Bacterial DNA is packed with the help of polyamines and proteins called nucleoid-associated proteins. Protein-associated DNA occupies about 1/4 of the intracellular volume forming a concentrated viscous phase with liquid crystalline properties, called the nucleoid. Other research also indicated that the genome of bacteria occupies approximately 10-15% of the bacteria's volume. Similar DNA packaging exists also in chloroplasts and mitochondria. Bacterial DNA is sometimes referred to as the bacterial chromosome. Bacterial nucleoid evolutionary represents an intermediate engineering solution between the protein-free DNA packing in viruses and protein-determined packing in eukaryotes.
Sister chromosomes in the bacterium Escherichia coli are induced by stressful conditions to condense and undergo pairing.  Stress-induced condensation occurs by a non-random, zipper-like convergence of sister chromosomes.  This convergence appears to depend on the ability of identical double-stranded DNA molecules to specifically identify each other, a process that culminates in the proximity of homologous sites along the paired chromosomes.  Diverse stress conditions appear to prime bacteria to effectively cope with severe DNA damages such as double-strand breaks.  The apposition of homologous sites associated with stress-induced chromosome condensation helps explain how repair of double-strand breaks and other damages occurs.