Two ancestral nucleoid-associated proteins called Hha and YdgT contribute to the negative regulation of several virulence-associated genes in
Salmonella entericaserovar Typhimurium. Our previous work showed that Hha and YdgT proteins are required for negative regulation of SalmonellaPathogenicity Island-2 and that hha ydgTdouble mutants are attenuated for murine infection. Interestingly, hha ydgTmutant bacteria exhibited a non-motile phenotype suggesting that Hha and YdgT have a role in flagellar regulation. Results
In this study we show that the non-motile phenotype of
hha ydgTmutants is due to decreased levels of the master transcriptional regulator FlhD4C2 resulting in down-regulation of class II/III and class III flagellar promoters and lack of surface flagella on these cells. The horizontally acquired pefI-srgDregion was found to be partially responsible for this phenotype since deletion of pefI-srgDin a hha ydgTdeletion background resulted in transient restoration of class II/III and III transcription, expression of surface flagella, and motility in the quadruple mutant. Conclusion
These data extend our current understanding of the mechanisms through which Hha and YdgT regulate flagellar biosynthesis and further describe how
S. Typhimurium has integrated horizontal gene acquisitions into ancestral regulatory networks.