No abstract

Evidence for premature initiation of deoxyribonucleic acid (DNA) replication after thymine starvation of Bacillus subtilis W23Tis presented, based on (i) increase in the number of ade+ relative to met+ transformants yielded by the DNA isolated from cultures after starvation (the ade-marker being near the origin of replication, whereas met-is close to the terminus), and (ii) increase in both the initial rate and final level of tritiated thymine incorporation in the presence of chloramphenicol after release from starvation. The marker ratio data agree quantitatively with the hypothesis that the initiation is induced only on one arm of each chromosome which was replicating prior to starvation.

The intercellular transfer of competence during growth under the conditions specified by the transformation procedure of Spizizen was investigated with Bacillus subtilis 168. The rate of competence development as assayed uniformly in medium B was not affected by variations in the cell concentration, although the first appearance of transformants occurred earlier with high cell densities in medium A, approximately in proportion to the onset of the stationary phase in the culture. Growth in the presence of Pronase enhanced the frequency of transformation, but did not detectably alter the kinetics of competence development. The rate of competence increase in physiologically noncompetent cultures was not changed by mixing with competent cultures either in medium A or in medium B; however, an early appearance of transformants was noted in mixed cultures in which the proportion of competent to noncompetent cells prevented exponential growth of the noncompetent strain. These experiments indicate that the normal development of competence in B. subtilis is not mediated by a soluble or loosely bound protein factor capable of transmitting competence directly via cell contact. The onset of competence is thus a function of internal physiological changes which are induced by the overall metabolic state of the culture.on July 31, 2020 by guest