January 23, 1947.
Dear Dr. Braun,

I was happy to hear from you that you are continuing with the
genetic aspects of the nature of your Phytomonas forms. Prof. Tatum
and I have developed a simplified technique for the detection of
biochemical mutants of bacteria, which works quite well with some
organisms. A reprint is enclosed. If Phytomonas will form regular
colonies in minimal agar mecium, mtkk of satisfactory size, and
little variation in size, this technique should work wery well in
screening large samples of irradiated bacteria to finc mutants.
Otherwise, the older techniques described by Gray anc Tatum, etc.,
would be preferable. The only possible quirk that mst be mentioned
is that is probably advisable to incubate the irradiated cultures
for several hours in fresh medium before plating them out. hile
we have not yet completed critical studies on this point, this should
be necessary to allow the possible segregation of mutated from un-
mutated nuclei in what appears to be a di-karyotic cell. With material
such as yours,however, where the occurrence of star forms is apparently
frequent under certain conditions, it may not be necessary to rely
on biochemical mutants. Dr. Burkholder, in this lsbor:tory, spent
considerable time last sumer tn looking for mutants in Fhytomonas,
without success. This may have been because the importance of the

incuba. ion period was not fully understood.
The rarity of the recombir. tion process in E, cold required
us to use mutant characters mateh for the recombinations of which
we could select by manipulation of the medium. Since that tice, we
have teen using nutritional characters as a means of selecting for
tre recombination cells, but have used other markers whigha cen
be more conveniently scored (such as coluny form, lactose fermentation,
virus resistence, etc.) On the hjpothesis that the stars represent
or contsin zygotes, almost any reasonably stable mutant charzcter
should be adecuate; the occurrence of recombinations pf such characters

. (plated in toto)
in cells of colonies obtained from stars, .nd not otherwise woula
be critical evidence. Such mutants should be readily picked up
to judge from the work of Lincoln and Gowen on F. stewartil. Another
type of character that can be obtained very readily is drug resistance:
Several drugs are avsilable which will select for mutant tacteria
resistant to then, md cdo not show cross-resistance , e.g. penicillin
and streptomvcin,
‘At any rate, the best of luck to you, and let us hear what

comes out.

Yours sincerely,

1 i / 7 :
: ai :

Jostma Lederberg.