BIOSYNTHETIC LATENCY IN EARLY STAGES OF DEOXYRIBONUCLEIC ACID TRANSFORMATION IN BACILLUS SUBTILIS

Nester, E. W. (University of Washington, Seattle) and B. A. D. Stocker. Biosynthetic latency in early stages of deoxyribonucleic acid transformation in Bacillus subtilis. J. Bacteriol. 86:785–796. 1963—In the Bacillus subtilis deoxyribonucleic acid (DNA) transformation system, transformants do not increase in number for 3 to 5 hr after the addition of DNA. During most of this period, the transformants are resistant to the bactericidal action of penicillin under conditions which result in the killing of over 90% of the recipient population. This lag in growth and nonmultiplication of the transformants (inferred from penicillin resistance) is also reflected in a lag in the synthesis of an enzyme specified by the donor DNA. Thus, when a cell population deficient in the enzyme tryptophan synthetase is transformed to tryptophan independence, activity of this enzyme cannot be detected in whole cells until 3 to 4 hr after the cells have been exposed to the DNA. Recombination between donor and recipient DNA occurs long before this. Even 30 min after exposure of a competent population of try2−his2+ cells to try2+his2− DNA, 20% of the total try2+ activity found in re-extracted DNA exists as recombinant DNA, try2+his2+. This value, the maximal linkage obtained, remains constant during incubation of the DNA-treated culture for an additional 5 hr. In addition to the heterogeneous response of a DNA-treated competent culture to penicillin killing, the recipient culture appears to be heterogeneous in ability to undergo transformation. Thus, the frequency of joint transformation of two unlinked markers is much higher than would be expected on the basis of the random coincidence of more than one DNA molecule entering the same cell in a uniformly competent recipient population. A possible relationship between these two aspects of heterogeneity of a DNA-treated recipient population is discussed.