The Hha protein facilitates incorporation of horizontally acquired DNA in enteric bacteria.

Hha-like proteins are an evolutive trait of members of the family Enterobacteriaceae. These proteins mimic the oligomerization domain of the nucleoid-associated protein H-NS and interact with this latter protein to modulate gene expression. In this report, we provide evidence that, as has been shown for H-NS, Hha-like proteins play an essential role facilitating acquisition of horizontally transferred DNA in both Escherichia coli and Salmonella. Incorporation of conjugative plasmids such as pHly152 or R27 results in a fitness cost in E. coli or Salmonella strains that lack Hha-like proteins. E. coli spontaneous derivatives from double hha ydgT mutants that showed an increased growth rate and a restored fitness overexpressed the H-NS protein. In addition to reinforcing the role of H-NS/Hha-modulating xenogeneic DNA, the results obtained demonstrate that the Enterobacteriaceae display regulatory features not found in other bacteria that facilitate incorporation of horizontally transferred DNA.