Tutorial 5 Rios

Question 1

What are the two fermentation processes based on the oxygen consumption?

Answer 1

• aerobic

- anaerobic

Question 2

What is the oxygen requirement for anaerobic fermentation?

Answer 2

The provision for aeration is not needed. The air in the headspace is replaced by N2, H2, CO2

Question 3

What is the oxygen requirement for aerobic fermentation?

Answer 3

Provision for adequate oxygen access using a sparger. These fermenter may have a mechanism for stirring and mixing of medium and cells.

Question 4

What are the two fermentation processes based on the physical state of the media?

Answer 4

• The submerged culture method

- Solid State fermentation

Question 5

What is the submerged culture method?

Answer 5

The organism is grown in a liquid medium which could be vigorously agitated and aerated if aerobic mode is used (or not if anaerobic mode is used) in large tanks called fermenters

Question 6

Give examples of substances grown by the submerged culture method

Answer 6

antibiotics, proteins, insulin

Question 7

What is solid state fermentation?

Answer 7

Microbial growth and product formation occur at the surface of solid substrates

Question 8

Give examples of substances grown by solid state fermentation

Answer 8

Mushroom cultivation, mould ripened cheese

Question 9

What are the four growth phases of cell cultures?

Answer 9

1. Lag phase
2. Exponential/ Log growth phase
3. Stationary phase
4. Death phase

Question 10

Describe the lag phase

Answer 10

Growth does not usually begin immediately after inoculation. Only a small number of cells are reproducing.

Question 11

Why do only a small number of cells reproduce in the lag phase?

Answer 11

The necessary genes are slowly getting activated, enzymes are synthesised for the medium they are in, cells are growing in size before they are reproducing, cells are adapting to the new medium conditions

Question 12

Describe the exponential/ log growth phase

Answer 12

The bacterial cell numbers are doubling within a set time period. The growth rate is at a maximum. Growth is exponential - numbers double in a constant period.

Question 13

Are there any limiting factors in the exponential growth phase?

Answer 13

No. There is plenty of oxygen and nutrients. And the waste products do not poison the cells

Question 14

Describe the stationary phase

Answer 14

The number of new cells balances the number of cells dying. There is no net increase or decrease in cell number. The rate of production of new cells is slow. number of new cells = number of cells dying.

Question 15

Why does exponential growth not occur indefinitely?

Answer 15

Essential nutrients are used and there is an accumulation of waste.

Question 16

What are the limiting factors of the stationary phase?

Answer 16

The concentration of nutrients/ oxygen is low and there is competition for them. There is an extreme pH and the metabolism or the toxins are killing the cells.

Question 17

Describe the death phase

Answer 17

Death of cells exceeds the production of new cells. Waste products/ toxins are rapidly killing cells. The cells are overcrowded and starved of oxygen and nutrients. Spore forming organisms form spores as part of their survival mechanism.

Question 18

What are the four potentially limiting steps in the transfer of oxygen from the bubble to the biomass?

Answer 18

1. Transport across the boundary layer of the bubble
2. Transport across medium if high viscosity or poor mixing
3. Transport across boundary layer around biomass
4. Transport through biomass

Question 19

What is the oxygen transfer rate?

Answer 19

OTR = k(L)*a*(Cs-Cl)
where k(l) is the local liquid phase mass transfer coefficient
a is the interfacial area
Cs is the oxygen concentration in the liquid at the gas-liquid interface in infinite time
Cl is the local dissolved oxygen concentration

Question 20

What is the mass balance for the oxygen concentration?

Answer 20

V dC/dt = FinCin - FoutCout + Vk(l)a*(Cs - Cl) - V.OUR
where
OUR is the oxygen uptake rate

Question 21

What is the equation for the general mass balance?

Answer 21

input - output + generation - consumption = accumulation

Question 22

How do you find the growth rate graphically?

Answer 22

Plot a graph of ln(X) against time or ln (OD600) against time because the optical density is related to the number of cells present.
mu = (ln(Xf) - ln(Xi))/(tf - ti)

Question 23

How to find x for the equation F= muvX/ (Y* [Gly])?

Answer 23

Plot a graph of OD600 vs. gCDW/L and then this will give a linear relation between the two. Knowing the initial , can find 1 OD600 = ? gCDW/L. Then find x at time t by OD(final) * initial Dry weight/ 1 OD (initial).

Question 24

How does the length of the lag phase affect the time for the growth phase in a given time period?

Answer 24

If the lag phase increases then there will be less time for the growth phase in a given time period.

Question 25

What is the equation for the number of cells present in a culture?

Answer 25

X = 2^n * X0
where X0 is the initial number of cells
n is the number of generations