April 22, 1953

Dr. D. M. Bonner
Yale University OBL
New Haven, Connecticut

Dear Dave:

I enclosa a transplant of K-12, directly from our lab stock. I have
not looked at it explicitly: we have had no trouble whkth mucoid character
on most of the media we use. As I remember, some prototroph recombinants,
though usuaily not K-l2 itself, would tend to bscome aucoid on Davis! minimal
ugar, especially after a couple of days at room temperature, I suspect it
would help to cultivate the bacteria at 37°, and to use the Tatum-Gray rather
than Davis' ag the minimal medium, if this is raquired,

if thia K~iz culture behavaa Like the ove you ave, you had better give
468 Mors d6talid of ihe clireumstancea undew which you are having trouble.

Yours sincerely,

Jostna Ledarberg