New views of the bacterial chromosome

Abstract

The Keystone Symposium on Bacterial Chromosomes was held between 7 and 12 February 2004 in Santa Fe, New Mexico, USA. The conference was organized by S. Gottesman, N. Kleckner and J. Roth. ![][1] From the study of bacteria we know a great deal about DNA replication, recombination and repair, transcription, translation and gene regulation, and cellular metabolism. However, despite powerful molecular genetics tools, our understanding of the organization and behaviour of bacterial chromosomes has lagged behind, simply because their dynamics have been difficult to observe directly. Bacteria lack a mitotic system, and an equivalent prokaryotic mechanism for the separation of duplicated chromosomes remains mysterious. Confounding the picture is the complexity of the bacterial cell cycle, which is unlike the orderly and interdependent progression of events in eukaryotes. The application of fluorescence microscopy techniques, flow cytometry and cell synchronization has revolutionized our understanding of chromosome dynamics and the cell cycle in bacteria. Much of this conference was devoted to how chromosomes are organized, faithfully replicated and segregated to daughter cells, a few highlights of which are presented here. Dominating the discussion were studies of two model organisms— Bacillus subtilis and Escherichia coli —that diverged from a common ancestor over two billion years ago and are very different beasts. Despite this, these organisms share a number of common features. Both are rod‐shaped cells, about the size of a yeast nucleus, that divide at midcell. Both initiate replication at a single origin ( oriC ) in a circular chromosome, and bidirectional forks converge near a terminus region ( ter ) that has special properties to ensure chromosome segregation to daughter cells. Although there is no true nucleus in bacterial cells, a region of condensed chromosomal DNA (called a ‘nucleoid’) divides and separates before cell fission. In slow‐growing cells, replication is temporally separated from cell division, similar to the … [1]: /embed/graphic-1.gif