Part 2a: Microbial Cell Factories

Question 1

Briefly describe binary fission

Answer 1

1) Increase in cell mass and ribosome number
2) Duplication and partitioning of bacterial chromosome
3) Cell wall and cell membrane synthesis
4) Septum formation and cell division

Question 2

How would we optimise cell growth?

Answer 2

1) Optimise bioreactor conditions
2) Genetically modify the strain so it is fast growing
3) Use effective media with sufficient nutrients

Question 3

What is direct weight measurement

Answer 3

Measurement of the dry/wet weight or volume of cells after centrifugation

Question 4

Indirect viable cell counts

Answer 4

Plate cell culture on agar surface and count the number of CFUs

Question 5

Turbidity measurements

Answer 5

Determines light scattered by a cell suspension. Optical density is directly related to cell mass

Question 6

Direct microscopic counts

Answer 6

Uses counting chambers to count cells under a microscope

Question 7

Direct chemical measurement of cell components

Answer 7

Direct measures component such as total protein/ DNA content

Question 8

Indirect measurement of cell activity

Answer 8

Measures CO2 production/O2 consumption/ ATP production

Question 9

Describe the lag phase

Answer 9

As microbes adjust to the environment there is no cell division, but the cells may increase in size

Question 10

Describe the exponential phase

Answer 10

Regular cell division occurs at a constant rate, causing exponential growth expressed as generation/doubling time

Question 11

Describe the stationary phase

Answer 11

Population growth is limited by exhaustion nutrient supply or space, or production of inhibitory metabolites.
Cell division = Cell death causing population growth to stagnate

Question 12

Describe the death phase

Answer 12

Viable cell population declines exponentially as cells die off

Question 13

What is batch culture

Answer 13

Growth of biomass characterised by the lack of input or output of materials after inoculation.

Question 14

Def: Primary metabolite

Answer 14

Formed during the exponential growth phase and essential for cell growth. (ethanol, lactic acid, citric acid)

Question 15

Def: Secondary metabolite

Answer 15

Formed at the stationary growth phase and not growth associated. (Antibiotics, biopolymers)

Question 16

Equation: Final cell number

Answer 16

N = N(o) x 2^n

Question 17

Equation: Rate of change of biomass

Answer 17

dX/dt = μ X

Question 18

Equation: Biomass

Answer 18

X = X(o) x 2^n

Question 19

Equation: ln biomass

Answer 19

ln X = ln X(o) + n ln 2
ln X = ln X(o) + μ t

Question 20

Equation: Doubling time

Answer 20

ln 2 = μ x t(d)
2 =e^(μt)

Question 21

Def: Specific growth rate, μ

Answer 21

The genetic and environmental influences that are specific to each organism

Question 22

Equation: Monod equation

Answer 22

μ = μ(max) x ([s]/Ks+[s])

Question 23

What is on the axis of a lineweaver-burke plot

Answer 23

1/μ on y-axis
1/[s] on x-axis

Question 24

What is on the axis of an eadie-hofstee plot

Answer 24

μ on the y-axis
μ/[s] on the x-axis

Question 25

Def: Cell yield

Answer 25

Unit amount of cell mass produced per unit of substrate consumed

Question 26

What is continuous culture

Answer 26

A continuous feed of influent solution (nutrients and substrate) and a continuous drain of effluent (cells, metabolites, waste) causing the fermenter to operate at the growth phase for extended periods of time.

Question 27

Equation: Rate of change of biomass in a chemostat

Answer 27

dX/dt = μX - DX

Question 28

Equation: Critical dilution rate

Answer 28

Dc = μ(max) x ([s]/Ks+[s])

Question 29

Def: Washout

Answer 29

Occurs when the dilution rate has passed Dc meaning cells are not reproducing quick enough. Population growth cannot keep up with the outflow of effluent, causing the cells to wash out of the bioreactor.