RfaH is a unique bacterial protein that enhances transcription of a select group of long operons in many Gram-negative bacteria. Operons regulated by RfaH possess an upstream operon polarity suppressor sequence, which recruits the RfaH protein to the RNA polymerase during transcription of genes, most of which are involved in the synthesis of cell-surface features. These include synthesis of the lipopolysaccharide (LPS) core and O-antigen in Salmonella and Escherichia coli, as well as F-plasmid conjugation pilus and capsule in E. coli. LPS is an important virulence factor in many Gram-negative bacteria, and protects Y. pseudotuberculosis against host antimicrobial chemokines. Recently published high-throughput transposon mutant screens have also suggested a role for RfaH in the ability of Y. pseudotuberculosis to colonize mice. However, the role of RfaH in Y. pseudotuberculosis and its descendent Yersinia pestis has not been carefully examined. In these studies we investigated the effect RfaH has on the structure of the LPS in both species at different temperatures. We also identified LPS-synthesis related genes that are regulated by RfaH. We determined the effect of RfaH on bacterial resistance to host defense peptides, and the ability of Y. pseudotuberculosis to colonize mice. We found that the loss of the rfaH gene had different effects in Y. pseudotuberculosis and Y. pestis. Loss of rfaH caused a truncation in the core region in Y. pseudotuberculosis strain IP32953 at both 21°C and 37°C, but only at 37°C in Y. pestis strain KIM6+. Similarly, we found that transcription of individual genes that are predicted to function in core or O-antigen synthesis were downregulated in the rfaH mutant strains in both species, but the impact of rfaH deletion was greater in Y. pseudotuberculosis. When tested for their ability to survive in the presence of antimicrobial peptides, the Y. pseudotuberculosis rfaH deficient bacteria were much more susceptible than wild-type to killing by polymyxin and by the antimicrobial chemokine CCL28. However, the Y. pestis rfaH mutant strain was equally susceptible to CCL28 as the wild-type strain. Infection of mice with Y. pseudotuberculosis show that rfaH deficient bacteria were able to survive as effectively as the wild-type following oral or intravenous inoculation, with or without the pYV virulence plasmid. Overall, our results show that while RfaH controls LPS gene expression in both Y. pseudotuberculosis and Y. pestis, its impact is much greater in Y. pseudotuberculosis. Furthermore, although loss of rfaH greatly reduces the ability of Y. pseudotuberculosis to resist antimicrobial peptides, it is not required for virulence in this species.



College and Department

Life Sciences; Microbiology and Molecular Biology



Date Submitted


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rfaH, lipopolysaccharide, CCL28, Yersinia pseudotuberculosis, Yersinia pestis



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Microbiology Commons