I've got a bacterial culture stock of E. coli (JM 109 strain) and I´m using it for a phage cultivation which works because of bacterial F-plasmid. I would like to ask how many passages can I do without losing the F-plasmid? I have read it´s disappearing spontaneously. Thank you for all answers.
I've never had an opportunity to work with E.coli, although I think this case looks very similar to mine previous studies. As it comes down to the loss of some abilities by cells. I would passage my yeast cultures two or three times at most. Then I would passage it again from a stock I prepared and kept frozen. Renewing your cultures and passaging new cultures every week enables you to keep your cultures fresh and ensure the correctness of your result, Best luck!
The F' plasmid in JM109 complements for some metabolic deficiency in the host, so just grow the strain in minimal medium to select for F+ cells. You'll have to look up the genotype, though -I think it is thiamine or proline, but cannot remember now.
The F' episome makes the strain prototroph fro proline, therefore you just have to passage your strain on proline-free medium to select for cells that have retained the F'. Anyway, the F' plasmid is rarely lost. However, be sure to grow the strain at 37 °C to ensure good piliation, since lower temperatures will lead to loss of pili
Pierre and Alejandro are right in that you can select for the F' in JM109 by selecting for proline prototrophy. Normally F is rarely lost as Pierre says, however the F' in JM109 has mutations to limit transfer and the result is it is lost at a higher rate than wild type F plasmids. I always make a stock by picking a colony from a minimal plate (lacking proline).
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