An unknown regulator affects cell division and the timing of entry into stationary phase in Escherichia coli

When an essential nutrient is depleted from the medium, cultures of wildtype E. coli cells enter a period called stationary phase. The transition into stationary phase is marked by distinct changes in cell physiology, gene expression, and morphology. Pr???? and Matsumura (18) found a mutant strain of E. coli that was able to continue growing exponentially at a time when wild-type cells had stopped growing and entered stationary phase. They concluded that FlhD, a transcriptional activator of flagellar genes, was responsible for this growth phenotype and that it is a regulator of cell division (17, 18). Contrary to the findings of Pr???? and Matsumura, research in our lab has shown that the mutant growth phenotype observed in the strain used by Matsumura and Pr???? is flhD independent. This study sought to identify the second mutation, which we call cdr (cell division regulator) in the strain used by Matsumura and Pr????. We used Hfr mapping and P1 transduction to localize the mutation to a specific region of the chromosome. We also sought to determine if this growth phenotype was due to loss of function or gain of function and whether the mutation in the cdr gene was sufficient to cause the observed growth phenotype in other strain backgrounds. In addition the growth phenotype of these two strains was compared to that of other wild-type and standard laboratory E. coli strains. Our results indicate that the cdr mutation is located in the 88.5. region of the chromosome and is due to loss of Cdr function. We also discovered that the growth phenotype assigned to the mutant strain more closely reflects that of other wild-type laboratory strains as did the morphology of cells in stationary phase. This evidence suggests that the actual mutant strain might be the one that was designated as the wild-type strain by Matsumura and Pr???? and both strains may contain mutations that actually cause a decrease in cell number instead of an increase as previously reported.