Q29
Oct. 3, 1955 Note for MGB

BIOTIN REQUIREMENT OF CULTURES DERIVED FROM E. COLI Kel? Strain 58.

E, L. Tatum (1945, Proc. Nat. Acad. Sci,, 31:215) isolated a mmber of diauxo-
trophic mitants from the previously isolated biotinedependent, strain 58, These in-
cluded strain 58-161, which originally required biotin and methionine (Be Me), and
which has been an important parental stock in recombination studies, Subsequently,
the biotin requirement appears to have been lost, apparently by reverse mutation.
(Miss Phyllis M. Fried failed to obtain any B~ recombinants in outecrosses, and we
have observed no effect on segregation ratios of the addition of biotin to plating
media for crosses.) Probably most extant strains of "58-161" are B+eM-, We have
designated this reversion of 58-161 as W-6, to distinguish it from the original B-M-,
Fortunately, through the courtesy of Mrs. Miriam Bonner, we have secured lyophil
tubes of early cultures of these derivatives, and have been able to reisolate BeM-
components from them, The following are now available:

Yeo BeM-V,” We13 BeM-v,”

Yo87 = BeM-V,7 Lace Well BtM-V,* Lace

The "Y.87" described by E. M. Lederberg (1952, Genetics 37:69) was doubtless Bie
since the BeM- form fails to papillate and produces small colonies on FMB lactose
agar (unless extra biotin is added) while a newly reisolated B+M- reversion agrees
with the published description of Ys87 as a lactose-mutable strain, The Be allele
does not appear to be unusually unstable, but remarkably enough our stock nutrient
and EMB agar media appear to be relatively deficient in biotin (or may contain
biotin antagonists) so that B+ reversions are eventually selected ovt,

The cultures noted are available on request, Other workers who have received
these cultures are urged to check their mitrition, if relevant to local needs, and
give them the indicated designations. Since the Me marker itself appears to be ab-
solutely stable, the Be mutation may be of only incidental importance in most work.

Dorothy C,. Gosting and J, Lederberg
Department of Genetics, University of
Wisconsin