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|Title:||Regulation of Iron Sequestration Systems in Escherichia Coli and Salmonella Typhimurium (Heme, Outer Membrane)|
|Author(s):||Worsham, Patricia Lynne|
|Department / Program:||Microbiology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Regulation of iron uptake systems by iron, growth temperature, and heme was examined. Operon fusions were constructed in which the lactose utilization genes were fused to the promoter of the iron-regulated gene which encodes the colicin I receptor. Regulation by iron was shown to be at the level of transcription. A regulatory mutant was isolated from a cir-lac operon fusion strain which was aberrant in response to iron. When grown in high iron medium, (beta)-galactosidase activity was eight times higher in this mutant then in the parental strain. The mutation, which I call cirR, was linked to cirA, the receptor structural gene, at approximately 45 minutes on the E. coli chromosome. A CirA('+) CirR('-) strain bound four-fold greater amounts of ('125)I-colicin Ia when grown in high iron medium than the parental strain (CirA('+) CirR('+)). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of outer membrane proteins isolated from a cirR strain revealed an increase in the level of the 74K protein which functions as the colicin I receptor. The levels of other outer membrane proteins normally regulated by iron were not affected. CirR was found to be a cis dominant mutation.
The effect of growth temperature on three systems normally induced under conditions of iron limitation was examined: synthesis of the siderophore enterochelin (enterobactin), transport of ferric-enterochelin, and production of the outer membrane protein which serves as the colicin I receptor. While S. typhimurium produced less enterochelin when grown at 42(DEGREES)C, synthesis of this siderophore was not diminished in E. coli grown under the same conditions. Growth at 42(DEGREES)C under a condition of iron stress led to a reduction in the ability of cells to transport ferric-enterochelin in both organisms. A two to three-fold decrease in the number of colicin I receptors was observed in cells of E. coli or S. typhimurium grown at 42(DEGREES)C as compared to cells which were grown at 37(DEGREES)C. The colicin I receptor was shown not to be inherently unstable at 42(DEGREES)C. Using the cir-lacZ operon fusion, it was shown that at least a part of the decrease in receptor levels found in cells grown at high temperature was the result of decreased transcription of cir, the receptor structural gene.
The effect of growth temperature on these systems was shown to be independent of Fur, a regulatory element which mediates their enhanced production in response to iron stress. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2014-12-16|