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Different Plaque Sizes for One Phage

| posted 03 Dec, 2021 13:31
I have recently isolated a bacteriophage for E. coli from soil. The phage has been purified through 6 rounds of serial dilution and has given consistent plaques after the second purification. That is why my professor and I consider it as isolated. The only issue is that it always displays two distinct plaques: a large, clear one of about 0.5 cm and a smaller clear one of about 0.2 cm. There are no sizes in between. It is either or. When I tried to take bacteriophages from the small and from the large plaques, I resulted in the exact same two plaque sizes. Taking from these as well still gave one large and one small. It has been my understanding a phage gives only one unique plaque size which is dependent on absorption rate into the cell, not two distinct plaque sizes. Does anyone have any ideas why this is happening?
| posted 03 Dec, 2021 15:32
Dear ,
It is a common morphology for some of our phages to do this. Six rounds of replating a well isolated plaque means you have purified well. Our Cluster A phages are notorious for doing this.
I think that they are the same plaque morphology and it is the landscape differences that do this OR just as likely, it is a cell growth issue and not cells are in the same growth period when infection started so some plaques have a head start on the others.
What is 'dangerous' is to 'over-purify' and find the clear plaque mutant that has lost /integration function. If there is a genotypic difference between the 2 populations, a good Illumina sequence run may show it.
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