The effects of nalidixic acid on respiratory activity of asynchronous and synchronous cultures of Alcaligenes eutrophus.

Nalidixic acid inhibited DNA synthesis and cell division during asynchronous growth of Alcaligenes eutrophus but treated cells continued to grow as monitored by A550, respiratory activity and cell volume. Differential effects on cell division were seen when the antibiotic was added at different times during synchronous growth. The earlier in the cell cycle the time of addition the greater the inhibition of cell division. These results suggests that chromosome replication is confined to the first half of the cell cycle in A. eutrophus grown at 30 degrees C. Respiration rates of cells selected by continuous-flow centrifugation and immediately treated with nalidixic acid increased in a stepwise fashion. These steps were similar to those observed in untreated control cells and imply that the DNA-division cycle is not the causal factor for the periodicities in respiration rates and ATPase activity that have been previously reported in this bacterium.