Bacterial growth and cell division Flashcards
What is the difference between growth and generation time?
Growth - increase in number of cells
GT - time required for one cell to divide and form 2 cells
What are the four phases of bacterial growth?
1) lag phase
2) exponential phase
3) stationary phase
4) death phase
What is happening in the lag phase of bacterial growth?
The cells are adjusting to new conditions e.g. frozen to room temperature - they’re becoming non - dormant. they’re synthesising the required metabolic enzymes required for growth.
What is happening in the exponential phase of bacterial growth?
Optimal growth, the rate of growth and the number of bacterial cells increases rapidly.
What is happening in the stationary phase of bacterial growth?
growth is limited due to nutrient depletion and the accumulation of toxic metabolites. the rate of cell production is level with rate of cell death.
What is happening in the death phase of bacterial growth?
Gradual loss of viability (working effectively or surviving successfully), toxic metabolites outweigh bacterial cells.
What are methods to measure bacterial growth?
- planting methods
- turbidity methods
- direct counting methods
- flow cytometry and FACS
What are planting methods?
This shows us all viable (living) cells and relies on watching bacterial growth. Bacteria is grown in a culture, after 4 hours we take a 1ml sample from a 10ml culture and serial dilute it, then lay the sample on a petri dish with nutrients and optimum conditions. We wait for the colonies to form. 1 colony = 1 cell. Then times it b the dilution factor.
What are turbidity methods?
This measures light scattering by cells - simple and convenient. However, it does measure all cells including dead cells. The more cells -> less light coming through.
What is direct counting method?
It is a microscopic count of a known volume of culture and can accommodate for clumping and chaining. It includes live and dead - unless a staining method is used.
To do it - a microscopic slide with a grid copied over it, the sample is placed over the grid, and this helps us count.
What is flow cytometry and FACS?
Particles in a microfluidic flow are measures, fluorescence is measured at multiple wavelengths. FACS (fluorescence activated cell sorting), cells can be stored. It uses a laser instead of light. the bacterial particles are forced through a narrow tube so they go through single file and uniform, they travel pass the laser causing the laser to ‘flicker’ and therefore they can be counted. It can also determine the cell size, allowing separation to take place.
Summary of the division cycle:
1) cell grows and structures duplicate
2) daughter chromosomes segregate to opposite poles of cell
3) a septum forms in the middle of the cell, and new cell poles are synthesized
Summary of bacterial DNA replication:
Replisome = DNA replication machinery.
Bacterial chromosomes are circular, replication occurs bidirectionally (opposite directions) starting from a singular origin of replication (oriC) to the terminus (terC). The double helix is unzipped forming the replication fork, replisome moves from 5’ to 3’, synthesising 2 new DNA strands. It takes 40 mins for the full cycle and termination is followed immediately by re-initiation - 1000bp replicated per second.
E.coli can divide every 20 mins, this is because as the replisomes are half way through, another set attaches to the original template and double replicate.
3 examples of bacterial modification:
Cyanobacteria (anabaena) - make differentiated heterocyst’s. they don’t divide and focus on getting nitrogen for the whole chain of bacteria.
Bdellovibro grow inside other bacteria, using the other cells resources and energy.
Myxococcus - eats other bacteria and makes complex fruiting bodies that wait to create myxospores which will float elsewhere to make a new colony.
