SePteaber 2, 19/8.

Dr. S.C. hittenberg,
Department of Bacterivlogy,
University of Southern California,
Los Angeles 7, California.

Dear Dr. Rittenberg,
Thank you for your most interesting letter.

The methods which you tried to test recombination (or similar processes)
in Salmonella had occurred to us. but ve considered the serological approach
unfeasible, as you found it to be in practice, For the application of the phage-
selection method, we were hindersd, ainfortunately by our inability to secure
frou dadison sewige appropriate phage stoeks, The phages which we were able
to recover (fer typhimriun) did not permit of tie dsvelopmont of sharply resis-
tant mutants, and experiments comparable to your own in which typhimurium of
independent origin, and with initially different phege responses were used, did
not give any evidence of exchange of phave-resistance characters! i.e., a mix-
ture of phages lysed the entire population tested. You are to be congratulated
on the promising outcone of the experinents which you wrote about, and we were
very much interested to hear about then.

Since my last letter, we hive d=veloped a hethod which facilitates the
isclution of bioenemical mitants (and which I will be glad to. send you if you
have any further use for it), and with this nethod have succeeded in obtaining
a iarge number of miltiple mtants in farther Salmonella strdins. Two additional
typhimrium cultures have been rather rigonously tested for recombination of
biochenieal factors, comparable to B. coli K-i2, and with an equally disappointing
Conclusion, However, we intend to continue with these experinents.

ie would, in view of your rdsults, like very much tc explore further the
possibility of reconbination in the 5. poona and Ss. cholerae suis that you have
been using, and would anpreciate receiving those cultures, as well as the phages
specificauily active against them. I connection with your expsrinents, I assune
that you have already examined a number of the phage resistant, tants phic! are
produced Py your individusl cultures, and ruled out thetPOssibility that suc
mutants huve altered antigens.

We have some glutamic-less Ff, coli K-12, in the form of a double mutant with
a threonine ae The mutant also responds to proline and to a~ketoglubahate.
I am sending the wild type,k-12, threonineless 679, and threonine-glutamicless,
679-662, and hope they will satisfy your needs. get uve 3 me others, but I can
not recall at the moment. s