requires high-density binding of HU on DNA, one HU dimer per 9-20 bp DNA. But there is only one HU dimer every ~150 bp of the chromosomal DNA based on the estimated abundance of 30,000 HU dimers per cell (4600000 bp /30,000). This indicates that the flexible bends are more likely to occur in vivo. The flexible bending would cause condensation due to a reduction in the persistence length of DNA as shown by magnetic tweezers experiments, which allow studying condensation of a single DNA molecule by a DNA binding protein. However, because of the cooperativity, the rigid filaments and networks could form in some regions in the chromosome. The filament formation alone does not induce condensation, but DNA networking or bunching can substantially contribute to condensation by bringing distant or nearby chromosome segments together. IHF Integration host factor (IHF) is structurally almost identical to HU but behaves differently from HU in many aspects. Unlike HU, which preferentially binds to a structural motif regardless of the sequence, IHF preferentially binds to a specific DNA sequence even though the specificity arises through the sequence-dependent DNA structure and deformability. The specific binding of IHF at cognate sites bends DNA sharply by >160-degree. An occurrence of the cognate sequence motif is about 3000 in the E. coli genome. The estimated abundance of IHF in the growth phase is about 6000 dimers per cell. Assuming that one IHF dimer binds to a single motif and nucleoid contains more than one genome equivalent during the exponential growth phase, most of the IHF molecules would occupy specific sites in the genome and likely only condense DNA by inducing sharp bending. Besides preferential binding to a specific DNA sequence, IHF also binds to DNA in a non-sequence specific manner with the affinities similar to HU. A role of the non-specific binding of IHF in DNA condensation appears to be critical in the stationary phase because the IHF abundance increases by five-fold in the stationary phase and the additional IHF dimers would likely bind the chromosomal DNA non-specifically. Unlike HU, IHF does not form thick rigid filaments at higher concentrations. Instead, its non-specific binding also induces DNA bending albeit the degree of bending is much smaller than that at specific sites and is similar to the flexible bending induced by HU in a linear DNA at low concentrations. In vitro, the bending induced by non-specific binding of IHF