Chromosome Architecture and Segregation in Prokaryotic Cells

lated about these model organisms. This review is intended to provide an overview of the mode of chromosome segregation in bacteria in general and on what is known about chromosome dynamics in archaeal cells [see review by Samson and Bell (pp. 420–427)] and to give information on some groups of bacteria that have been studied in greater detail. In bacteria such as E. coli and Bacillus subtilis , chromosomal DNA does not extend throughout the entire cytoplasm, as is the case for Caulobacter crescentus , but is condensed into a structure called the nucleoid ( fig. 1 ). Compaction is mediated through nonspecific DNA-binding NAPs (which however do have a preference for certain DNA structures) [reviews by Dorman and van der Valk et al., pp. 316–331 and 344–359, respectively] and SMC proteins [Graumann and Knust, 2009]. The separation of duplicated chromosomes is extremely robust: only 1 in 10,000 cell cycle events shows a failure in DNA partitioning in B. subtilis , even when cells contain multiple replication forks and contain multiple chromosome copies [Ireton et al., 1994]. It is also possible to integrate an entire cyanobacterial chromosome (3.5 Mbp) into the B. subtilis chromosome (4.2 Mbp), and cells still grow fairly well [Itaya et al., 2005], revealing great plasticity of a bacterial genome. A dedicated segregation motor has remained elusive; ParA proteins in C. crescentus [Ptacin et al., 2010] The 3-D structure of prokaryotic chromosomes, their copy number, replication and segregation have gained an enormous interest in the past 15 years, for the most part because the spatial dynamics of chromosomes have become amenable for analysis through fluorescence microscopy techniques and other single-cell-based assays. And, of course, because these issues are of fundamental biological importance and impact on many cellular processes such as global gene regulation and the cell cycle. This special issue of Journal of Molecular Microbiology and Biotechnology deals with various aspects of bacterial and archaeal chromosomes; their arrangement, their dynamics and segregation mechanisms. Several reviews in this issue deal with different aspects of chromosome organization and partitioning in selected model bacteria, and processes such as dimer resolution and important factors such as nucleoid-associated proteins (NAPs), SMC proteins and topoisomerases are discussed in greater detail in the following chapters. Bacteria can have vastly different numbers of their chromosome, which is discussed in one chapter [Soppa (pp. 409–419)], the domain structure of the Escherichia coli chromosome [Messerschmidt and Waldminghaus (pp. 301–315)], and the dynamics of the two chromosomes in Vibrio cholerae [Ramachandran et al. (pp. 360–370)] have received their own chapters, because considerable knowledge has accumuPublished online: February 17, 2015