In response to adverse environmental factors,Escherichia colicells actively produce Dps proteins which form ordered complexes (biocrystals) with bacterial DNA to protect the genome. The effect of biocrystallization has been described extensively in the scientific literature; furthermore, to date, the structure of the Dps–DNA complex has been established in detail in vitro using plasmid DNA. In the present work, for the first time, Dps complexes withE. coligenomic DNA were studied in vitro using cryo-electron tomography. We demonstrate that genomic DNA forms one-dimensional crystals or filament-like assemblies which transform into weakly ordered complexes with triclinic unit cells, similar to what is observed for plasmid DNA. Changing such environmental factors as pH and KCl and MgCl2concentrations leads to the formation of cylindrical structures.