Here is some real-world data describing expected yields we may expect from some of these routine lab procedures or services.
Oh, and this is a good one:
How well my determination of flask “confluency” actually correlated with cell counts. I mean, sure, there must be some error being imparted by the actual measurement of the cells when counting, but I think we all know it’s mostly that my estimate really isn’t precisely informative.
In this previous post, I showed how many reads we’ve gotten from our Plasmidsaurus and AMP-EZ submissions. Well, now’s also time to see whether the amount of DNA that we gave correlated with the number of reads we got back.
As you can see above, since this is miniprepped DNA, it’s usually quite easy to reach the 300 ng needed for submission. One time, when we submitted closer to 200ng, it worked perfectly fine. One other time, when we submitted ~ 100ng, it did not, albeit this was not plasmid DNA and instead was a PCR product, so it’s an outlier for that reason as well.
This is the more important graph though, since all of our AMP-EZ submissions are from gel extracted PCR amplifications, and it can be quite difficult to do it in such a way that we have the 500 ng of total qubitted DNA available for submission. Well, turns out that it’s probably not all that important for us to hit 500 ng of DNA, since it’s worked perfectly fine in our attempts between 200 and 500 ng. I imagine people in my lab will simultaneously be happy (knowing they don’t have to hit 500 ng) and sad (knowing they had spent a bunch of extra effort in the past unnecessarily trying to reach that number) seeing the above data, but hey, it’s good to finally know this and better late than never!
At some point, I was chatting with Melissa Chiasson about plasmid DNA yields, and she mentioned that her current boss had suggested using terrific broth instead of Luria broth for growing transformed bacteria. I think both of us were skeptical at first, but she later shared data with me showing that DNA from e.coli grown in TB had actually given her better yield. I thus decided it was worth trying myself to see if I could reproduce it in my lab.
There are two general types of plasmids we tend to propagate a lot in my lab. attB recombination vectors, for expressing transgenes within the landing pad, and also lentiviral vectors of the “pLenti” variety, which play a number of different roles including new landing pad cell line generation and pseudovirus reporter assays.
I first did side-by-side preps of the same attB plasmids grown in TB or LB, and TB-grown cultures yielded attB plasmid DNA concentrations that were slightly, albeit consistently worse. But I eventually I tested some lentiviral vector plasmids and finally saw the increase in yield from TB that I had been hoping for. Relaying this to Melissa, she noted she had been doing transformations with (presumably unrelated sets of) lentiviral vectors herself, so these observations had been consistent after all.
Thus, if you get any attB or pLenti plasmids from me, you should probably grow them in LB (attB plasmids) and TB (pLenti plasmids), respectively, to maximize the amount of DNA yields you get back for your efforts.
