Why does the amount of plamids transformed affect colony count? - (Oct/03/2010 )

Hi,
In class we did a triple plasmid transformation, I was wondering why its colony count is lower than all the single plasmid transformations we carried out....


Thanks

ohsnap on Mon Oct 4 02:14:04 2010 said:

Hola,I think that you are transforming with three plasmid with different resistence each one, and select colonies with three antibiotics so the probability of entering the three plasmid in a cell is lower. In your transformation there are bacteri that no receive any plasmid, other one or more copies of one, other some copies of two and few have copies of the three plasmids. Good luck

I remember being taught that transforming with multiple plasmids at once is very hard, as higher copy number plasmids will always out-compete the low copy-number plasmids unless there is other selective pressure (such as multiple sntibiotic resistance) until the bacteria only contain the high-copy plasmids.

IF the copy-numbers are the same however then I would assume that it is due to the rarity of transforming with all 3 plasmids in the same bacteria, compared to bacteria only receiving 1 or 2 of the plasmids.

i.e. if the probability of a bacteria being transformed by a single plasmid is 1/3, then the probability of being transformed by each of the 3 plasmids is 1/3³=1/27