Part 2a: Microbial Cell Factories Flashcards
Briefly describe binary fission
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
How would we optimise cell growth?
1) Optimise bioreactor conditions
2) Genetically modify the strain so it is fast growing
3) Use effective media with sufficient nutrients
What is direct weight measurement
Measurement of the dry/wet weight or volume of cells after centrifugation
Indirect viable cell counts
Plate cell culture on agar surface and count the number of CFUs
Turbidity measurements
Determines light scattered by a cell suspension. Optical density is directly related to cell mass
Direct microscopic counts
Uses counting chambers to count cells under a microscope
Direct chemical measurement of cell components
Direct measures component such as total protein/ DNA content
Indirect measurement of cell activity
Measures CO2 production/O2 consumption/ ATP production
Describe the lag phase
As microbes adjust to the environment there is no cell division, but the cells may increase in size
Describe the exponential phase
Regular cell division occurs at a constant rate, causing exponential growth expressed as generation/doubling time
Describe the stationary phase
Population growth is limited by exhaustion nutrient supply or space, or production of inhibitory metabolites.
Cell division = Cell death causing population growth to stagnate
Describe the death phase
Viable cell population declines exponentially as cells die off
What is batch culture
Growth of biomass characterised by the lack of input or output of materials after inoculation.
Def: Primary metabolite
Formed during the exponential growth phase and essential for cell growth. (ethanol, lactic acid, citric acid)
Def: Secondary metabolite
Formed at the stationary growth phase and not growth associated. (Antibiotics, biopolymers)
Equation: Final cell number
N = N(o) x 2^n
Equation: Rate of change of biomass
dX/dt = μ X
Equation: Biomass
X = X(o) x 2^n
Equation: ln biomass
ln X = ln X(o) + n ln 2
ln X = ln X(o) + μ t
Equation: Doubling time
ln 2 = μ x t(d)
2 =e^(μt)
Def: Specific growth rate, μ
The genetic and environmental influences that are specific to each organism
Equation: Monod equation
μ = μ(max) x ([s]/Ks+[s])
What is on the axis of a lineweaver-burke plot
1/μ on y-axis
1/[s] on x-axis
What is on the axis of an eadie-hofstee plot
μ on the y-axis
μ/[s] on the x-axis
Def: Cell yield
Unit amount of cell mass produced per unit of substrate consumed
What is continuous culture
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.
Equation: Rate of change of biomass in a chemostat
dX/dt = μX - DX
Equation: Critical dilution rate
Dc = μ(max) x ([s]/Ks+[s])
Def: Washout
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.