Biotechnology is the industrial use of living organisms (or parts of living organisms) to produce food, drugs or other products for human use.
Microorganisms in biotechnology
Microorganisms are often used in biotechnological processes because:
- Grow rapidly in favourable conditions, with a generation time as little as 30 minutes.
- Often produce proteins or chemicals that are given out into the surrounding medium and can be harvested
- Can be genetically engineered to produce specific products
- Grow well at relatively low temperatures, much lower than those required in the chemical engineering of similar processes
- Can be grown anywhere in the world and are not dependent on climate
- Tend to generate products what are in a more pure form than those generated via chemical processes
- Can often be grown using nutrient materials that would otherwise be useless or even toxic to humans
Standard growth curve of microorganisms
Lag phase: Organisms are adjusting to the surrounding conditions. This may means taking in water, cell expansion, activting specific genes and synthesising specific enzymes. The cells are active but not reproducing so population remains fairly constant. The length of this period depends on the growing conditions.
Log phase: The population size doubles each generation as each individual has enough space and nutrients to reproduce. In some bacteria the population can double every 20-30 minutes. The length of this phase depends on how quickly the organisms reproduce and take up the available space and nutrients.
Stationary phase: Nutrient levels decrease and waste products like carbon dioxide and other metabolites build up. Individual organsisms die at the same rate at which new individuals are being produced. In an open system this would be the carrying capacity.
Death phase: Nutrient exhaustion and increased levels of toxic waste products and metabolites leads to the death rate increasing above the reproduction rate. Eventually, all of the organisms will die in a closed system.
Adsorption: Enzyme molecules are mixed with the immobilising support and bind to it due to a combination of hydrophobic interactions and ionic links.
Covalent bonding: Enzyme molecules are covalently bonded to a support, often by covalently linking enzymes together and to an insoluble material using a cross-linking agent.
Entrapment: Enzymes are trapped, for example, in a gel bead or network of cellulose fibres. Substrate and product molecules can pass through the material to the enzyme, but the enzyme cannot pass through to the solution.
Membrane separation: Enzymes are physcially separated from the substrate mixture by a partially permeable membrane. The substrate and product molecules can pass through the membrane, but the enzymes cannot.
Immobilised enzymes in large-scale production
Enzyme can be removed and used again.
Enzyme leaves a pure(r) product, so cheaper and easier downstream processing.
Enzyme is more stable, efficient and works bettern because it is less susceptible to pH and temperature changes or extremes.
Continuous culture and batch culture
- Growth rate is slower because nutrient level declines with time
- Easy to set up an maintain
- If contamination occurs, only one batch is lost
- Less efficient as fermenter is not in operation all of the time
- Very useful for processes involving the production of secondary metabolites
- Growth rate is higher as nutrients are continuously added to the fermentation tank
- Set up is more difficult, maintenance is required, growing conditions can be difficult to achieve
- If contamination occurs, huge volumes of product may be lost
- More efficient, fermenter operates continuously
- Very useful for processes involving the production of primary metabolites
Primary metabolites are substances that are produced by an organism are part of its normal growth. The production of primary metabolites matches the growth in population of the organsim.
Secondary metabolites are substances that are produced by an organism that are not part of its normal growth. The production of secondary metabolites usually begins after the main growth period of the organism and so does not match the growth in population of the organism.
The growing conditions can be manipulated and controlled in order to ensure that the microorganism is growing in its optimum conditions, and so the yield can be maximised.
- Temperature: Too hot and enzymes will be denatured, too cold and growth will be slowed
- Type and addition of nutrient: This depends on whether the product is a primary or a secondary metabolite
- Oxygen concentration: Most organisms are grown under aerobic conditions so there must be a sufficient supply of oxygen for respiration to prevent the unwanted products of anaerobic respiration and a reduction in growth rate
- pH: Changes in pH can reduce the activity of enzymes and therefore reduce growth rates
- Salt concentration: Affects osmosis by changing the water potential
- Waste gases (carbon dioxide): Must be removed to reduce pressure and prevents explosion of fermenter
- Speed of stirrer: Controlled to ensure even mixing and an even temperature
Importance of asepsis
Asepsis is the absence of unwanted microorganisms which could:
- Compete with the culture microorganisms for nutrients and space
- Reduce the yield of useful products from the culture microorganisms
- Cause spoilage of the product
- Produce toxic chemicals
- Destroy the culture microorganisms and their products
Pasteurisation kills harmful microbes and denatures enzymes