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Related Experiment Videos

Scale-down model to simulate spatial pH variations in large-scale bioreactors.

A Amanullah1, C M McFarlane, A N Emery

  • 1Centre for Bioprocess Engineering, School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.

Biotechnology and Bioengineering
|April 26, 2001
PubMed
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pH fluctuations in large-scale bioreactors impact microbial metabolism. Bacillus subtilis product formation decreased with longer exposure times to pH variations, affecting key enzymes and metabolite production.

Area of Science:

  • Biotechnology
  • Microbial Physiology
  • Biochemical Engineering

Background:

  • Large-scale fermentations can experience pH fluctuations due to poor mixing and reagent addition.
  • These pH variations can affect microbial growth and metabolite production, particularly for sensitive organisms like Bacillus subtilis.
  • Bacillus subtilis is a model organism sensitive to dissolved oxygen and pH changes between 6.5 and 7.2, impacting acetoin and 2,3-butanediol production.

Purpose of the Study:

  • To investigate the impact of pH fluctuations, mimicking large-scale operations, on microbial metabolism using a laboratory-scale system.
  • To determine the effect of varying exposure times to pH shifts on Bacillus subtilis growth and metabolite production.
  • To understand the underlying mechanisms linking pH sensitivity to enzyme activity and metabolite synthesis.

Related Experiment Videos

Main Methods:

  • A two-compartment scale-down model comprising a stirred tank reactor (STR) and a plug flow reactor (PFR) was employed.
  • pH was controlled in the STR at 6.5, with alkali addition in the PFR to simulate localized pH excursions.
  • Residence times in the PFR were varied to simulate exposure duration, and dissolved oxygen effects were normalized across experimental conditions.

Main Results:

  • Biomass concentration of Bacillus subtilis was unaffected by pH variations.
  • Product formation (acetoin and 2,3-butanediol) was significantly influenced by residence times in the PFR of 60 seconds or longer.
  • Metabolic changes are attributed to the pH sensitivity of key enzymes and the inductive effects of dissociated acetate.

Conclusions:

  • pH fluctuations in large-scale bioreactors can negatively impact microbial product formation, even if biomass remains stable.
  • Enzyme sensitivity to pH and acetate induction are critical factors in altered metabolic pathways.
  • Scale-down models are valuable tools for studying the effects of process variations on microbial systems.