April 22, 1952

Dear Hayes:

I hope you will tolerate this barrage of correspondence; you should be
allowed some respite.

One of my students, Miss Elise Gahn, has been trying to confirm your
experiments on the fertility of S” cultures. I had entertained no doubts
whatever about them, especially as my own experiments on the crossability
of cultures on minimal-sm agar agreed so well with yours.

Her results have been, however, rather surprising. Indo not know yet
how much consideration should be given to them, but it seemed necessary
to compare gur experiments in more detail. She has been inactivating the
cultures (S‘) by adding about 50 u/ml dihnydrostreptomyein to young broth
cultures. After 2 or so hours, she washed the cells in saline. The residual
sm,if any,was not enough to inhibit added K-12, or S® recombinant prototrop}is
when these appeared. Her Brosges were done on minimal agar, with various
combinations of SY x S and S’ x S*, If A= 58-161 (F+) and B= W677 (F-),
the resultd may be summarized: There were about 5-6 decades of killing, ile.

about 500 viable S

1. A x B (various controls) (i's. ca 102 \ per plate.
plate
2.A xB Oo 3
3. 4 x Be + (all s°, of course)
t. oF
4. AU XB = tat parent recovered with surprising

frequency from minute
eolonies or mixed with
r t prototrophs ]
5. A xB ++ Mostly s°.

Some of these results are flatly contradictory to those reported in your
paper, and to my own expectations from the crosses on minimal~sm. We would like
to learn the details of your technique of inactivation, etc., in hopes of
learning the reasens for the discrepancy.

Wononpangsmabctink Do you agree that 8” cells are far less fertile x S®
than x S™? If so, I think we must concede that the St cells do retain some
bound streptomycin or streptomycin-like substance (with respect to the response
of S™), If this is accepted, the s* cella cannot be regarded as corpses, but as
cells whose further growth is inhibited by the bound streptomycin. It would be
useful to have some agent capable of removing the bound am (like BAL for
Hg**). We are checking on the possibility that untreated cells may act
in this way.

Yours sincerely,

Boshua Lederberg