Digitized Honors Theses (2002-2017)

Date of Award

5-2007

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Biomedical Sciences

Faculty Mentor

Michael P. Spector, Ph.D.

Advisor(s)

Zari Aliabadi, Ph.D., Julio Turrens, Ph.D.

Abstract

Salmonella enterica serovar Typhimurium is a frequent agent of food-borne disease in animals and humans. Throughout its life within and outside of hosts this bacterium encounters a variety of sub-optimal potentially lethal environmental conditions. S. Typhimurium is known to initiate the starvation-stress response (SSR) when it is starved for a carbon-energy (C)-source, a common stress encountered by this bacterium. The SSR leads to dramatic morphologic, physiologic and genetic changes in the cell. During C-starvation, changes may result from the activation of the rpoE gene product ( ) and the rpoS gene product (crs), both of which are part of RNA polymerase that guide it to the correct promoter region on the DNA. Previous gene array studies suggested that expression of the cdgR (ydiV) gene is dependent on and is C-starvation-inducible.This suggests cdgR is expressed during the SSR of S. Typhimurium. Since CdgR is a cyclic-diguanylate (c-diGivlP) phosphodiesterase, this further suggests that c-diGl\1P levels are critical to the development of the SSR in S. Typhimurium. Based on this, we hypothesized that the cdgR gene is a member of the C-starvation-inducible-dependent branch of the SSR and is needed for maximal development of the SSR Here we report the characterization of a plasmid construct pCMKS3 containing the cdgR promoter region cloned in front of a promoter-less lacZ gene. Using this plasmid we showed that cdgR is C-starvation-inducible, crE-regulated and crs-regulated. This is the only gene reported to be regulated by both crE and cr8. We are currently attempting to construct a cdgR "knock-out" mutant (lacks a functional cdgR gene). This mutant will then be compared to the wild-type bacteria for its ability to develop a maximal SSR; the mutant and wild-type strains will be tested for long-term C-starvation survival and C-starvation­ induced cross-resistance to physiologic stress resulting from oxidative, high temperature, low pH and antimicrobial peptide challenge.

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