CMB1003/L03 Bacterial Growth Flashcards
Give 3 ways in which recombinant E. coli can be used.
Express proteins for research
Medical
Commercial purposes
What can cause bacterial growth to plateau? (2)
Limiting nutrients
Accumulation of toxins
What is the ‘lag phase’ of bacterial growth?
Cells adjust to new conditions, synthesis required metabolic enzymes and metabolites
What is the ‘exponential phase’ of bacterial growth?
Optimal growth with regular doubling in cell numbers
What is the ‘stationary phase’ of bacterial growth?
Growth limited by nutrient depletion or accumulation of toxic metabolites
Rate of new cell production balanced with rate of cell death so no overall growth in cell culture
What is the ‘death phase’ of bacterial growth?
Complex gradual loss of viability but with some cell turnover
Name 4 methods of measuring bacterial growth.
Plating methods
Turbidity
Direct microscopic counting
Flow cytometry
What is the difference between total and viable cell count?
Total cell count includes dead cells
Viable cell count is living cells
Describe plating methods. (3)
Culture plated onto solid nutrient medium after serial dilution
Each colony assumed to represent progeny of single viable cell
CFU extrapolated to give cell numbers in original culture
Give 2 advantages to plating methods.
Highly sensitive
Growth conditions can be customised so only species of interest grow
Only measure viable cells
Give 2 disadvantages to plating methods.
Underestimates for cells in chains or clusters
Number of colonies dependent on growth conditions
Describe turbidity methods.
Measures light scattering by cells using a spectrophotometer and a photocell filter
Give 2 advantages to turbidity methods.
Simple, convenient
Non-destructive and continuous
Give 2 disadvantages to turbidity methods.
Low sensitivity (>10^6 per ml lower limit)
Measures total cell count
Culture turbidity has to be with a range to be accurate
Describe direct counting methods.
Count microscopic count of known volume of culture and multiply to amount of volume needed
Give an advantage to direct counting methods.
Can accommodate clumping and chaining
Give 2 disadvantages to direct counting methods.
Doesn’t discriminate live/dead cells
Laborious (but can be automated)
Describe flow cytometry and FACS.
Measure particles in microfluidic flow
Give 2 advantages to flow cytometry and FACS.
Highly automated
Can measure fluorescence at multiple wavelengths
Cell sorting possible
Give a disadvantage to flow cytometry and FACS.
Requires the correct (expensive) equipment
What does FACS stand for?
Fluroescence Activated Cell Sorting
How do most bacteria grow?
Binary fission
Elongation and splitting down the middle
Describe binary fission. (6)
Cell grows
Cell structures duplicated
Chromosome replicated
Daughter chromosomes segregate to opposite poles
Septum forms mid cell and Z-ring forms
Cell division mid cell
What is the start and end point of replication called in plasmids?
OriC and terC
How can replication of bacterial chromosomes be described?
Bidirectional from a single origin
Describe simply bacterial replication.
Replisomes bind to oriC
Bidirectional replication of DNA
Chromosomes segregate and cells divide
How do bacterial cells such as B. subtilis and E. coli overcome the replication conundrum?
Initiating replication in the previous cell cycle
What is the Z ring made from?
Z protein and agrin
How do cyanobacteria such as Anabaena fix nitrogen and preserve nutrients?
Making differentiated heterocysts (fixing) and akinetes (preserving nutrients)
How do Bdellovibrio survive?
Inside other bacteria
How do Myxococcus survive?
Eats other bacteria
Makes complex fruiting bodies
