Novegber 3, 1952

Dear Es:

of EB, coli,

I never have seen a Bé-less mutant, but the way we run our tests,
we're not likely to pick up vitamin auxotrophs, and we don't see very
many. If reversion is the problem, agar technique certainly should
help (although there may be an additional complication if the agar
is appreciably contaminated). Two possible angles: try other E. coli
strains, and use rather dilute inocula, very well washed, in the peni-

cillin selection (see Davis' comment, p.10, Meth. Med. Res. {.
Good luck/

Joshua Lederberg

P.S. Have you ever thought how awful the ~~trophy terminology is in
this field! What would you think of the much more self-dexplanatory
apoaynth or hyposynth or something along these lines.