Beadle and Tatum (1941) and Tatum and Beadle (1942) have reported the isolation, from cultures of the ascomycete Neurospora exposed to x-rays, of mutant strains which require certain specific growth factors for normal growth. This report is concerned with the isolation and study of mutant strains of Escherichia coli. Although it has not been possible to establish a genetic basis for the growth-factor-requiring strains of E. coli, as Beadle and Tatum were able to do in the case of the fungi, the similarity between the results of the two studies leads us to consider the different strains of E. coli as mutants. Haberman and Ellsworth (1940), in a study concerned primarily with the effect of x-rays on colony morphology of bacteria, obtained several variants or mutants which differed in certain physiological activities from the parent strain. Although they did not obtain mutants requiring specific growth factors, they refer to a variant of different morphology which they could not isolate. It is possible that they were concerned with a mutant strain requiring an essential growth factor which was not present in their culture medium but which could be synthesized by the parent strain. METHODS Cultivation of normal and mutant strains A stock culture of E. coli was selected for use in this study. Although this strain usually grows well in a synthetic medium containing only inorganic salts and glucose, growth appears to be sensitive to slight changes in the medium. The addition of asparagine assures full growth after 16-18 hours of incubation at 37 C with relatively small inocula. Thus, the basal, synthetic medium used was that described by MacLeod (1940) with the following composition: NaCl, 5.0 g; (NH4)2SO4, 4.72 g; KH2PO4, 2.72 g; glucose, 2.0 g; asparagine, 2.0 g; 1 ml of a solution containing 1 g of each of FeCl2, MgCl2 and CaCl2 in 600 ml; distilled water to make 1 L. The pH is adjusted to 7.0 with n NaOH, which requires approximately 15 ml. The "complete" medium used for growth of the treated cultures consisted of Difco A.C. Broth Experimental, with the addition of 0.2 ml of a crude liver extract (supplied through the courtesy of Dr. Y. SubbaRow of Lederle Laboratories, Inc.) per liter of medium. The liver extract was sterilized by filtration and added to the autoclaved broth. Although A.C. broth alone is sufficient for the growth of the more fastidious bacteria, the liver extract was added to assure as complete a medium as possible. In determining the growth requirements of the mutant strains, the test sub-401

No abstract

No abstract

No abstract