Tingting Ju | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Tingting Ju. This seminar is open to the general public to attend.
Thesis Topic: Defining the role of gut commensal microbes and the host-microbe interactions

PhD with Dr. Ben Willing.

Abstract:

Changes in gut microbiota have been correlated with positive and negative health outcomes; however, the mechanisms of causality in microbial modifications and resulting host responses are largely unknown. In this thesis, a mouse model was successfully established by colonizing mice with gut microbial communities that differ only in the presence of a single commensal bacterium. Mouse commensal Escherichia coli and Parasutterella strains were selected as model microorganisms to investigate the mechanisms of host-microbe interactions with different perturbations.

To determine the impact of E. coli colonization on host response after antibiotic treatment, mice were colonized with E. coli and subsequently treated with metronidazole. E. coli colonized the mouse gut readily without causing notable changes in microbiota or host response. However, the presence of E. coli strongly affected metronidazole-induced microbial community structural shifts. Remarkably, E. coli in the context of a complex microbiota led to variations in the host response to metronidazole treatment including increased expression of antimicrobial peptide genes and intestinal inflammation. This proof of concept study provides an explanation for variability in animal models using antibiotics, and also encourages the development of personalized medication in antibiotic therapies.

The enrichment of family Enterobacteriaceae induced by high-fat diet (HFD) feeding has been correlated with impaired glucose homeostasis. To investigate the relationship between the enriched Enterobacteriaceae and the development of HFD-induced metabolic disease, the commensal E. coli strain was added to the mouse model with HFD intervention. When mice were maintained on a standard chow diet for 16 weeks, no difference in metabolic outcomes was observed between the control and E. coli-colonized mice. In contrast, under the HFD regime, the presence of E. coli significantly increased body weight and adiposity as well as induced an impaired glucose tolerance, which was accompanied by elevated levels of plasma leptin. In addition, with HFD treatment, the colonization of E. coli led to increased inflammation in adipose tissue. The results demonstrated the role of commensal E. coli in glucose homeostasis and energy metabolism responding to HFD treatment, indicating contributions of commensal bacteria to the pathogenesis of obesity and insulin resistance.

To characterize the role of the genus Parasutterella, a core component of the human and mouse gut microbiota, Parasutterella mc1 was isolated from the mouse gut and characterized in vitro and in vivo. Mouse, rat, and human Parasutterella isolates were all asaccharolytic and producers of succinate. The murine isolate stably colonized the mouse intestine without shifting bacterial composition. Notable changes in microbial-derived metabolites were aromatic amino acid, bilirubin, purine, and bile acid derivatives. The impacted bile acid profile was consistent with altered expression of ileal bile acid transporter genes and hepatic bile acid synthesis genes, supporting the potential role of Parasutterella in bile acid maintenance and cholesterol metabolism. This experiment provides the first indication of the role of Parasutterella in the gut, beyond correlation, and provides insight into how it may contribute to host health.

A preliminary study was conducted to investigate host adaptions of Parasutterella strains in colonizing mouse gut. The chicken Parasutterella strain and pig Sutterellaceae strain failed to colonize the mouse intestine, whereas the mouse and human strains were able to colonize and persist. However, the mouse strain outcompeted and overcame the human strain in the competitive colonization experiment, indicating a better ecological fitness of the mouse isolate than the human strain. The study suggests host selectivity of Parasutterella species and the co-evolution between Parasutterella and the host.

Collectively, the thesis provides information about the role of commensal bacteria, E. coli and Parasutterella, in microbial interactions and host physiology using a well-controlled tractable mouse model.