Usually the protocol for preparing electrocompetent E. coli cells calls for growing the cells at 37deg and 225rpms until they reach OD of 0.3. I was wondering, is there any reason they should grow at optimal conditions for growth, instead of at suboptimal, for example at 30 degrees? Also, what is the physiological/epigenetic difference between a culture of OD 0.2 vs 03. vs 0.3?
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1$\begingroup$ I don't know for sure, so I won't post as a formal answer, but my guess is that you want to maximize cell health and viability. Transformation of electro competent cells kills a lot of them, and you want to maximize the chance some of them survive. $\endgroup$– DrosophilaFeb 23, 2013 at 22:17
2 Answers
I'm new so I can't make this a comment, and I don't think the other commenter addressed your questions so here it goes: I don't think there will be much difference, if any, between 0.2 and 0.3 OD. Once you get higher and the cells start transitioning into a stationary phase is a different story. Did you mean to ask about 0.03 OD as well (you wrote 03.)? I'm not an expert in E. Coli, but they would probably be less likely to produce proteins that are contact inhibited. Sub-optimal temperatures may have a minor effect on growth, but I don't believe this will initiate much change or induce production of large amounts of cold shock proteins.
I did electroporation of E.coli before using common protocol "growth at 37oc until OD 0.4-0.6, and pellet cell and dowstream works at cold condition". Recently, some publications gave different protocols with much higher efficiency. Briefly, (i) they growth E.coli at 18oC and did the same procedure; or (ii) they growth E.coli at 37oC and pellet cell, transformed at 24oC.. The references tittles are shown: "Growth of E.coli at low temperature dramatically increases the transformation frequency by electroporation" and "Room temperature electrocompetent bacterial cells improve DNA transformation and recombineering efficiency" You may try and find out protocol suited to your works.
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2$\begingroup$ Welcome & thanks for your answer. Can you add those references? $\endgroup$– AliceD ♦Jun 11, 2018 at 18:57