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28 Sep 2018

1.) If we started with a culture containing 2,000 cells in a total of 3mL of broth and have exponential growth immediately at a rate of 30 minutes per generation, what is the theoretical population after 3 hours? (show your work)

My answer: 128,000 cells

2.) What would be the concentration of cells in the culture from question #1 at 3 hours? (show your work)

***I think I answered #1 correctly, but I am lost on how to answer #2. Please help!

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Related questions

These are questions from my microbiology lab. PLEASE show yourwork so I can understand this better! Thank you.

1.) If we started with a culture containing 4,000 CFU in a totalof 3 mL of broth and have exponential growth immediately at a rateof 30 minutes per generation, what is the theoretical populationafter 4 hours? (show your work)

2.) Give two reasons why an observed/experimental concentration at4 hours is always less than the theoretical concentration (fromquestion #1). One reason should pertain to the beginning of growthand the other toward the end of growth.

In your research lab, one of the students has been propagating her culture of Rhidospirilla huskyii for 5 months (150 day) because it is easier to do experiments that way. you told her this is a bad idea because microbes evolve fast. Based on what you know about the rate of evolution, explain why you think her culture likely evolved already.

Useful information:

1. she transfers her culture daily, making 100-fold dilution into new media each time (i.e. population increases 100-fold each day)

2. How many generations (divisions) is that per day? 100=2^n

3. the population size transferred is: 1*10^7 cells. (i.e. this is the population that gets to reproduce)

Note: Your answer must be organized and well-written and logical. You will have access to a calculator, so I expect you to show the equations you use and also solve them.Most importantly, I expect a very thorough and convincing argument that the culture described in the question has evolved and may be different than it was before it was propagated. Your answer should touch on everything we studied that affects the rate of evolution, except mutation rate (you can choose a mutation rate for the purposes of the question). Pretend you are arguing with a very skeptical student who is under the impression that evolution takes a long time.

Please answer questions at the end.

In this lab, you will add different volumes of “cell-free supernatant” (CFS) to fresh cultures of V. harveyi and observe bioluminescence. The CFS is prepared by culturing V. harveyi in liquid medium overnight, then separating the cells from the supernatant by centrifugation.

MATERIALS • overnight culture of V. harveyi in AB medium • fresh AB medium • 1 microcentrifuge tube • 3 glass culture tubes

PROCEDURE

1. This experiment will be performed with your lab group. Label the microcentrifuge tube and 3 glass cultures tubes with your group number. Also, label the 3 glass culture tubes as follows: “Media only,” “Cells+fresh media,” and “Cells+CFS.”

2. Using aseptic technique, pipet different volumes of fresh AB medium into the glass tubes as follows: 1 mL in the “Media only” tube, 800 ul in the “Cells+fresh media” tube, and 500 ul in the “Cells+CFS” tube.

3. Pipet 500 ul of the overnight culture into a microcentrifuge tube and centrifuge at maximum speed (>13,000 x g) for 5 min to pellet the cells.

4. After centrifugation is complete, transfer 300 ul of the cell free supernatant (CFS) from the microfuge tube to the glass tube labeled “Cells+CFS”. Be careful to avoid the cell pellet.

5. Remove the remaining supernatant from the microfuge tube using a micropipette and discard as culture waste.

6. Add 500 ul of fresh AB medium to the cell pellet in the microfuge tube and pipet up and down to resuspend until no clumps are visible.

7. Add 200 ul of the cell suspension to the “Cells+fresh media” tube and 200 ul of the cell suspension to the “Cells+CFS” tube. Note the time.

8. Place the 2 glass tubes containing cells in the 30 degree incubator/shaker.

9. After 1 hour and 2 hours, observe your tubes next to the “Media only” tube in a dark room. You will need to let your eyes adjust for at least 30 seconds (count to 30 slowly in the dark) before you can evaluate whether the cultures are luminescent or not. Also, make sure you try swirling the tubes in the darkroom and observe the tubes for a minute after you have stopped swirling. After the observation at the 1 hour time point, put your tubes back in the incubator shaker until the 2 hour time point.

10. Note your observations. At the end of the lab, place your tubes in the tube waste.

Questions

1. What were the expected results? Explain the rationale of the experiment. If you didn’t obtain the expected results, hypothesize why not and describe how the experiment could be improved.

2. What are differences between luminescence and fluorescence?

3. Why do V. harveyi cultures glow more brightly when swirled vigorously? Be specific.

4. Imagine you have a mutant V. harveyi strain that can’t synthesize autoinducer and another mutant V. harveyi strain that makes a defective luciferase. If you streaked both strains near (but not touching) each other on the same plate, would you expect to see light produced? If so, by which strain, where, and why?

5. You have two identical tubes of wild-type V. harveyi (with the same cell concentration in each tube) in fresh media. To one tube, you add CFS from a light-producing V. fischeri culture, and to the other tube you add an equal volume of fresh media. If both tubes of V. harveyi have the same light production, what can you conclude? Explain.

6. Many biomedical research labs study quorum sensing in V. fischeri or V. harveyi. How is studying light production in marine bacteria relevant to human health? List at least 3 different examples.

7. Why do you think it is important for bacteria to be able to control the expression of some genes based on the number of individuals present?

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