Lecture 10: Bacteria genome replication and gene expression Flashcards
Name two instruments that can be used to grow anaerobic bacteria.
The anaerobic jar and the anaerobic chamber
What is the role of the catalyst chamber in the anaerobic jar?
It contains palladium pellets that catalyze the reaction of hydrogen and oxygen.
H2 + O2 –> 2 H2O
What is the role of indicator strips in the anaerobic jar?
They start blue but lose their colour as the oxygen concentration decreases. They are a visual indicator of O2 concentration.
What is the role of the gas generator envelope in the anaerobic jar?
It adds H2, which gets rid of the oxygen, and CO2, which promotes rapid growth of microorganisms.
When is an anaerobic jar not suitable for an experiment? What should be used instead?
If the bacteria are so sensitive to oxygen that they can’t survive the duration when the reaction is completed by the palladium pellets. Instead, we can use an anaerobic chamber.
Explain the difference between growing cells on solid vs liquid media.
In liquid cultures, the cells are all surrounded by the same environment via the liquid medium. On solid media, different cell positions in a colony will face different environmental conditions.
In a culture growing on a solid medium, cells at the center are […]
In the stationary or death phase because there is no food left inthe center
In a culture growing on a solid medium, cells at the edge are […]
Actively growing (exponential phase), because they are reaching into areas that still have a lot of nutrients.
In a culture growing on a solid medium, the cells at the surface experience […] conditions
Aerobic
In a culture growing on a solid medium, the cells under the surface experience […] conditions
More anaerobic
When comparing within bacterial cultures, it is best to use a […] medium because […]
Liquid, because the condition are more consistent for different cells.
Name two techniques to quantify the quantity of cells in a liquid culture and the difference in purpose between them.
Using a spectrophotometer or the cell count technique. The spectrophotometer will yield a mass estimation, while the cell count technique will yield an exact quantity.
Explain how a spectrophotometer can be used to obtain a microbial mass measurement.
Light is shined through the culture and the turbidity is measured. If there are few cells, there will be a lot of light (less turbidity), yielding a higher signal. If there are many cells, there will be less light (more turbidity), yielding a lower signal. Knowing the typical turbidity figures for the culture, you can determine roughly how many cells are in the culture.
Describe the main steps involved in the cell count technique.
Take 1 ml of your culture sample and put it into 9 mL of fresh broth (media) to yield a 1:10 dilution. Repeat this 4 more times to yield a 1:100,000 dilution. Take 1 mL of this and either spread it directly on agar or mix it with agar beforehand. The culture with either grow on the agar surface or in it. You can then count the colonies and count backwards with the dilution factor.
After doing the serial dilutions cell count technique, you count 225 colonies. Knowing that you diluted to 1:100,000 before plating, how many cells did you start with in your culture?
Since plating 1 mL counts as another tenfold dilution, the final dilution factor is 1:1,000,000. So 225 colonies x 1,000,000 = 225 million cells/ml.
What is the formula for total population number starting with a single cell? What is the problem with this method?
2n = cell population after nth generation
The problem is that in reality, we never start with a single cell in a culture.
