Studies of a Purine-Requiring Mutant Strain of Escherichia Coli

Studies of a Purine-Requiring Mutant Strain of Escherichia Coli. Ii. Selection of Revert Strains and Its Evolutionary Significance

“…4, the P+ strains were selected against in medium A much more than any of them were selected against in medium B. This selection explains the difference in tube-reversion in medium A and B that was previously reported (GUTHRIE 1949). Even strain 4, which is not suppressed in either medium, grows much better than the P organism in medium B, while in medium A there is no appreciable difference in selection for the two organisms.…”

“…Portions of this work at the Sloan-Kettering Institute were supported by the American Cancer Society through Institutional Grant 10 and by Grant C-1391 containing approximately equal numbers of a revert P+ strain and the purinerequiring Pparent, was grown in the two liquid media, A and B, containing various levels of purine. Medium B, described in detail elsewhere (GUTHRIE 1949), was prepared by supplementing medium A with acid-hydrolyzed casein, nine water-soluble vitamins, uracil and thymine. The media were distributed in ten cc amounts in 22 X 175 mm test tubes.…”

A Purine-Requiring Strain of Photobacterium Fischeri

“…There are descriptions in the literature of purines that may function as essential growth factors or stimulatory substances for particular organisms. Guthrie (1949) has described an Escherichia coli mutant that possesses purine requirements quite similar to those of the P. fischeri mutant described here. Tatum (1946) produced a mutant strain of E. coli which required purines, and Pappenheimer and Hottle (1940) found a strain of hemolytic streptococcus with a purine requirement.…”

Microbiological Assays

“…Bacillus subtilis have been published as an abstract (91). The technique has been improved by Guthrie (90); 30% of the colonies picked are auxotrophs.…”