Another Plaque Morphology Question
by Deborah Jacobs-Sera
For clarification, this picture contains two plates of Mycobacteriophage Myrna that were set up identically except for the fact that the plate on the left was incubated at 37 C and the plate on the right was incubated at 30 C.
Questions:
1. Describe your observations.
2. Pose a question for others to answer or to address something you would like to know. Identify what kind of question you are asking.
3. Pose a testable question about this. Describe an experimental objective (plan) to begin answering your question.
So I guess I'll be the first to comment. My best guess it that Myrna infects and lyses the cells slower than they are able to reproduce at 37 C so the plaques show up as turbid clearings because the cells are growing to quickly for the phage to keep up. However, when the cells at grown at 30 C, they divide slower and Myrna can keep up with their growth and infects and lyses them more completely. Is there a way to test this other than growing plates at several temps between 30 and 37 and seeing how they turn out?
It appears that the phage infects better at 30 than at 37 degrees. Although, the plaques on the 30 plate appear to go from completely cleared to no plaques at all, whereas those on the 37 plate appear more normal, being reduced by a factor of 10. I agree with Victoria that this involves the reproduction rates of Myrna and the smeg cells. My question is, do other phages infect better at lower temps? If not, could myrna be a phage that infects organisms other than humans?
Kaitlin - does myrna infect humans? what is the the factor of 10 demonstrated on the plate. Are there more plaques on the plate grown at 30 C or are the same number of plaques just bigger? Victoria - what does keep up mean? What will plates at several temps between 30 and 37 not exactly tell you? Is there a better experiment? In general, is there a name given to how many phage are produced per infection? What is that? Why is that relevant here? What is an experiment that can determine that? Describe the biology of that and apply it to what is going on on these plates. Do you expect most phages to do this (have bigger plaques) at 30C? why or why not? How does this effect the growing/purification of your phage?
Here's some questions/comments for all to consider: 1) Are the plaques on the 37 degree plate more turbid? Maybe they're just smaller. Or, are they both? 2) What if the phenotype we're seeing here has nothing to do with the phage/bacteria interaction? What else could it be? 3) The number of phage particles released per lytic infection is called "burst size." 4) Debbie's questions are really good (especially those referring to burst size) and they deserve some thought... as well as comments!
I saw that Myrna had a greater phage to bacteria infection rate in the 30C incubation, which caused the clearings to be clear. The 30C incubation caused clearings to more further diluted spots than the 37C did. The plaque morphology is different in both, why? 37C has a halo, 30C doesn't. Is it really like what Victoria said? "Because the cells are growing to quickly for the phage to keep up"?
Jessica, The photo is a the plating of titers of Myrna. Unless you enlarged the photo well, it is almost impossible to see individual plaques on the 37C plate. There are no haloes present on either plates. You called something 'phage to bacteria infection rate' - that has a more formal name - what is it? Victoria's response is quite plausible.
I think temperature an issue here but different from what I would expect. I would have expected more growth with the higher temperature environment. The case could be that for this phage the proteins efficiency begins to decrese at the higher temperature. When the protein activity is slow normal processes such as grow slow down as well.
Is it Possible that there is some thermodynamic explanation for the difference in plaque morphology? Perhaps the phage is able to better attach to the bacteria at 30 degrees as opposed to 37?
Patrick, What thermodynamic principle do you want to apply? It is plausible that the temperature affects 'attachment' - is that the right word? What other things can temperature affect?
Ogechi, Where is our bacteria - smeg- most likely found (its 'natural' habitat)? What temperature exists there? What is 'growing' in the sample?
The plaques on the left look older than the plaques on the right. Also the phages on both plates appear to be different one cloudy vs. clear. A question I have is why does the second and third phages on the left have a circle in the middle of the plaque?
Jamil, So both plates were set up at the same time. So what does older look like? The cloudy vs. clear is a great question. Why? What are some possible explanations? You last statement carries the same implications as Jessica's comments. Are you looking at phages? What does second and third phage mean? Are you looking at plaques on these plates? If so, where are they? Or more importantly, Where are they not!!!?
Dear Phagehunters, You have all commented on what you see, but except for Victoria' first comment, I don't see testable hypotheses. Please respond with one and how you would test for it!