Resporulation of outgrowing Bacillus subtilis spores

Abstract

Germinated spores of B. subtilis were incubated in outgrowth medium and tested periodically for capacity to sporulate when suspended in sporulation medium. Concurrent measurements were made of DNA content and numbers of cell division septa and nucleoids. Sporulation potential is shown to reach a peak at about 110 min, at which time the chromosomes are probably well into the second round of replication. Experiments with nalidixic acid show that sporulation potential can be generated in the outgrowth medium even when DNA synthesis is largely prevented. Further experiments show that nalidixic acid apparently does not prevent the formation of DNA initiation complexes, which can subsequently function after resuspension in the sporulation medium. The results support those previously obtained with a temperature sensitive DNA mutant which indicated that sporulation could only be induced at a specific stage of chromosome replication, and then only if the cells are in a state of nutritional 'step down'.