H-NS-like nucleoid-associated proteins, mobile genetic elements and horizontal gene transfer in bacteria

• H-NS-like proteins are expressed by mobile genetic elements (MGE), including plasmids.
• MGE H-NS-like proteins modulate expression of some chromosome-encoded H-NS protein gene targets.
• MGE H-NS-like proteins modify fitness, ameliorating the impact of horizontal gene transfer.
• It is likely that MGE H-NS-like proteins play an important role in bacterial genome evolution.

Horizontal gene transfer plays an important role in the evolution of bacterial species, conferring new genetic traits on the recipient bacterium that extend its range of phenotypes and plasmids make important contributions to this process. However, the inappropriate expression of newly acquired genes may lead to a loss of competitive fitness, resulting in the elimination of the new gene-bacterium combination. It is thought that transcriptional silencing of horizontally acquired genes offers a route out of this dilemma and that nucleoid-associated proteins, especially those related to the H-NS protein, play a particularly important role in the silencing process. The discovery that many plasmids express orthologues of nucleoid-associated proteins adds an interesting dimension to current models of regulatory integration following lateral transfer of DNA. Other horizontally acquired genetic elements, such as genomic islands, also express nucleoid-associated proteins of their own. Here the interactions of H-NS-like nucleoid-associated proteins encoded by the core genome, genomic islands and plasmids are described.