Standard E. coli Strain for BioBricks
This project intends to build a standard strain for use with BioBricks in which most systems can be run.
We will be making a series of mutations from wildtype K12 Escherichia coli.
- lacY (lactose and IPTG transporter)
- arabinose transporters
- no F plasmid
Even some of the simple devices I work with appear to behave differently in different strains. Therefore, the strain in which your systems operates is yet another variable that can affect system performance. Ideally, we should be able to design our systems so that they are independent of the strain in which they operate but currently we are not yet there. Thus, this project seeks to build a strain in which we can characterize and test most devices in the hopes that standardization of background will solve some of these observed problems.
The key feature of this project is that it is likely of use to several people but yet a lot of work for any one person to tackle. Add to these features the fact that most people can scrape along by using existing strains and you have a project that everyone would like to see done but that no one wants to commit to. I hope to use this wiki page to achieve a detailed project plan. Then perhaps several people can work on this project in the background and update this page with project status in order to keep it going forward. It is unclear at this point whether this approach is at all feasible.
Below I have included some email correspondence concerning the status of this project so that all the information is in one place. I'll be organizing this information further as I try to more definitely outline what all steps need to be done. Feel free to contribute as well. These emails are in chronological order from earliest to latest.
I have in the freezer multiple copies of first-generation MG1655 duplicates from the ATCC stock.
I also have ATCC stock (currently ungrown) of E. coli with plasmid pKSS, carrying the mutant pheS gene described in the paper Kast94 (see below).
I also have sigma p-chlorophenylalanine in the freezer.
There is a set of other relevant papers in this directory: [link not included cause it contains copyrighted papers]
The literature confusingly (to me) uses the words "positive selection" to mean what I think of as negative selection -- namely, selection of mutants that *do not* express some protein. Apparently the idea is that when you clone something (the positive?) into them, then the gene is no longer functional. In any case, the paper Young-Jun02 has a review of some "positive selection" markers.
The sequence for pKSS is in Genbank U01668.
The Reyrat98 paper basically describes the approach I think we want to make to chromosome editing, except by doing it with the Wanner approach, we eliminate the plasmid ori integration. Johnston99 uses a plasmid integration approach with N. gonorrhoeae, using a mutant version of rpsL which conveys dominant sensitivity to streptomycin, in the same way that pheS(mut) conveys dominant sensitivity to p-chlorophenylalanine.
So, in summary the approach looks like this:
- Isolate left and right flanking regions around the point of insertion/deletion as insertion sites. These need only be 35-50 bp if I recall correctly.
- Construct a linear DNA fragment (pcr?) with left.kanR.pheS(mut).right where kanR and pheS(mut) genes have constitutive promoters.
- Transform and select with kanamycin, giving cells with chromosomal insertion of the cassette (and deletion of any intervening region).
- Construct a linear DNA fragment with left.insert.right for any (or null) insert.
- Transform result of (3) with this fragment, select on p-chlorophenylalanine plates, selecting for removal of the cassette.
- PCR across the gap and sequence verify edit.
Saving some of the strains from (3) in the freezer would allow us to easily insert constructs into the genome at that spot in one step.
I dug out the Yanisch-Perron/Messing paper on the JM1xx strains. They really a hodge-podge -- a result of mating experiments with unclear and confusing parentage. But the paper is worth a look to see what features they were aiming for.
I also scanned the Doug Hanahan paper describing the DHxx strains as Hanahan83.
These are the things I think we clearly want:
- no lambda lysogen (we use lambda cI)
- no F plasmid (we want to be able to use F ori (cosmid) plasmids)
- no lacY
- no hsdR restriction system (we don't want our DNA cut up randomly on transformation)
- appropriate mutation of ARA operon/transport
I'm not sure I know how to cure the F plasmid, but I'm sure it's in the literature somewhere.
There is a note in Yanish-Perron85 that recA+ strains cause plasmids to form multimers. This is interesting. I'm not sure we know how to detect these, or if it just looks like a larger copy count.
I'm ready to move on to trying to chromosome engineer MG1655 with pKSS. Can you bring me up to speed on where you are with recombination, the strains for recombination? Can you remind me of the edits we initially proposed before Christmas for MG1655? I think I heard someone say that we had biobricked some antibiotic cassettes ? I'm looking for Kan or Cm.
There wasn't much success with the work that was attempted. But here is what was done mostly by Bram (a new IAP UROP) working with Caitlin and myself. As Bram is no longer with us, and Caitlin is away, let me know if you need any of these raw ingredients, including primers/plasmids/strains.
We took the cassette that the Sauer Lab uses for selection during chromosomal recombination. Tried to biobrick the markers. Only got KanR in the end. However, there were problems b/c kanR has a PstI cut site within it. Ended up using an Eco/Spe insertion to get it in. The sequence is in the attached file.
designed primers for amplification of pKSS using published sequence in genbank (LOCUS:U01668 gi:405986)
two sets of forward primers, w/ and w/o possible promoter driving expression
TTC CGA ATT CGC GGC CGC TTC TAG AGA TGT CAC ATC TCG CAG AAC TG
PheS forward w/ possible promoter
TTC CGA ATT CGC GGC CGC TTC TAG AGC ACG ACA GGT TTC CCG AC
TTC CAC TAG TAT TAT TAT TTA AAC TGT TTG AGG AAA CG
PCR didn't work in Bram's hands.
Haven't done any recently, but we have all the requisite materials. I think I gave you the main Wanner plasmid already (pKD46). I think lambda red genes on this plasmid are controlled by arabinose induction if my memory serves me correctly. the plasmid is also temperature sensitive. I would look up the recombineering papers by Don Court (PMID: 12429697) and the paper by Datsenko and Wanner (PMID: 10829079)
Edits to MG1655
- First is perhaps a deletion of lac operon
- delete endA (as a cloning strain)
- make some of the edits needed for arabinose linearity (see Keasling's paper)
- can't remember others off the top of my head.
I don't have the antibiotics biobricked but I have primers to amplify Kan and Cm with flanking XhoI sites. It includes a constitutive promoter. (Though I don't know anything about this promoter except that it works in pSB1AK3-1 ... a high copy plasmid). It never had a PstI cut site in it (it used to have an Xho I site in it, but that has been mutated out).