TTHE WESTERN PENNSYLVANIA HOSPITAL

INSTITUTE OF PATHOLOGY
PITTSBURGH, PENN’A

cl

December 11, 1946

Dr. Joshua Lederberg
Osborn Botanical Laboratory
Yale University

New Haven, Connecticut

Dear Dr. Lederberg:

I have examined rather carefully your K-12 culture of B. coli, which you
were kind enough to give me during my recent visit to Yale. So far, I
have not been able to find anything in the culture that even resembles

the bodies that we spoke of as zygospore-like. Sometimes these may appear
under unusual cultural conditions, and I am using now a couple of differ-
ent media to see if anything suggestive turns up. If it does, I shall let
you know.

I enjoyed very much reading the reprints you gave me that day, and it does
appear certainly that you have the biochemical and genetic equivalent of
the sexual process, because, as Dr. Tatum pointedly remarked, as long as
you can get re-combination of genes, that is about all that you could hope
for from the sex process itself.

In my Microbic Heredity paper Number 3, page 140, it is of interest that
true "stalked" zygospore-like structures occurred when the coccoid-phase
of the coli organism was grown in a sterile filtrate of the coli-communior.
This recalls the Dienes effect with his proteus strains.

I checked the September, 1945 JOURNAL OF BACTERIOLOGY reference and find
nothing there that accords with the zygospore-like bodies. Their Figure I
I would call chlamydospore-like. The simple fusiform enlargements may pos-
sibly be an initial stage of the former.

‘Vith my kindest regards to you both, and with best wishes for the continued
fruition of your most interesting studies, I am

Sincerely yours,

(art. lider —

Ralph R. Mellon, M. D.
RRM rbp Director, Institute of Pathology