I agree with the answer above by Pierre. In addition, a further reason for using a minimal medium such as M9 is to induce expression under reduced growth rate conditions. Growth rates will be faster in richer media such as 2TY and LB and for the expression of some proteins such as those possessing rare codons, a reduced growth rate is thought by some to be more advantageous for production. And in the case of membrane proteins slower cell growth/division may be advantageous for correct folding of the newly synthesisied proteins into the membrane.

M9 medium is used if you want to incorporate specific residues into your protein (e.g. selenomethionine or 13C amino acids) for structural studies. However, rich media, such as 2YT or LB will increase the yield of biomass and consequently th yield of the target protein

I agree with the answer above by Pierre. In addition, a further reason for using a minimal medium such as M9 is to induce expression under reduced growth rate conditions. Growth rates will be faster in richer media such as 2TY and LB and for the expression of some proteins such as those possessing rare codons, a reduced growth rate is thought by some to be more advantageous for production. And in the case of membrane proteins slower cell growth/division may be advantageous for correct folding of the newly synthesisied proteins into the membrane.

Mary Phillips-Jones

Thanks alot Mary for clearing it up, the slow induction makes a lot of sense to me now.

I also have a follow up question. What would considerations for using 2xTY vs LB media? I remembered someone transferred colonies from LB plate to 2xTY media for expression, and I was wondering what is the potential rationale for this? Why not simply stick to LB media?