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Title:Elucidating the mechanisms by which the human pathogen staphylococcus aureus resists host-imposed zinc starvation
Author(s):Grim, Kyle P
Director of Research:Kehl-Fie, Thomas E.
Doctoral Committee Chair(s):Kehl-Fie, Thomas E.
Doctoral Committee Member(s):Metcalf, William; Kuzminov, Andrei; Imlay, James
Department / Program:Microbiology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Staphylococcus aureus
Abstract:During infection, the host sequesters essential nutrients such as zinc, iron, and manganese in order to prevent pathogens from obtaining them, a process termed nutritional immunity. In response, bacterial pathogens such as Staphylococcus aureus have evolved mechanisms to overcome this starvation. One common mechanism bacteria employ to evade this defense is expression of high-affinity transporters. However, to date, the zinc transporters in S. aureus remain unknown. Expression and growth analysis revealed that S. aureus expresses two zinc transporters, AdcABC and CntABCDF, with the latter system belonging to a family that had not previously been associated with zinc import before. The cnt locus also encodes proteins that are involved in the synthesis and export of the broad-spectrum metal chelator, staphylopine. Further investigation revealed that the Cnt system uses staphylopine to import zinc in a mechanism analogous to siderophore-mediated aqusition of iron. Other bacteria, including pathogens and environmental microbes, make staphylopine-like molecules, suggesting metallophore mediated uptake is a strategy broadly used to acquire zinc in zinc-poor environments. While both AdcABC and CntABCDF contribute to staphylococcal virulence, the Cnt system is the primary zinc importer that competes with the host for zinc. The export of staphylopine is also important for S. aureus, as accumulation of intracellular staphylopine impairs its growth. Surprisingly, this is not due to intracellular metal chelation by staphylopine, but rather a chelation-independent mechanism. Despite possessing the high-affinity Cnt system, S. aureus codes for other proteins that have increased expression when zinc limitted, suggesting that it may still experience zinc starvation during infection. One of these proteins is an alternative ribosome protein, RpsN2, which is a zinc-independent variant of a zinc-dependent protein. The expression of rpsN2 is induced during zinc limitation, while loss of rpsN2 sensitizes S. aureus to host-mediated zinc starvation in culture. Interestingly, an rpsN2 mutant does not have a virulence defect during infection, suggesting that S. aureus successfully acquires zinc during infection. Cumulatively, these findings establish the importance of zinc acquisition during S. aureus infection and reveal a new family of zinc transporters system bacteria use to acquire this essential metal.
Issue Date:2020-05-06
Rights Information:Copyright 2020 Kyle Grim
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05

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