Continually faced with changing environmental conditions, free-living bacteria are under enormous pressure to develop new traits and gain a selective advantage over competing strains. Crucial to bacterial adaptation and survival is the ability to obtain new genetic material via horizontal gene transfer (HGT). HGT, which has been described as ‘evolution in quantum leaps’, allows bacteria to rapidly acquire novel functions such as the ability to survive within eukaryotic host cells, combat other bacteria, and gain resistance to antimicrobial agents. Despite their potential benefits, however, newly acquired sequences are particularly problematic to bacteria.
Silencing of foreign DNA in bacteria. Current Opinion in Microbiology 19 January 2012
Xenogeneic silencing proteins facilitate horizontal gene transfer by silencing expression of AT-rich sequences. By virtue of their activity these proteins serve as master regulators of a variety of important functions including motility, drug resistance, and virulence. Three families of silencers have been identified to date: the H-NS like proteins of Gram-negative bacteria, the MvaT like proteins of Pseudomonacae, and the Lsr2 proteins of Actinobacteria. Structural and biochemical characterization of these proteins have revealed that they share surprising commonalities in mechanism and function despite extensive divergence in both sequence and structure. Here we discuss the mechanisms that underlie the ability of these proteins to selectively target AT-rich DNA and the contradictory data regarding the mode by which H-NS forms nucleoprotein complexes.