Structure and Dynamics of the Bacterial Chromosome in E. coli

Abstract

The bacterial cell's ability to control the topology of a long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of bacterial chromosomes is minimal, partly because their dynamics have been difficult to observe directly. To visualize bacterial chromosome conformation within living cells, we have developed a bacterial strain containing fluorescent gfp-fusion versions of a chromosome folding protein, Fis, under inducible control. Bacterial chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows a relation between chromosome segregation and cell division under different growth conditions, and it also shows how domain structure and overall conformation of chromosomes vary during rapid and slow growth. In order to study the bacterial chromosome outside of the cell, we have developed methods for isolation of single bacterial chromosomes and directly examining nucleoid mechanical properties as a function of protein levels using micromanipulation methods.