between quorum sensing and light emitted? Is the amount of light always directly
ID: 56340 • Letter: B
Question
between quorum sensing and light emitted? Is the amount of light always directly proportional to the concentration of bacteria? Why or why not?
Investigate the relationship between Vibrio Fischeri and it’s host, the bobtail squid. Describe the relationship. How does the growth of Vibrio Fischeri in the light organ benefit the bobtail squid? At what times does this interaction occur?
Write a hypothesis or multiple hypotheses for your experiment. Be creative and explore literature on Vibrio Fischeri and its nutrient requirements of growth!
What is the lux operon? How does this apply to quorum sensing? What else is quorum sensing used for? What aspects of the lux operon does Vibrio Fischeri illustrate?
What does it mean to have a countable plate? In roughly what dilution would you expect to find a countable plate?
You are given a sample of unknown Bacilus subtilus and need to find out the cell concentration of the original sample. Describe your experimental design. Draw out a dilution map that illustrates your experimental design. Be sure to label the amount of autoclaved water going in to each vial, volume of bacteria sample transferred, the plating volume and determine the resulting concentration that it will produce after being plated.
What is the original cell density of a sample that produced 117 colonies on a plate that was inoculated with a 0.1mL sample from a tube containing a 10-5 dilution?
What is the original cell density of a sample that produced 32 colonies on a 10-7 dilution plate?
If you only have three agar plates left that are suitable to grow V. fischeri and your original cell sample was 2.6x105, which three dilution vials would you inoculate in order to guarantee yourself a countable plate? Assume the inoculation volume used on each plate was 0.1mL and that each vial had a dilution factor of 10.
Explanation / Answer
1)
Yes, the amount of light always directly proportional to the concentration of bacteria. This is because each bacterium emits certain amount of light against a chemical signal.
2)
Quorum sensing is a type of cell to cell communication in the bacterial cells, which occur by exchanging small molecules or signaling molecules such as N-acylhomoserine lactone (AHL). The signaling molecules are necessary for the coordination of gene expression. Quorum sensing in the bioluminescent bacterium, Vibrio fischeri produces light only if the bacterial cells are at high density.
Therefore, it should be noted that in the bobtail squid the bioluminescence property was exhibited only when the organism (Vibrio Fischeri) number within the squid was found to exceed a particular quantity.
4)
The bacterium, Vibrio fischeri and other gram-negative bacteria uses an N-acylhomoserine lactone (AHL) signal, which for required for the synthesis of small molecules. These molecules can be catalyzed by an enzyme called AHL synthase, which is the product of the luxI gene. The luxI gene is responsible for positive autoregulation.
In the process of transcription, the transcription luxI gene increases by the accumulation of AHL in the cells. This is mediated by the transcriptional activator LuxR, which is active at the time of binding with the AHL. The luxI is activated only at the base level without AHL-activated LuxR.
The AHL diffuses out of the cell and accumulates in the environment. The concentration of AHL increases both outside and inside the cell. This is due to the density of the cell increases and the concentration gradient reversed.
The AHL return back to the cell and bind to activate LuxR, which is responsible for high level transcription of luxI gene. The gene products are required for bioluminescence. Quorum sensing is also called autoinduction and the AHL signal called autoinducer (AI).
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