Bacterial Growth And Measuring It Flashcards
What is generation time
Time needed for 1 cell to double
Eg 20 mins = 2 cells formed
What is the word to describe growth of bacteria
Exponential - doubles at constant time
Name the 4 phases in the growth cycle
1- lag
2- exponential
3- stationary
4- death
Explain the lag phase
There is slow growth due to new conditions
New metabolites and enzymes synthesised for growth
Explain exponential phase
Rapid growth with abundant nutrients and enzymes available for growth
Explain the stationary phase
Nutrients start to depleat and build up of toxic products
The exponential growth is constant with death rate
What happens in the death phase
Death overtakes exponential growth
No more nutrients
Toxic byproducts produced by bacteria
Name the 4 ways to measure bacterial growth
1- plating method
2- turbidity/ optical density
3- direct counting
4- flow cytometry/ FACS
Explain the plating method
Bacteria in culture placed in serial dilution plates
This makes them easier to count
To find out the amount in original you do
Dilution factor x 10 x count = original
Which cells does the plating method count
ONLY VIABLE / LIVE cells
What is an advantage with the plating method
You can maintain conditions to match the pathogen you want to grow and avoid others growing
What is a disadvantage of plating methods
You can’t count clusters of cells making it inaccurate
How does the turbidity/ optical density method work
Light shines into a filter and slide with cells on it
If cells are present and they move then will move and diffract light
Scattered light DOESNT pass through photo cell
Higher absorbance on spectrophotometer if more bacteria present
Why is optical density method good
Not destructive to the bacteria and easy to measure
Why is turbidity inaccurate in measuring viable cells
They can count dead cells too and other particles which scatter light
Explain the direct counting method
Bacteria placed on a cover slip with a grid
Bacteria are counted on grid and x by volume
Which is the most direct way of counting growth
Direct counting method
What is an issue with direct counting
Counts all cells not just viable
It takes a long time
How does flow cytometry / facs work
Bacteria attached with fluorescence are passed into micro fluid flow
They can measure them via the fluorescence in the micro fluid
Why can flow cytometry be used to distinguish species of bacteria or dead from Alive
They can use stain which distinguishes different species eg antibodies with specific targets (immunofluorescence)
What is the downside to flow cytometry even if it sorts species
It needs equipment and expertise
Do all bacteria divide by binary fission?
No
Explain what happens first in cell division
Cell elongates and chromosomes replicate at the oric
Cell structures like cell wall and ribosomes double ready for division
What happens in stage 2 of division
Chromosomes / plasmids seperate to opposite poles of cell before division
What happens in stage 3 of division
A septum forms in the middle of the daughter cell to separate cell due to z ring restrictions
What happens on final stage of division
Daughter cell splits when z ring contracts and nee poles have formed
Each daughter has identical copy of chromosome
What is the replication machinery called which causes replication bidirectionally from oric
The replisome ie holoenzyme dna pol 3 complex
What is the site called which replication of Chromosome stops at
TerC
How does bacteria get over the fact replication takes longer than binary fission
Replication will start before the cell even starts cell elongation , it occurs in the previous division
New oric is established and replisome will bind there
What happens to the orics when poles are established in the cell to move chromosomes there
Orics shift at 1/4 and 3/4 of the cell from the halfway point
Each pole receives 1 copy
Dna A allows replication from oric, what blocks replication
Seq A
What is the z ring part of
The divisome - many proteins together to form new poles, wall and division
Name 2 proteins needed in the z ring / divisome complex
FTSZ - z ring
MreB - cell wall synthesis actin protein
What is cell pole position/ division site controlled by
Spatial cues
Which protein stops division at cell poles instead of middle
The min protein
Which protein/ system stops division in middle of chromosome nucleoid area
Nucleoid occlusion
Which zone does division occur in
Inhibition free zone in middle of cell
