Lec 1 - Batch Culture

Question 1

Describe the 4 methods of measuring microbial growth

Answer 1

• cell dry weight - slow because have to remove all of the nutrients taken up by the cell from the environment
• cell count - total cell count (haemocytometer), viable cell count (streak plate)
• optical density - change wavelength depending on type of cell & its pigments
• specific cell components - measure the increase in a specific cell component eg protein - has to be directly related to growth rate

Question 2

What is a batch culture?

Answer 2

Involves the growth of microorganisms in a fixed volume - divide by binary fission to generate 2 genetically identical daughter cells (can also bud to create 4/8 daughter cells)

Question 3

Why is unrestrained growth of microorganisms in batch culture not possible?

Answer 3

• nutrient limitations
• autoinhibition - production of products that stop the growth of own bacteria. eg production of acetate reduces the pH medium so growth cant be supported

(from this we get a characteristic growth curve)

Question 4

Describe the 4 phases of a typical growth curve.

Answer 4

• lag phase - generation of enzymes etc (especially when entering minimal media) for metabolism
• log phase - exponential growth - all cells of the population have the same division time here
• stationary phase - numbers of cells do not change eg cells die and cells grow when dead cells release nutrients to media (no overall change in no.)
• death phase - exponential decay - more cells die than grow

Question 5

Give the equation that relates final cell number (Nt) , initial cell no. (No) and the number of generations in exponential phase (n)

Answer 5

Nt = No * 2^(n)

Question 6

What is the generation time (g) equivalent to? What are the units of g?

Answer 6

g equivalent to the doubling time (td)

units = hours

Question 7

What is the equation that links g and u (mu), what is u?

Answer 7

g = 0.693/u 
u = specific growth rate of culture (h)

Question 8

How do you work out the mean generation time? (give the equation)

Answer 8

g = t/n 
t = time in exponential phase 
n = no. cells

Question 9

What are the limitations of a batch culture?

Answer 9

whilst we can measure growth rate kinetics..

• not representable of what happens in the environment (growth curve is a laboratory artefact) - eg microbes have to scavenge for nutrients - therefore no growth curve
• properties of cells vary continuously throughout the growth cycle (even in exponential phase - nutrients @ start and end of exponential differ therefore a range of metabolic pathways/enzymes)

Question 10

How can the limitations of a batch culture be overcome?

Answer 10

using a continuous culture