Date of Completion


Thesis Type

College of Arts and Science Honors



First Advisor

Brigitte Lavoie

Second Advisor

Gary Mawe


Gut, bacteria, serotonin, tryptophan


The proper function of the gut is imperative to human physical health, and recently has been shown to affect the brain and contribute to proper mental health through the gut-brain axis. Serotonin (5-hydroxytryptamine; 5-HT), one of the primary signaling molecules in the gut, influences many of the processes that allow the gut to function. 5-HT is synthesized in the gut from the essential amino acid tryptophan (Trp), which is acquired mainly through dietary intake. Though most Trp comes from the diet, certain bacteria within the gut can synthesize Trp from indoles. This project utilized Bacillus (B.) subtilis bacteria for its Trp synthesizing ability. This study measured expression of 5-HT related proteins and levels of 5-hydroxyindoleacetic-acid (5-HIAA) in the distal colon of mice treated daily with B. subtilis or PBS for seven days. Protein expression was measured with RT-qPCR; 5-HIAA content was measured with HPLC. The data showed no significant effect of B. subtilis treatment, a result that is thought to be due to the small sample size or an inappropriate length of treatment.