Bacterial Growth

Question 1

What is binary fission ?

Answer 1

An asexual process of cell division in which a single cell divides into two separate and identical daughter cells.

Question 2

Process of binary fission

Answer 2

1. The cell elongates and DNA is duplicated
2. Cell and plasma membrane begin to divide = septum formation
3. Septum completes
4. Daughter cells separate

Question 3

Ways bacteria can grow

Answer 3

1. Sessile:
   - Colonies - 24hrs = 20-30 divisions of a single cell
   - Biofilms - thinly spread over an inert surface
2. Planktonic:
   - Turbid suspension - 24 hours = 10^7 - 10^9 cells per mL
   (Floating in liquid)

Question 4

Plane of division and cell arrangement

Answer 4

Bacteria would form diplococci to begin with then a chain = streptococci. Further = tetracocci — sarcinae — staphylococci

Question 5

What is generation time ?

Answer 5

The time required for a cell to divide and the population to double.

Question 6

Stages of growth curve

Answer 6

• Lag
• Log
• Stationary
• Death

Question 7

Lag phase

Answer 7

1. No increase in cells
2. Intense metabolic activity

Question 8

Log / exponential phase

Answer 8

1. Maximum possible growth rate for the environment
2. Measure the rate of growth in this phase
3. Measure doubling time at this stage

Question 9

Stationary phase

Answer 9

1. The balance between cell division and death
2. Metabolically active
3. Exhaustion of nutrients
4. Accumulation of waste
5. Harmful changes in pH
6. Oxygen depletion
7. Spore formation

Question 10

Death phase

Answer 10

Cell lysis occurs = bacteria pops.

Question 11

Advantages of continuous culture

Answer 11

• Continuous log phase
• No nutrient limitation
• Closed system = easy to control growth conditions e.g, pH, temp, O2 conc etc

Question 12

Nutrient requirements of fungi

Answer 12

• Use a wide range of organic substrates
• Important in breakdown of dead plant matter

Question 13

Nutrient requirements of Protozoa

Answer 13

• Ingest other microorganisms/ organic particles by phagocytosis
• Important in aquatic environments and soil

Question 14

Secondary metabolites

Answer 14

Low molecular mass products that are not essential for growth of the producing cultures but very important for human health.

E.g, antibiotics such as penicillin which is produced from penicillium (mould)

Question 15

Calculating generation time from a growth

Answer 15

Generation time = t log 2/ logb - logB

• t = time in hrs/mins between B and b
• B = number of bacterial CFUs at time 1 (measured in log phase )
• b = number of bacterial cells at time 2 (measured later in log phase)

Units = minutes