Advisory Committee Chair
Michael Gray
Advisory Committee Members
Craig Maynard
Eric Ubil
Jessica Scoffield
Todd Green
Document Type
Dissertation
Date of Award
1-1-2025
Degree Name by School
Doctor of Philosophy (PhD) Heersink School of Medicine
Abstract
The human immune system utilizes a variety of weapons against bacterial communities within the body, which allow it to control the overall microbial population. Understanding how some bacterial species are able to better deal with and survive damage by the immune system while others are not, can help us elucidate the complex relationship between us and our microbiome. One tool that immune cells use for microbial control is the potent oxidant hypothiocyanite/hypothiocyanous acid (-OSCN/HOSCN). The response mounted by Escherichia coli and other bacterial species in order to survive damage caused by HOSCN is the focus of this dissertation. In the first part of this work, we discovered that the rcl operon in E. coli is a specific bacterial defense factor against HOSCN, making it the first of its kind described in the literature, and that the encoded oxidoreductase enzyme, RclA, protects E. coli from oxidative stress by reducing HOSCN into its precursors, thiocyanate (SCN) and water. Furthermore, RclA is highly conserved among epithelial-colonizing bacterial species, and homologs taken from Streptococcus pneumoniae, Staphylococcus aureus, and Bacteroides thetaiotaomicron were also protective. Subsequently, we characterized E. coli’s overall transcriptional response to HOSCN and found that it is notably different from previously described responses to other immune oxidants such as hydrogen peroxide (H2O2) or HOCl, and different from the responses of other bacterial species to HOSCN. We also found that there is a transcriptional effect on the gene encoding outer membrane porin ompC when rclB and rclC are mutated, as well as a slight post-transcriptional effect on protein OmpA when the entire rcl operon is deleted, suggesting a role for one or both of these genes in affecting envelope permeability to HOSCN. Taken together, these results demonstrate a method of immune system tolerance in bacteria that was previously not well-understood. Our data show that E. coli utilizes a specific genetic response to HOSCN in order to limit damage, including the rcl operon, which directly reduces HOSCN in the cytoplasm, and potentially limits envelope permeability in response to HOSCN treatment. These studies improve our understanding of how mammals exist and interact with the bacteria they host.
Recommended Citation
Meredith, Julia, "Reducing stress: The role of the rcl operon in bacterial stress response to hypothiocyanite" (2025). All ETDs from UAB. 6871.
https://digitalcommons.library.uab.edu/etd-collection/6871
Comments
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