Stationary-Phase Chromosomes

Abstract

One of the most remarkable features of prokaryotes is their ability to remain viable for very long periods under conditions that are not propitious for growth. The intrinsic chemical and physical vulnerability of DNA molecules and the lethal effects caused by unrepaired DNA lesions, even if they occur at low frequency, highlight the need for particularly efficient DNA protection mechanisms. The chapter presents a concise survey of data derived from light and electron microscopy techniques on the architecture of the chromosome in actively growing bacteria. It proceeds to briefly describe phase transitions that characterize DNA molecules. The chapter considers these two issues a prerequisite for a deeper understanding of the factors that determine the structure of chromatin in stationarystate bacteria. The organization of the chromosome within bacterial cells and the factors that dictate and modulate this organization remain less thoroughly understood than the structure of eukaryotic chromosomes. Several factors conspired to bring about this situation. These include the small size of the prokaryotic cell that restricts the effectiveness of light microscopy, the relatively low content of DNA-binding proteins associated to the bacterial chromosome which resulted in severe artifacts in conventional electron microscopic studies, as well as the apparent absence of structural order and architectural hierarchy within the nucleoid. Although this survey is concerned with stationary-phase chromosomes, a sideways glance at sporulating bacteria seems to be in place.