industrial-scale fermenter and 'scaling up'
commercial applications of biotechnology often require the growth of a particular mircroogranism on an enormous scale. An industrial-scale fermenter is essentially a high tank which may have a capacity of tens of thousands of litres. The growing conditions in it can be maipulated and controlled in order to ensure the best possible yield of the product.
The precise growing conditions depend on the microorganisms being cultured, and on whether the process is designed to produce a primary or secondary metabolite. They are;
- Temperature-too hot and enzymes will denature, too cold and growth will be slowed.
- Type and time of addition of nutrient-growth of microorganisms requires a nutrient supply, including sources of carbon, nitrogen and any essential vitamins and minerals. The timing of nutrient adiition can be manipulated, depending on whether the process is designed to produce a primary or secondary metabolite.
- O2 concentration-most commercial applications use the growth of organisms under aerobic conditions, so sufficient O2 must be made available. A ack of O2 will lead to the unwanted products of anaerobic respiration and a reduction in growth rate.
- pH-chanegs in pH within the fermentation tank can reduce the activity of enzymes and so reduce growth rates.
Such large cultures need large 'stater' populations of microorganisms obtained by taking a pure culture and growing it in sterile nutrient broth.
Batch-the microogranism stater population is mixed with a specific quantity of nutrient solution, then allowed to grow for a fixe period with no further nutrient added. At the end of the period, the products are removed and the fermentation tank is emptied. Penicillin is produced using batch culture.
- Easy to set up and maintain
- if contamination occurs, only one batch is lost.
- very useful for processes involving the production of secondary metabolites.
- Growth rate is slower as nutrent level declines with time.
- Less efficient, fermenter is not in operation all the time
continuous culture-nutrients are added to the fermentation tank and products removed from the fermentaion tank at regular intervals, or continuously. Human hormones such as Insulin are produced from continuous culture of genetically modified Escherichia coli bacteria.
- Growth rate is higher as nutrients are continuously added to the fermentation tank.
- More efficient, fermenter operates continuously.
- Very useful for processes involving the production of many metabolites
- Set up is more difficult, maintenance of required growing conditions can be difficult to achieve.
- If contamination occurs, huge volumes of product may be lost.
Asepsis in biotechnology
Aseptic technique-any measure taken at any point in a biotechnological process to ensure that unwanted microorganisms do not contaminate the culture that is being grown or the products that are extracted.
The nutrient medium in which the microorganisms grow could also support the growth of many unwanted microorganisms, or contaminant.
- compete witht he culture microorganisms for nutrients and space
- reduce the yield of useful products from the culture microorganisms.
- may cuase spoilage of the product
- may produce toxin chemicals
- may destroy the culture microorganism and their product.
In processes where foods or medicinal chemicals are being produced, contamination means that all products must be considered unsafe and so must be discarded.
They use aseptic techniques to ensure contamination does not occur from isolation of initial culture through scaling up, fermentation, to product harvesting.
- At laboratory and stater culture level;
- All aparatus for carrying/moving microorganisms is sterilised before and after use, for example by heating in a flame until glowing or by UV light. Some equipment is steam-sterilised at 121 degrees C for 15 minutes in an autoclave or large pressure cooker.
- Work can be carried out in a fume cupboard or a laminar flow cabinet where air circulation carries any airborne contaminants away from the bench space.
- Cultures of microorganisms are kept closed where possible and away from the bench surface when open and in use.
- At a large-scale culture level
- Washing, disinfecting and steam-cleaning the fermenter and associated pipes when not in use removes excess nutrient medium and kills microorganisms.
- Fermenter surfaces made of polished stainless steel prevent microbed and medium sticking to surfaces.
- sterilising all nutrient media before adding to the fermenter prevents introduction of contaminants.
- Fine filters on inlet and outlet pipes avoid microorganisms entering or leaving the fermentation vessel