Abstract
Nalidixic acid, an antibiotic which affects DNA synthesis through interacting with DNA gyrase, the enzyme which catalyzes the supercoiling of DNA, was used to inhibit DNA synthesis in Escherichia coli B/r/1. Cultures of bacteria grown in a minimal salts and glucose medium were synchronized and at various cell ages were treated with nalidixic acid. After the antibiotic was removed the recovery cell division was examined. It was found that after a short period of treatment the pattern of recovery cell division was synchronous and contained a delay in division exactly proportional to the period of the treatment. In these cases, the growing points of the chromosome which existed prior to the treatment continued to their terminal after the recovery and cell division proceeded predictably and in a synchronous manner. With longer treatments recovery cell division was asynchronous and protracted. The ability of cells of various ages to divide synchronously during recovery from treatment appears to be unrelated to a specific cell age. Cells of all ages recovered synchronously from short periods of treatment and asychronously with longer inhibitions. These results suggest that the ability of E. coli B/r/1 to continue with an interrupted synchronous cell cycle brought about by a transient inhibition in DNA cycle depends on the duration of the treatment and not the cell age.
