Diversity and redundancy in bacterial chromosome segregation mechanisms

Bacterial cells are much smaller and have a much simpler overall structure and organization than eukaryotes. Several prominent differences in cell organization are relevant to the mechanisms of chromosome segregation, particularly the lack of an overt chromosome condensation/decondensation cycle and the lack of a microtubule-based spindle. Although bacterial chromosomes have a rather dispersed appearance, they nevertheless have an underlying high level of spatial organization. During the DNA replication cycle, early replicated (oriC) regions are localized towards the cell poles, whereas the late replicated terminus (terC) region is medially located. This spatial organization is thought to be driven by an active segregation mechanism that separates the sister chromosomes continuously as replication proceeds. Comparisons of various well-characterized bacteria suggest that the mechanisms of chromosome segregation are likely to be diverse, and that in many bacteria, multiple overlapping mechanisms may contribute to efficient segregation. One system in which the molecular mechanisms of chromosome segregation are beginning to be elucidated is that of sporulating cells of Bacillus subtilis. The key components of this system have been identified, and their functions are understood, in outline. Although this system appears to be specialized, most of the functions are conserved widely throughout the bacteria.