[Microbiology] Re: E.coli MC4100 thi- genotype

David F. Spencer via microbio%40net.bio.net (by DSpencer from Dal.CA.BLOCK)
Wed Mar 25 14:53:59 EST 2009

Julian Spagnuolo wrote:
> Hello fellow slaves of science.
> I'm trying to create a pspA reporter plasmid by linking the psp
> promoter using the thi- genotype of E.coli MC4100 as an auxotrophic
> marker, however I'm having 'a little' trouble finding out which gene
> has actually been deleted or mutated so that I can incorporate it into
> my plasmid.
> Does anyone out there know what gene the thi- in E.coli MC4100 actually is?
> Thanks,
> Julian

I don't mean to appear unkind but I assume you have a reason to believe this
strain really is a thiamine requirer? (It is true that many K-12 strains are).
I have done some searching to trace the pedigree of MC4100 but I can find no
reference to its being thi- (nor in fact for any of its ancestors).
MC4100 is a derivative of MG1655 which is in turn a fairly recent derivative
of W1485, a strain very close to the original K-12. It is through the W1485
derivative W2637 that W3110 was produced (W3110 being a fairly well-known
K-12). Some of this is detailed in Barbara Bachmann's classic 1972
Bacteriological Reviews paper 'Pedigrees of Some Mutant Strains of Escherichia
coli K-12'.
I have never seen a genotype for MC4100 that mentions 'thi', and none of the
ancestors of MC4100 are acknowledged to have a mutation in any thiamine
synthesis or related gene(s).

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