Dynamic organization of bacterial chromatin by DNA bridging proteins

Bacteria often experience external challenges, such as changes in environmental conditions or attacks by bacteriophages. To cope with these challenges, bacteria need to be able to adapt quickly to the challenges. Key to the survival of bacteria is to be able to adapt to environmental stresses, to acquire new genetic characteristics through horizontal gene transfer to remain competitive and to silence these foreign genes as long as they do not provide any benefits. The Histone-like nucleoid structuring (H-NS) protein is a key regulator of the dynamic bacterial genome. The protein is conserved among enterobacteria and plays a determinant role in the architecture of their nucleoid acting as a global genome organizer and gene regulator. We used a homolog of H-NS, MvaT from P. aeruginosa, in which we scrutinized its structural/function relationship in response to changes in the surrounding ionic strength. We have combined integrative structural biology methods and biochemical assays to decipher the structural changes in MvaT that drive the switch between its DNA stiffening and bridging activities under different salt conditions. These structural changes appear to be conserved within the H-NS family of proteins: analysis of primary sequences of H-NS family members revealed conserved positions of charged residues.