Bacterial Mutation in a Stationary Phase and the Question of Cell Turnover

Abstract

During a stationary phase induced and maintained by the exhaustion of histidine, the total number of histidineless Escherichia coli (h-) remains constant as does the cyto-logical appearance of the cells. If glucose is available to the starved bacteria they die at a rate of c. 10-2 per hr., while mutations to a histidine-independent (h-) condition occur at a rate of c. 10-9 per bacterium per hr. Bacteria adapted to use lactose behave in essentially the same way when lactose, instead of glucose, is available during starvation; but if the starved cells are not fully adapted, death does not occur or is very slow (c. 10-3 per hr.) and the rate of mutation is c. 10-10. When no carbon source is available to the starved cells, mutations cannot be detected. A number of tests were made to check the hypothesis of cell-turnover, that is the hypothesis that some bacteria lyse and are replaced by the growth of others. These tests exclused the hypothesis of cell turnover. It was concluded, therefore, that the bacteria were not dividing and that mutations were taking place among them. Reasons are given to suppose that the mutations result from errors in the replication of genetic material which is in the process of turnover with the non-dividing cells.