2.6) Environmental Control of Metabolism

Question 1

• What are the 3 classes of micro-organisms?

Answer 1

1. Archaea
2. Bacteria
3. (Some species of) eukaryotes

Question 2

• What are the important uses of micro-organisms?

Answer 2

• Micro-organisms use a wide variety of substrates for metabolism and produce a range of products from their metabolic pathways.
• Micro-organisms are also used because of their adaptability, ease of cultivation and speed of growth.

Question 3

• How can microbial cultures be grown?

Answer 3

• They can be grown usng an inoculum of microbial cells on an agar medium.
• Or in a broth with suitable nutrients.

Question 4

• What are the requirements for growth media?

Answer 4

• Growth media requires raw materials for biosynthesis and an energy source
  ➞ either derived from chemical substrates or from light in photosynthetic micro-organisms.

Question 5

• What are the most optimum culture conditions and what are their benefits?

Answer 5

1. Sterility 🧼 (prevents contamination of culutre)
2. Temperature control 🌡️ (optimum enzyme conditions)
3. Oxygen levels 🫧 (optimum respiration conditions)
4. pH 🧪 (optimum enzyme conditions)

➞ Sterile conditions in fermenters reduce competition with undesired micro-organisms for nutrients and reduce risk of spoilage of the product

Question 6

• Describe the parts of fermenters and their functions?

Answer 6

1. NUTRIENT SUPPLY:
   ➞ (food source of microbes - glucose)
2. STERILE AIR SUPPLY:
   ➞ (oxygen source for microbes - respiration conditions)
3. TEMPERATURE & pH MONITOR:
   ➞ (maintains suitable temperature and pH - optimum enzyme conditions)
4. STIRRER:
   ➞ (mixes yeast with glucose - maintains a constant temperature)
5. COOLING WATER:
   ➞ (maintains suitable temperature)

Question 7

• Describe the LAG PHASE of the growth of microbes.

Answer 7

• The lag phase is where enzymes are induced to metabolise substrates
• There is little/no change in number of microbes, but their metabolic activity is high and adjust to the specific conditions of the growth media.

Question 8

• Describe the LOG (EXPONENTIAL) PHASE of the growth of microbes.

Answer 8

• The log (exponential) phase contains the most rapid growth of micro-organisms due to plentiful nutrients.
• The microbes multiply at a constant rate - as long as there is a constant supply of nutrients and appropriate environmental conditions (temperature, pH, oxygen levels)

Question 9

• Describe the STATIONARY PHASE of the growth of microbes.

Answer 9

• The stationary phase occurs due to the nutrients in the culture media becoming depleted and the productions of toxic metabolites.
• Secondary metabolities are also produced - such as antibiotics. In the wild, these metabolites confer an ecological advantage by allowing the micro-organisms which produce them to outcompete with other micro-organisms.
• During this phase, the number of bacteria being produced is the same as the number dying so there is no overall growth.

Question 10

• Describe the DEATH PHASE of the growth of microbes.

Answer 10

• The death phase occurs due to the toxic accumulation of metabolites or the lack of nutrients in the culture.

Question 11

• What are the differences between a VIABLE cell count and a TOTAL cell count?

Answer 11

• When carrying out a:
  ➞ viable cell count (only living micro-organisms will be included) whereas when carrying out a:
  ➞ total cell count (both viable and dead cells are included)
• Only viable cell counts will show a death phase where the cell numbers are decreasing.