April 7, 1954

Dr. 3. R. Luria
Bacteriology Department

University of Diifois
Urbana, Tl.

Dear Lu:

Seymour tranamitted your reqestdéd for a pair of Salmonella atrains that
would be appropriate, as he unmlerstood it, for a study of the effects of
motility on the rate of phage adsopption. I have been thinking over what we
should expire that would best fit your needs, and avert some obvious traps.
The main ¢onsideration, I thought, would be to ensure and be able to verify
that motility was the only difference. Unfortunately, our methods for selec-
ting motile strains are always likely to have some effects on the level of
somatic antigen, presumably the receptor substance. This is a feature that
is never easy to control in Salmonella anyhow.

On this basis, I would recommend yeing as a non-motile strain one sufficiently
unstable that you wpuld have no difficulty in reisolating motile variants at
will. In addition, the flagella themselves might play some role in either
hindering or facilitating adsorption, independently of their motility function.
For this reason, I have selected a flagellated, non-motile ("paralyzéed")
strain, SW- 578, which can be compared with its motile cousin, SW- 575.

The former is moderately unstable, ani should be repmrified from single
colonies every now and then, but not to a degree at all likely to interfere
with your experiments. As required, you can select for motile reversions from
S¥-578 with the help of "motility agar". I am also sending SW-573, also
related to the other two, and which is a stable, non-flagellated variant
(probably also carrying the "paralyzed" mutation as well).

You may be interested, if not already cognizant, that Strain C (B. coli
NCTC 122) is moderately motile when grown at lower temperatures. I am trying
to select an actively motile derivative, and if this is successful, I would
imagine you wuld find this system more feasible than the Salmonella, as the
T phages would be applicable. VWould you be interested?

Please let me know if I have misconstrued your request, ar can be of
any other service.

Yours sincerely,

_-‘Joahua ‘Lederberg