Decemher 13, 1951

Dr. Paul R. Burkholder
Yale University OBL
New Haven, Cona,

Dear Paul:

I would indeed appreciate having the auxotroph mutants of
S. grisaas that you offared in your letter. The double mtant
would be gost useful, but s few well-defined monoauxotrophs
with a low residual growth would be welcome as well, Might I
also hava the wlld type strain, and its designation, from which
these autants were isolated?

In the last few weeks, I have managed to isolate a few mutants
frou UV-treated spore auapensions, tested by replica-plating. Alhout
but two or three showed residual growth, or were extraordinarily
seneitive to aynbrophic stimulation. Some combinations have behaved
in such a way that I am convinced that heterokaryos!s occurs (not
toc readily’, and there is a strong indication of further genetic
interaction, presumably recombination. This work was all done with
a streptomycin-sessitive S$. griseus. I think it would be worth-
while tc extend the tests to other "species". Do such forme as
S. lavandulae, S. coelifolcr, &. venezuslae and S. anreofaclens
grow as well on synthetic medium as does S. griseus? If you think
they would be technically cuitable, could you send me suthentic
cultures of than?

Thanks for recalling Couch's sporangiel actinomycete-- I'll look
intomit.

I wish I could say that silica gel was a reliable method for
preservation of cultures.It ought tomwork very well if the optimal
conditions are found. The two obvious variables are the proportion
of water to gel, and the type of suspending fluid. We have gotten
encouraging results to date by simply adding about .04 ml of bac-
terial suspension in peptone to 1 gm silica gel (in a tube previously
baked to sterilize and dehydrate). The tube is then sealed off
directly in air. Some more work will be needed to justify and stan~
dardize the method. The silica gel is Grade 40, 6-16 mesh, Davison Co.,
Baltimore.

Yours sincerely,

Joshua Lederberg