Digitized Honors Theses (2002-2017)

Date of Award

5-2004

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Biomedical Sciences

Faculty Mentor

Michael P. Spector, Ph.D.

Advisor(s)

Brad Davis, Ph.D., Cindy Stanfield, Ph.D.

Abstract

Salmonella enterica serovars elicit the starvation stress response (SSR) when the bacteria encounters stress due to the starvation for a carbon-energy (C-) source. This response serves to combat the long-term effects of C-starvation and to provide cross-resistance to other environmental stresses the bacteria may encounter. The rpoE gene encodes an alternative sigma factor, crE, found to be involved in the SSR. During cell envelope stress, crE functions to regulate the expression of certain extracytoplasmic functions (ECFs). We propose that the shift from the utilization of glucose to an alternative carbon source requiring an outer membrane (OM)-associated component, will produce extracytoplasmic signals that lead to the activation of cl- and the induction of the cl- - dependent regulon, including the rpoE gene itself. To test this hypothesis we subjected a wild-type Salmonella enterica strain carrying a plasmid possessing: (a) no promoter (plasmid vector; pRS1274), or (b) the cr°-dependent promoter of the rpoE operon (pTF­ pl), or (c) crE--dependent promoter of the rpoE operon (pTF-p2), controlling the expression of the lacZ gene, to growth in the presence of glucose and an alternative C­ source. Growth and -galactosidase activity were monitored over time. An increase in cl- activity, reflected by increased -galactosidase activity, was not obs_erved during a shift from glucose to sugars that do not have OM-associated components needed for utiliz.ation (glycerol, fructose, or L-arabinose) supporting our hypothesis. Maltose, which requires an OM component (encoded by the lamB gene) for its utilization, increases cl­ activity. A strain carrying a MudJ-lac insertion in the lamB gene (lamB-lacZ fusion) was identified using PCR analysis and confirmed by demonstrating that the lamB-lacZ fusion is induced during the transition from glucose to maltose utilization. Future direction of study include: (a) monitoring the effect of lamB overproduction on cl- activity, (b) the effects of a lamB knock-out mutation on cl- activity, and (c) determining ifthe increase in cl- activity observed during certain C-source shifts correlates to an increase in cl-protein.

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