All ETDs from UAB

Advisory Committee Chair

Michael J Gray

Advisory Committee Members

Terje Dokland

Todd Green

Rakesh Patel

Jamil Saad

Document Type

Dissertation

Date of Award

2021

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Inflammatory bowel diseases (IBDs), like Chron’s disease and ulcerative colitis, affect millions of people worldwide. There are limited treatment options available for these diseases because their direct causes are unknown. IBDs are characterized by chronic inflammation of the gastrointestinal tract and changes in the composition of the gut microbiome. Enterobacteria, including Escherichia coli, bloom to high levels in the gut during inflammation and contribute to the pathology of IBDs. E. coli must tolerate high levels of antimicrobial compounds produced by the immune system to survive during persistent inflammation. A large proportion of such compounds are reactive oxygen and reactive chlorine species (RCS) produced by neutrophils, which are innate immune cells that contribute to the chronic inflammation of IBDs. The RCS hypochlorous acid (HOCl) is a very strong oxidant that indiscriminately damages bacterial and human cells alike. This project is focused on characterizing the HOCl response of E. coli to better understand mechanisms by which the bacteria may be surviving within the gut of patients with IBDs. There are four HOCl-sensing regulators in E. coli, including the RCS-specific transcription factor RclR, which regulates expression of rclABC. The rcl locus was shown previously to confer HOCl resistance in vitro but the functions of these genes and whether they increase survival within an animal host had not been determined. In the first part of this work, we show that RclA catalyzes the reduction of copper (II) to copper (I) and that this activity protects E. coli against damage caused by the combination of HOCl and intracellular copper. E. coli lacking RclA were defective in colonizing an animal host in a manner dependent on the host’s ability to produce HOCl. In the second part of this work, we examine the transcriptomic response of the human commensal strain E. coli Nissle 1917 (EcN) to HOCl as well as examine the role of RclR in this organism. Using RNA sequencing we report that the HOCl response of EcN is similar to other strains of E. coli and identify sixty-eight genes that are differentially expressed in EcN lacking rclR during HOCl stress. The largest difference in expression was observed in a homolog of flu, encoding antigen 43, a known auto-aggregation factor important for biofilm formation in other strains. We therefore examined the capacity of wildtype and ΔrclR EcN to form biofilms in response to HOCl stress but found that there was no significant difference between our strains. Taken together these studies illustrate the importance of the Rcl system in surviving host-mediated inflammation within an animal host and elucidate some mechanisms by which the system is protective in E. coli.

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