dune 18, 1947 «

Ir. F. Strandskov,
Research Lepartment,

Wallace and Tiernan, Prods.,Ic.,
Bellewille, NJ.

Your recent paper in J. Bact. "Inhibition of methionine
synthesis in E, coli by 2-C1-PAB and SA" was very interesting
to me, particularly in the light of the genetical problem which
it seems to introduce: namely, the induction of heritable resis-
tance by the drug to which the induced mutant is re: istant.

I would enjoy wery much, sometl e, the opportinity of repeating
your experiments on a strain of “. coli in which genetic analysis
is possible (see a paper in the next forthcoming J. Bact.) For
this purpose, I would a preciate it if you could send me a

Sample of 2-Chloro-p-AminoBenzoic Acid, if that is convenient.

However, before I can wholeheartedly accept your conclusion
that the inhibitor plays a direct role in the production of the
adapted types, I would appreciate your opinion on an alternative

interpretation, As I understand it, the crucial finaing is that

a) resistance is rather slowly developed a
> .

i

iyuid medium, and
b) a large proportion ( 10%) of the vod chao heritable
resistante when inocu'ated into asur medium. It is not clear
from your paper whether a resistant culture, when plated into
Cl-pab agar shows the same lag in the developmpe::t of colonies
from single cells, as in the ""selection"" of the resistent
cells from the original sensitive population. If there is no

such lag, the conclusion is of course inescapable that there are
not cells in the original sensitive population comp rable to
those which you found after the treatment. If this were so, then

_ the only loophole left open is perhaps that there is some growth @
of the sensitive cells (perhaps to microcolonies of 107-104)

which is not readily perceptible, but which provides a population

large enough for an occasiohal spontaneous mutation to resistance,

then selected for and forming the 10-25% yield of visible colonies.

I hope you will not find obnoxious this kind of heckling, but

in the light of the little genetic knowledge we have of bacteria

the geneticist is still inclined to fight to the last ditch against
directed

Claims of specific adaptive mutations.

For the slow manifestation of "resistant mutants" in liquid
culture, I have but one additional thought to sugcest, namely that
thbre may be an interaction between the sensitive and resistant cells,
such that in the presence of Cl-pab, the resistants are inhibited
to a greater extent than they would be in the absence of the sensi- 6
tives. This could be checked very easily bg using artificial mixtures.
This is not a purely hypothetical occurrence, since lr. Ryan has
been finding just such an interaction between histidineless and wild
type E. coli, and he and I have described a similar sort of behavior
in Neurospora heterocaryons. (Adaptation and reverse mutation of
leycineless Neurospora- Proc. Nat. tcad. sei. )

Finally, a reprint would be ap»reciated.

Yours sincerely,

Joshua Lederberg: