title: [Effects of gene pta disruption on L-tryptophan fermentation].
abstract: OBJECTIVE
  To study the effects of gene pta disruption on biosynthesis of L-tryptophan.
  
  
  METHODS
  The pta gene of the L-tryptophan producing strain E. coli TRTH was disrupted by Red recombination technology and a pta mutant E. coli TRTHdeltapta was constructed. Fed-batch fermentation of E. coli TRTHdeltapta was carried out in 30-Liter fermentor to investigate the biomass, L-tryptophan production, organic acid content and the concentration of NH4+, lactate, pyruvate and succinate. The metabolic flux balance model of L-tryptophan synthesis by E. coli was established. Based on this model, the practical metabolic flux distribution of E. coli and its pta mutant were determined with the linear program planted in MATLAB software.
  
  
  RESULTS
  Compared with E. coli TRTH, the pta mutant was able to maintain higher growth rate at exponential phase, the final biomass and the L-tryptophan production were increased by 52.7% and 46.8% respectively. Meanwhile, the data analysis of organic acids accumulated during fed-batch culture showed that the concentration of acetate was decreased to 2.5 g/L, which was only 19.5% of that of the parental strain; as the decreased concentration of succinate, the accumulation of pyruvate and lactate was increased. The concentration of Na+, K+, PO4(3-) were consistent with E. coli TRTH during the fed-batch culture, the concentration of NH4+ was decreased by 33.2%. The metabolic flux analysis indicated that EMP pathway and TCA cycle were reduced by 7.4% and 32.2% respectively, but PP pathway was increased by 8.4% compared with E. coli TRTH during the middle and late period of the fed-batch culture.
  
  
  CONCLUSIONS
  In the process of L-tryptophan fermentation, pta gene deletion in E. coli TRTH led to change in metabolic flux and acetate content, which derepressed its inhibition on cell growth and production of L-tryptophan and finally made a substantial increase of bacterial biomass and L-tryptophan production.
authors.affiliation: College of Biological Engineering, Tianjin University of Science & Technology, Key Laboratory of Industrial Microbiology of Education Ministry, Tianjin 300457, China. hhenry.kaka@163.com
authors.forename: Jing
authors.initials: J
authors.lastname: Huang
authors.forename: Jianming
authors.initials: J
authors.lastname: Shi
authors.forename: Qian
authors.initials: Q
authors.lastname: Liu
authors.forename: Qingyang
authors.initials: Q
authors.lastname: Xu
authors.forename: Xixian
authors.initials: X
authors.lastname: Xie
authors.forename: Tingyi
authors.initials: T
authors.lastname: Wen
authors.forename: Ning
authors.initials: N
authors.lastname: Chen
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D005285:Fermentation; D019344:Lactic Acid / Q000378:metabolism; D010709:Phosphate Acetyltransferase / Q000235:genetics* / Q000378:metabolism; D017384:Sequence Deletion; D014364:Tryptophan / Q000096:biosynthesis*
chemical_list: D029968:Escherichia coli Proteins; D019344:Lactic Acid; D014364:Tryptophan; D010709:Phosphate Acetyltransferase