22.7 Culturing Microorganisms on an Industrial Scale

Question 1

What are primary metabolites?

Answer 1

substances produced

as an essential part of the normal functioning of a microorganism

typically produced during growth phase

(ethanol, ethanoic acid, amino acids, enzymes, e.t.c)

Question 2

What are secondary metabolites?

Answer 2

substances produced

which are not essential for normal growth, but are still used by cells

produced during stationary phase (as a result of increased competition)

(e.g penicillin antibiotics)

Question 3

What are the 2 different types of fermentation in bioprocessing?

Answer 3

BATCH

CONTINUOUS

Question 4

Outline the process of batch fermentation:

Answer 4

1. Microorganisms inoculated into fixed volume of nutrient medium
2. Growth takes place >> nutrients used up, biomass & waste accumulate
3. Culture removed just before death phase, after formation of desired products
4. Whole system sterilised for new batch culture to be set up

Question 5

Outline the process of continuous culture:

Answer 5

1. Microorganisms inoculated into nutrient medium.
2. Sterile nutrient medium added continuously after culture reaches log phase.
3. Culture broth continually removed >> volume of culture remains constant

Question 6

What factors must be controlled in a bioreactor during fermentation?

Answer 6

• TEMPERATURE
  
  • temperature must be high enough to maximise rate of enzyme-controlled reactions
  • but not too high to denature enzymes
    
    • bioreactors have heating/cooling mechanism
• CONCENTRATION OF NUTRIENTS & O2
• DISTRIBUTION OF SUBSTANCES
  
  • Substances cannot diffuse as efficiently through viscous mixture
  • Mixing with paddles ensures even distribution throughout mixture
• ASEPSIS - absence of microorganisms
  
  • Most bioreactors are sealed:
    
    • prevents contamination from microorganisms in air
    • prevents GM microorganisms from release into environment