9:00 am - 10:00 am
Event details: 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 Andrew Forgie. This seminar is open to the general public to attend.
Understanding the role of dietary phytochemicals and vitamin B12 in microbe-host interactions to support host gut integrity and health
Meeting ID: 945 7212 8091
PhD with Dr. Ben Willing
Diet is a great modifier of gut microbe-host interactions that alter host physiology and immunity against pathogenic bacteria. Some dietary components are required to support host defences that maintain gut homeostasis and symbiosis, whereas others can be detrimental, leading to changes in microbial communities and impaired intestinal barrier function and immunity. In this thesis, a mouse model of infectious Citrobacter rodentium was used to challenge the effects of diet, specifically those associated with phytochemicals and vitamin B12 consumption, on intestinal ecology and integrity to promote host health.
To determine the effect of phytochemicals on microbe-host interactions and intestinal health, the seed coat of two cultivars of peas (Pisum sativum) rich and poor in phytochemicals were fed to mice as raw or acid hydrolyzed fractions. In accordance with a previous study, the acid hydrolyzed anthocyanidin fraction reduced weight gain in mice fed a high fat diet. Supplementation of both cultivars altered the microbial communities and encouraged pathogen colonization by day three post-infection; however, the proanthocyanidin containing diet had a more robust antimicrobial affect and consistently lead to higher pathogen loads as determined by fecal enumeration. Acid hydrolysis processing to both cultivars reduced the effect on the microbiota and ability of C. rodentium to colonize the gut. In addition, pea phytochemicals increased mucin accumulation in the intestinal lumen, and this may have improved the ability of C. rodentium to colonize the gut. This study shows how pea phytochemicals directly contributes to microbial ecology and provides insight into how their antimicrobial and mucin accumulating activities affect the gut environment and pathogen colonization resistance.
The effect of mucin accumulation in the gastrointestinal lumen in response to phytochemicals has previously been associated with beneficial health outcomes. Since our study shows that increased mucin corresponded with higher levels of C. rodentium colonization, we set out to determine the contributions of mucin to gut ecology and the dietary phytochemicals that stimulate their effects in the gut. Germ-free mice fed the proanthocyanidin-rich containing fraction had increased mucin accumulation in the feces, indicating that phytochemicals directly impact the mucus layer independently of the microbiota. Supplementation of red Osier dogwood extract, a hydrolysable tannin, and our non-hydrolysable proanthocyanidin-rich pea fraction shows that a common compound is likely directing the increased fecal mucin phenotype. Both diets led to greater mucin levels in the gastrointestinal lumen and corresponded to an enrichment in the Lachnospiraceae and Clostridium leptum species and reduction in Romboutsia species. This study highlights the direct effects of phytochemicals on gut mucus layer properties and their ability to manipulate the gut microbiota.
Vitamin B12 is a known modulator of the microbial ecosystem. To determine how B12 impacts the gastrointestinal microbiota, we supplemented drinking water at 100 times the amount found in diet and challenged mice with C. rodentium. Survival and early colonization models show that mice supplemented B12 were more susceptible to pathogen colonization and virulence. Cecal meta-transcriptomics revealed that the activities of the Firmicute population was altered by B12 supplementation and this contributed to a more virulent C. rodentium population as confirmed by reduced glucosidase and increased virulence genes. In addition, interleukin-12p40 cytokine levels were determined to be dependent of B12 supplementation and the subsequent alterations to the resident microbial population, suggesting B12 impacts host tissues by changing the microbiota.
Collectively, this thesis adds to our understanding of diet-microbe-host interactions that impact intestinal integrity to advance nutritional strategies and therapies to combat infectious disease and improve health.