Date of Award


Degree Type

Honors College Thesis

Academic Program

Biological Sciences BS


Biological Sciences

First Advisor

Janet Donaldson, Ph.D.

Advisor Department

Biological Sciences


Listeria monocytogenes is a gram-positive foodborne pathogen that results in the infectious disease listeriosis. The second messenger molecule cyclic-dimeric-GMP has been found to be responsible for the regulation of expression of many of its virulence factors with diguanylate cyclases and phosphodiesterases regulating the intracellular concentration of cyclic-di-GMP through synthesis and degradation, respectively. This study investigated the possibility that the availability of oxygen is the environmental signal crucial to the regulation of these enzymes. Prior research in our laboratory has demonstrated that the intracellular concentration of cyclic-di-GMP is elevated when exposed to anaerobic conditions. Due to this, it was hypothesized that diguanylate cyclases are upregulated and phosphodiesterases are downregulated in response to lack of oxygen availability. Listeria monocytogenes has three recognized diguanylate cyclases, dgcA, dgcB, and dgcC, and three recognized phosphodiesterases, pdeB, pdeC, and pdeD. This study analyzed the expression of these genes under aerobic and anaerobic conditions by qPCR. Results showed that two of the diguanylate cyclases were upregulated in anaerobic conditions in comparison to aerobic conditions, and one phosphodiesterase was upregulated under anaerobic conditions. This suggests that there is differential regulation of the diguanylate cyclases and phosphodiesterases in response to anaerobic conditions. This study also analyzed whether oxidative stress could pose as an environmental signal affecting the concentration of cyclic-di-GMP within the cell. To test this, hydrogen peroxide was added to aerobic cultures, and the concentration of cyclic-di-GMP was compared to the controls. Results indicated a significant increase in cyclic-di-GMP in cultures that were treated in comparison to untreated controls. The results of this research suggest that anaerobic conditions and reactive oxygen species likely play a pertinent role in the regulation of expression of cyclic-di-GMP within the cell. Further research into the mechanisms involved within the cyclic-di-GMP signaling pathway is required to decipher the modes of regulation utilized by diguanylate cyclases and phosphodiesterases and the methods used by Listeria when faced with oxidative stress.