: Ur. d. en

Tuberculosis Research Laboratory,
411 East 69th St., New York 21, N. Y.

December 12, 1951.

Sir Cyril Hinshelwood,
Physidal Chemistry Laboratory,
Oxford University,

South Parks Road,

Oxford, England.

Dear Dr. Hinshelwood:

I was interested to read in the Journal of the
Chemical Society that you and Dr. Dean had not been able
to obtain nutritionally deficient mutants of Aerobacter
aerogenes by means of the penicillin method. We, too,
found that the procedure used with E. coli was not success-
ful with Aerebacter. By a 5-fold increase in the penicillin
concentration, however, together with a reduction of the
exposure time to 4 hours, Dr. Vogel of this laboratory was
able to obtain a variety of amino acid auxotrophs with no
difficulty. These resembled closely their counterparts in
the B. coli series, most of them being quite stable and easy
to maintain if kept in a medium that would not select in
favor of occasional reversions. These mutants are, of course,
freely available to you.

Sincerely yours,

Bernard D. Davis

BDD/h1