering (BK21 Plus Program), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon, 305-701, Republic of Korea. vidalsungsun@kaist.ac.kr.
authors.forename: Sung Sun
authors.initials: SS
authors.lastname: Yim
authors.affiliation: Department of Biotechnology and Bioengineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 500-757, Republic of Korea. leesh@chonnam.ac.kr.
authors.forename: Seung Hwan
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Chemical and Biochemical Engineering, Dongguk University-Seoul, 30 Pildong-ro 1-gil, Jung-gu, Seoul, 100-715, Republic of Korea. taekkang@dongguk.edu.
authors.forename: Taek Jin
authors.initials: TJ
authors.lastname: Kang
authors.affiliation: Department of Environmental Engineering and Energy, Myongji University, 116 Myongji-ro, Cheoin-gu, Yongin, Gyeonggido, 449-728, Republic of Korea. parksj93@mju.ac.kr.
authors.forename: Si Jae
authors.initials: SJ
authors.lastname: Park
authors.affiliation: Department of Chemical and Biomolecular Engineering (BK21 Plus Program), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon, 305-701, Republic of Korea. kjjeong@kaist.ac.kr.|Institute for the BioCentury, KAIST, 335 Gwahagno, Yuseong-gu, Daejeon, 305-701, Republic of Korea. kjjeong@kaist.ac.kr.
authors.forename: Ki Jun
authors.initials: KJ
authors.lastname: Jeong
mesh_terms: D048230:Corynebacterium glutamicum / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007218:Industrial Microbiology / Q000379:methods; D060847:Metabolic Engineering / Q000379:methods; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D015203:Reproducibility of Results; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000096:biosynthesis*
chemical_list: D029968:Escherichia coli Proteins; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; D005947:Glucose