eptB Pseudogene Formation As A Novel Mechanism of Typhoidal Salmonella Virulence

<p>PROJECT SUMMARY Salmonella enterica is a highly diverse species of Gram-negative bacteria that can begrouped into typhoidal and non-typhoidal serovars. Non-typhoidal serovars, such as S.Typhimurium, cause gastroenteritis and inflammatory diarrhea, whereas typhoidal serovars,such as S. Typhi, cause typhoid fever, a systemic disease with a comparatively decreasedinflammatory response. However, the virulence strategies that set typhoidal Salmonellaserovars apart from non-typhoidal Salmonella serovars remain understudied. Experimentsproposed in this application are aimed at addressing this important gap in knowledge. Our long-range goal is to elucidate the molecular mechanisms by which typhoidal Salmonella serotypesmanipulate host responses during infection. Previously, comparative analysis of Salmonellagenomes revealed that typhoidal serovars contain a higher number of pseudogenes than non-typhoidal serovars, suggesting that pseudogene accumulation may contribute to the differencesin disease manifestation caused by these serovars. One such pseudogene in S. Typhi is eptB,which encodes a phosphoethanolamine transferase that specifically modifies the outer keto-deoxyoctulosonate (KDO) residue of lipopolysaccharide (LPS). Our central hypothesis is thateptB pseudogene formation in S. Typhi represents a novel virulence mechanism thatcontributes to the stealth and immune evasion properties that characterize typhoidal Salmonellaserovars. The objectives of this application are to identify the mechanism by which eptBpseudogene formation moderates the host immune response and to determine how acquisitionof the eptB pseudogene synergizes with accumulation of additional pseudogenes to promotethe virulence of typhoidal Salmonella serovars. To test our hypothesis and accomplish theseobjectives, we will examine how eptB pseudogene formation impacts binding of the host protein,intelectin, to LPS to regulate host responses to LPS (specific aim 1) and also determine howeptB pseudogene formation offsets the acquisition of other typhoidal pseudogenes to enhancePeyer's patch colonization (specific aim 2). Our analysis of this novel virulence mechanism intyphoidal Salmonella serovars will be useful and necessary to understand how the interplaybetween pathogen and the innate immune system gives rise to responses that distinguishtyphoid fever from gastroenteritis, thereby ushering in a significant conceptual advance.</p>