I saw a protocol for recombinant protein expression that recommended working in larger volumes (1L cultures) without antibiotics after inoculating overnight in antibiotics. How practical can this be?
You should still get protein expression when you grow the second culture without antibiotics because typically you only grow the second culture for a short time (maybe three hours) and harvest it in log phase growth. Cells from the overnight culture will have many copies of the plasmid (if it was high copy). Over time your culture will slowly lose the plasmid if their is no selection, but this only happens after many cell divisions. In fact, if you grow and overnight culture with selection and then dilute it 1/100 or 1/1000 in non-selective media and grow overnight again, then plate a small portion on selective plates, you will get confluent growth. This indicates plasmid loss does not happen real fast. A plus of growing without selection is that cell are a little happier and can grow to a higher density than with antibiotics that inhibit protein synthesis (like kanamycin).
You should still get protein expression when you grow the second culture without antibiotics because typically you only grow the second culture for a short time (maybe three hours) and harvest it in log phase growth. Cells from the overnight culture will have many copies of the plasmid (if it was high copy). Over time your culture will slowly lose the plasmid if their is no selection, but this only happens after many cell divisions. In fact, if you grow and overnight culture with selection and then dilute it 1/100 or 1/1000 in non-selective media and grow overnight again, then plate a small portion on selective plates, you will get confluent growth. This indicates plasmid loss does not happen real fast. A plus of growing without selection is that cell are a little happier and can grow to a higher density than with antibiotics that inhibit protein synthesis (like kanamycin).
My experience in mammalian or insect expression system allowed me conclude that protein expression is better without any antibiotic as compare to the one with antibiotic selection. Presumably due to the less antibiotic stress to cells.
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