title: Enhanced hyaluronic acid production of Streptococcus zooepidemicus by an intermittent alkaline-stress strategy.
abstract: OBJECTIVE
  Enhanced hyaluronic acid (HA) production of Streptococcus zooepidemicus by redirecting carbon flux through an intermittent alkaline-stress strategy.
  
  
  RESULTS
  pH value was kept at 7.0 for the first 6 h, and then intermittently switched to 8.5 for 1 h and back to 7.0 for 1 h until the end of fermentation at 16 h (one pH switch cycle every 2 h). With this intermittent alkaline-stress strategy, HA production was increased to 6.5 +/- 0.2 g l(-1) from 5.0 +/- 0.1 g l(-1) of the control, in which pH was always kept at 7.0. In addition, biomass and lactic acid concentration decreased by 24% and 14%, respectively, while acetic acid concentration increased by 10% under intermittent alkaline stress. The redirection of carbon flux from lactic acid to acetic acid was further supported by the decreased lactate dehydrogenase activity and the increased acetate kinase activity. As indicated by the increased NADH oxidase (NOX) activity, intermittent alkaline-stress induced a more oxidative intracellular environment which would facilitate HA synthesis.
  
  
  CONCLUSIONS
  Overproduction of HA was realized by redirecting carbon flux through the proposed intermittent alkaline-stress strategy.
  
  
  CONCLUSIONS
  This study clearly demonstrated the importance of metabolic-pathway-analysis based fermentation strategy in industrial processes and provided an alternative optimization approach for high viscosity fermentation.
authors.affiliation: School of Biotechnology, Jiangnan University, Wuxi, China.
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Wang
authors.forename: G
authors.initials: G
authors.lastname: Du
authors.forename: J
authors.initials: J
authors.lastname: Chen
mesh_terms: D000084:Acetate Kinase / Q000378:metabolism; D019342:Acetic Acid / Q000378:metabolism*; D001709:Biotechnology / Q000379:methods; D003470:Culture Media; D005285:Fermentation; D018869:Heat-Shock Response; D006820:Hyaluronic Acid / Q000096:biosynthesis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D018502:Streptococcus equi / Q000254:growth & development* / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D003470:Culture Media; D009097:Multienzyme Complexes; D019344:Lactic Acid; D006820:Hyaluronic Acid; C023107:NADH oxidase; D009247:NADH, NADPH Oxidoreductases; D000084:Acetate Kinase; D019342:Acetic Acid