Characterization of a Cold-sensitive Chromosome Segregation Mutant of Escherichia coli

Abstract

A cold-sensitive mutant defective in chromosome segregation, cs2-68, has been isolated from E. coli after NTG mutagenesis. When an exponentially growing culture of cs2-68 at 37°C was shifted to 20°C, the number of viable cells increased 3.2_??_4.0-fold in about 6 hr and gradually decreased thereafter. During the incubation at 20°C, most of the cells formed filaments and lost colony forming ability at the same time. A big nuclear mass in the central region of the filamentous cell at 20°C was observed by Giemsa staining. Macromolecular syntheses of cs2-68 including DNA, RNA and protein proceeded at a normal rate at 20°C. The number of viable cells of cs2-68 increased exponentially at 30° and 37°C but not at 20° or 25°C. When the portion of the culture of stationary phase at 37°C was introduced into the fresh medium and incubated at 20°C, the increase of viable cells was only 1.7_??_1.9-fold. The mutation has been mapped between approximately 70 and 80min on E. coli genetic map, a previously undescribed region involved in chromosome segregation.