Aromatic Amino Acid Metabolome In The Human Gut Microbiota

<p>Simple metabolites derived from common substrates are key candidates for host-microbiota crosstalk due to the potential for convergent biosynthetic pathways. Several human signaling molecules are simple structures derived from aromatic amino acids (phenylalanine, tryptophan, and tyrosine). In this thesis, I employed targeted and untargeted mass spectrometry-based approaches to identify novel bacterial metabolites that derived from aromatic amino acids. In chapter 2, I used a 3-step mass spectrometry pipeline to identify microbiota-dependent aromatic amino acid-derived signaling molecules in vivo, identify their commensal microbial producers and identify their biosynthetic genes. This led to the identification of <em>Enterococci</em> and <em>Streptococci</em> as commensal sources of LacPhe, an exercise-inducible metabolite that regulates appetite. Monocolonization of germ-free mice with <em>Streptococcus</em> restored the physiological concentration of LacPhe in the ileum, and analysis of human microbiome datasets revealed the microbial LacPhe biosynthetic gene,<em> pep</em>V, was abundant in the GI tract and correlated inversely with obesity. This study provides an example of cross-kingdom metabolite overlap and suggests that the microbiota's impact on LacPhe metabolism should be considered when examining the effect this metabolite has on appetite and obesity. In charpter 3, I described an untargeted metabolomics approach to profile the aromatic amino acid-derived metabolome of the gut microbiota. By feeding individual bacterial species with each aromatic amino acids, I discovered that these aromatic amino acids generate a diverse metabolome, much of which is absent from the current metabolite database. Among the 80 strains of human-isolated bacteria, C. <em>difficile</em> produces the largest number of metabolites, primarily beloning to Nacyl amino acids. Through comparison with synthetic standards, I identified 28 novel C. <em>difficile</em>-specific metabolites. Furthermore, C. <em>difficile</em> demonstrated the highest production levels of phenylacetic acid, a precursor of negative allosteric modulator (NAM) for β2-adrenergic receptor (β2AR). This work highlights several interesting metabolites specific to C. <em>difficile</em>, with potential biological roles that warrant further exploration.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Thesis

Year dc:date.available

2025

Author dc:creator

• Hsieh, David Chun-cheng

Contributors dc:contributor

• Sean F. Brady

• microbiota
• aromatic amino acids
• metabolites
• mass spectrometry
• LacPhe
• Clostridioides difficile
• Life Sciences

Repository record dc:identifier

https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/807

OAI identifier oai:identifier

oai:digitalcommons.rockefeller.edu:student_theses_and_dissertations-1811