Structure And Dynamics Of The Bacterial Chromosome In E. Coli

We address the question of whether the E. coli chromosome is folded into a self-adherent nucleoprotein complex, or alternately whether it is an essentially unfolded DNA molecule. We do this by in vivo visualization of the whole chromosome, via fluorescence of a controllably-expressed fusion of gfp and the nucleoid-associated protein Fis. 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. These observations support a self-adherent filament model of the chromosome, as opposed to a non-self-adherent “self-avoiding polymer” model. We have also developed methods for isolation of single bacterial chromosomes, in order to study the bacterial chromosome outside of the cell, to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Our further objective is to directly examine nucleoid mechanical properties using micromanipulation methods which could provide further insight into bacterial chromosome folding.