Jane 9, 1949.

My, Re J. Mandle,
Dept. Sotany,

U. of Pa.,
Phila, de Pade

Dear Mande: .

Under separate cover, I au taking the liberty of sending you strain
A6é of P. tumefaciens, and some "“matants" derived from it by Mr. Donald
A. Gordon working in tails laboratory. Mr, Gorden kindly offered the en-
Closed carbon copy of his report , but although he says he will not need
it, IL think it would be desirable that he got it back ot a later dete.

If you have not already used it, I think you will find the Aniline Blue
mediua very useful in two reppecia. Firstly, it is an excellent simmle
marker to susure ccntinuity as Phytoaonag and boospot posaible contaminants,
and second, mutations tc white, as exemplified on one of the slants, might
be used as a genetic color marker. Unfortunately, the bluc form mtates to
white too frequently for the blue character to be reliable, but on the
other hand, white has proven to be very stable and I think could profitably
be used. E. G., 4f a suitable synthetic medium vould be devised for demonstrat
ting the reaction, one might pick as recumbinants blue pretotrophs obtained
from mixtures of a blue mitant with a white mutant or protctroph, ent be
confident tnat the biue isulate originated from the blue parent or its pro-

geny.

The mitante GI aad GIT ars alike in responding well to sulfide, although
they show some differences in their responses to a varhet; of amine avids.
I have presumed, without proof, that the aa response was due to contamination
with reduced sulfur. Neverthelass, these mitants aight prove to be distinct
from the one(a) you have obtained, and if used in voncentrations whera rever—
siona would not appear, alght be suitable for selective recombination expts.

I regret very mich that we did not have a better opportunity to discuss
four interesting work. With best wishes for further succesa,

Sincerely,

Joshua Lederberg,
Assistant Professor of Genetics,