Phenotypic variation and bistability within flagellar gene network in Salmonella Typhimurium
Koirala, Santosh
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https://hdl.handle.net/2142/42464
Description
Title
Phenotypic variation and bistability within flagellar gene network in Salmonella Typhimurium
Author(s)
Koirala, Santosh
Issue Date
2013-02-03T19:46:29Z
Director of Research (if dissertation) or Advisor (if thesis)
Rao, Christopher V.
Department of Study
Chemical & Biomolecular Engr
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Salmonella
flagella
bistability
phenotypic variation
Abstract
In Salmonella enterica serovar Typhimurium, more than 50 genes divided among at least 17 operons are involved in flagellar biogenesis and chemotaxis. One of the critical features of this process is coupling of the gene expression to assembly. Like flagellar assembly, gene expression also proceeds in a sequential manner. Availability of nutirients in the cellular environment also plays a key role in switching between motile or sessile phenotypes. However, the response to nutritional cues could be very different even in closely related species. For example, E. coli upregulates flagellar synthesis under low nutrient conditions through cAMP-Crp control of the class 1 operon whereas Salmonella enterica serovar Typhimurium downregulates flagellar synthesis under low-nutrient condition. YdiV is responsible for the repression of flagellar synthesis in Salmonella enterica serovar Typhimurium which acts as an anti-FlhD4C2factor. Moreover, FliZ-dependent activation of Pclass2 promoters is more pronounced in low nutrient condition and is achieved by repression of the ydiV gene by FliZ. YdiV expression is enhanced in poor media and greatly reduced in rich media. Thus, FliZ and YdiV, in poor media, form a negative regulation loop which results in a bistable motility pheotype. However, the extent of bistability is unclear. This study aims to characterize the extent of bistability within the flagellar network in Salmonella enterica serovar Typhimurium. Our results suggest that two disntinct phenotypes, motile and sessile, coexist in an isogenic cell population under limited nutrient condition. The flagellar gene network is bistable and is mediated by FliZ-YdiV feedback loop.
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