Digitized Honors Theses (2002-2017)

Date of Award

5-2012

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Biomedical Sciences

Faculty Mentor

Michael P. Spector

Abstract

Salmonella enterica serovar Typhimurium is a pathogenic bacterium that, when starved of a carbon-energy source, undergoes a series of changes known as the starvation­ stress response (SSR). The SSR results in cells that are more resistant to the long-term effects of carbon starvation and other environmental stressors (known as carbon­ starvation inducible (CSI) cross-resistance). Sigma factors cr5 and crE, along with second messengers/signal nucleotides cAMP [with its cAMP receptor protein (CRP)] and guanosine tetraphosphate (ppGpp), are known to regulate the SSR in S. Typhimurium. Previous studies have indicated that the second messenger/signal nucleotide cyclic s·,3·_ diguanosine monophosphate (c-di-GMP) may also be involved in its regulation. Cyclic­ di-GMP is produced by proteins possessing a GGDEF domain involved in diguanylate cyclase (DOC) activity. Proteins with c-di-GMP phosphodiesterase (PDEA) activity possess an EAL domain and break down c-di-GMP to the linear pGpG. A previous study identified seven genes that encode proteins that contain GGDEF and/or EAL domains. three of which were found to be required for CSI cross-resistance to H202. The aim of this study was to determine if two of these genes (stm1987 and stm2503) were also necessary for CSI cross-resistance to polymyxin Band pH 3.3. The stm1987 gene product has a consensus active site GGDEF domain and is a putative DGC, while the stm2503 gene product has a consensus active site EAL domain and is a putative PDEA. The results presented here showed that both genes were required to develop CSI cross­resistance to H202and polymyxin B, but neither was required for CSI cross-resistance to pH 3.3. From this we can conclude that c-di-GMP, and its maintenance at an appropriate level, control the development of pathways in the SSR needed for CSI cross-resistance to H202 and polymyxin B, but not to pH 3.3.

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