Growth Curves and Cell Division
How do bacteria divide?
By binary fission.
What triggers the start of spore formation?
Starvation.
In what types of environments would you expect to find biofilms?
Where it is wet or the interface of wet and dry.
Examples include: plaque on teeth, implanted medical devices (e.g. catheters), water pipes, rocks in a stream, shower curtains, lung tissue, colon, plant roots, mat on top of hot springs in Yellowstone, etc.
What does it mean when bacteria are in pure culture?
When a single species is grown in the lab.
In which phase of the growth curves are cells preparing for growth?
Lag phase.
Which of the following is an example of endospore-forming bacteria?
a. E. coli
b. Mycoplasma pneumoniae
c. Helicobacter pylori
d. Bacillus anthracis
d. Bacillus anthracis
What material are biofilms composed of?
Material similar to a capsule is used to create a loose protective layer (Exopolysaccharides (EPS)) as well as other sugars and proteins.
Plaque is an example of what kind of growth?
A biofilm.
In what phase do cells stop growing and shut down their growth machinery while turning on stress responses to help retain viability?
Stationary phase.
Name two things that endospores are resistant to.
Desiccation (drying out - spores can be viable for around 100 years!), chemicals, radiation, and temperature.
Streptococcus mutans is a bacterial species that initiates biofilms on teeth. Once the biofilm has formed, the cells close to the teeth (where there is less oxygen) ferment sugars (sucrose) and produce acid. What medical problem does this lead to?
The acid damages the enamel on the teeth, causing cavities.
What is E. coli's doubling time?
~20 minutes.
Name two environmental factors that can affect the rate of growth of microorganisms.
Temperature, pH, pressure, how much oxygen is available, etc.
Some cells can be identified under the microscope due to the location of the endospore and whether or not the cell bulges around the endospore. If a spore is located toward the end of the mother cell and creates a bulge in the cell, what species of bacteria are we observing?
Clostridium botulinum.
Describe the process of biofilm formation.
Swim to find a location, attach to a surface, signal to other cells to attach, alter gene expressions (stop making flagella, start making EPS), EPS (exopolysaccharide) production, certain cells on the surface leave and swim away to start a new biofilm (dispersal).
Dense communities face lots of competition and must grow quickly when food is available. Name two areas where you would expect to see dense communities of microorganisms.
Human gut, soil, etc.
What is our body trying to do when we get a fever from an infection?
It's trying to increase the body's temperature in order to trigger a number of physiological responses. Of those responses, the one our body is trying to encourage is to slow the microorganisms growth by creating an unfavorable environment (temperature wise) for them to grow in.
Describe the process of endospore formation.
After the cell becomes starved, it divides asymmetrically while staying together. The larger cell (the mother cell) engulfs the smaller cell (the forespore). This forms extra layers of cell wall and cortex around the forespore. Much of the water is then removed from the spore and the DNA is circularized before the mother cell is lysed, releasing the spore.
After several weeks of taking microbiology, you find that you are fascinated by microbes! Unfortunately for your roommate, this means you have taken an interest in the plaque growing on their teeth.
After having your roommate use mouthwash, you inspect their teeth and notice that the plaque microbes were not effectively killed.
You decide that the best thing to do is prevent the plaque from forming in the first place, so you experiment with different types of inhibitors. Your very agreeable roommate agrees to try one chemical that inhibits flagella and another chemical that inhibits pili. Which of these two is likely to prevent plaque from forming? Explain your answer.
The chemical that inhibits pili will be more likely to prevent plaque from forming because, in order to for the plaque to form, the bacteria need to attach themselves to the surface of the teeth. Flagella are used for movement of the cell, and pili are used for attachment. Therefore, by inhibiting the cell's ability to attach to surfaces through the inhibition of pili, the plaque should not be able to form.
Following the bioterrorist anthrax attacks in the fall of 2001, a news commentator suggested that people steam their mail for 30 seconds before opening. Why doesn't this work?
Bacillus anthracis, the anthrax bacteria, is an endospore forming bacteria. Endospores are resistant to changes in temperature, and will survive even after being steamed.