title: Integrated isotope-assisted metabolomics and (13)C metabolic flux analysis reveals metabolic flux redistribution for high glucoamylase production by Aspergillus niger.
abstract: BACKGROUND
  Aspergillus niger is widely used for enzyme production and achievement of high enzyme production depends on the comprehensive understanding of cell's metabolic regulation mechanisms.
  
  
  RESULTS
  In this paper, we investigate the metabolic differences and regulation mechanisms between a high glucoamylase-producing strain A. niger DS03043 and its wild-type parent strain A. niger CBS513.88 via an integrated isotope-assisted metabolomics and (13)C metabolic flux analysis approach. We found that A. niger DS03043 had higher cell growth, glucose uptake, and glucoamylase production rates but lower oxalic acid and citric acid secretion rates. In response to above phenotype changes, A. niger DS03043 was characterized by an increased carbon flux directed to the oxidative pentose phosphate pathway in contrast to reduced flux through TCA cycle, which were confirmed by consistent changes in pool sizes of metabolites. A higher ratio of ATP over AMP in the high producing strain might contribute to the increase in the PP pathway flux as glucosephosphate isomerase was inhibited at higher ATP concentrations. A. niger CBS513.88, however, was in a higher redox state due to the imbalance of NADH regeneration and consumption, resulting in the secretion of oxalic acid and citric acid, as well as the accumulation of intracellular OAA and PEP, which may in turn result in the decrease in the glucose uptake rate.
  
  
  CONCLUSIONS
  The application of integrated metabolomics and (13)C metabolic flux analysis highlights the regulation mechanisms of energy and redox metabolism on flux redistribution in A. niger. Graphical abstract An integrated isotope-assisted metabolomics and (13)C metabolic flux analysis was was firstly systematically performed in A. niger. In response to enzyme production, the metabolic flux in A. niger DS03043 (high-producing) was redistributed, characterized by an increased carbon flux directed to the oxidative pentose phosphate pathway as well as an increased pool size of pentose. The consistency in (13)C metabolic flux analysis and metabolites quantification indicated that an imbalance of NADH formation and consumption led to the accumulation and secretion of organic acids in A. niger CBS513.88 (wild-type).
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. luhongzhong2006@126.com.
authors.forename: Hongzhong
authors.initials: H
authors.lastname: Lu
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. alice.liu@mail.ecust.edu.cn.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. huangmz@ecust.edu.cn.
authors.forename: Mingzhi
authors.initials: M
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. jyxia@ecust.edu.cn.
authors.forename: Jianye
authors.initials: J
authors.lastname: Xia
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. juchu@ecust.edu.cn.
authors.forename: Ju
authors.initials: J
authors.lastname: Chu
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. ypzhuang@ecust.edu.cn.
authors.forename: Yingping
authors.initials: Y
authors.lastname: Zhuang
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 200237, Shanghai, People's Republic of China. siliangz@ecust.edu.cn.
authors.forename: Siliang
authors.initials: S
authors.lastname: Zhang
authors.affiliation: DSM Biotechnology Center, P.O. Box1, 2600 MA, Delft, The Netherlands. henk.noorman@dsm.com.
authors.forename: Henk
authors.initials: H
authors.lastname: Noorman
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001234:Aspergillus niger / Q000378:metabolism*; D018533:Biomass; D002247:Carbon Isotopes / Q000737:chemistry / Q000378:metabolism; D002952:Citric Acid Cycle; D004734:Energy Metabolism; D005087:Glucan 1,4-alpha-Glucosidase / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D064688:Metabolic Flux Analysis; D055432:Metabolomics; D010084:Oxidation-Reduction
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D005087:Glucan 1,4-alpha-Glucosidase